944T calipers on my 911

[jwetering]

I've installed the front brakes from a early model 944 turbo on my SC. The turbo brakes are aluminum 4 piston brembos. They stop great, but I'm not ecstatic about the pedal feel. They pump up hard, but the first application is typically spongy. They lines have been bled and bled again - my mechanic tells me the lines are as air free as they are going to get. I have stainless stell lines installed.

q1: How soft is an SC pedal supposed to feel? I've driven a few pre78 911 and post 83 carts and all their pedals feel harder than mine.

q2: I know SC caliper pistons need to be oriented a certain way so that the leading edge of the pad hits the rotor first, do 4 piston calipers have the same "toe in" setup? The reason this is a factor is that the 944T has these brakes installed at the rear of the disc, while the SC has the caliper atr the front, I guess this would only matter if the left caliper was installed on the right side and visa versa.

[ChrisBennet]

The 4 piston calipers displace more fluid so a larger master cylinder would probably be in order. The pistons are differentially size i.e. the leading edge ones are smaller. You often (usually?) just swap the bleeders and the line that connects the brake calipers if you are mounting the caliper "backwards" from its original orientation. -Chris

[GeorgeK]

Jwetering,
I hope you did invert the position of the bleed screws when you put the calipers on the front of the disc. If not, then 2 things:
- the bleed screws are at the bottom, meaning there could well be a ton of air in the calipers, or..
- You put the left caliper on the right side so that the bleed screws are on top, but then you end up with the pistons in wrong order in regards to the rotation of the disc.
BTW I put 964 calipers (same caliper, slightly smaller pistons) on my'76 Carrera 3.0, which has the same MC, and I have a very nice hard pedal, easy to modulate, with NO sponginess.
GeorgeK

[911pcars]

"They pump up hard, but the first application is typically spongy."

I'd guess a bad master cylinder. This typically happens after bleeding the system using the "pump-the-pedal-to-the-floor" technique. Abnormal stroke in the MC tears the seal lip and prevents a total seal when brake pedal is applied. I think it should be fine if you replace the MC and bleed using a gentler, kinder bleeding method.

Front 944 brake calipers have fairly large pistons. Bill Verberg can confirm if this requires a larger MC.

Sherwood Lee
http://members.rennlist.org/911pcars

[Bill Verburg]

True 944t front calipers come in 3 different flavors 36/38, 36/40 and 36/44. The rears came in only 1 size 28/30. there are other caliper that are externally identical to the above, ie 30/34 rear from 964t and 964RS.
Only the larger caliper will need a bigger MC when used with the stock M rear calipers. You have not improved your brakes in any way unless bigger 930 rotors were installed at the same time. However your f/r bias is way out of wack. You will have way too much front brake bias. When moving calipers from trailing mount to leading mount just swap the external bridges and bleeders. The bleeders must be at the top of the caliper.
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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[IMONBOOST]

Excuse my ignorance, but do calipers have specific designs to work under an ABS environment, such as 944 turbo and 964?

[Bill Verburg]

No! ABS is just a fine tuning compensation that responds to dynamic variables. Basic f/r bias is still necessary. ABS does allow slightly more aggressive basic bias though.
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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page



[This message has been edited by Bill Verburg (edited 10-30-2001).]

[SprintStar]

Originally posted by jwetering
I've installed the front brakes from a early model 944 turbo on my SC.

I'm curious about this modification. Is it a bolt-on or does it require adaptors?

And what can I do for the rears? I don't suppose the rears of a 944 Turbo would fit?

Thanks for any info. I'm considering brake upgrade options now.

Sprint.

[Bill Verburg]

I'm curious about this modification. Is it a bolt-on or does it require adaptors?

There are 2 ways to do it
the wrong way(potentially dangerous) by hogging out the mounting holes and fitting over Carrera rotors.

The right way by machining the calipers to accept axial/radial adaptors and using 930 rotors



The rear is actually easier in some respects as long as 930 rotors are used


In addition the m/c needs to be updated.

[Randy Webb]

Bill, What do you think about those kits to put Brembos on the front of early cars? They include the calipers and Perf. Prod. sells them in their glossy catalog.

[SprintStar]

Originally posted by Bill Verburg
There are 2 ways to do it
the wrong way(potentially dangerous) by hogging out the mounting holes and fitting over Carrera rotors.

The right way by machining the calipers to accept axial/radial adaptors and using 930 rotors

In addition the m/c needs to be updated.

Does anyone make the adaptors or it is a home project?

Hmm... Using 930 rotors means I have to move on to 16" wheels?

Thanks for the info, Bill!

Sprint.

[Glasgow 911SC]

Won't 15" wheels will still work with the 930 rotors....just?

[Bill Verburg]

Does anyone make the adaptors or it is a home project?

Either way there 's nothing particularly special about the adapters. However the caliper maching required is non trivial. When I did those there were not as many superior options(not requiring any machining) as are currently available.

930 calipers and rotors fit closely in 15s


The small Brembos will as well.

Bill, What do you think about those kits to put Brembos on the front of early cars?

There are 2 different front kits manufactured by Race Technology, Wayne sells them here as do most other retail outlets in North America. They are very nice kits.

[absinthe]

I know I am being cheap but the chance of getting this set up from some where like rancho recylcers seems a lot higher than other kits...

so how much machining for the calipers? where to buy adapters etc? Im trying to find a way to upgrade the brakes on my carrera with out dropping 3500 on a 930 setup. I would love to find brakes on a junkyard car and do the rebuild and work my self, how fesable is this.

[Bill Verburg]

JMHO(but what do I know)

It's not worth trying.

If you don't have the $ use Carrera front rotors and calipers w/ the most efficient cooling ducts/pads/fluid that you can afford.

[Colby]

I know this "upgrade" is looked down upon, but I too upgraded my '84 911 brakes to '87 944T calipers. I kept the Carrera rotors up front and used 930 rotors rear. The other options were just not economically feasible.

Most ppl will say nothing is too be gained by upgrading to 944T calipers if you don't also upgrade to 930 rotors. However, this was my rationale (even if incorrect): 1) the 944t calipers are much lighter resulting in less unsprung weight, 2) the 944t calipers have more clamping power, 3) the 944t brake pads have greater surface area allowing more dissipation of heat.

The downsides I have heard are mainly aimed at using a skinny little Carrera rotor with the larger caliper, the end result being you overheat and warp the rotor far easier. If you can lock up the brakes, clamping force isn't what needs to be addressed, brake fade is, and that is addressed by improving heat dissipation. Heat dissipation is improved by the larger pad surface, but the other (and more significant) improvement is the larger rotor.

To address this, I installed a front brake duct kit. Not as good as a turbo rotor, but a lot less money.

If you use a front Carrera rotor, then the swap is relatively easy. I elongated the holes slightly on each caliper to make it fit (as mentioned already, this isn't the safest way to do it, but I know of several track cars that have run them this way for years w/o problems). On the rear, you need take the calipers to a welder to fill in the stock holes, then drill new holes slightly closer in. The rear caliper also won't fit over the thick 930 rotor, and a few places need to be ground down just a little. Not a big deal.

I guess my question is why does this whack out the f/r bias? If caliper size, not rotor size, determines clamping force, and this matching set ('87 9444t f&r calipers) was used on the same car, why can't it be used on another car? Or was it meant that the largest 944t caliper w/ the smallest rear was a poor combination?

Colby

P.S. This project costed me $200 for the set of calipers off Ebay, $300 for all 4 rotors which I needed to replace even if I stayed w/ stock calipers (new Zimmermans..again an Ebay dealer), and $10 in hardware for a the cold air brake ducts.

[absinthe]

Bill most people trust what you have to say and given the state of both your car and your reputation they preceed you.

I was just looking for something with a bit more stopping power to go with weight i had lost off the car.

Two questions:

are the common 4 piston upgrades any lighter than stock carrera ones?

would there be any benifit or is it even possible to go to a floating or 2 pc rotor with the stock calipers? less weight? better cooling?

[Bill Verburg]

Caliper size, rotor size, piston size, pad material, rotor material, rotor operating temp and pad operating temp are all major contributors to bias. Change any of them and bias changes.

The 944t caliper on a 20mm rotor is down right asking for trouble, it is merely dangerous on a 24mm rotor.

[absinthe]

I get that part, I was wondering if you thought there would be anything to gain from going to a slotted 2pc rotor in the same size as stock with the stock caliper?

I have heard the lost wieght will be similar to a minor increase in active spring rate is this true?

Also is it true that 2 pc rotors cool more effectively than 1 pc rotors if so would this be a good match tto the ducts i have?

[Bill Verburg]

The following is quoted from a previous thread
"Here are some weights of some others
A caliper 11# w/ pads & hardline
M caliper 8# w/ pads & hardline
965rear cal 8# w/ pads, cal 6.5#, pads 1.5#
S4 front 9.25#w/pads
Bigred 10.25# w/pads

It's not the calipers that are heavy it's the rotors The 930 rotors are almost 2x as heavy as the 911s, the 322x32 is another 5# ea. You do make some savings w/ 2 piece rotors. If you are toasting your brakes any weight penalty is justifiable."
previous thread

There are lots of possible 2 piece rotors available
here's a possible front 290x25.4 from AP

another possible front 290x28


The benefit of bigger brakes is almost entirely in the larger rotors. The design goal should be to have the smallest rotors/pads that last for the entire duration of an event but no longer!

have you read this brief ?