1983 brakes all overheating at the same time

[..P]

Hi guys,

been a while since I posted much, as the car has been sitting up for awhile and it is now gladly back on the road, but I still have some issues.

Brakes started heating up and really dragging, it got so bad that when I was on the interstate it would cause vibration too.

So of course I went through the following steps:

• Replaced rotors on the front as they were still original and perhaps warped.
• Replaced pads of course,
• Changed fluid and bled brake lines of course.
• Had the brake master cylinder replaced professionally by a good shop.
• Personally rebuilt the calipers after the master cylinder change did not do the job.
  
• Now I am still getting heating of all brakes while driving.

The other night there was so much pressure in the brake system the brake lights were on. What does that tell you?

I am puzzled.

I need help.

I once heard where old lines would gum up inside and allow pressure to the pistons because the master cylinder would provide enough pressure to overcome any internal constriction, but upon release from the master cylinder, then the gummed lines may keep some pressure on the pistons and keep them from retracting. Has anyone encountered this, is this valid. If so I'll immediately replace all lines.

Help!

(and thanks)

Paul

[..P]

I used a brake caliper lube, as noted in the kit I received and I belive in the workshop manual too. The lube was put around each piston as it was inserted.


edit comment: I suppose there may well be some of that lube inside the piston cylinder, maybe it is retracting into the hose and causing the piston to not retract? There was nothing in the kit or on the lube container that said to keep it out, seemed that it could be used liberally. I guess now that I have it down, I could pop all the calibers off again and be sure everything is clean. sheesh.

Paul

[..P]

More info:

I have been using a hand held pyrometer to check temperatures. After a 15 mile run it is not uncommon to see brake rotors approaching 500 degrees, and this is without much if any use of the brakes themselves.

I was wondering if there is some sort of a proportioning valve that has been overlooked.

As of now, I guess my alternative is to replace hoses and pop all the calipers off again to be sure they are clean, flush the system. If I am going to do the hoses, that would not be all that much additional work I guess.

Yes I do have the C-shape on the piston pointed in the proper direction upon insertion back into the caliper.

thx,

Paul

[Pete R]

Do you have the proper play in the pedal? Sounds like it's not releasing all the way

[..P]

Originally Posted by Pete R

Do you have the proper play in the pedal? Sounds like it's not releasing all the way

Yes, in the morning the pedal is gentle, but after the sytem heats up it is very tight and firm. It is almost like steam has built up inside the system and caused pressure, but any pressure due to hot fluid expansion should just push a little fluid back into the reservoir, right?

I may have some air in the system, a quick bleed would check that, but still if that is causing some sort of pressure in the system I would think it would just push a little fluid back to the reservior.

Paul

[Mrmerlin]

/the flex lines are suspect and should be replaced,
but I think that the push rod from the pedal does not have enough play in it.
NOTE there is also an adjustable pushrod on the engine side of the brake booster. and there is also a possibility that the brake booster isnt working properly have you done any work on the vacuum lines?
what fluid type did you use?
I suggest to use ATE super blue racing,
NOTE mixing different fluid especially the synthetic types can cause the seals to swell this will cause the MC and calipers to not return to the rest position and cause the issues your having

Also the ABS unit may need to have the rear brake pressure limiter replaced as these can rust and clog the system?

[MPDano]

Originally Posted by Mrmerlin

Also the ABS unit may need to have the rear brake pressure limiter replaced as these can rust and clog the system?

ABS on an 83?

[neil30076]

IIRC, ABS introduced in 84

[..P]

Yes indeed, this 83S does not have ABS.
I will check the pushrod play for sure.
The fluid I used was an approved type, but gosh I just can't remember the brand right now.

This whole issue began on its own, it seems, one day I just started noticing the drag, then it got worse, then I started in with attempted solutions, which lead me to replace the master cylinder, etc.
Since the brake lines are still original, I will replace those. Natually I'll flush the system again too.

Is there a proportioning valve or some sort of a gizmo that might be in need of adjustment. I should know this but I have not had my head in the workshop manual for a while and they don't tell a lot about diagnostics, just how to disassemble and reassemble. I'll hunt

The brake lines seem to be an issue here. It is really odd however, that the other night when the 4 wheels were hot, the brake lights were on, as if there was pressure in the system, and guess what there WAS pressure in the system becuase the pedal was much harder. Again, the adjustment on that pedal is also suspect, but when the car is cold that pedal seems normal, but i will certainly check again.

thanks guys,

comments are very much appreciated,

Paul

[Danglerb]

Never touched the insides of a brake in my life, but ... trouble in all four wheels makes me think the issue is up stream, something is pressurizing your brake lines. The two options seem to me to be pedal or booster. I would sort this out without driving it.

Motor off parked. Work the brake pedal as if you were driving and see if it firms up and then look for something wrong. Repeat this maybe a few times until any vacuum stored when the motor is running has worn off.

*** Talk to a real 928 mechanic.

[..P]

Okay guys, I'm going to do some more testing and I will report in.

comments always welcome!

thanks,

paul

[harborman]

With the car on jacks, are the wheels still hard to turn?? Sounds like something with the master Cyl, peddle, as Mrmerlin pointed out. How is free play in brake peddle? After the brake job was done, how did the wheels turn?? Very strange.

[MPDano]

I have to agree with Mike (DanglerB) and it being upstream. I don't think lines would be an issue if it's at all 4 wheels. Even though the Master Cylinder was replaced, are you sure it was a good one? Even when a Brake Booster doesn't work, it would just be hard braking (more effort of the foot pressure). Something is not releasing and I think it's your Master Cylinder. Did you rebuild all 4 Calipers? Without spending a grip on Brake Fluid, use normal dot 3 fluid from the local auto parts store for testing.

[MPDano]

Here's what I found online.

What causes brake drag?

A: Brake drag can be caused by a failing master cylinder, incorrect use of Residual Pressure Valves, misaligned calipers, seals in need of replacement or a badly adjusted brake pedal.

[neil30076]

Remove the vacuum line from the brake booster and plug the end that goes to the engine. Test drive ( carefully - you have no boost assist!) and see if the problem still exists. I have had the booster fail on a previous car ( 924 Porsche) and it did exactly the same - applied enough pressure to keep the brakes dragging on the discs and create excessive heat.

[Landseer]

Wow. Good info.

[MPDano]

Yo ..P!! Looks like you had the same issue 6 years ago.

928 Sliding Caliper brakes, pad replacement, overheating issues

928 Sliding Caliper brakes, pad replacement, overheating issues
The 1983 928 used a sliding caliper brake system, and I'm not sure how many years this was used. My passenger side disc has been heating up, so I went in for a look and while I was there I photographed eveything. If you need documentation photos, take a look, the system is really pretty simple. I like the big air duct on the 1983 928S which blows air right onto the disc too!

http://www.network54.com/Forum/message?forumid=426130&messageid=1126987073

Anyone having any tips about this overheating, please comment, because I'm not sure the issue is resolved yet, and anyone else out there in Porsche Land may be able to use the tips too.

regards, P

[aluminum]

To check for incorrect Play in the Master Cylinder Just loosen the Mounting bolts > about 1/8 inch <
and drive the car to check if the Problem is absent . Make sure you don't loosen it so much it well come off when you hit the brake.
Incorrect Push Rod play (to tight ) well build Pressure and apply the brakes . they well heat up Evan the fluid. This is a easy to miss Problem when replacing a Master Cylinder as one is removed and another installed but the Push Rod on most all cars Stays coming from the Pedal or linkage and is not a replaced part .
I never changed one on a 928 but have seen this Problem happen some dozen times or so.
Some linkage or pedal assembly get changed or someone adjusts the Push Rod incorrectly.
Too much Play well simply result in Low Brake pedal > to little Brake drag / pressure increse as the car is driven .
Could be some bad Valve also but I would look at the Adjustment first > simple to test it >

[MPDano]

Another reason to replace fluid now:

When should I flush out my brake fluid?

A: Once brake fluid has boiled, it no longer has the ability to resist further boiling, creates air in the system and should be completely flushed from the system.

[..P]

Hi guys,

Yes indeed, in 2003 I had brake issues too, but a disassembly, cleaning and reassembly of the calipers at the time seemed to fix it, without acutally opening them up. In cool weather it didn't seem to affect the system, maybe it was a coincidence. Sometimes when the system heats up, drags, vibrates a bit, then things settle down and I can run 50 miles without an apparant issue. It's driving me nuts. And yes, I did take the car into a professional shop, told them all about it, and the result was a new master cylinder I apparently did not need.....sheesh.

As miles continued to rack up however, the problem has come on more and more, causing me to pop all the pistons out and rebuild the system. As you can see in one of the photos there was some varnish on the pistons and a little internal pitting. This was cleaned up with a hone, very lightly.

The more I think about it and the more good comments I see, it appears to be a component failing with time and not a rod adjustment too long. My technique of replacing parts will soon tell if it is the brake lines, and if it is not, well at least I will have good brake lines. I sure appreciate the comments, I will go through them and spend some quality time with the car in the near future. I have a 13 year old niece visiting over the holiday so I don't think it will be car time over the 4th.

best,

Paul