disc brakes hanging up

joewilly

New member
Mar 5, 2020
22
2
3
Victor, Iowa
having a problem with the middle axle disc brakes hanging up-not releasing.maybe fronts also

I have the Lee Harrison disc brake with I think is the P30 master cyl

I was driving along and slowed down going through small town and that is when I think they didn't release

Not knowing I kept driving for about 5 miles and and was having trouble maintaining 55mph so I pulled over and checked brakes with the laser gun and found the middle dics at 450+ deg. front discs were hot also about 350 rear drums where at 265.

can anyone point me in the right direction as what to look for that could cause this?

proportioning valve? master cyl?

your input/ideas would be appreciated

thanks
joe
 
having a problem with the middle axle disc brakes hanging up-not releasing.maybe fronts also

I have the Lee Harrison disc brake with I think is the P30 master cyl

I was driving along and slowed down going through small town and that is when I think they didn't release

Not knowing I kept driving for about 5 miles and and was having trouble maintaining 55mph so I pulled over and checked brakes with the laser gun and found the middle dics at 450+ deg. front discs were hot also about 350 rear drums where at 265.

can anyone point me in the right direction as what to look for that could cause this?

proportioning valve? master cyl?

your input/ideas would be appreciated

thanks
joe
Here are some ideas:
- Caliper pins/slides can stick. Disassemble, clean, lube, and reassemble. It would be somewhat unusual for this to happen on multiple wheels unless the coach was sitting for a long time.
- Flexible brake hoses at the wheels can start to break down internally which restricts their ability to release properly. Replace, ideally with braided stainless hoses ($$). Again, unusual for this to happen on multiple wheels at the same time.
- The MC has internal return springs that could potentially go bad. Dave Lenzi is a great resource for brake issues/parts. Let me know if you need contact info.
 
Here are some ideas:
- Caliper pins/slides can stick. Disassemble, clean, lube, and reassemble. It would be somewhat unusual for this to happen on multiple wheels unless the coach was sitting for a long time.
- Flexible brake hoses at the wheels can start to break down internally which restricts their ability to release properly. Replace, ideally with braided stainless hoses ($$). Again, unusual for this to happen on multiple wheels at the same time.
- The MC has internal return springs that could potentially go bad. Dave Lenzi is a great resource for brake issues/parts. Let me know if you need contact info.
thanks Christo,
I agree that it seems like master cyl is the problem. and yes I would like to get Daves contact # from you.
there is a lot of opinions on using the P30 master or using the OEM with rear disc and reversing lines do you have a preference/opinion on this?
I also have not been able to find a proportioning valve, can this brake system operate without one?
 
having a problem with the middle axle disc brakes hanging up-not releasing.maybe fronts also

I have the Lee Harrison disc brake with I think is the P30 master cyl

I was driving along and slowed down going through small town and that is when I think they didn't release

Not knowing I kept driving for about 5 miles and and was having trouble maintaining 55mph so I pulled over and checked brakes with the laser gun and found the middle dics at 450+ deg. front discs were hot also about 350 rear drums where at 265.

can anyone point me in the right direction as what to look for that could cause this?

proportioning valve? master cyl?

your input/ideas would be appreciated

thanks
joe
Hey Joe, as a test, to eliminate the chance of replacing the wrong parts, you can try to narrow it down. With the offending wheels off the ground...
See if you can get them stuck again. If you can, go crack open the appropriate line on the master cylinder to relieve any pressure. If the wheels become unstuck, then the problem is with the MC.

Also, with MC swaps, it's not uncommon for the pushrod to not quite have the right travel. You can run another test by getting the offending wheels stuck, then unbolting the MC from the firewall. This should take any potential force off the pushrod. If the brakes release when unbolting the MC, then it might indicate that your pushrod isn't withdrawing quite as far as it needs to. You see this on the hotrodder forums all the time with custom brake setups.

If fiddling with the MC doesn't help at all, you can look farther down the line. Try cracking the line at the appropriate output side of the proportioning valve. If that doesn't help, try cracking the line at the caliper. If relieving hydraulic pressure at any of the locations does not help, you probably have a mechanical binding issue that Christo outlined above, and it's time to clean/lube the moving parts.
 
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