Community Forums

Longford · 05-23-2022, 09:14 AM

Hello,
Any Ideas on what to do next on my 2003 w22.
Rear brakes get very hot after about 20 miles.

On the rear, in the last month Its had 2 sets of new Callipers, pins, pads, new rotors, new flexi hoses and a brake fluid flush. But they still cook after about 20 miles. the left rear slightly worse than the right.
The fronts, which are also new never get hot.
If i go down the highway for long enough without touching the brakes, maybe 40 miles the rears will eventually cool off a bit. But then cook after a while if i need to start using them again in traffic.

This Rv also has the grease port on the linkage under the hood and the linkage all appears to be working correctly.
plus I had an auto electrician check the ABS was working.

Any ideas what to do next? i've read about people adding air cooling systems for the callipers on these chassis.

Maybe its normal for the rears to be red hot and the fronts be cold? although the rears have locked up and melted the abs wires when ive been in a lot of traffic in the past.

Flyer15015 · 05-23-2022, 09:27 AM

First place I would look is the proportioning valve, which tells the rears to engage first.
Second place is the master cylinder. Piston not returning ?

Mike in Colorado

Longford · 05-23-2022, 09:32 AM

Hi thanks for the reply. Im not a mechanic, so I'm learning as I go on this. Any idea where the proportioning valve is located? Also what it looks like?
I was wondering about the master cylinder, but the fronts are working correctly.

Arch Hoagland · 05-23-2022, 10:31 AM

How are you measuring the heat....IR gun?

Who did the brake job and did you return it to them to look at?

Longford · 05-23-2022, 10:43 AM

Hi, a pal of mine is a mechanic for a car racing team. He did the brake work for me. He's very competent and has a 2007 model w22. We've compared against his w22 and his rears don't get hot like mine.
Not checked with an IR gun but I ordered one a few days ago.

arcaguy · 05-23-2022, 10:54 AM

Quote:

Originally Posted by Flyer15015

First place I would look is the proportioning valve, which tells the rears to engage first.
Second place is the master cylinder. Piston not returning ?

Mike in Colorado

For some reason the brake pads are staying in contact with the rotors. There are only a few reasons for this, the two stated above and the brake pads binding up on whatever they slide on or the caliper pistons binding up. This isn't rocket science. Have your buddy loosen the bleeders on the rear calipers. If brake fluid shoots, not dribbles, out you have an issue with the proportioning valve or the master cylinder causing residual pressure in the system. If no brake fluid shoots out the pads or the caliper piston are binding up somewhere. Good luck.

IdahoBen · 05-23-2022, 11:13 AM

I had this issue on the front brakes. The original rubber brake lines (that go between the hard lines and the caliper/drum) collapse on the inside. Think of sucking a shake/malt through a straw. It's a pretty inexpensive fix, but you will need to bleed your brake system after doing it.

Longford · 05-23-2022, 11:24 AM

Hi, thanks for that, we'll try the pressure test on the bleed valves and see what that tells us.
I agree it seems like brake imbalance as I can't imagine that both rear calipers are faulty or getting bound up on any mechanism. They've been replaced twice in the last month and had sliders cleaned, greased and checked both times. I'm just getting tired of throwing money at the problem without fully understanding the cause

Longford · 05-23-2022, 11:26 AM

Quote:

Originally Posted by IdahoBen

I had this issue on the front brakes. The original rubber brake lines (that go between the hard lines and the caliper/drum) collapse on the inside. Think of sucking a shake/malt through a straw. It's a pretty inexpensive fix, but you will need to bleed your brake system after doing it.

Hi thanks for the reply, but we changed them already.

edgray · 05-23-2022, 03:40 PM

Just a shot in the dark here, but do you know if the sets of new calipers your friend has installed have the “rv specific” improvements that were mandated by the 2010 Bosch caliper recall?
I was told that “not all” (especially reman) calipers have the increased piston to bore clearance and “more powerful” piston seal (said to aid in retraction) that were included in the ones Bosch made for RV use.
Otherwise, I agree there must be a problem with the MC. IRDK if there even is a proportional valve in the service braking system on the W-22 series chassis.

RKL2 · 05-23-2022, 03:59 PM

Sounds like classic case of rubber brake lines portion of the system being blocked by rubber breakdown from hot brakes at one time. The rubber lines plug up with calcified rubber and will not let brake fluid floe back into the reservoir. The result is that the caliper can’t release the brake fluid pressure that was applied when the power assisted brakes were pressed. Easy to test for by removing rubber brake line and trying to blow air through each way. A good brake shop will do this if you ask. Important to flush system after removing old rubber brake line and before putting new ones in. Good luck but I am sure this is your problem. Happened to me every trip after hard mountain braking out west. Finally figured it out and problem solved for good. Rkl

MoCoTom · 05-23-2022, 06:01 PM

Quote:

Originally Posted by RKL2

Sounds like classic case of rubber brake lines portion of the system being blocked by rubber breakdown from hot brakes at one time. The rubber lines plug up with calcified rubber and will not let brake fluid floe back into the reservoir. The result is that the caliper can’t release the brake fluid pressure that was applied when the power assisted brakes were pressed. Easy to test for by removing rubber brake line and trying to blow air through each way. A good brake shop will do this if you ask. Important to flush system after removing old rubber brake line and before putting new ones in. Good luck but I am sure this is your problem. Happened to me every trip after hard mountain braking out west. Finally figured it out and problem solved for good. Rkl

His post said he already replaced the rear flex lines

Longford · 06-08-2022, 06:00 AM

Update. 1000mile trip and things seem better.

Ive changed my driving style and theyre no longer overheating and sticking on.

On a long highway run and without use, the rear bake calipers sit at around 200 degrees. And in stop start traffic and hills they got up to 300 degees.
Not hot enough to melt the abs wires or bind the calipers on.
Although it seems strange that the calipers would be hot even when your not using them. But from what i can gather this is normal on a workhorse of this era, ive read quite a few posts with people reporting the same kind of figures.
As far as driving style goes...im just a lot kinder to it...anticipating my braking rather than standing on them or riding them all the way down a hill...im using my grade brake now and generally being a lot less aggressive...Calm driving it seems is what a workhorse needs!
Thanks for the suggestions.