Brake vacuum issue....whats my problem? (Page 1/1)
Kitskaboodle NOV 29, 01:00 PM
Hi guys, here is the issue on my 85 GT Auto:
After a drive on the freeway, when I take the off ramp for my exit and hit the brakes, they are quite weak and spongy until I pump the pedal a few times to get the pressure back. After this they are acceptable. It does this around town as well but since in stop and go driving you are starting and stopping much more, it’s not as noticeable.

Anyways, here is a curious new update to the story.... I have distinctly noticed that when I first start my car on a cold morning, my engine goes to a good 1700-1900 rpm during the cold idle circuit. It takes a few minutes of driving for the rpm’s to go down to normal. Anyways, during this brief period of higher than normal rpm, I noticed brake pressure is much better and I don’t need to do any pumping of the brakes at this period of time.

As an FYI I replaced the booster and m/c about two years ago and this problem was not there after I replaced them. The brakes are all stock and the pads are probably about at 50%. R-brake all hooked up and working fine.
I don’t think this is an air in the brakes issue but rather a booster or check valve issue.
What tests can I perform to narrow down the problem? Your thoughts?
Thanks, Kit
fierosound NOV 29, 10:50 PM
The vacuum line for the power brake booster has a filter on the engine firewall.
It's likely clogged or melted. (it's not a check valve - that's at the booster)



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[This message has been edited by fierosound (edited 11-29-2020).]

Spoon NOV 29, 10:59 PM

quote
Originally posted by fierosound:

The vacuum line for the power brake booster has a filter on the engine firewall.
It's likely clogged or melted. (it's not a check valve - that's at the booster)





Does this pic need an edit? Shows firewall but filter is marked as check valve. Its late but I could be wrong.

Spoon

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theogre NOV 30, 02:31 AM
This is second post of same thread. Ignore this and follow other one because is Not boost vac problem.

The above is Not the valve but filter. Valve is on the booster where line connect to.

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[This message has been edited by theogre (edited 11-30-2020).]