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What's killing my Master Cylinder?

J

jrowell

NAXJA Forum User
Location
Bakersfield
I have an 87 Cherokee with a 96 Master cylinder & Booster swapped in. Worked great for about 5 years. In the last 6 months I've went through 3 master cylinders! I put a new one in, it works good for a month or two, then bam... breaks go to the floor. If I hit the pedal hard they'll work then bleed off and go to the floor. If I hit them normal they just go to the floor. No leaks, fluid looks good and has been changed with every new MC. What's doing in my MC's?

Jeremy
 
I don't want to sound like an absolute asshole, but are you POSITIVE that you have no leaks anywhere? My rear wheel cylinder's in the drums on my 97 were blown apart and leaking badly and you could not tell until you pulled the wheel, I lucked out and found em swapping my LTB's off for my A/T's, brakes were soft and I was troubleshooting and found them.
 
just a thought... did you clean the whole system of the old fluid ?

if someone accidently put something other than brake fluid in there the rubber internals will go bad, and you will keep going through MCs unless you flush out all the lines and calipers and cylinders. (ie. motor oil)
 
replace all the soft lines, and lift the caps on the wheel pistons to look for moisture

I replaced the whole brake system on my Cadillac and one of the wheel cylinder had a tiny leak that didn't show up unless the rubber cap was lifted up
 
I'm pretty sure there are no leaks. If I put a new MC on, it will work good again for a couple months. When I put a new MC on, I pump out 2 or 3 resevours full through the system. Wheel Cylinder have been insprected and look ok. I don't know, I'm at a loss.
 
Where are you getting them from? Are they reman or new?
 
Southern Auto (Carquest) Reman. When the 1st one went out (5 years after the swap) I got a reman from them. It lasted a week. returned it and got another and it lasted 3 months. So now it's time for a new one again. Bad batch maybe?
 
jrowell said:
Southern Auto (Carquest) Reman. When the 1st one went out (5 years after the swap) I got a reman from them. It lasted a week. returned it and got another and it lasted 3 months. So now it's time for a new one again. Bad batch maybe?
Click to expand...

Found your problem.
 
joe_peters said:
Found your problem.
Click to expand...

X2. I used to play the reman game (MC, starters, alternators, etc.) until I got tired of changing parts in cold, on the side of the road, or out of town. I have found that if you can't buy a NEW part, then get an OEM junkyard part in the meantime, it's usually a higher quality part.
 
ive never had good luck with reman stuff.

make sure your getting all the old fluid out, and no leaks anywhere. other then that, next time use a new unit.

ive got a YJ with a TBI 350 in it. i think im on my 4th water pump since ive owned it. I keep going with reman pumps because theyre free under the warranty, and its a pretty easy part to replace. but im pretty much counting on this one going again this summer, and when it does ill be replacing it with a 100% new one. by the time I add up all the coolant ive had to buy for pumps i could have nearly bought a new one. and it no matter how cheap, or easy it is to replace, its always out of your ability when your on the side of the highway somewhere, and no where near where the part is warrantied
 
I did the exact same thing with my CJ. 3 reman cylinders in 3 months(one leaked at install) A lot of the remanufacturing is done out of country now, by lowest bid/price. A lot of stuff gets new seals and sent right back out the door without ever being re-machined, honed, or even inspected/tested.

Sucks when you remember you used to be able to get quality rebuild kits for that stuff for a couple bucks.
 
Yep...went through 4 reman. master cylinders in 2 years. I just installed an OEM wj booster/master cylinder so hopefully that will do the trick.
 
It seems that most remanufactured parts are crap.
I have had the very same experience with water pumps, power steering pumps and alternators in just the last year.
I'm at the point that I always buy new if possible.
My time is too valuable to do these types of jobs twice (or more).
 
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