N.Masco

The wife and I were driving home from a nice day in Malibu today, with mostly stop and go traffic on the return trip, but then significantly improving in Van Nuys. All of a sudden, the car does not want to move! I glanced at the dash lights, fearful that the TB had slipped since I'm about due for a retension, but nothing was glowing red. I punched on the hazards and got to the shoulder, with the car coming quickly to a stop. It seemed as though the brakes were locked! The engine was fine, but the brake pedal felt rock solid and the car did not even want to roll in neutral. I was certain that I had a seized caliper if not something making all four bind.

So, after a flatbed trip home and staring the car cold, the brakes seemed to work fine. I just pulled it up the slope into my garage, but felt no resistance. A cursory inspection of the brake discs with what is visible through my factory flats revealed nothing noteworthy. The fluid was changed recently with ATE Super Blue. Any ideas of what could have caused my AAA card to get a workout?

Lizard928

adjust brake pedal freeplay!

jpitman2

If the first cup in the master cyl is old and has gone soft, the edge can get close to occluding the bypass port (tiny hole) allowing fluid back into reservoir - or could be something blocking the port. Then as the fluid heats up and expands the brakes drag on more and more. Drive around the block until it warms up and see if it recurs. If it does, pop open the most accessible brake connection (carefully) and see if the fluid is under pressure, and check for a hot wheel/caliper.
jp 83 Euro S AT 49k

928Quest

Any fluid leaking to places unknown??? I needed to "top up" my resovoir every 4-6 months, because the fluid was leaking from the master cylinder to the brake booster. I did not know that at the time. After a couple of years of this, I had a very similar event occur, twice. Once on the freeway, the brakes came on forcing me to go to the emergency lane. Brake pedal was rock hard. When I shifted into park, the pedal suddenly went back to normal. Second occurance was similar, happened as I arrived at home, next morning everything was back to normal.

UKKid35

http://www.nichols.nu/tip615.htm

Mark

That definitely sounds like a master cylinder failure. NOT an overly expensive repair - and DIFINITELY a DIY!

BTDT!

Kaz

Masco is your car white? I think my ex girlfriend saw you pull to the shoulder on the 405. She said a white car like mine had just pulled over and I even mulled driving up there to see who it was until she told me the traffic was kind of brutal getting over the hill on the 405.

Jim M.

Sounds like the brake pedal push rod is misadjusted, it must be just slightly loose when the brake pedal is released. There’s a small bleed hole in the sidewall of the master cylinder, and should be located in front of the piston cup. When the pistons and cups are in the full released position, the exposed hole allows fluid to pass from the cylinder to the reservoir and back. If the brake pedal push rod is adjusted so the piston cups cover the hole, the fluid is trapped in the system. Heated fluid expands, lightly applying the brakes, heating the fluid more, which applies the brakes more, which heats the fluid, more, etc. If all four wheels are being applied, the problem is the master cylinder. If only one or two wheels are being applied, the problem may be a bad brake hose. The line acts as a check valve, allowing pressure to flow out to the brake caliper, but not back. A dragging brake will be hotter than the others.

Jim Mayzurk
93 GTS

Bill51sdr

Exact same thing happened to me on a previous 928. It had ABS so I was able to keep it moving until it got off the freeway. It is DEFINITELY the master cylinder, don't bother adjusting anything and trying again. Just change the master cylinder and be over it. Good luck!

N.Masco

Yup Kaz, that was me. It was not exactly the best place to stop but I had little choice. Thankfully AAA got there fairly quickly.

I also saw a sweet red 928 while at Gladstone's yesterday. Was that anybody here?

Anyway, I guess I'll try checking the rod before replacing anything. I am guessing this thing is in the passenger compartment at the brake pedal? I really have not looked at it since I got home yesterday so after I unwind from work today I'll poke around a little.

Thanks to all who replied.

-Neil Masco

'87 928S4

N.Masco

OK, so the rod adjustment did not do the trick for me, and I have a replacement master cylinder for it. The problem is that the reservoir is full of all sorts of crap that I would like to clean out, but this does not seem to be an easy task. I suspect that this crud is why I had this problem to start with. Does anybody have any advice for cleaning out the reservoir?

TIA,

Neil

jpitman2

Remove it and wash it in methylated spirits (or some solvent that is compatible with brake fluid). It just sits in 2 cheap grommets (~$3, same as used by MB, BMW etc - ATE parts). Might take a tug to release from the barbs, but then you can replace the grommets. When I got my 83 it had a soft long pedal - nothing in the reservoir. On filling, it just leaked straight out at the grommets as they were stuffed. $6 later it was all fixed.
jp 83 Euro S AT 49k

Mrmerlin

Hi Neil, to get the resivour off first get a turkey baster with a small hose attached, suck out as much fluid from the res as possible, replace the cap,then after covering your fender and engine with towels gently rock while pulling upwards on the res it should come out try to hold your fingers over the bottom of the 2 holes on the res as fluid will be dripping out, discard any remaining fluid, flush with brake cleaner, then wash the inside with some simple green and rinse out with warm water, this will get all of the stuff that the brake cleaner wont remove, after this pour in some alcohol and shake the res drain this out and repeat then blow dry with compressed air your res should look brand new, let this sit in a warm place or in sunlight and remove your master cylinder, after all the lines are snug on the master reinstall the res it might help to lube the 2 feed ports with a little bit of brake fluid they will slide into the new master, bleed the master first then start at the furthest wheel and work towards the the front of the car, good luck, Stan

N.Masco

Thanks, Guys. I got the reservoir mostly cleaned out, but now I am wondering what the crud was. It seemed to be way and coated the entire reservoir. Any thoughts?

This has me thinking that I should replace my hoses as well...

jpitman2

I think a thorough bleed through with new fluid will clean ost stuff out of the lines. Pressure bleeding will make this easier, just keep going until its clear.
jp 83 Euro S AT 49k