Power booster pushrod length.

Infiniti Dave · May 24, 2025

Has anyone attempted to adjust the power booster pushrod to master cylinder length on a 79 "F Body" ? I can't find any specs in the appropriate service manual and most of the posts seem to have a lot of guess work. Any procedures and spec is appreciated!!

AMC Diplomat · May 25, 2025

You need a gauge to make it easy. Everyone carries them.

Mikes5thAve · May 25, 2025

You adjust it so it doesn't press the plunger but it's about to.
You shouldn't have to adjust it at all unless you're mixing parts.

Infiniti Dave · May 25, 2025

Found out after I bought the car that the brakes wouldn't release after driving several miles. Someone before me either mismatched parts or played with that depth. Unfortunately my time at a Dodge Dealer years ago always said "don't ever mess with that". Now I'm in uncharted waters for me. Thanks to all for the sound advise. The tool is ordered and we'll see soon.

Mikes5thAve · May 25, 2025

You can feel if it's touching or pushing the rod when you put the master cylinder on. Put it in place but don't put the nuts on. If there is any resistance before the flanges sit flat on the brake booster the rod is too long.

The tool looks simple to use, I saw they're cheap on Amazon.

AMC Diplomat · May 25, 2025

It's one of those silly tools you'll use once every few years, if that. It made my booster replacement really easy. All it did was confirm the booster pushrod was perfect out of the box.

If your brakes aren't releasing, I'd suspect old swollen brake hoses before I would think to check booster pushrod length.

Mike is right though, if you have to bolt it down to get the master cylinder to sit flush against the booster, then that push rod is too long

Infiniti Dave · May 25, 2025

Got new lines and hoses, so if that's the issue it'll get repaired during the process. The only concern is that when the brakes wouldn't release, I got it home by cracking a line at the master cylinder to release the pressure. Not sure a restricted hose would respond that way . Thanks !!

Aspen500 · May 25, 2025

I would suspect the master piston is not all the way released just enough to block the compensation ports, and holding some pressure in the system. With the brakes dragging, the fluid heats up and expands, but can't return to the reservoir. Then the brakes drag more and more.

Never ran into it on a Mopar, but did on other makes at work. Toyota seemed to be the leader. From what I understand, the plate in the booster gets bent out over time, and reduces the pushrod depth. Ended up replacing the booster on those to solve the problem. Most weren't adjustable btw.

8T2TOP · May 31, 2025

Infiniti Dave said:
Got new lines and hoses, so if that's the issue it'll get repaired during the process. The only concern is that when the brakes wouldn't release, I got it home by cracking a line at the master cylinder to release the pressure. Not sure a restricted hose would respond that way . Thanks !!

They have a common problem with proportioning valve under MC...

AMC Diplomat · Jun 1, 2025

8T2TOP said:
They have a common problem with proportioning valve under MC...

You're 100% right, those later proportioning valves aren't brass, they're some kind of iron and they can rust on the inside

Power booster pushrod length.

Infiniti Dave

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AMC Diplomat

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Mikes5thAve

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Infiniti Dave

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Mikes5thAve

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AMC Diplomat

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Infiniti Dave

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Aspen500

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8T2TOP

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AMC Diplomat

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