brake booster, probably

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J

jblueridge

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I installed an 80-series brake MC and vacuum booster. Testing that new setup, I found the brakes to be much improved BUT if I pumped the brake pedal it seemed like I was not getting any help from the booster after the first push.
A few days later and it feels like I am not getting any vacuum booster action at all. Dash brake light comes on.
Also, when I turn off the key the engine will continue to run. If I hold the brake pedal down, the engine will run without the key On forever, maybe.

A vacuum gauge plugged into the booster line shows a lot of vacuum, 26" Hg. With the engine off, when I disconnect the vacuum line, there is vacuum in the booster.

I'm not sure how it can hold a vacuum but still leak enough to allow the engine to run on.
 
Manual transmission? If so, look at the clutch booster. There are threads here that discuss changing a seal in these boosters (clutch, not brake).
 
I had read at least one of those.
I figured the high vacuum reading would rule out the clutch booster idea.
When i pulled & plugged the brake vacuum line the engine behaved normally.

I'll pull and plug the clutch line and see if theres a change.
 
The vacuum pump keeps running as it's chasing a leak but I'm still thinking you have two issues going on because the booster has vacuum but your not getting assistance at the brake pedal. If the booster came from a 80 with rear drums it will be fine but if it came from a 80 with rotors on all corners that may be a issue as well.
 
The booster is supposed to be for an early 80-series with rear drums. 1990-92, I think.

Oz, the pushrod on the pedal side had to be lengthened with a coupling and some more threaded rod.
On the MC side I left it as it was sent to me.

All this is odd since the brake booster action deteriorated rapidly from working almost correctly down to no help at all.
 
I would try and adjust the push rods between the booster and master cylinder. You need to make the SST to adjust the push rod length or do it by trial and error. My old 1991 sahara had rotors on all corners.
booster 001.webp
 
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Got my booster and MC back.
Installed them.
Brakes work well except when I pump the pedal quickly.
If I do that I use up the vacuum and the booster can't boost.
Vacuum gage shows about 26.5 in Hg.
Install a larger or sevond reservoir?
 
I plan to replace vacuum hoses and examine the steel lines.
Vacuum gauge shows a lot of suction from vacuum pump.

Do you have a pic or link to the vacuum tank you used?
 
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