'84 300sd no power brakes on startup

[74baja]

Hi all,

It seems that sometimes on startup (particularly after not running for a few days), I have no power brakes for a minute or so. No visible fluid leaks. The brakes could probably use a bleeding, but work fine once running for a while. Is something wrong with my master cylinder, or booster?

Thanks,
Jack

[whunter]

You have a serious vacuum issue.

The vacuum pump needs to be isolated from the brake booster to test vacuum supply pressure.

My best guess.

If the supply is good:
* The large black plastic vacuum line has a check valve that may have failed = replace the assembly.
* The O-ring, master cylinder to brake booster may have failed = replace the O-ring.
* The brake booster may have failed = replace the assembly.

If all of this tests good = you have one or more massive leak in the secondary vacuum system = emission, transmission or climate control.



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