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

[super vw]

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

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]

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]

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]

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]

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]

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]

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

[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