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On cold start up after sitting all night the brake booster is very slow to work on my V40 (2001). It takes as long as a minute or so before the power assist for the brakes comes on. Once it starts working for the day, it seems to be fine. Is this a vacuum leak? or what should I be looking for. The bake fluid level is fine.
Jim
If you look where the valve/hose attaches to the booster that valve is usually what goes bad.
But you have to buy the line for the valve.
Or also check the relay for the vacuum pump.
I'm having a similar problem. Sometimes at the end of the day it's ok, but every morning and some evenings on cold startup it's almost impossible to hold the car stationary in reverse or drive at first. One minute down the road I don't have a problem stopping.
Some other data points:
- Vacuum booster fuse was blown when I bought the car, I replaced and it is ok so far
- I also suspected the booster pump relay and replaced that but it made no difference
- I believe I am hearing the vacuum pump when I have the bad brakes, but no other time (sounds similar to a car auto-leveling pump--not the same as ABS chattering)
- ABS indicator is normal - turns on then off with other warning lights at "ignition on"
- I haven't tried activating the ABS yet (i.e. slam on brakes), I probably should
- Giving the car a few seconds to warm up and pumping the brakes before leaving the driveway doesn't make a difference
- Vacuum lines appear to be fine, little bit of looseness and visible grease where check valve attaches to booster (the big UFO saucer thing), also a little looseness where vacuum line attaches to engine - I assume this is all normal
How does this brake booster check valve work and why would it only be a problem when I'm starting out? Autozone sells generic check valves for $5 but I have no idea how I could use that because I only have a basic understanding of the system's operation and it appears that this system is more complex than a simple valve with an "in" and an "out". I'm hesitant to pay a lot for a new Volvo check valve assembly unless I'm sure it's the problem. Can you offer any advice?
Last edited by ArizonaV40; Apr 29, 2009 at 09:14 PM.
I need some new ideas on the brake problem (see my above post). I replaced the engine to booster vacuum line ($140+ at the stealers), but I still have the problem. After the car has sat all night, there is no brake boost for 2 or 3 minutes of running. The problem does not occur during the day when it sits for less than 4 hours or so. Could there be another vacuum leak somewhere, and where should I begin looking?
Jim
Note: the approach outlined below may not work. After fitting the part, I took the car to the mechanic to further diagnose and they found the new switch was not working. I don't know if the new switch was faulty, or if the left hand drive part simply can't be used as I describe below. Anyhow I have left the info below in case it helps someone.
The brake vacuum check valve is no longer available for right hand drive cars (part number 30620959).
I didn't want to put on a second hard part, so I struggled and eventually managed to fit the left hand drive part (part number 30616993) as follows:
1. bought a 1/2" to 3/8" reducing hose barb (i.e. it has a hose barb on both ends) and cut about 5mm off each end (it was too long)
2. put 1/2" hose from the check valve to the reducing hose barb, and then 3/8" hose from the reducing hose barb to the pipe on the car's firewall (see red arrow)
3. bought a Gates Z-hose (3/8") and cut out the part that has the nice tight curve (see green arrow)
4. cut the end off the vacuum line from the manifold to the check valve, and used copper pipe to join it to the Gates Z-hose (blue hose).
Last edited by steve_jj; May 18, 2021 at 04:25 AM.
Reason: add warning that the method described may not work
Brake problem
