Brake lag after starting

TexasCoder · Post by **TexasCoder** » 18 Feb 2011, 08:34

trstjohn: I can't comment on the hand pump bleeders, I have always used compressed air (http://www.harborfreight.com/brake-flui ... 92924.html) But as long as you can get a good bleed on each brake caliper and know that you have the most air bubbles out, then you should be good.

This is certainly one area to look at as you investigate the vacuum pressure and ensure that is operating properly, as jimmy57 mentioned.

trstjohn · Post by **trstjohn** » 18 Feb 2011, 10:57

just an fyi, I'm not sure this is cold weather related. It's 50+ today in PA and I'm still getting the brake lag.

Post by **jimmy57** » 18 Feb 2011, 12:33

The exhaust cam is advanced and timing is less advanced on all starts below approximately 125F coolant temp. These actions reduce engine produced vacuum.
The test for this is simple. If you turn on key and depress brake pedal you should hear vacuum pump usually on second "pump" of brake pedal. If you get hard pedal and you do not hear pump running then find out why.

The pump is fitted to these for your exact complaint so it should be checked before you spend time on causes less likely to contribute to braking difficulties after engine is started cold.

trstjohn · Post by **trstjohn** » 19 Feb 2011, 10:07

jimmy57--
I did the test and I do hear the vacuum pump. I also visually checked the fuse and didn't notice anything. What do you suggest next?

Post by **jimmy57** » 19 Feb 2011, 11:54

The problem is gone after engine runs for a few minutes is what I'm understanding.
IF vacuum pump is functioning properly, and it is from doing the test, the booster is suspect.
I'm also working on the assumption your problem is really no normal stopping with normal brake pedal apply force when this is occurring but harder brake pedal application does make the deceleration greater?

I'm still stuck on the vacuum pump. The vacuum pumps have given enough problems that are related to the switch. Either running continously when vacuum is high enough to have shut it off or running very briefly when vacuum is low enough tht it should be running much longer.
If I were working on it I'd have a vacuum gauge T'd into hose to booster and check for vaccum levels when pumping brake pedal with engine off causes pump to come on and at what vacuum it goes off. On when goes down to 14 inches and off when it builds to 18-20 inches is normally observed.

WinterDriver · Post by **WinterDriver** » 03 Mar 2011, 12:36

Actually if you read in your owners manual it will actually tell you if the brakes are cold, or wet, brakeing time is increased. Also that is why you should let your car idle down to 1.5 rpms before moving.

trstjohn · Post by **trstjohn** » 03 Mar 2011, 17:57

WinterDriver wrote:Actually if you read in your owners manual it will actually tell you if the brakes are cold, or wet, brakeing time is increased. Also that is why you should let your car idle down to 1.5 rpms before moving.

I'm still getting the lag even in dry warm weather.... Something else must be going on....

Post by **stone36** » 12 Mar 2011, 12:57

Mine does this too, very sporadically and only when first pulling out of my parking space, but I find that if I notice the pedal is hard right away and take my foot off the brake pedal and then push it again it works fine. As for a bleeder, I have the one from MOTIV products, it is about $50 but comes with the cap for Volvo and it works on all Volvos. I have bleed the brakes twice and that doesn't fix the problem, there is something other than air going on. But it happens so infrequently and my "pump the pedal once" trick has so far been 100% successful...

Post by **matthew1** » 12 Mar 2011, 16:13

This sounds similar to a problem with my 2004 V70 -- https://www.matthewsvolvosite.com/forums ... =9&t=36775

trstjohn · Post by **trstjohn** » 05 Apr 2011, 13:29

jimmy57 wrote:The exhaust cam is advanced and timing is less advanced on all starts below approximately 125F coolant temp. These actions reduce engine produced vacuum.
The test for this is simple. If you turn on key and depress brake pedal you should hear vacuum pump usually on second "pump" of brake pedal. If you get hard pedal and you do not hear pump running then find out why.

The pump is fitted to these for your exact complaint so it should be checked before you spend time on causes less likely to contribute to braking difficulties after engine is started cold.

I finally decided to get an expert opinion on the brake lag. I took it to my mechanic and he said I need a new vacuum pump as you suggested. He estimated at $1k for a new one (IPD is telling me $250). BTW, he always seems to over estimate how much parts costs. However, he did, off the record, say that a 25V fuse would alleviate the problem.

Any thoughts on the 25V fuse?