Brake Booster Issue?

[stefhelm]

Hi All,
I've had an ongoing issue for quite a few years. It hasn't really got worse so I have not spent too too much time on it as of yet.

What I get is a hard brake pedal when I hop in the car, before I start it, as though you have pumped it several times with the engine off. It only happens when it is quite cold out (let's say -15C or less), and even then, it is intermittent, as all my issues seem to be! It recovers almost immediately when the car is started and I can't say I notice any issues when the engine is running, but without any assist, you have to press pretty hard on the brakes if you are parked on a hill when you go to start it. When it does loose the "boost", it seems to happen fast. I ran in to a store for maybe 5 mins today and the brake pedal was hard when I came out.

I have checked the vac lines up to the booster and the check valve at the booster seems to still work (at least at the time I check it... Could be failing at colder temps?)

I'm curious if there are any know common wear items here, or if this sounds more like a booster issue or master cylender issue. Maybe something simple, like the grommet at the brake booster, or intermittent failure of the check valve. I'm not super sure what would cause these symptoms.

Thanks all for reading!

 

[ekkoh99]

I have similar issues. When it is cold out and I park outside when I go in reverse out the driveway and hit the brakes, it takes a little bit to stop. Then when i press the accelerator, it takes a few seconds for the RPMs to go up and then everything is fine. Im going to take a look at the tandem pump because of a leak in the back but will also replace the brake booster line. Ill let you know if that improves things.

 

[stefhelm]

Sounds pretty identical, yup!

So even if there was trouble at the tandem pump connections, or in that line through the firewall heading to the booster, my thought is that things should stay under vac from the check valve right by the booster through to the booster. I would expect that check valve is a safety for just that - if you lose vac in a hurry, at least the booster retains whatever vac it has and likely will allow for a brake or two. This last time it happened to me, it was an in-and-out trip to the store. It was not sitting long, so vac must have dropped quickly. Also, I did my best to check the other components with a MityVac, so I think they are ok - but cold weather changes everything!

So a loss in the system would still be an issue, but for the pedal to be rock solid when you jump in, I'd think the check valve, the short line between check valve and booster, or the grommet in the booster are not behaving. Or, the booster is shot, I don't know exactly what the booster guts look like, but I suspect a big diaphragm that would either hold vac, or not. If that diaphragm started leaking, it would be a more consistent issue...maybe?

For sure let me know how things go on your end!

 

[Mozambiquer]

That's not uncommon for older cars, basically what would be happening is that the vacuum is leaking off. Check for vacuum leaks in the system. The best way I've found is to use a smoke machine, though not everyone has one of those. I had intermittent power brake issues, as well as low power sometimes on my Passat, and hooked smoke up and almost immediately found a crack in the line coming out of the vacuum pump. I repaired it and haven't had issues since.

 

[stefhelm]

I was able to pull and hold vacuum with a mityvac up to the check valve but it got a little tricky to both seal and pump out enough volume from the last leg of the tube, and the booster. Smoke would be ideal!

 

[DivineChaos]

Either check valve in booster is bad it your vac pump needs to be rebuilt.

 

[stefhelm]

I have had this issue through two tandem pumps, so I'm not expecting it to be the pump. I think the check valve either acts up when really cold, or, the rubber grommet it slides in to is not sealing when cold.

Has anyone actually had a brake booster fail? My thoughts are to just play the odds... If boosters don't generally fail, and I can measure vac from pump and it checks out, I may just get a new line with a check valve, along with the grommet, and replace due to being the most likely of causes.

 

[DivineChaos]

I have had this issue through two tandem pumps, so I'm not expecting it to be the pump. I think the check valve either acts up when really cold, or, the rubber grommet it slides in to is not sealing when cold.

Has anyone actually had a brake booster fail? My thoughts are to just play the odds... If boosters don't generally fail, and I can measure vac from pump and it checks out, I may just get a new line with a check valve, along with the grommet, and replace due to being the most likely of causes.

In all my years I've replaced 2 boosters

 

[stefhelm]

Any ideas on what a superceded part number for this line is? This looks to be the line I want to replace, but shows as not available on many sites.

Brake Booster Vacuum Pipe - with Check Valve - (NO LONGER AVAILABLE)

Found under the rain tray

www.ecstuning.com

 

[IndigoBlueWagon]

Are you looking for the hose that goes from the tandem (fuel and vacuum) pump to the brake booster? That's this one: https://www.idparts.com/vacuum-pump-brake-booster-line-b55-bhw-3b0611931e-p-4441.html

The pipe you show from ECS is no longer available. No supersession.

 

[stefhelm]

The line in your link goes from the tandem pump to the firewall, and then another line that I need goes from the other side of the firewall (in plenum area where battery lives), over to the booster.

 

[IndigoBlueWagon]

You could poke around in Europe and see if you can find one. Othewise you'll probably have to try to harvest one from a wreck or have it made.

 

[stefhelm]

Looking that way. I'm sort of surprised - have not had this happen with this car!

 

[IndigoBlueWagon]

Oh, it's happening. That car is 18 years old, low production, that engine code was unique to the North American market.

 

[stefhelm]

oh, its's not unexpected. haha. Just has not happened so far.
She is getting old. Have something new on order, and will probably keep this for the kids to learn on.

 

[BobZ]

I've replaced the booster on my car twice. First time, wife was driving and the brake pedal was hard as a rock. Replaced it and it lasted a couple of years to happen again to me. Turned out, there was oil getting into the vacuum line and turned out to be from the tandem pump. After it failed the second time, I properly diagnosed so I wouldn't have to replace it again... Oil and the bladder don't blend. Maybe not helpful to your research - but I wasn't thinking it was the tandem pump as I had replaced that a few years prior to booster going the first time... Tomorrow's project(s) are replacing the rear calipers (second time around on these) due to the seals at the emergency brake going and leaking fluid & coolant flange replacement due to coolant leak. Yours sounds like vacuum leak and hate to throw parts at it like replacing the tandem pump...GL

 

[stefhelm]

Thanks for that. I've had the vac line off now and it is clean, so likely not the case. For now, I pulled line and grommet, removed some rough looking paint and cleaned and sprayed the area around the opening on the booster with some rust proofing paint. Was a bit awkward to tape of and area and plug the whole, but got it sorted. Installed a new grommet and re-seated the line. Have not driven enough to know if it did anything.