Brake issue, 84 Carrera

[jlr69s]

Okay, time to revisit this problem. Just bled the brakes, starting at the passenger rear, driver rear, passenger front, then driver front. I also bled the hard lines at the master cylinder. Still no fix! Brakes still only stop about half power, cant lock anything up... Master cylinder in 3 years old, about 5,000 miles. Faulty??

I dont think its the proportioning valve as if it were defective the front would still work fine and the rears would lock up asap, correct?

[UrQuattro]

Is it possible that there is an obstruction inside of the vacuum booster assy? From your description, it doesn't sound like a screwed up circuit, as that generally causes the pedal to travel fartherthan normal and requires more effort, but you would still be able to lock up the wheels that have brakes working correctly.

You said it is like it hits a "stop", so the pedal no longer is able to move through the normal range of motion, correct? If that is true, then I would focus on the pedal assy, the vacuum booster, an the new master cylinder as it may be binding and defective. Also, try checking the free play setting for the pedal, maybe there is something going on in the actuating rod.

And I second the second poster's second line. Don't drive it at all. You never know.

Michael

[UrQuattro]

Oh, one more idea, try disconnecting the master cylinder from the hydraulic lines and then see if the pedal will move through the correct range of motion. Obviously this will require bleeding the he'll out of the MC, but it will isolate the problem to either from that point out, or that point in.

Michael

[Flieger]

Or just disconnect the MC rod and move the pedal. Then you do not have brake fluid everywhere.

[jlr69s]

So.... took the Carrera to the shop yesterday to have them look at it. I've been stumped. Guess what???? They couldn't find anything wrong and the guy (owner) said the brakes felt fine Brakes have been bled, new brakes lines, new master cylinder.

To reiterate what I'm feeling... Say Im driving at 50mph, slam on the brakes and slow down. I slow down pretty good, but I used to be able to lock up the brakes if I pushed hard enough. And it seemed that the harder you push the faster you stop. Now, the pedal pushes in a bit and hits a stop where I cant push it in any farther.

If I slam on the brakes, I hit this 'stop' in the brake pedal motion and slow down, albeit fast, I cannot lock up the brakes...

Any other suggestions before I start replacing pricey braking items?

[uwanna]

Originally Posted by uwanna

I had an identical symptom on my '80 SC. Tried everything with no luck, till I changed out the master cylinder. Voila! had super brakes once again.
your problem may be something else, but sounds like you've tried everything else!

EDIT: just reread your post and saw you replaced the MC, maybe the new one is defective. Just guessing.

Your problem is PRECISLY the problem I had on my car. Everything you have mentioned about not being able to do an agressive stop happened to me. I know exactly what you mean about feeling a "hard stop" in the pedal under hard braking. I mentioned that I had replaced the MC, but neglected to also mention that I replaced the power booster as well! In fact I bought a complete unit, MC, booster on Fleabay and all still assembled. Installed, and good as new! I initially thought it must have been the MC that fixed it, but now I'm sure it was the power booster. Given everything you have done, I would bet you also have a faulty power booster unit.
As an aside, I have seen complete units on sale recently on Fleabay from the several Pcar dismantlers that sell there. Here is one from the same guy I bought mine from. I have bought many parts from this guy and have been very pleased with value and fast shipping. (no connection, just happy customer) This is a relisting, because it went unsold at $49.00 !!!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200453681874

[gabenheimer]

From what I've read, you can eliminate the master cylinder, booster and pedal linkage as the problem. If you have a firm pedal and no leaks, then the master cylinder is fine. If you can drive normally and stop normally then the brake booster is working. If you are getting a full range of motion to bleed the brakes, then the linkage is also working. Sounds like your problem is only under hard braking. Do I have this right?

So what's left? Pads, calipers and rotors. Early in the thread you mentioned that you replaced the pads. How many miles are on the pads now? Did they get bedded in properly? You said that the rotors still have thickness but have some rotational grooves in them. If the rotors are dished or grooved the pads will not seat correctly. The rotors will develop hardened groves and the pads will never feel right.

I learned this lesson first hand. After rebuilding my calipers I replaced the pads using rotors that were slightly grooved. There was an improvement in the braking with the pads but I soon had erratic braking once again. I finally decided to replace the pads and rotors. That way everything was straight and true. I also made sure the caliper pistons were aligned at the proper angle.

Viola, I had the awesome braking power that Porsches are known for. After a session at Drivers Education event, I was practically giddy since I could break hard before a turn without locking up one wheel. I could also brake later because the pads were finally bitting.

I've had two carreras and both requried more pedal pressure than our '91. It can be quite a workout if your used to newer cars. I have to use twice the force to stop my '87 Carrera than with my '00 Jetta. Nothing will stop the Tahoe because it's a POS. I know because I have one.

Good luck!

[uwanna]

[QUOTE=gabenheimer;5256990]From what I've read, you can eliminate the master cylinder, booster and pedal linkage as the problem.

I would disagree that you can eliminate the booster. As I stated in my previous comment, I had "EXACTLY, PRECISLY" every symptom jlr69s mentioned in his thread. The only thing I did to fix was replace complete MC and booster unit!
It also seems he's done absolutley everything else with the exception of the booster. If I were a betting man I would put money on the booster being the fix!

[Dixie]

Based on the symptoms described, I second it's the booster. The reistance your feeling in the pedal travel is the booster rod going into "fail safe" mode.

[jlr69s]

Well thanks to all of you, uwanna, Capt. Carrera, and gabenheimer. That MC/booster combo is cheap enough that I will try my best to win it, no one bid please Even if its not it Ill have a spare, oh well. I do have another set of brake pads so I install those and Ill go ahead and buy new rear rotors as they are the ones with the grooves. So, once again we will see what happens!!! What is the proper way to bed in new brake pads??

[Dixie]

What is the proper way to bed in new brake pads??

Street pads? You'lll hear all sorts of answers. Personally, I just put them in and drive..

[uwanna]

jr69s,
Saw the brake booster on Ebay has sold, did you score it? Hope so, it was such a deal at $50. The booster alone at our host is $692.25!!!

[gtc]

Sounds to me like a bad seal in the master cylinder.
I have heard they can be damaged during the bleeding process if the pedal is pressed down too far.

[jlr69s]

Originally Posted by uwanna

jr69s,
Saw the brake booster on Ebay has sold, did you score it? Hope so, it was such a deal at $50. The booster alone at our host is $692.25!!!

YUP!! I won it!!! Cant wait to get it in! I did see the cost of a new booster and freaked out. So now I can eliminate two birds with one stone so to speak. $50 is a steal, and Ill have a spare brake booster or master cylinder (which ever one isnt defunct) so maybe I can make my money back.

Cant wait for this Friday, maybe Ill have it in and can work on it over the weekend, fingers crossed!!!

[uwanna]

Joe,
I think your problems are about to end! Glad you won the booster. You will be very pleased with "70RSR" as an Ebayer. He ships immediately, packs well, and has quality stuff.
One tip, when I installed the unit I received, everything worked well, but then had no brake lights! Turns out that there are different brake light switches on some MCs. Don't know when they changed, but some are 3 connector, and some are 2 connector. I have an '80sc and it had 3 connector brake switches, then installed the replacement booster/MC unit. It had 2 connector brake switches on it (but I failed to notice!). Turns out the cable to the switches fit either switch, arghh! So after the install, I had to troubleshoot why I had no brake lights!
Then had to contort my "ham hands" into the cramped space to replace the switches. Just make sure what you have before you install!
Good luck with the install, and let us know the result.
Grant

[jlr69s]

Thanks Grant... turns out I didnt win the auction. Someone bid at the last second and won... but thats ebay, I guess. I did, however, find another auction for a MC only for $50 shipped so I took it. Should be here soon and Ill let you know the out come. I did notice the different brake switches available from out host. I will have to see if they are different. I hope they were different between the SC and the Carrera, in that case I should be fine with the ones I have as this MC is from a parted out '88.

Talk soon!!

-Joe

[uwanna]

sorry you lost out on the booster that 70rsr had, looked like a nice one. You said you bought an MC on EBAY. Did you mean an MC and booster, cause your problem is probably the booster. Just a new MC will leave you with the same problem.

You probably got sniped on that booster! See below on how to prevent that!

Here's a tip on buying stuff on Ebay. Get yourself a "sniper program". I have one called Auction Sentry, it's awesome! Go online and Google "Action Sentry" . You can download it for free and have a 30day free trial. After the free trial it cost
$9.95 a year. When you set it up, you choose an item you want to bid on, decide the maximum you want to pay, and how long before the end of the auction, you want to "snipe" i.e.bid . I set mine to bid 8 seconds before the end of the auction! Then you forget about it, except when anyone bids it pops up a window and lets you know the status of your item. When the end of the auction comes, at 8 sec before the end Auction Sentry bids for you and WHAMMO, you bought it. You can be out working on your Pcar, or lovin on your honey and your bidding is on automatic! You don't have to bid in "tit for tat" bidding, and you never tip your hand or bid up items, only to see the price go up. I have scored tons of items this way, and the $9.95 has payed for itself many times over! Try it, you'll like it!

[jlex]

auction sentry

[rbarton]

Hi, bringing an old thread back in hope that the OP can share how they resolved this. Or maybe there are other ideas if he is no longer active on the forum.

My '86 Carrera has the same issue as described - the brake pedal feel normal for the first part of it's travel but then seems to hit a 'stop'. I can push (very) hard and the car will stop pretty well, but I can't get the brakes to lock up. It has done this since getting the car running again after an extended hibernation.

This car has newer soft lines and the brakes have been completely bled twice now. I just put in a new master cylinder hoping it would resolve this, but nope...

I'm leaning toward the booster at this point, but note that it does seem to function at least to some extent - I can pump the pedal a couple of time and start the engine while maintaining pressure and the pedal will drop slightly. I also verified good vacuum at the inlet to the booster when I had the master cyl assembly out.

Any other way to see if the booster is causing this? It looks like there are limited options on coming up with a replacement. Or other ideas?

Thanks for the help!