1992 Volvo 240 sedan

ABS brakes

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When coming to a stop the car stops fine.
When you pump the pedal it holds pressure...so far so good.

The problem is that when driving and you come to a stop (say a red light) after about 30 seconds or so you start creeping forward and suddenly notice that there is room for the brake pedal to travel, when just before it was pressed until it hit that familiar wall (not a hard stop but the point where you have say "maximum" brake pressure. This is my first 240 with ABS so is it expected behavior? am I going crazy? where could the potential issue lay?

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I checked all the pads and rotors

flushed the system using the IPD flushing kit

all the lines look good and there are no leaks (no wet spots and the fluid level remains toped off

And there is a vacuum on the brake booster even if the car has been shut off for a significant time.

 

Sounds like the Master Cylinder, it leaks internally...

 

I have the same thing happening to me. I come to a stop and then after sitting briefly the car starts to roll and the pedal seems soft so I quickly release and depress the pedal till hard. Now it's doing it more often and during my first depression of the brake pedal while I'm still moving. Kinda freaked me out just today.

If you say it's the master, which is what I thought as well, because there are no visible leaks anywhere, how hard is it to replace? I've done brake/master cylinder work before on VW's and misc. brake work on Jeeps. Is there a tutorial somewhere on this site to guide me along.

Thanks.

MJ

 

P.S. If the info isn't there, I have a '91 240

 

It is probably a leaky master cylinder, or alternatively, if your car has ABS, the ABS unit may be leaking. It is easy to tell if it is leaking--the paint underneath the ABS unit will be ruined, typically bubbling, peeling and wet. My ABS unit is leaking like mad and i have to refill the brake fluid reservoir about once every 6 weeks. That said, it has been leaking longer than that, although I didn't realize it, and just thought it was the brake master cylinder.

 

Where is the ABS unit located. I don't think anything is leaking. The reservoir is full.

 

the ABS modulator is usually on the left side of the engine compartment somewhat behind the headlight and forward of the wheel well. its a space age looking thing with lots of brake lines coming off of it (2 lines from the master cylinder, 3 or 4 lines to the various wheels). there's two halves to it, an electronic/control half, usually under a black plastic cover, and the hydraulic actuator/pistons, generally anodized machinery with said plumbing. most every one I've seen clearly says ABS on it.

here.

 

Thanks!

 

I'm thinking it's the master cylinder. I'm not seeing any external leaking anywhere but will snoop around a little more.

Are there any tutorials online for replacing the master? I found a video on youtube by Eric the car guy on a Corolla which seems pretty straight forward. I'm working without a manual.

Thanks.

MJ

 

It really isn't any different than any other car other than the brake bleeding sequence. Before installing the master cylinder you want to bench bleed it. Once installed (2 nuts, 2 brake lines), bleed the wheels in this order:

Driver Side (US) rear
Driver Side front upper
Pass. Side front upper
Pass. Side rear
Pass. Side lower outer
Pass. Side lower inner
Driver Side front outer
Driver Side front inner

While bleeding, make sure you keep the fluid topped off so you don't run out and have to start all over.

 

In my case it was simply the master cylinder. the first of the 2 valves was leaking due to a bad o-ring, the second half was working fine. Replaced it to be safe and its all good.

the ABS system rarely goes bad, however it can leak. Mine is fine, no leaks or anything. A leak here would be obvious.

 

Not quite understanding the bleeding sequence act1292. I'm only aware of 4 bleeder valves, one at each brake cylinder. What am I missing?

 

One more question. Is there anything special I need to know about separating the reservoir from the master cylinder?

 

the front brake cylinders on these cars have TWO bleeds, top and bottom as they have two lines leading to them. this way if a brake circuit fails, you still have half braking on both front wheels plus one rear wheel.

 

Which wheels are the Pass. Side lower outer and Pass. Side lower inner located on, front or rear?

 

the front wheels have dual pistons, driven by separate circuits.

one half of the master cylinder drives the top piston on both front wheels and one rear wheel. the other half of the master cylinder drives the bottom pistons on both front wheels, and the other rear wheel. this design ensures that if a circuit fails completely, you still have adequate braking.

 

Precisely how mine failed

 

Are you guys sure? I think that only applied I non abs units. With abs, I think they eliminate that system, else how do you you get a single brake to run with abs?

 

Pass. side = passenger side of the car (United states model)

There are THREE bleed screws on each front wheel of the 240s (Pierce - the 740s may be different):
Upper means the top-most bleed screw
Lower outer means the lower bleed screw towards the outside of the wheel
Lower inner means the lower bleed screw towards the inside of the wheel

Pull one of the front tires off and you should be able to see what I am referring to.

To remove the reservoir, just pull it out of the rubber sockets. It may take some wiggling but it should come out.

 

Thanks to all!