I have a very old 1990 Volvo 740 SW Turbo with ABS…
(also called a 2.3L L4 SOHC 8V TURBO).

It generally drives great,
the problem is after driving for 15 mins or so and after things warm up
the brakes start to activate on their own (argh)!
Only slightly at first but gradually more and more firmly until I can’t drive it any more with all the resistance,
tapping the brakes sometimes releases their grip with a snap but then it starts self engaging again soon after or a min or 2 later.

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I heard from a local Volvo mechanic that it probably needs 1 of the following,
(I guess I’ll try 1 at a time, probably start with the booster.)

+ Brake Booster - I think it’s the 3rd one down in this list?:
https://www.rockauto.com/en/catalog/vol ... oster,1884
(Another forum ace thought it's most likely a bad booster!)

+ Maybe a ABS Hydraulic unit - ( on device is written Bosch part # 0 265 200 054 )
I can’t find it in rockauto.com's catalog but should be a fairly common item.
Crazy expensive new so hope to find a used one for $130 or less IF needed , gulp.
Might try eBay for my 1st time... I live in California, anyone know where to get one?

(Fwiw, it’s our 2nd car used only to drive within a 5 mile radius a few times a week...
it's nearing it's end of life and at 200k miles not worth a lot of repair investment.)
Thanks for any tips!
Rand

 

You can also go used. Try using car-parts.com to find some local yards or drive out to Rancho Cordova (recycle yard heaven!). Usually the ABS pump will set a code but the valves and stick and you don't get pressure to one or a pair of wheels. Could be the brake booster or the hoses - do you hear any whistling noises or a woosh when you first press the bracked after a bit of driving?

 

The brake booster may be the issue . Before you start buying parts either yourself or someone do a vacuum test on the brake booster. If the diaphragm is leaking it will give you the problem you have.

 

Had a similar problem with my '92 Dodge Dakota pickup. If I was on the freeway the brakes would be cooled off and they wouldn't lock up. But around town they'd run hotter and eventually lock up. I was attempting to get a salvage title for it, after a hit n run accident, and had to get a brake and lamp inspection. The mechanic checked out all 4 brakes and said one(the one that locked up) had a "hot spot". I guess that means it was slightly warped and as it heated and expanded couldn't turn any more(and probably transferred that heat to the caliper). If only 1 wheel is doing this then maybe this is your problem?

 

5 miles max a few times a week is barely enough to warm the engine up properly.

another source of such thermal related brake issues is air bubbles in the brake lines due to improper brake bleeding... those air bubbles expand when hot and apply pressure to the brakes.

 

The reason I considered the booster was from my personal experience with my Jaguar XJ6. I was driving to work at 60 mph on a local parkway when the car started to slow down and I kept pressing on the accelerator to keep speed up. Started smelling brake material and pulled off the road. Took my foot off of the gas and the car stopped with all 4 wheels locked up. Got out and all disc's were red hot. Towed it home and relieved pressure on each caliper to unlock the brakes. After a few hours when I pumped down the brake booster it wouldn't hold vacuum. Pulled it and took it apart. Diaphragm was split. Had it rebuilt and reinstalled it and all was good again. Just my experience.

 

Wow! What a gold mine this place is!
You all are very cool to reply so well and fast!

More info below if you have the time
but basically I think I'll replace the booster with a used one
& try to cheaply get the brakes bleed at the same time.
THX!!!!



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+ As far as a vacuum test on the brake booster...
I did the simple test I read online earlier today where I pumped the brakes 10 times before starting,
then pushed the brakes slightly when I turned the car on
and the brake pedal DID move down a bit,
which I was told means the vacuum in the Booster is ok(?).
I looked at hoses connected to booster too and they seemed ok.

- I haven't heard any air or swoosh when I brake.. sounds normal.
Basically the car runs great then after 20 mins or so of city driving (after it gets warmed up)
the issue first appears by making the car need a bit more gas against the slight resistance and could come to a stop on it's own with no gas,
and after a mile or so further would make it hard to move forward at all...
'sometimes' tapping the breaks numerous times would release the grip for a block or 2.

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Maybe some further notes will help...
though I understand if this is just too much info or impossible to narrow down with just words!:

+ Once when it started acting up badly I used some tissue to take out some of the brake oil from the master cylinder reservoir
because it seemed filled to high and that seemed to help.
+ I sometimes wonder if Jiffylube put the wrong fluid in it!
---
+ When it first did this behavior 8 months ago it seemed to effect 1 wheel..
The 1st mechanic thought is was the old caliper and replaced it on that wheel, but alas it didn't go away.
+ 2nd mechanic said he wanted to bleed the brakes. Though he never had time to do it. ;/
+ Then over time it felt like it effected all wheels...
and the 3rd mechanic said he let it warm up outside for 20-30 mins and put it on a rack and said all wheels wouldn't turn by hand.
He's the one who said it's either the booster or expensive ABS Hydraulic unit.

+ Parts - I've never used either but is car-parts.com better than rockauto.com?

Thanks SO much for any further tips!

 

Rock auto . As for a vacuum tester I made one up using and old hollowed out plastic vacuum valve. Tapped in a vacuum pump and gauge. Pumped it up and as expected it wouldn't hold. Found my problem. Oh I didn't have ABS on that car. Good luck

 

Random-Did you ever resolve this? Get another booster?

 

I'm planning on buying one from RockAudio and will report back... thx!
I'm debating to do it myself or have a volvo mechanic do it..
does anyone know if it's very hard to install properly?
thx!!!!!!!!!
Rand

 

Try driving on the freeway for the same amount of time. I'm pretty sure your brakes wont lock up. It's the stop n go of city driving that heats them up fast and a warped disc along with an over heated caliper will lock up pretty quickly.

 

thx for comments guys!!!

I don't think it's warped disc since 1 mechanic said after letting it warm up for 20 mins he couldn't turn all 4 wheels when put on rack.

Hey! - I just did a bunch of brake & vacuum checks recommended on net.. all pass BUT 1 doesn't..
I let it idyl for 4 mins.. turn off engine, apply breaks and it ever so slowly goes way down.. so this indicates hose leak or bad booster or check valve.. so the test says.

 

Sorry but just an assumption here as I would have thought that the brake hoses were checked. A bad hose will also prevent fluid from returning.

 

I agree it could be hoses .. or fluids or booster or master cylinder or ABS Hydrolic unit...

I just talked to my last Volvo mechanic who had put it on racks..
He (now) says he still thinks it's the ABS Hydraulic system.. but that it could be booster too.. and that the parts and labor for them is very expensive.
He also said they don't make the booster anymore and had 1 customer who put 3 'rebuilds' in that all failed within a year..
When I told him I can get a rebuilt one from RockAudio - which is really from A1 Cardone - he laughed and said he wouldn't trust something so cheap.
Arrgh, this car has over 200k miles and I'm starting to feel like I should just unload it since I can't see putting more than $250 into this brake fix.
Basically the more I go into it the more I could be chasing 1 possible solution after another.

Thx for all the friendly suggestions though!!!