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testing a brake booster

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mbwicz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mbwicz Quote  Post ReplyReply Direct Link To This Post Topic: testing a brake booster
    Posted: Jan/23/2022 at 12:49pm
I bought my 70 AMX without it running, but the brakes did work.  I tore the car down for a complete rebuild.  I've read a bunch of posts over the last 3 years about people getting their booster rebuilt.  How can I test mine to see if it needs to be rebuilt?  Is it as simple as putting a vacuum on it and making sure it doesn't bleed down?

Thanks,
Mike
1970 AMX, one step forward, one step back. Both steps cost time and money.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Jan/23/2022 at 1:31pm
This is just spitballing so take it with a bag of salt.  Get a relatively high volume vacuum pump (A/C version comes to mind) and pull about 20 InHg on the booster.  Gently push the input rod into the booster in small steps.  The output rod should start moving.  When you stop, the output rod should stop.  When you start again, the output rod should start moving out again.  Then pull the input rod out, again in steps, and see if the output rod follow it.

The key is that the output rod should follow the input rod.  If you do this, you may want to have an assistant hold the output rod against the booster.  Without the MC there is nothing to stabilize the output rod or press it back against the booster.

This is so much easier with the booster in the car!
Roger Gazur
1969 'B' Scheme SC/Rambler
1970 RWB 4-spd Machine
1970 Sonic Silver auto AMX

All project cars.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Jan/23/2022 at 1:38pm
IMO since you're going this far, why not get it rebuilt why it's off the car and you're not in a hurry? What's a couple hundred dollars in the big scheme of the whole project? Besides that rubber diaphragm is 50+ years old already. Just saying.. Wink

"Hemilina" My 1973, 5.7 Hemi powered Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mbwicz Quote  Post ReplyReply Direct Link To This Post Posted: Jan/23/2022 at 2:01pm
Originally posted by Mopar_guy Mopar_guy wrote:

IMO since you're going this far, why not get it rebuilt why it's off the car and you're not in a hurry? What's a couple hundred dollars in the big scheme of the whole project? Besides that rubber diaphragm is 50+ years old already. Just saying.. Wink

Honestly, I had it painted and reinstalled before I thought about it.  My past life working on GM cars it didn't seem to be as common a problem as on the AMC's, so that is why I didn't do anything with it.  But your point is valid....

Mike

1970 AMX, one step forward, one step back. Both steps cost time and money.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: Jan/23/2022 at 3:41pm
You can test it with a Mityvac.  The boosters also commonly crack on the rear metal surface due to vibration.  Mine did, and when I talked to "Booster Dewey" he said, "oh yeah, we see that all the time...."
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