G Man

I have gone through the brakes on my 81' and the brakes still feel llike they are only stopping at about 1/4 of their ability. I know that these cars are not known for their breaking ability, but mine are way low on power. I have had the rotors turned to make sure they are not warped and installed new pads and bled the system until I had nice clean fluid out of the bleeders. I have done the booster test "bleed all vacume out of the system and start the car with the brake pedal pushed and see if it depresses a little." Can any one tell me what the hydraulic pressure at the caliper should be if measured through the bleeder screw port. I looked in the archives and found a post where someone said somewhere between 250 psi and 700psi. That seems like a bit of a large spread. I consulted my local hydraulic shop and they told me about 5 psi. I think this would be the easiest way to tell if there is a problem with the pressure regulators or possibly something else. My local "brake" shops were useless for info. I don't want to just start throwing parts at my car as the budget is tight. If any one here has experience with these brake systems can you please advise me. It is to the point that I don't want to drive my shark and that is not good.

GlenL

I've never seen a number for the pressure, but it ain't 5 psi. Hundreds is more like it.

Does it pull? What pads do you have? Did the pistons go back when you replaced the rotors? Front and rears? Is the brake pedal firm without sinking?

Can you lock-up the brakes at speed? Find a deserted street and lock them up at about 25 mph then get out and check for skid marks.

Your car has a diagonal pressure balance in that the RF is tied to the LR and the LF is tied to the RR. These are supplied through separate pistons inside the master. I'd think that there would be pulling if one was weak.

John Struthers

Jim,
Not much, but FWIW.
I have a 82' Weissach, and I bought my son a 81'. Both are 3 spd auto's.
1. While I haven't read any 60 to 0, or, 80 to 0 time and distance to stop tests I really have to say the brakes are great on the 81' and phenominal on the 82' Though the 81' seems to be a bit spongy and sometime hard peadles -no feel -.
2. Do yourself a favor and mic' the rotors. If you have done all of what you described above the only thing I could think of is the Booster, Master, irregardless of testing.
OR... you weren't the only owner to have turned the rotors.
For all you know they have been faced 3, maybe 4 times and you could be under spec.
The rotors are fairly beefy -in my opinion- and while they still look GOOD the pistons and pads may be in for a stretch.

Old & New

5 psi sounds like the pressure that the dreaded blue hose pops off at the master, when you are bleeding with one of those garden sprayer gizmos...

G Man

Glen the pedal is nice and firm and does not sink. I did push the pistons in a little to make room for the new pads. I CAN NOT lock up the brakes from any speed and believe me I have tried a panic stop and it was a joke. The car does not pull, it just won't stop. I put in metal master pads and the rotors were mic'd to make sure they were within spec both before and after turning. Is there another test for the booster that I can try other than the one I described earlier?

ViribusUnits

I'm deffently thinking vacuum brake booster.

You should be able to lock the brakes up sometimes, some how, at some speed.

If you can't, there is something preventing you from getting full pressure, and the easyest explination is bad vacuum booster.

Old & New

Make sure you have vacuum at the booster! Clogged valve, leaks, etc? Defective booster?

GlenL

Sounds like the booster needs to be checked. A miti-vac can be used to check for leaks. Could be the rubber grommet at the inlet.

As an outside chance, stick a piece of string into the booster to check for fluid. If the master leaks in can run inside the booster.

Does the A/C system work right? The brake share that vacuum supply.

John Struthers

ERK!
Could this be a simple case of the 'BLUE" checkvalve being backwards?
I think the method of checking it was to remove and BLOW, flows one way only. Not sure about mis-routed Vacuum lines.
V Units had a leak quite awhile ago and was noticeable to him only when he saw the slick on the inner fender well below the Master Cyl.
I don't recall him mentioning a brake warn/caution, or. any brake problems for that matter but his car did swap ends on him once or twice.
VU ???

ViribusUnits

The swaping ends has nothing to do with brakes or lack of brakes. It has everything to do with too much throtal on worn tires, uneven roadway, overcorrection, and a little moisture. I've kept my foot of the right pedel, kept good rubber on the ground, and done a little practiceing, and am much better now, thank you.

I had a leak through the body of one of the brake light switchs. All of the brake fluid leaked out, and then I had no brakes. I mean NO brakes. I had to stop with the parking brake. The problem quickly became ovious when I poured more fluid in, and it started pooling below the car. I traced it back up, and found the switch as the problem.

However, my problem was off/on type deal. When I had brakes, I had BRAKES, when I didn't have brakes, I couldn't stop!

SharkSkin

That may be your problem. Metal pads may not always be suitable for the street, as they tend not to work too well when cold. Find yourself a place where you can safely do some 60-0 tests. If my hypothesis is correct, you will find your second and third stops will be shorter, the brakes will begin to work better. This is aside from the normal and expected need to "bed" any brake pads before they work properly, especially if the rotors were turned too smooth.

If there is no fluid leaking anywhere, and you can get to a suitable spot with plenty of room in the event of brake failure, try a couple of hard stops to get the brakes hot and see if they improve.

Be VERY VERY careful though, and until you get this figured out drive the car as if it had NO brakes at all. Hopefully this will keep you out of trouble in the event something lets go.

John Struthers

Some other things...
Why didn't you replace the rear pads?
I read your earlier posts' on the brakes, did the brake pressure Warn stop?

Thom1

See http://www.pelicanparts.com/techarti...eed_brakes.htm for brake BLEEDING procedures. I use a one man bleeding tool. It is just a check valve (one way) that slides over the bleeder. I pump the pedal with the car running until I see solid blue going through the tool's clear hose, add some more pumps, then close the bleeder valve. (However, now I would start by using the check valve type of bleeder valve (speed bleeder). I keep filling the reservoir up to where I can see fluid so I am sure no air is getting in. Pressurizers that keep adequate fluid in the reservoir should be fine, too. BLEED SEQUENCE: Master Cylinder, RR, LR, RF, LF. Do inner bleeder then outer on each caliper before moving to the next caliper. Use ATE Super Blue Racing brake fluid. Alternate flushes with Gold formula. It is German with a high boiling point.
PICTORIAL PROCEDURES:
1. John Pirtle’s site: http://members.rennlist.com/pirtle/svc.html
2. Tony’s Site: http://members.rennlist.com/v1uhoh/brakepad.htm
3. Portia’s Site: http://www.kondratyev.com/porsche/vacuum_boost.htm
Greg Nichols’ site has WRITTEN troubleshooting PROCEDURES and more at: http://www.nichols.nu/tips.htm

G Man

Thanks all for the input thus far. Dave, I put in metal masters because that is what the german car repair shop had on the shelf. I searched the archives and found some info on metal master pads. It seems that they are the prefered pad of many listers. No I did not replace the rear pads because they look to be almost new in terms of wear. I did get the brake pressure warning to clear by disconnecting the battery ground for a few seconds. The old fronts were barely worn but since I was having the rotors turned I had to put in new pads. I have good vacume to the booster and the check valve is working properly. Also the booster holds vacume when tested. I still don't know if this means the booster is good. I am not loosing brake fluid so I know I have no leaks in that area. I did some research and found a place in NC called master power brakes that gave me some good info. I was asking in an earlier post about caliper psi and did not get a definate answer. The tech at master power said I should have about 1000psi at the caliper while applying moderate pedal pressure. Bought a hydraulic pressure guage from the local hydraulic shop and now I am playing hell trying to find adaptor fittings to mate the 1/4' npt of the guage to the caliper bleeder threads. Once I get past this obstacle I can see what I have for clamping pressure at the caliper. I know I will figure it out one of these days. It is only fluid being pushed through a few valves and lines. Just a matter of finding the weak link. I will report my findings when the battle is done. Thanks again for the input.

Marc Schwager

FWIW on my 1980 (with 85 rotors and calipers) I can definitely lock up the front wheels when I stand on the brakes.