87 3.2 Carrera Brake Issue

[popngear]

Hey guys,

I'm a new owner of an 87 Supercharged 3.2 Carrera and have been getting to know it over the last couple of weeks. One of the things I've noticed is that the brake pedal pressure it's extremely stiff (which is normally fine) but the stopping power is very lacking. There is no brake squeal whatsoever, just poor stopping power. Is the system likely in need of an upgraded pad? The braking strength is so poor I can't believe this is anywhere close to how it left from the factory.

Thanks

[KFC911]

Originally Posted by popngear

...., just poor stopping power. Is the system likely in need of an upgraded pad? The braking strength is so poor I can't believe this is anywhere close to how it left from the factory.

Thanks

Do you know the "history" of your car? You're correct....brakes are "awesome" on these cars if functioning properly. Personally, I'd do a complete R&R....new rubber brake lines (at the calipers) if they are still original, flush/replace fluid, new pads, etc. It's a fairly easy DIY project for a new owner imo.....good luck!

[Bill Verburg]

Originally Posted by popngear

Hey guys,

I'm a new owner of an 87 Supercharged 3.2 Carrera and have been getting to know it over the last couple of weeks. One of the things I've noticed is that the brake pedal pressure it's extremely stiff (which is normally fine) but the stopping power is very lacking. There is no brake squeal whatsoever, just poor stopping power. Is the system likely in need of an upgraded pad? The braking strength is so poor I can't believe this is anywhere close to how it left from the factory.

Thanks

Check to see what m/c is installed
stock is a 20.6
some owners throw a 23.8 from a 930 on, this makes for a lot of effort for any stop.

another possibility is pads, for street use a street pad should be in there

[MConn]

Put your foot on the brake pedal, and start the car - if the pedal feel doesn't change, your vacuum assist on the master cylinder may be bad, the pedal should go down once the engine vacuum helps push on the pedal. I have a car with a bad vacuum assist, and if seems like the brakes don't work as well as the car I have with a working vacuum assist.

Mike

[Bill Verburg]

Originally Posted by MConn

Put your foot on the brake pedal, and start the car - if the pedal feel doesn't change, your vacuum assist on the master cylinder may be bad, the pedal should go down once the engine vacuum helps push on the pedal. I have a car with a bad vacuum assist, and if seems like the brakes don't work as well as the car I have with a working vacuum assist.

Mike

that would do it too, one failure mode is for the booster to fill w/ b/f

[popngear]

Originally Posted by MConn

Put your foot on the brake pedal, and start the car - if the pedal feel doesn't change, your vacuum assist on the master cylinder may be bad, the pedal should go down once the engine vacuum helps push on the pedal. I have a car with a bad vacuum assist, and if seems like the brakes don't work as well as the car I have with a working vacuum assist.

Mike

I tried this out and the pressure does not change. Is there an online DIY on how to remedy this? Thanks for the advice doctor.

[popngear]

Bump ... anyone have a DIY on fixing a bad vaccuum assist?

[Bill Verburg]

Originally Posted by popngear

Bump ... anyone have a DIY on fixing a bad vaccuum assist?

Pull the vac hose off the booster and see if there is vac there. You can use a vac gauge but it's pretty obvious if there is vac or not.

Th booster can or m/c are the most likely failure points, If unfamiliar w/ basic diagnosis take it to a shop that knows 911s

[69-912-swt]

Would having a Supercharger have anything to do with it ?? Doesn't the vacuum on a na-3.2 come from the intake manifold ??

[DRACO A5OG]

Yes, Vacuum does get pulled from the intake manifold.

As far as OP's brakes, check to see if there is a leak in the brake line system, especially under the stone guard, there are T fitting and a straight fitting thru the tunnel, that may be leaking if not at the calipers.

[scarceller]

The super charger may be related, check closely what may have been altered on the line that feeds the Brake Booster. This vacuum port is located on the rear of the LHS intake chamber, right above cyl #3. At the rear of that chamber it has a big port that feeds the hose to the front master cyl. Can you take a photo of that plumbing so we can compare to the stock setup?

When they super charge they need to address this area since under boost you'll feed positive pressure to the brake booster, not good idea. So if they did nothing top help with this you'd pressurize the master cyl with whatever PSI the super charger can deliver.

[The cap'n]

Yup. The brake booster isn't working. It could be one of the many issues associated with adding a supercharger to a N/A 911.

The Cap'n

[Quicksilver]

A supercharged system will still create vacuum at idle otherwise it wouldn't slow down to an idle.

So the big question: Is the throttle butterfly before or after the supercharger?

If it is before you will simply need to make sure that the brake vacuum is coming from between the butterfly and the supercharger.
If it is after you will want to make sure there is a vacuum check valve near the vacuum port to retain vacuum in the system. You may need a vacuum reservoir (which often contains the check valve.) so there is more vacuum available for the system. In extreme cases you might need a vacuum pump.

But ... (there is always a but)
It sounds like you system is just kaput so the questions are:
- Is it hooked up? Simple vacuum test at idle by pulling the hose at the brake booster and seeing if it is sucking.
- If it is sucking then obviously the booster must be toast. So does the system have a vacuum check valve? The booster wasn't designed for a pressurized system so the boost could damage it.

The questions about vacuum reservoir would be asked after the basic system is working. Try tapping the brakes a couple times with some left foot braking while you are at cruising throttle. If it doesn't brake consistently then a reservoir would be a good idea.

[Travis Neff]

This may be of interest!

vacuum leak you probably didn't ever think of

[scarceller]

Could have been damaged if the super charger pressurized it. How much boost we talking about 5-7PSI? You really need to see if anything was done to prevent pressure from being seen by the brake booster, like a 1 way check valve? If nothing was done to assure no pressure ever gets to the booster you can easily destroy another new Brake Booster. Who did this super charger?

Originally Posted by The cap'n

Yup. The brake booster isn't working. It could be one of the many issues associated with adding a supercharger to a N/A 911.

The Cap'n

[popngear]

Thanks for all the suggestions and info, much appreciated. The supercharger is made by Paxton though I can't photograph the setup right now as the car is currently in Vancouver (I live in the Seattle area). To answer the boost question, the setup runs maximum of 5psi. Lots of awesome suggestions, the cheapest ones which I will start with first

[luyckxglen]

guys i have the exact same issue on my carrera / no supercharger..
I have no brake assist. i replaced all brake lines on the calibers- and what allso happens is on my rear calipers they stick a little for couple minutes before releasing.. now couple weeks ago one really got stuck.. and it destroyed my disc because i still had to drive home while it was stuck.. meaning big overheading of the disc+ brakepads etc..
Now i replaced the entire caliper+ brakepads But it still sticks after a lil driving..
Now before i replace the disc i want to fix it..
Any ideas im not familiar with vacuum etc i still have to replace all the fluid because i have noo idea how old it is..

[DRACO A5OG]

Originally Posted by luyckxglen

guys i have the exact same issue on my carrera / no supercharger..
I have no brake assist. i replaced all brake lines on the calibers- and what allso happens is on my rear calipers they stick a little for couple minutes before releasing.. now couple weeks ago one really got stuck.. and it destroyed my disc because i still had to drive home while it was stuck.. meaning big overheading of the disc+ brakepads etc..
Now i replaced the entire caliper+ brakepads But it still sticks after a lil driving..
Now before i replace the disc i want to fix it..
Any ideas im not familiar with vacuum etc i still have to replace all the fluid because i have noo idea how old it is..

Sounds like you may need to rebuild the rear calipers. Next time this happens do not drive her. But in a pinch, use your lug nut wrench and press the brake pedal down about 2 inches and open up the bleeder valve to hopefully release that frozen caliper and carefully drive home or better yet have it towed.

[luyckxglen]

yes but my brake booster is allso not working.; and i have replaced both rear and front calipers..