Good job guys.
The "Master cylinder push rod adjustment" team wins!!
The "Master cylinder push rod adjustment" team wins!!
Brakes overheating after driving a while
- Thread starter Austin Schlegel
- Start date
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BillGrissom
Well-Known Member
I just went thru this on my 1996 Plymouth Voyager (I know, not an A, but Mopar and same issues). I thought I knew how to adjust the booster tip of the new booster. Without the rubber vacuum seal (A's don't have), move the MC onto the booster, feeling for when the rod just touches. Screw the rod out (if adjustable) until it just touches as the MC seats. To be safe, screw the rod in 1 turn from there. That will give a very slight dead-zone in the pedal before the MC piston starts to move. If the MC piston can't fully retract, the fill port won't be exposed which will leave the fluid locked up. It may work fine for a while, but after some hard braking, the fluid can heat and expand to jam on the calipers. A related issue is that you want the pedal stop lamp switch to be retracted (or off) while doing this. Many make that mistake. That switch must only sense pedal motion, not affect its stroke.
First pass, I was silly and set so the rod just barely touched. That probably worked on my A's with drum brakes since they have a little play in the shoes so are more forgiving than calipers. Regardless, you want the fill port(s) to get exposed fully. Took me a while to figure it out as the calipers mostly locked on my daughter who drives more aggressively (totaled 2 cars first year). I had an earlier problem where the left caliper was jamming by itself (original) and had changed both calipers, new shoes and hoses. When the brake overheating recurred, I then suspected "bad new hose", but changing one didn't help. At some point I also changed the booster since original and rebuilt was only $54. It finally locked both front calipers, even after sitting overnight, and found that cracking the tube nuts at the MC relieved the pressure. After another MC didn't help, I focused on the booster rod, repeated the "feel for it as MC mates" and screwed the tip in 1.5 turns. No more problems.
Finally, you can buy a booster rod tip setting tool on ebay or Amazon. I had tried using a vernier caliper, between booster and MC measurements, but very hard to get the measurement exact (need ~2 mil), using plates and subtracting, especially when in the engine bay. The tool makes it much easier. There is a metal tool for ~$30, intended for vintage GM (Corvette I recall), but too short for my Plymouth MC. It might work on a vintage Mopar. I bought the $15 plastic one, which had long enough legs, but still didn't fit since the legs weren't wide enough apart to clear a protrusion on the MC. But looks like it will work on my old Mopars.
First pass, I was silly and set so the rod just barely touched. That probably worked on my A's with drum brakes since they have a little play in the shoes so are more forgiving than calipers. Regardless, you want the fill port(s) to get exposed fully. Took me a while to figure it out as the calipers mostly locked on my daughter who drives more aggressively (totaled 2 cars first year). I had an earlier problem where the left caliper was jamming by itself (original) and had changed both calipers, new shoes and hoses. When the brake overheating recurred, I then suspected "bad new hose", but changing one didn't help. At some point I also changed the booster since original and rebuilt was only $54. It finally locked both front calipers, even after sitting overnight, and found that cracking the tube nuts at the MC relieved the pressure. After another MC didn't help, I focused on the booster rod, repeated the "feel for it as MC mates" and screwed the tip in 1.5 turns. No more problems.
Finally, you can buy a booster rod tip setting tool on ebay or Amazon. I had tried using a vernier caliper, between booster and MC measurements, but very hard to get the measurement exact (need ~2 mil), using plates and subtracting, especially when in the engine bay. The tool makes it much easier. There is a metal tool for ~$30, intended for vintage GM (Corvette I recall), but too short for my Plymouth MC. It might work on a vintage Mopar. I bought the $15 plastic one, which had long enough legs, but still didn't fit since the legs weren't wide enough apart to clear a protrusion on the MC. But looks like it will work on my old Mopars.
Phreakish
Well-Known Member
Same, and in my case both front wheels did fail around the same time. Car had sat for about 10 years before it was out back on the road. Figure the weather took its toll and hit both sides just as hard.
Even with the issue fixed, replacing old lines is probably prudent.
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