The MB's are running great but a quick brake question on my Volvo if you'll allow it:

The power assist went the other day. Brakes work ok with a strong leg. However, after running hard, the power assist will kick in for one time on the pedal and then return to hard. Why the inconsistency? I can generally fix stuff but need you guys to steer me in the right direction??

Thanks,

Don

__________________
DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

This is an easy one! There is either a small tear in the diaphram of your booster or one of the vacuum hoses is leaking. I'm not sure what the Volvo system looks like, but I would be willing to guess that there may be a "valve" somewhere in the system. This could also be sticking. (like a ball check type deal in the vacuum line , the big one) I know that a VW has a one way valve in it. If it gets crud in it , it will act this way. When the car "runs hard" it makes more vacuum , right? This may be just enough for it to work "a little", or sporatically. Check the "cheap" stuff first, cracks in the hoses, and the presence of a valve etc. It is definately a "vacuum" situation, also check to see if your vacuum pump is indeed working properly. Take the big hose off and put your finger/thumb whatever over the end of the hose while the car is running and see if it's making vacuum. ( before you blame the booster!) I had a friend who replaced a booster on his Rabbit when all he needed was to rebuild his vacuum pump. ( this was a $75.00 used vac. booster vs. a $12 rebuild kit for the pump!)

Let us know what you find! Tom

Don:

You have either a leak or bad pump. One shot of power brakes with no boost until you drive for a while suggests a pump.

Does your vacuum pump still clatter? If not it is probably shot.

Vacuum systems on Volvos are pretty simple -- pump (on the side of the head, about the middle, can't miss it!), hose to brake booster and to AC controls, booster and AC unit. Cruise has it's own pump.

If you can get the lines off (ha, hard as rocks!), check three things :

1. does the pump generate and hold vaccuum? (use the trusty MitiVac!) It can be rebuilt rather easily, not a nice as the MB one (requires a vice to hold the diaphram spring down)

2. Does the check valve at the booster hold vacuum?

3. Does the booster hold vaccuum? (including the rubber seals, etc).

Remove and plug the AC hoses while checking the booster -- this will tell you if the leak is there instead.

it will take a while to pump the booster down with the Mitivac, but if you never make any progress, there is you problem. I've had several boosters die over the years -- gas engines are easier to diagnose as the idle goes funny when the booster leaks -- had the old Dodge die when I stepped on the brakes cold, for instance.

The other thing that can happen to the vacuum pump is for one of the two drive plungers to stick -- this is bad, as the body of the pump is aluminum and will therefore be nonrepairable.

Good luck!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Speaking of brakes, I replaced the front brake pads on my newly acquired 1987 300TD. It was so easy. I have done the rear brakes before on a 124 but not front. Compared to the rear, the front is a lot easier. No pins to punch out.

When I replaced the rear brakes, I could use a long screw driver to force the piston back. I tried that on the front, no luck. It was very tight (I did have the fluid reservoir cap off). So I took out my C-clamp. Here is a tip iif you use a C-clamp to force the piston back. Use a replaced rear brake pad in between the C-clamp and the caliper piston. Work wonders and won't damage the piston.

Loubapache,

I once wrote in a detailed procedure I use to change brake pads and am a little too lazy to rewrite it again unless it is wanted. But the idea is to change your brake fluid at the same time you change your pads. I do this by fitting a little hose over the bleed fitting on the caliper, then unscrewing it slightly, and letting the fluid drain into a pint jar as I pry against the old pad. Once the fluid level in the jar covers the end of the hose (and you will notice this fluid is not clear, especially if you have not changed it in more than a year) you can bleed the brakes with or without an assistant.

Anyway, the added cost of a bottle of brake fluid or two when you change pads just seems trivial. I have been doing this for thirty years, and have never had a problem with my calipers, and it is relatively cheap.

Jim

Edit Note:

The point of the procedure is to avoid having to push fluid back up through the system, and make it easy to push the pads back so the piston goes into the caliper bore with relatively little force. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

JimSmith:

Thanks for the tip.

No, I did not flush the fluid as I was planning on doig it next spring.

The color of the fluid in the reservoir was fairly clean so I decided to wait till spring.

thanks a ton for the info. my internet has been down (thanks excite ....)

will be printing your very helpful notes to paper and getting them all oily as i begin to hunt down the leak.

thanks again

don

__________________
DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed