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Touchy (but then not so touchy) brakes

1990 Ford F350 diesel here. I just replaced the vacuum brake booster on the truck as the old one was leaking, and I think having the additional “boost” has helped to identify a different problem.

Most of the time when I press the brakes I have to get on them pretty well to bring the truck to a stop. nothing dangerous or too out of the ordinary…but I assumed this was normal as every truck/car has a different feel to the brakes. HOWEVER

Sometimes, for no apparent reason I will suddenly get a ton more braking power with much less pedal push (I think in my front wheels) - I will depress the brake pedal as normal…and the brakes will start working as I expect, and then all of the sudden, I get a TON of brake power all at once…if I happen to be pushing hard enough the front wheels will completely lock up. Then after the first occurrence they will be touchier than usual for a while and eventually go back to being normal…

I suspect this is a stuck caliper - or possibly something to do with the master cylinder? Thoughts?

Thanks in advance!

The vacuum check valve is cheap and easily replaced and a likely cause of the problem so replace it and hope for the best.

Does your truck have load sensing rear brakes? If so, they could be acting up.

The next time you get the extra brake assist, crack open the bleeder screws on the calipers.

If brake fluid squirts out, the calipers still have hydraulic pressure being applied to them.

This is usually caused by a caliper brake hose deteriorating internally and acting like a check valve.


The vacuum pump may not be operating properly, measure the vacuum supply to the brake booster.