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-   -   early 944 brakes, stock MC....dosent feel right (https://www.germanlook.net/forums/showthread.php?t=4595)

super vw July 17th 2004 22:53

early 944 brakes, stock MC....dosent feel right
 
Well i got all my plumbing done for my 1303 project, i have early (single piston) 944 brakes on all four corners and i am using my stock master cylinder for now... i already have it mounted so i thought i would see if it would work.

I dont think its going to cut it, the pedal has a fair amount of travel till it engages the brakes, but if you push on it REAL hard it almost hits the bulkhead. kinda soft/squishy feeling, not firm like on our 73 Thing.

I have not driven the car or rolled it yet becuase their is no motor, no running gear..ect so i cant say if they work ok or not. but my the feeling of them now, i dont think they would.

So the question is what next to try, i cant be spending a lot or money trying everything out there. so what is a proven MC to use with this setup?

I have heard to use the 944 unit (but it originaly had a Servo/Booster) and to use an early 911 unit (no booster correct?)
Anyway i look at it, i cant use a booster, no room, and most importantly, i dont want to deal with mounting one up at this point, im sure it would involve a lot of fab and hacking to make one work.

So what to use, somthing that has been used... not just a sugestion on what may work... somthing proven to work.

Thanks!
Jonathan

LOAF July 17th 2004 23:15

Super VW

Great question, would like to hear what people will say.. I am in a similiar boat.. Not too long ago at a swap picked up a new VW M/S for my 1303 but I had the same suspisions..

Some folks have used 911 and 944 but not sure how.. not yet there.. but I believe there may have been some bias issues..

Be patient and some folks who are a little ahead of us will respond..

ALex

zen July 18th 2004 09:59

i am running 951 brakes with a 944 M/C, so i can't speak with authority, but i think there are more than a few guys running 944NA brakes with a stock M/C. and you are sure they are fully bled right?

boygenius July 18th 2004 12:28

I am with Zen, double check that ALL the air is out of the system.

You have a super correct with the 944 spindle/hub/caliper swap via a kersher ball joint.

Did you have good brakes before you did the swap.

Are you using new (newer) rubber/stainless brake lines. One of mine had a tiny pin hole in it and it drove me crazy because I could never get a firm pedal but when I would look under the car I couldn't find a drip untill I finally replaced the lines and when I bent one of the lined I could see a little crack with brake fluid seeping out of it.

Check that you still have the required clearence between the brake pushrod and the master cylinder. If thre is no clearence the fluid won't return properly and you will never get the air out.

Make sure ALL of your fittings are tight. Double check them. If they are a little loose the fluid realy won't leak out but when you release the pedal air will be sucked into the line.

Hope that helped...

super vw July 18th 2004 14:00

Now that you mention it, there MIGHT be some air in the system still. i went and applied the brakes this morning and could here a slight squish of air near the MC. so i think your right... i need become a killer and let this sucker bleed :D

i have not noticed any leaks of fluid, but when i was using a hand held bleeder deal that sucks the fluid/air out it would let some fluid out but more air than fluid. then all of a sudden it would just drop in pressure and suck only air. But when we went to try bleeding it the manual way (one person pumps, one opens valve...) their was only fluid coming out maybe tricking us that we had it fully bleed...

So i will give it another try today and see what happens.

Thanks, ill tell ya how it goes.

Jonathan

boygenius July 18th 2004 14:06

Sometimes the vaccum bleeders will suck air from around the fitting on the caliper. The rubber cap from the vaccum pump hose that goes over the bleeder should fit tightly, if not it will suck a little air from around the fitting. I would still double check the tightness of your fittings. Good luck.

Jeza July 18th 2004 19:32

I'm also in a similar boat.

944 single piston calipers all around and a stock bug 19.06mm master cylinder.

I also have a fair amount of pedal travel and quite a bit of squish. It does get firmer with some pumping but I'm pretty sure I've got the air out of there. I'm not getting any air when the calipers are bled, unless it's hiding elsewhere.

I've been suggested to check out shimming down the front pistons instead of using the 944 mc. The reason behind this is that the 944 is a front engined car and the brake balance will be set up as such.

I reckon if the front calipers are approx 44mm diameter the front to rear ratio will be about right, and similar to the CB kits, just bigger and vented.

Do the 4 pot calipers have less volume / fluid area? The 4 pistons make them more efficient. This may effect the pedal feel.

Hopefully this sparks some thoughts

Cheers
Jeremy

Jeza July 18th 2004 23:20

Okay a quick ask around brake shops at lunch yielded no results- so perhaps my comment about shimming / sleeving the front calipers was barking up the wrong tree.....

Any comments

Cheers
Jeremy

ricola July 19th 2004 03:48

I'll add my experience...

I started off doing the rear brakes first as there was a delay on sorting my front bearing adapters. Using the bug m/c, that was the best combination by far so I should have just drilled the front discs to Porsche pattern.
The bug m/c has not got enough displacement for the single pot front calipers no matter how much bleeding you do.

I tried the 924 which I think is 22mm both circuits, that was too hard and no improvement in bias. I settled on the aluminium 944 m/c which still wasn't perfect but the best of the three options (23/19 I think). Ideally a twin m/c with bias bar would have got the best result.

Rich

Jeza July 19th 2004 05:05

Rich

Thanks for the comments. I agree with you, the stock 19mm (Bug) master cylinder just doesn't have enough volume for the huge front calipers. I also wonder if it gives too much mechanical advantage / leverage allowing you to flex the front caliper (single pots are flexier than the 4 pot cousins), hence the spongy feel.

I think I will fit the 944 master cylinder, its front to rear ratio (having actually done the calculation now) isn't as bad as I suspected it would be.

Did you have any difficulties fitting the 944 master cylinder Rich? From memory people have said it bolts on, requires a tee piece to be used for the brake light switch, and use the remote "plugs" in place of the reservoir.

Cheers
Jeremy

ricola July 20th 2004 04:27

Was an eaasy fitment, just requires bolts with nuts as it isn't threaded like the steel bug m/c. Just a bit of bending of the hard lines and the switch fitted in a T. If I remember correctly, one of the front connections was very close to the tunnel side so it would be easier to fit that one before you tighten it all up fully to give you some movement.
Rich

Jeza July 22nd 2004 05:56

Rich and anyone else how has fitted a 944 MC to a beetle / aircooled VW.

How did you get around dealing with the remote reservoir. I thought it was just a case of using the VW fittings in the 944 MC, but the 944 rubber bungs ID is too big and the rubber bungs from the VW OD is too small for the 944 MC.

Is it just a case of fitting new rubber bungs?

Cheers
Jeremy

Jeza July 23rd 2004 06:50

1 Attachment(s)
Right everybody I've found the answer.

It turns out that orignial German MC's have small diameter plastic connector fittings and small rubber bungs.

After market ones have larger ones that are the same size as the ones used for the 944 MC.

These people have both:
Small
http://www.bughaus.com/master_cylind..._113611153.htm

and large
http://www.bughaus.com/master_cylind...113611153C.htm

And an image of the large connecting pipe, that I believe will fit the rubber bungs on the 944 mc once the reservoir is removed.

Cheers all
Jeremy

super vw July 23rd 2004 12:06

cool, i have a new MC (1303 unit) but i think its aftermarket SO i might be in luck when i got with a 944 MC.

So you have the 944 MC in hand correct?
When you get it all working, tell us how it works!

BTW whats the part number of the 944 MC you have?

Thanks !!

Jonathan

Jeza July 24th 2004 02:46

Jonathan


Not sure what the part number is - there aren't any part number like numbers that I can see on it. But it is the "ate" item.

I'll let you know when its in with the results.

At the moment I'm planning to separate out the front lines (there is 2 front line ports in the 944 mc). I'll use a plug in one side of the front T piece and run one new front line to one side and adjust the old front line to the other side.

The rear is lengthed with a T piece to use the pressure brake light switch and a short line to the new mc port - same as every one else.

Also an update on the plastic remote reservoir fittings. I had a lot of trouble tracking these down. None of the brake shops could help. I eventually found some in an old big BMW (7 series? from 70's?) at pick a part. So if you end up stuck then try the BMW parts department.

Cheers
Jeremy

Wally August 2nd 2004 16:39

Quote:

Originally Posted by ricola
I'll add my experience...

I started off doing the rear brakes first as there was a delay on sorting my front bearing adapters. Using the bug m/c, that was the best combination by far so I should have just drilled the front discs to Porsche pattern.

I agree!
Quote:

The bug m/c has not got enough displacement for the single pot front calipers no matter how much bleeding you do.
Rich
Thats not my experience...
I still use the stock m/c on my 1303 with 944 Turbo Cup brakes front and rear. The Cup brakes are even larger than the stock turbo ones, but I have a very hard pedal; can easily lock front brakes, but bias sucks! The back should give more brake action, so I'am not sure what the best way is. Mounting a m/c with even more travel up front certainly is not (for my car that is). Maybe a 23/23 m/c which can be squeezed in the front lines or s/th like that.
Because of the rear engine and 'reverse' weight distribution of the bug compared to a front engined/watercooled car, mounting the same m/c seems pointless to me. Fitting a m/c with 21/19 cups rear/front would make more sense to me...

I also have the 944 N/A brakes on my squareback now and, as with the bug, the pedal got harder after the swap! Logical, cause the drum brake always needs more travel to get to the drum, after which the spring retracts it.

I suspect, m/c diameters front/rear are just used to also get the required balance from the factory. The displaced volume when breaking may just be so little (with good seating, well broken-in pads), that 19 or 21 mm may not make a noticeble difference in that aspect.
Really, really make sure your pads are broken in properly before you judge any 'sponginess' you may think you encounter. Usually our bugs are not driven that much nowadays, so judging too soon the pedal feel is an easy mistake, I suppose.

Good luck all,
Walter

ricola August 3rd 2004 04:02

From all previous posts, the consencus seems to be that the single pots need more fluid than the 4 pots even though they have a smaller area, the longer stroke they require must be the reason. The sliding caliper seems to be pushed slightly at an angle by the 'spring' that holds one half onto the other fixed half's sliding face. If you see what I mean!
Maybe your N/A brakes were borderline and as they wore together that reduced further the fluid required as everything beds in together resulting in a pedal that is OK.

Rich

LOAF August 4th 2004 16:25

I have a question,

With all the debate of which M/C to use, can I propose another option..

Not sure if this will work, but food for thought.. I was looking thru the Wilwood Catalogue and noticed they sell may different bore sized tandemn master cylinders.. As well as Proportioning valves.

It may be the more expensive route but at least you could get the front to rear biase correct..

Here are the part numbers that I was looking at..
ADJUSTABLE PROPORTIONING VALVE
PART NUMBER: 260-8419
1” TANDEM MASTER CYLINDER WITH REMOTE RESERVOIRS
PART NUMBER: 260-7563

Haven't gone further with research yet... mounting seems similiar to beetle,
Attachment point to pedal, may require creativity...
They have long strokes to push a good amount of fluid..

All in in would seem like a good option, but not being a brake expert would like to hear some thoughts.. If to much over sized M/C you could use two proportioning valves.. One for the front mounted in the trunk and the other for the rear by the e-brake and play with it till you get it right..
Again just some thoughts.. since I am in the same boat.. except that my parts are still in the basement.. getting there, but not yet..

V/R

ALex
NNJ

zen August 4th 2004 16:49

i think Sandeep took a similar path. don't know if he used Wilwood, but similar path.

Pillow August 5th 2004 11:01

Why not just use a 911 MC?

Mike Ghia did that on his oval and from what I remember worked out quite well. That is what I would do for a Beetle with all discs.

On my '66 splittie I am running a 944 MC (ATE one - not Girling) with 944 single pots all around. So far the braking has been excellent... But of course a bus is much different than a Beetle weight wise.

Also you can get the "self bleeder" screws if you end up doing the brakes alone a lot. Kind of rich at about $10 each but well worth it if you end up playing with the brakes a lot.

Good Luck,

LOAF August 5th 2004 11:31

Pillow,

I read his write up on the 911, but he went with the vacuum assisted Servo and MC I believe.. It seemed like a lot of work for servo assisted brakes..

Not sure if you can run the 911 without the servo.. would be curious..

I just thru out the idea of Wilwood since the are reputable and seemed like a option, that had not been mentioned..

Alex

zen August 5th 2004 16:47

i think BoyGenius ended up sticking with the 911 m/s and removed the servo. maybe he will jump in here (assuming he is taking any time off of his new bike). :D

Pillow August 5th 2004 23:26

Thanks fot the update Loaf, I did not realize he used the servo on his oval.

But if memory serves me right the early 911s did not have a servo on them, maybe added this feature in 1974...?

Like in my Split the 944 had a servo to begin with but runs just fine without it.

... Just use the 911 MC without the servo, no problem! :)

I have a 1971 Chevy C-10 pickup with manual brakes. If you have enough leg for that then a Beetle is no problem, trust me on that!

LOAF August 6th 2004 08:29

Pillow, Zen

Thanks for the update..
I will recheck BG posts to see how much extra work is needed.. If it is minimal, then this seems like a great option.. with what seems like a better break bias..

If this is correct, why isn't everyone using the 911 MC? Seems like a no brainer.. but that's coming from the peanut gallery (me :) )

Alex

boygenius August 8th 2004 10:04

I used a 1987 911 sc (if it matters) and I removed the servo. The bolt spacing on the 911 M/C is the same as the beetle at least for the years of 911 that use the same M/C as mine. The M/C is not threaded so I used some longer bolts nuts with lock tite. There is also a flat rubber O-ring on the back side to seal up against the servo but it looks like it will seal up against the frame head nicley. There is one less opening in the M/C for brakes lines so I had to run a "T" fitting in for the front curcuit to retain the brake sensor. Also the angle of the rear exit requires a "LOOP" in the line to avoid kinks so my stock line was too short. If I was going to run a porportioning valve at this time it would fit perfectly right before the rear brake line grommet under the rear seat area since the stock line is too short. I used a Vanangon line since it was something like 8" to 10" longer and I just looped it at the end. The guide tube for the 911 push rod needs to cut down due to the angle at which the beetle rod enters the M/C. The pushrod also needs to be shortened to retain proper pedal geometry but I posted that somewhere before, I'll try to find it... I also ended up replacing most of the stock hard lines with longer ones from my local auto supply store. I'll see if I can put all the information together today if I have time. ( One note though... I haven't actually finished assembling the system so I don't even know how well it will work... )

Jeza August 10th 2004 00:50

Boygenius - what size is your 911 master cylinder.

Comments have been made before that the 944 brakes work as a system and although they came off a front engined car using the single pot calipers with the 19mm VW MC makes it even more front biased. From memory the 911 MC has no variation in the front and rear diameters to make up for the ratio of the 944 fronts (huge 54mm) vs the rears (36mm).

Shad Laws made some comments in this thread that are very relevant to this discussion.
http://www.germanlook.com/Forums/showthread.php?t=2183

I'm am slowly getting the 944 MC in so I will let you know what that feels like when its working.

Cheers
Jeremy

Wally August 10th 2004 02:50

Jeremy,
That old post of Shad is indeed very informative and gives us the possibility to put some ratio numbers to our 'feel'.

There is one thing that doesn't seem to add up with Shad's calculations though:
Using his front/rear bias ratio calculation, a bigger front cup diameter in your m/c, would yield a more rear biased set-up!?
To stay with the title of this thread: 'that doesn't seem right'

I can't figure this out yet as to why or what I am missing here...?

BTW, I'am running now the N/A 944 rear disks on my square (has stock 42mm front cup caliper diameter), which would give a F/R ratio of 1,36.
It brakes great, but feels just not as powerfull as my former 1303 with the stock 40mm front cup caliper diameter disk and rear 944 N/A, which gave a 1,23 F/R ratio, but that 1.23 ratio may be on the edge in wet conditions.
Because of the square d², a little variation in diameter gives quite a different result in the ratio!

All this leads me to believe that between 1.30 and 1.35 should be about 'right'.

Jeza August 10th 2004 06:04

Quote:

Originally Posted by Wally
There is one thing that doesn't seem to add up with Shad's calculations though:
Using his front/rear bias ratio calculation, a bigger front cup diameter in your m/c, would yield a more rear biased set-up!?
To stay with the title of this thread: 'that doesn't seem right'

I can't figure this out yet as to why or what I am missing here...?

It a leverage thing, if you increase the diameter of the slave cylinder in relation to the mc you increase the power to the brake. Increasing the MC diameter will increase the hardness of the pedal but not the power to the brake. Jeff Hibbard has a section in his book Baja Bugs and Buggies that explains it well without getting too technical. The most common example is those that increase the size of the slave cylinder in the rear drums / fit T3 drums to increase the braking.

Quote:

Originally Posted by Wally
BTW, I'am running now the N/A 944 rear disks on my square (has stock 42mm front cup caliper diameter), which would give a F/R ratio of 1,36.
It brakes great, but feels just not as powerfull as my former 1303 with the stock 40mm front cup caliper diameter disk and rear 944 N/A, which gave a 1,23 F/R ratio, but that 1.23 ratio may be on the edge in wet conditions.
Because of the square d², a little variation in diameter gives quite a different result in the ratio!

All this leads me to believe that between 1.30 and 1.35 should be about 'right'.

What you have now is probably a very good ratio for a rear engined car.

I also ran my beetle with the stock fronts and 944 rears (stock mc) and it brake quite unusually being so rear biased. I imagine you would get away with this most of the time, but my main concern is the differing way they would react when pushed, ie the rears would remain very cool and responsive while the fronts would get very hot and possibly fade (non vented rotor and small pad area in comparison to the rear).

The 944 brakes with the 944 MC gives a ratio of 1.41, which I reckon will probably work quite nicely.

Cheers
Jeremy

PS have you done brake performance comparisons or is it just a feel thing when you mention your 1303's powerful brakes?

Wally August 10th 2004 07:38

Quote:

Originally Posted by Jeza
It a leverage thing, if you increase the diameter of the slave cylinder in relation to the mc you increase the power to the brake.

I agree; it also complies with the formula Shad used.
Quote:

Increasing the MC diameter will increase the hardness of the pedal but not the power to the brake.
Now that doesn't comply with the leverage formule from Shad!. Tho I think you are very right about the hardness aspect of the pedal thingy.

Quote:

What you have now is probably a very good ratio for a rear engined car.
Yeah, I agree. Probably safer also in extreme situations than an even lower ratio.

Quote:

The 944 brakes with the 944 MC gives a ratio of 1.41, which I reckon will probably work quite nicely.

Cheers
Jeremy
Yes, I agree, but the mean reason for the calculated relatively low ratio (for a front engined 944) is that the 23mm (IIRC its 21mm, not 23 mm like in the thread where Shad chimes in, but lets use 23mm for calculations sake) front m/c cup diameter is in the lower part of the equation, thus decreasing the slave/master ratio of the front brakes!!!!!!!
i.e. : 944 fronts:
(54mm caliper cup diameter / 23 mm front m/c cup diameter)²= 5.51
944 rears:
(36mm rear caliper cup / 19.06 mm rear m/c cup diameter)²= 3.57
F/R ratio would then be 1.54
With a 21/19 m/c the ratio would be even higher at (54/21)² / (36/19)² = 1.85.
THATS the point I a trying to make in this equation:
The bigger the front cup of the m/c, the more REAR biased the set-up gets!!!!

Therefore, 180 degrees from my beliefs before, to get a more rear biased set-up from the stock front setten-up 944 brake system, you DO NOT install the stepped m/c the other way around: i.e. 19mm side to the front and the 21/23mm side to the back. That would worsen the problem.
The above holds only true of course IF Shads formula is correct (and 'knewing' Shad, he is quite an educated guy (even then), so I must really believe him)

Jeremy, I am realy curious what your or others thoughts are about my above 'conclusion'. True or false?

This would also explain the enormous front biased'ness' of my current 944 turbo Cup brake set-up on my 1303 SB with the stock 19/19 m/c ! I think I need the biggest step m/c (23/19?) I can find and maybe additionally a bit smaller front calipers or a front propotioning valve (if possible).

Quote:

PS have you done brake performance comparisons or is it just a feel thing when you mention your 1303's powerful brakes?
No, just a feel thing, but when I drove that car every day back then, I was very aware of any change, even the very subtle ones and this wasn't subtle, but a very, very strong brake action. You can only draw the conclusion that stock bugs are set-up very very conservative with rear break bias.

Greetings,
Walter

Jeza August 10th 2004 18:24

Quote:

Originally Posted by Wally
The bigger the front cup of the m/c, the more REAR biased the set-up gets!!!!

Therefore, 180 degrees from my beliefs before, to get a more rear biased set-up from the stock front setten-up 944 brake system, you DO NOT install the stepped m/c the other way around: i.e. 19mm side to the front and the 21/23mm side to the back. That would worsen the problem.
The above holds only true of course IF Shads formula is correct (and 'knewing' Shad, he is quite an educated guy (even then), so I must really believe him)

Jeremy, I am realy curious what your or others thoughts are about my above 'conclusion'. True or false?

Walter
You have hit the nail on the head. Now all we need to do is to spread the word, as I think this is where a lot of people get confused and go wrong.

My 944 MC however is definately a 23mm one as it is cast into the body. Actually 23.86 as they are imperial measures which should give me a good front to rear bias (although I don't know where I got the figure above?)

Quote:

Originally Posted by Wally
This would also explain the enormous front biased'ness' of my current 944 turbo Cup brake set-up on my 1303 SB with the stock 19/19 m/c ! I think I need the biggest step m/c (23/19?) I can find and maybe additionally a bit smaller front calipers or a front propotioning valve (if possible).

Steve C was chatting to someone on the shoptalkforums a while ago and the comment that came up was that sometimes the science can be taken too far. Sometimes feel / and a few test emergancy stops is the best way to go. To get things perfect you may need one of these
http://www.wilwood.com/products/Peda...fmbp/index.asp

Quote:

Originally Posted by Wally
No, just a feel thing, but when I drove that car every day back then, I was very aware of any change, even the very subtle ones and this wasn't subtle, but a very, very strong brake action.

It would be good to compare a few test emergancy stops to see how the different setups compare.

Cheers
Jeremy

boygenius August 10th 2004 21:37

Quote:

Originally Posted by Jeza
Boygenius - what size is your 911 master cylinder.


Cheers
Jeremy

To be honest I have no idea. I think I found the specs before I bought it but I can't remember what they are now. There are not any real significant markings on the M/C to denote bore size but the number (20) does appear over the front half of the M/C. Maybe somebody here has access to a porsche 911 service manual and can answer this question.

Wally August 11th 2004 01:55

Quote:

Originally Posted by Jeza
It would be good to compare a few test emergancy stops to see how the different setups compare.

Cheers
Jeremy

Glad you agree. It all makes more sense now! Need to get a 23/19 m/c for the 03 :)

Yeah, I did several emerency stops with my car then, both dry and in the wet and the fronts always (just) locked up first!
A friend of mine with exactly the same set-up (stock VW front disks, 944 n/a rear and stock m/c) but in a 1300 ('68) model and a 2,7 ltr type 4 engine took it to the circuit and reported that on braking hard and steering into a corner, the rear did lock up first.
Now that is a very extreme situation, but shows it really is depending what you do with the car that dictates how you want to set it up!

Thanks Jeremy,
Walter

LOAF August 11th 2004 10:27

As I had mentioned earlier, I am leaning on using the Wilwood product line, instead of the 944 MC.

They have a 1-1/16" Tandem Master Cylinder Part # 260-4893

Dimensions and specifications for this master cylinder are as follows:
Piston Diameter 1-1/16 inch, which is equal to 26.98 or 27mm

Fluid Displacement 1.20 Cubic Inches
Stroke Movement 1.35 inch

Bias Split 69% Front, 31% Rear

Given these dimensions, can anyone “guesstimate” if it would be in the ballpark. I would imagine using a proportioning valve for the front. But I am still learning..
Based on earlier readings I would think that the stroke and amount of fluid would be enough to move the 944 N/A single calipers in the front and back.

Thoughts, or comments appreciated?
But based on the front to rear ratio, it would seem like to high 2.2:1.
Alex

Wally August 11th 2004 17:06

Quote:

Originally Posted by Wally
Need to get a 23/19 m/c for the 03 :)

Just got out and measured the cup sizes of my 944 turbo Cup brakes:
Front: 44,0 mm and 36,0 mm (radial mounted 928S alike)
Back: 30,0 and 28,0 mm

With a 944 n/a 23,81/19,05 (which is even more accurate if the bores are indeed 15/16" and 12/16"), that would give a ratio of 1,23 which is low, but similar to my old 03 which had 1,26 and braked like a boat achor :D
Already saw one on ebay ;)

Greetings,
Walter

Jeza August 12th 2004 02:47

Quote:

Originally Posted by LOAF
As I had mentioned earlier, I am leaning on using the Wilwood product line, instead of the 944 MC.

Good idea.
Quote:

Originally Posted by LOAF
Based on earlier readings I would think that the stroke and amount of fluid would be enough to move the 944 N/A single calipers in the front and back.

It should be plenty.
Quote:

Originally Posted by LOAF
Thoughts, or comments appreciated?
But based on the front to rear ratio, it would seem like to high 2.2:1.
Alex

Sorry I can follow Shads calculations and use them on my car but thats where my knowledge stops. As you say the ration front to rear comes out as very front biased, but I don't know how the % bias affects that ratio. I suspect you may be better choosing an option with an adjustable bias bar. This would be a better option than fitting a proportioning valve.

Walter did you do the calculations of your current cup set up (with the 19mm Bug MC) as a comparison?

Cheers
Jeremy

LOAF August 12th 2004 09:54

Jeremy..

What is an adjustable Bias Bar..

I assume that this is something built into the MC..

Why is this better than a proportioning valve.. Please explain..

I think I may know why, might have an idea, but in the interest of not sounding to silly please explain..

Thanks
ALex

Wally August 12th 2004 10:23

Quote:

Originally Posted by Jeza
Walter did you do the calculations of your current cup set up (with the 19mm Bug MC) as a comparison?

Cheers
Jeremy

Yes, I did: that is now a whopping 1.92 F/R ratio !!
As said before, this does explain my current enormous front bias. I hardly wear off the light rust on the rear disk!

Greets,
Walter

Jeza August 12th 2004 17:00

Quote:

Originally Posted by LOAF
Jeremy..

What is an adjustable Bias Bar..

I assume that this is something built into the MC..

Why is this better than a proportioning valve.. Please explain..

I think I may know why, might have an idea, but in the interest of not sounding to silly please explain..

Thanks
ALex

Alex

I believe that a bias bar allows you to adjust the ratio between the front and rear brakes at the MC. It keeps it even no matter what pressure you put on the pedal. So the percentage split you mentioned before would be adjustable on a bias bar type.

I had a quick look at proportioning valves once. My understanding was that they limit the maximum pressure to those brakes. ie the max pressure plateus at a value so even if you push harder their will be no more pressure applied. They are commonly used in the rear lines to prevent the rears from locking up first- so this makes sense, limit the max pressure available to the rears because at max braking (ie panic stop) there will be a lot of wieght on the front - even in a rear engined car (don't tell me you don't have wieght transfer- how hard are your springs!!! :D ).

But put the proportioning valve in the front line (which is commonly not allowed by authorities) and you limit the max power to the front brakes. I'm sure with an adjustable one it could be set up very well, but I think for the best set up you would be much better off with an adjustable bias bar.

Feel free to comment on anything that I may have explained incorrectly, its a big learning game for me too.

Walter- yes thats quite a difference between the Bug MC and the 944 MC. Ideally you'd get something in the middle that allows a bit of fine tuning to get it just right :cool:

Cheers
Jeremy

boygenius August 14th 2004 18:04

I found this regarding the 911 sc master cylinder bore...

http://www.germanlook.com/Forums/showthread.php?t=2908

Jeza September 19th 2004 18:34

Hello all

I have been meaning to reply for quite some time to let people watching this thread know how I got on with the 944 MC.

Well it took a bit of fiddling to make it fit which is why its taken so long. I ran 2 new front hardlines, and a short section to a T piece for the rear line. On the T piece I fitted the brake light pressure switch. I'll see how well this works, but have heard that its a bit slow to react. If need be I fit a micro switch to the pedal cluster.

The way I fitted the MC is nothing new, but being a RHD car I did discover that my rear line exits very close to the brace under the spare wheel well. This required a really tight curve to the brake line and also a bit of clearancing to the brace (punch and big hammer). I've also bolted the T piece to a bracket to support it, which I had noticed many people hadn't.

So its mostly bleed up and the pedal feel and travel is 100 times better. I have much less pedal travel than with the Bug master cylinder. The travel is about the same as a Bug MC and stock discs & drums. I have not driven the car yet, but that is hopefully getting closer and I can report back to any that are interested on how it stops and feels then.

Cheers
Jeremy


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