early 944 brakes, stock MC....dosent feel right

[Wally]

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!

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]

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]

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]

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

[Pillow]

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]

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]

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).

[Pillow]

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]

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]

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]

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]

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]

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.

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]

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.

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.

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.

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).

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]

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?)

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

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