The other day I was running some errands in the '80 Dasher. After running into the store for 5 minutes I started the engine, and the oil pressure light didn't turn off. I had checked the oil level that morning, and it was full so I thought the wire had fallen off again. I checked the wire, and when I got back in the car the brake light didn't turn off after releasing the parking brake. The brakes were HARD, so it seems like the light was on due to a loss of vacuum. Since I wasn't far from home I thought I'd drive it carefully back, and within 30 seconds of driving both lights went out and the brakes were back to boost.
Could it be that there's a problem with the vacuum pump which is allowing the oil pressure to escape into the booster?
Is there something else that would cause the same condition?
Tiny history on the brakes: I replaced the master cylinder (and a bunch of other things) last summer. When I pulled the MC I found that it had been leaking into the booster, which was full of brake fluid. I assumed the fluid was getting into the vacuum pump (perhaps killing it), but after finishing everything else the brakes worked great, so hadn't done the VP rebuild or replaced the booster yet.
the brake fluid can get very very corrosive when mixed with moisture.. especially in an area such as a vacuum pump... it's probably starting to eat away at the pump seals etc.
i guess i should also ask the question... how often does everyone bleed their whole brake systems out??? it would be a really good maintenance item... i've seen systems that connect to the reservoir and pressurize it, then the nipples are opened one by one to 'flush' the dirty fluid out.
http://www.motiveproducts.com/02bleeders.html
Bleeding hydraulic brakes annually is recommended in some manuals. I know if you wait a couple of years the stuff that comes out is fairly contaminated. The good part about an annual bleed is it keeps those bleed screws from seizing so that when you want to do a brake job or open the system to replace lines or hoses the chances of having to replace calipers or cylinders is reduced because you can still complete the bleeding to get air out of the system. Pretty tough to do that when half the bleed screw is in the wrench and the system is sealed tight by the other half stuck in the caliper!
HIJACKED!
So I'll have to get a vacuum pump rebuild kit and do it this weekend. I see there's two kits for the pump, an upper and a lower. Anyone know enough about them to make recommendations?
I did the whole brake job in the first place because the wheel cylinders were leaking. When I opened 'em up they were CAKED with crap, and so were the calipers. I'm suprised the lines hadn't become clogged with the stuff. The calipers were the same. I cleaned the calipers and replaced the seals, put in new wheel cylinders, new brake hoses, and MC in at the same time. All brand new brake fluid now. The Bentley and VW owner's manual for my car recommend flushing the brake fluid every other year.
As for pressure bleeding: I found
this page [
bmw-m.net] to be pretty informative for the DIY tool people. Haven't done it yet, but next time I need to do brakes I'll be putting something like it together soon.
HIJACKED!
hehe sorry about that... but i believe brake flushing to be relevant in that it was probably the main reason for your failures... and i am putting the brake flushing on my to do list when the temperature warms up. i don't want my vacuum pump & MC & brake calipers to fail due to improper maintenance...
to be honest i dont think any one does brake fluid flushing... unless someone actually tells them its a good idea. (my brother flushed his his hydraulic clutch system, and he says its quite possibly the best $80 he's ever spent!
)
If you think about it, it totally makes sense to change ALL the fluids in your car (or other machinery for that matter) on a regular basis. Regular could be every 1-2 years, but at some interval that keeps it from gumming up the works. This could be a whole new thread....
Got my diaphragm and valve kits yesterday. Pulled the pump last night, and it was a serious mess inside. Both brake fluid and engine oil had gotten into the valves. When I turned the shaft by hand the valves made a sickly weezing sound not unlike those little animal-sound canisters. You know, the ones that make a cow or sheep sound when you flip it over.
Anyway, Got it all apart and cleaned it out with solvent and a scrubby. After drying I put it all back together, and got it back in the car for a test around the block. Only made a small difference in how fast the vacuum built up again, but I think I caught the problem early enough that it hadn't seriously failed yet. I'll have to wait until I get it warmed up, shut down for a few minutes, then restart to see if my symptom is gone.
Note on the rebuild kit: The diaphragm kit did not come with an o-ring to replace the one in the pump. It's a tiny little thing. The one in my pump was still solid, so I reused it, but wish I had known the kit didn't come with one. Also, I recommend getting a new o-ring between the pump and block. I measured both before putting the pump together, so I'll try to remember to post the specs when I get home.
Question: The Bentley mentions an oil connection on the pump. Mine wasn't connected to an oil supply, but I could see where the oil supply fitting had been. Looks like the design was altered when they produced the type B pump (part # ends in B), and VW had removed the oil supply. Anyone know anything about this?