weird puzzler - brake pedal "drops" under harder braking

[shawn]

I'm baffled. about 20 - 40 % of the time that I'm braking hard the pedal drops down about an inch and it feels like something bad is going on. -the rest of the time its perfectly fine and normal.

i had a look at the brakes front and back today and couldnt see anything that didnt look right but it seems to be getting worse and more often the last couple of days.

i can't even tell if its coming from the front or the back but today when it did it it was like you could feel the pedal pulsing with the rotation of the wheels.

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i cannot always duplicate this and sometimes its just fine. but when its not -its really not!

[ejndssn]

just an :idea: did you look at the pedal itself :brows: i had a crack at the pivot point in mine replaced the pedal and it was all good after that

[Pete M]

I had a much greater drop in my 88 and it turned out to be a failed brake booster.

[Exgrayxj]

I had a much greater drop in my 88 and it turned out to be a failed brake booster.

:agree: I'm with Pete. Both my xj and the mj have exhibited the same symptom, on the xj it felt like the pedal would drop about an inch suddenly. Probably will get worse, mine did. :doh:

[shawn]

I had a much greater drop in my 88 and it turned out to be a failed brake booster.

:agree: I'm with Pete. Both my xj and the mj have exhibited the same symptom, on the xj it felt like the pedal would drop about an inch suddenly. Probably will get worse, mine did. :doh:

 

 

i thought possibly the master or even the calipers, but did not consider the booster. my first guess was maybe wheel cylinders but what you guys are saying makes sense. i have a 95 booster laying around and have been planning to do that mod anyway ( and maybe even use the xj distribution block) but the weather is so bad here right now, - is there anyway to check the booster to be sure ?

[carnuck]

Sticky wheel cyls, sticky load level valve, rear brakes out of adjust. If that's clean then the booster.

[raviolli]

my first thought was the booster

but a heads up, i have a vacuum leak in my booster and found a reman. booster AND master cylinder on rockauto for somewhere around $100.my dad and i have been ordering from them for a while and have never had any problems

[JeffN]

The pedal pulsing will be warped rotors

[87Warrior]

Sure sounds like the booster.

 

Do you see any fresh brake fluid on the ground? Could also be a small crack in a brake line that opens up when more pressure is applied.

[shawn]

havnt lost any fluid, and the wheel cylinders LOOK ok. can't wait to try another booster (thanks guys). but not looking forward to the job of changing it over ---especially with the crap weather we've been having lately.