96 960: issues with braking and brake pedal

Post by **CIK7** » 24 Oct 2020, 16:05

Since I bought the car, the brake pedal went down pretty far. The seller said this may have something to do with ABS, but I'm questioning that. But the pedal has stayed the same, not let me down. Yesterday I ran into a 6" deep pothole while turning left, the suspension made a huge bang, and now my brake pedal has been VERY strange. The first time I started my car with brake pedal depressed after the pothole, it let out a strange hiss, then resumed to almost normal. Today, it hissed again. Now the brake pedal almost completely bottoms out and when I do brake, it constantly sounds like air is being pumped, even while keeping the pedal still, in the same spot. Also I'm not sure if it's relevant but 2 (both front sides) black soot (like coal) spots, about 3-4" wide, appeared in my driveway. Do I need to adjust the brake booster, replace it, or is this a different issue?

Post by **volvolugnut** » 24 Oct 2020, 19:00

First thing, before you drive again, check the brake fluid level. You may have damaged a brake line and are leaking brake fluid. You should not have the brake pedal go to the floor. Read up on brake system design and repairs. I think you have a leak or maybe bad master cylinder.
Your 960 had low mileage the last few years, right? You may be due for a brake fluid flush.

volvolugnut

Post by **CIK7** » 25 Oct 2020, 09:52

volvolugnut wrote: ↑24 Oct 2020, 19:00 First thing, before you drive again, check the brake fluid level. You may have damaged a brake line and are leaking brake fluid. You should not have the brake pedal go to the floor. Read up on brake system design and repairs. I think you have a leak or maybe bad master cylinder.
Your 960 had low mileage the last few years, right? You may be due for a brake fluid flush.

volvolugnut

I've only had this car since 8/11/2020 with 140,205 miles, currently 141,846. Issue has nothing to do with the brake booster then, no? Edit: I just checked brake fluid. It seems to be good. It's up there at the max. Maintenance records indicate brake fluid flush at 60,240 miles. I already have brake fluid so I can do a flush, but I'll also look at brake lines too. I'll take a look at brake lines later on to find any tiny leaks. What do I do to figure out if it's a bad MC? Should I just replace it?

Post by **volvolugnut** » 25 Oct 2020, 10:25

If you have no leaks, the brake fluid tank is full, the brakes are well bleed of air, and the brake pedal goes to floor with engine off, then the master cylinder seals are likely bad. The seals are letting fluid past the piston and you are able to press the piston/pedal to the floor. What date was the last fluid change? Years are worse than miles. The brake booster only increases the force applied at the master cylinder.
Do you have a pump or helper to do the flush? You can get a quick idea of the quality of the fluid by drawing off some through a bleeder. Be careful not to let any air into the brake system. If the brake fluid is cloudy or dark, you have rust in the system.
volvolugnut

Post by **CIK7** » 25 Oct 2020, 11:09

volvolugnut wrote: ↑25 Oct 2020, 10:25 If you have no leaks, the brake fluid tank is full, the brakes are well bleed of air, and the brake pedal goes to floor with engine off, then the master cylinder seals are likely bad. The seals are letting fluid past the piston and you are able to press the piston/pedal to the floor. What date was the last fluid change? Years are worse than miles. The brake booster only increases the force applied at the master cylinder.
Do you have a pump or helper to do the flush? You can get a quick idea of the quality of the fluid by drawing off some through a bleeder. Be careful not to let any air into the brake system. If the brake fluid is cloudy or dark, you have rust in the system.
volvolugnut

Lol it's been a while 8/29/01. Yesterday I unscrewed the brake fluid cap. Was I not suppose to do that? I'm still a newb among the many things I know about P80s. Lol I'm goofy and your lugnut. Sounds about right.

no stains are in my driveway. So do I need to change the MC seals or MC? I'm guessing the giant jolt from the pothole could've disrupted the brake fluid pressure, popping the MC seals. Am I on track?

Post by **volvolugnut** » 25 Oct 2020, 11:33

CIK7 wrote: ↑25 Oct 2020, 11:09
Lol I'm goofy and your lugnut. Sounds about right. n

yes. it is funny.

Ok to open the fluid fill cap. Air from that end does not need to be bleed out. But do keep the cap on to keep out dust and moisture unless you need to add fluid. Some MC can have seals replaced, but you generally need to hone the cylinder of the MC. It is a tradeoff of work effort and costs to just replace the seals or entire MC. The MC should be separate part removable form the booster.
volvolugnut

Post by **CIK7** » 25 Oct 2020, 12:20

volvolugnut wrote: ↑25 Oct 2020, 11:33 Ok to open the fluid fill cap. Air from that end does not need to be bleed out. But do keep the cap on to keep out dust and moisture unless you need to add fluid. Some MC can have seals replaced, but you generally need to hone the cylinder of the MC. It is a tradeoff of work effort and costs to just replace the seals or entire MC. The MC should be separate part removable form the booster.
volvolugnut

Hone the MC meaning what? And cost related, do you mean it would cost pretty much the same whether replace seals or whole MC unit?

Post by **volvolugnut** » 25 Oct 2020, 13:20

https://www.homedepot.com/p/Powerbuilt- ... /204505222The MC piston moves in a cylinder like a piston in the engine bore. As brake fluid absorbs water, the cylinder will corrode. A brake hone smooths the master cylinder inside so the new rubber seals will not leak.
For cost comparison, check your favorite Volvo online supplier for MC seal kit and complete MC cost. For example, my Ford truck seal kit is $20 and the completed non rusty MC is $55.
volvolugnut

Post by **CIK7** » 25 Oct 2020, 14:07

volvolugnut wrote: ↑25 Oct 2020, 13:20 https://www.homedepot.com/p/Powerbuilt- ... /204505222The MC piston moves in a cylinder like a piston in the engine bore. As brake fluid absorbs water, the cylinder will corrode. A brake hone smooths the master cylinder inside so the new rubber seals will not leak.
For cost comparison, check your favorite Volvo online supplier for MC seal kit and complete MC cost. For example, my Ford truck seal kit is $20 and the completed non rusty MC is $55.
volvolugnut

The whole recondition for me also might be about $20. A new MC is $79 and reman MC is $45. Im wondering if I can use a fine sandpaper drill bit for the honing. Is this the seal I need or not (see pic)?

Post by **volvolugnut** » 25 Oct 2020, 14:56

No, this seal shown is the seal for the tank. Neither IPD or FCP have a seal kit. Beware of off brands that may have bad rubber.
A sandpaper flapper should work if it gets the cylinder smooth and shiny.
volvolugnut