O.B.1

Brakes are dragging on my '87 and won't release all the way. Did a fluid flush and this helped a little, but the fronts still won't release all the way. Car has a little over 10k on the clock and most everything is in great shape. Looking for suggestions on where to start next on trying to get this resolved. Thanks for looking at my request !!!

SeanR

Time to put in a new master cylinder.

karl ruiter

Sean has a whole lot more experience than me, but I have had a similar problem on my '88 and it was the pistons in the calipers. There is no dust boot on the early S4 caliper pistons so they can become pitted or dirty and start to stick.

Lizard928

I would be inspecting calipers and MC closely to ensure the MC ports are open, and the pistons have no damage.

dr bob

Caliper maintenance, old brake hoses replace with new, verify pedal free-play, verify that fluid flows with almost no pressure from master cylinder to each wheel. Master cylinder failure mode that causes this problem is swelling of piston cups to the point where the bypass/bleed port is blocked with pedal in full-up position, not allowing fluid to move back when the pedal is released. Swelling happens when the rubber bits are not compatible with the fluid, or when a petro-based something is contaminating the fluid.

There are booster failure possibilites in here someplace too, where the MC piston is lot allowed to fully retract.

There are several stories here on RL of failing brake hoses that become check-valves. As the caliper heats in normal use, fluid expands and applies pressure to the pads, adds more heat, more pressure, etc.

A caliper piston that doesn't retract is easy to diagnose with the car up and wheels off. Apply the brakes, release, and identify that the brakes are dragging. Crack a bleeder screw to relieve pressure, see if the dragging disappears. If it does, you have a hydraulic problem upstream of the caliper (either MC or hose). If it still drags, the caliper is sticking and needs rebuilt/replaced. If it isn't the caliper, you can do the same test again but this time crack the connection between the hose and the hard pipe in the wheelwell. If it releases the drag when you bleed that connection a little, problem is at the master cylinder. No relief means the hose is the likely problem.

O.B.1

Thanks Guys.... if it is a M.C. ,can you recommend the best to purchase a replacement (sponsors,NAPA,Autozone ect...)

Thanks Again for the responses !!!!

Lizard928

928srus.com
817-430-2688
roger 'at' 928srus.com

dcrasta

10k as in 10000 miles on an 87?

Ya flushing the Brake system would be a very important start. (DOT 3/4 absorbs water and the system can rust/corrode with old fluid)

Secondly inspect the color of the fluid. Black fluid in the MasterCylinder is usually a sign of deteriorating seals. Over time the seals decay and the sediment turns the fluid from clear to black.

Thirdly you should rebuild the calipers. If the car is a 10k on the clock and that mileage is accurate you have a high chance of pitted caliper pistons. With a light touch and some emery paper and crocus cloth you can clean the pistons and bore up. A new seal kit and you should be good to go (with the calipers).

I would also recommend replacing the brake lines they can get old and there have been instances (I do not know of any instances with 928s) where rubber lines can rupture, and this usually will occur at the worst possible moment (Max braking)

Sitting still ages cars arguable faster than driving, because driving cars keeps the seals lubricated with fresh oil/fluid rather than allowing them to become exposed to air and rotting over time.

In any case a 87 car with 10k miles is going to need a lot of work as all of the rubber bits are still 20+ years old (and not replaced as with a car that had been driven daily since 87).

Good luck, (and dont drive the car until you get the brake situation fixed 'CORRECTLY' )

O.B.1

Hey dCrastsa
Yes Sir....10,000 on the '87. Everything looks like brand new on the "outside" ,thats why is so hard to find the problems when they pop up. I will call Roger and get the M/C ordered and start there. I can't wait for the "3rd Coast" since I live about 25 miles away from Marble Falls. There should be some great cars and great folks attending!
Thanks for the reply

Dads928

for what its worth I had the exact same symptoms, mine were temperature related however. The brakes worked fine for 10 or 15 minutes, then start to drag and wont release.

Master Cylinder ...

replaced, no issues since. you need small wrenches or very small hands, its tight in there...

outbackgeorgia

Wow!
Wish my 87 had only 10k miles!
Dave

WallyP

I would suggest that you don't just "fix the problem". You have some good suggestions on here - do dr bob's checks at least.

O.B.1

Hey Guys
Just received new M/C and stainless hoses from Roger this afternoon. It looks like I will be doing the replacement of these parts on Wednesday . I did double check that the binding went away when I cracked open the brake line between the old M/C and caliper.
Thanks for the responses !

Mrmerlin

replace the bias valve thats screwed into the ABS unit,
I will bet you a MC that its also bad if it is an original part

WallyP

Completely flush the system - front and rear.