Weak Brakes on 95 T-5r

warmblood58 · Post by **warmblood58** » 25 Sep 2017, 20:56

I have plenty of pad material, front rotors turned lightly, pads scuffed, brake booster check valve replaced - still weak. I am beginning to suspect booster but will double check to ensure brake system is bled properly. I did notice that inboard caliper piston on passenger rear side is stuck. I put spacers in the calipers after removing pads and pumped breaks to observe piston travel. I popped stuck inboard piston back in (too a lot of effort). Any thoughts on all this? I checked check valve removed from booster with engine running -tons of vaccum. I can hear the bellows in booster when I apply brakes -seems normal, no hissing - Anything I am missing?

warmblood58 · Post by **warmblood58** » 25 Sep 2017, 21:15

just read something about the ABS pump needs to be bled separately - is this true? I did a standard bleed when I bled this car last -

Post by **theWIFES_S70** » 25 Sep 2017, 22:06

The ABS pump only needs to be bled if you're replacing the master or if by some chance you let the reservoir run low. Doesn't sound like air in your ABS pump.

Let's troubleshoot:
- a check valve (which you replaced, so it's probably not the case);
- the brake booster vacuum hose (which would hiss and result in a hard pedal, if I'm not mistaken);
- the master cylinder which gives you a squishy pedal that travels down when at a stop light;
- leaky clutch slave cylinder can also give a false master cylinder feeling;
- bad brake booster... which I don't know what that feels like!
- air in your brake lines? sometimes even the best of us have to rebleed brakes. have you done two or three bleeds of every wheel?
- that bad caliper will probably have to be replaced at some point if it's original...

How's your brake fluid level? Have you been keeping an eye on it? abscate recommends putting a sharpie on your reservoir and monitoring it. This is the only way to know if you're losing fluid into the brake booster... The fluid shouldn't really change until you start wearing down pads significantly.

Good luck troubleshooting.

warmblood58 · Post by **warmblood58** » 25 Sep 2017, 22:13

Thanks, fluid staying consistent - I think I will bleed again using a different sequence than previous and see what I get, LF RF, RL RR -I usually bleed furthest away (RR) but I have read threads to the contrary using Volvo's recommended technique- inboard piston first then outboard on the fronts?

Post by **scot850** » 25 Sep 2017, 22:56

Have you checked the or replaced the pipe from the intake manifold to the brake booster? With age they can crack/split and perhaps you are not getting vacuum to the booster. Some cars were fitted with an in-line filter in the pipe and they can get blocked with dust/dirt and reduce the flow of vacuum. Also I can't recall if the filter has to be orientated.The vacuum pipe has a join under the battery try if I recall on the 850 so make sure to check there too.

Neil.

Post by **rspi** » 26 Sep 2017, 10:42

Sounds like you said that you have a bad caliper?

AKJeeper · Post by **AKJeeper** » 26 Sep 2017, 16:52

What's the procedure for bleeding the ABS pump on these cars? My '96 850 has somewhat weak brakes - it got better after I replaced the master cylinder, but still not quite 'right'. New calipers, new pads, new rotors, new brake hoses...the biggest change was after I did the master cylinder. I'm thinking it might be air in the system, but I've bled the crap out of each wheel several times, no air came out.

Post by **scot850** » 26 Sep 2017, 19:21

Talking to several people on this they are a swine to get air out of the system without a pressure/vacuum system like a Mytvac or however they are spelled. Pumping the peddle doesn't seem to work and is most likely to damage the seals in the master cylinder.

Neil.

warmblood58 · Post by **warmblood58** » 26 Sep 2017, 22:46

I have tons of vac as I started the car with the check valve removed and held my finger to it - had the strength of a small shop vac!

Post by **mecheng** » 27 Sep 2017, 11:47

scot850 wrote: ↑26 Sep 2017, 19:21 Talking to several people on this they are a swine to get air out of the system without a pressure/vacuum system like a Mytvac or however they are spelled. Pumping the peddle doesn't seem to work and is most likely to damage the seals in the master cylinder.

Neil.

That is true but the fix for that is put 2x4s under the brake pedal to ensure when bleeding you are not depressing more than the typical full stroke.