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BobJones · 07-26-2020, 06:15 PM

Hi Guys!

I got my motorhome from my Dad and I've been in it for two years without it moving much. However, early on the brake pedal was noticeably sensitive. Hit it too hard and you went through the windshield - so to speak.

Two years later we took it out for a test flight and found the pedal very firm and you really had to stand on it to get it to stop. Dad drove it and confirmed the same. I had caged the brakes before parking it so the shoes would not rust to the drum. I'm used to having to grind away some rust before the brakes come back to 'normal'.

We drove it for ~ two hours and the pedal is still very firm. Anyone know what could cause this?

timex · 07-26-2020, 08:02 PM

Check at the base of the pedal where it pivots. I've seen on trucks where the metal shaft that the aluminum brake pedal pivots on corrodes causing it to not move freely. It in turn can't push down the piston on the air brake valve. If the pedal moves freely then I would have a truck mechanic look at the air brake valve. Good Luck.

camelot1 · 07-27-2020, 07:10 PM

Since you indicate the MH has set for some 2 years slide under and check for rust

on the braking surface of the drums. I have seen this many times on drum brakes that set around unused too long even after several miles of driving.
Be careful when crawling under unit.

Daryl.

BobJones · 07-27-2020, 07:16 PM

I'll check it out tomorrow as I have to cage the brakes anyway. At that point I will be able to see the drums quite clearly. Perhaps there was not enough braking applications to clean the rust off. As I recall, it's never sat for two years without being driven so it's easily possible that it needed more brake applications to clear it up. I'll post back my findings tomorrow

BobJones · 09-14-2020, 11:02 PM

I managed to get out for a second test drive and checked the drums for rust on the side of the road. 3 of the 4 were now clean with a small percent of one of the front wheels with a bit of rust left but soon to be ground off.

So it's looking like it's something else that's causing the issue. If it were a car, I would say the power brakes aren't working and they are manual only.

Farkey · 09-14-2020, 11:24 PM

I have the same issue with my 2002 Diplomat. I have had it for only 2 years and thought that was the way air brakes worked on a MH.

I just came back from a 2 week trip around south western Ontario and while travelling the 407, at one point the traffic came to a stop and I had to stand on the brakes and change lanes and pull into the right paved shoulder or I would have crushed the car in front of me. The brakes didn't lock up nor did the ABS work. But this I knew about when I bought the rig, the ABS light is on constantly and the shop that did the mechanical certification said it was not a big deal just meant the ABS would not work.

But now I'm concerned that the brakes did not lock up, nor did the toads either.

I'll take it to a shop that has been good to me with some other things and see if they can work it all out.

I'm sure that locking up air brakes should not be a difficult thing to do.

BobJones · 09-14-2020, 11:34 PM

All I can say is that my 2000 Diplomat always had 'sensitive' brakes. When I moved it across the park (to another spot) you had to be really careful with the brakes because, even at low speed, they would cause it to stop abruptly. I can recall several times where it would cause the suspension to compress even at parking lot speeds.

I drove it twice now for road tests, and, while the brakes work, there is no way you would want to attempt a panic stop. Several times I had to stand on the pedal. Too risky.

I'm looking into the brake valve mentioned above. It's the picture I keep seeing in my head when I'm driving the unit. Apparently dirt or debris is the number one issue. From what I've read.

But, from your description, it sounds like yours is the same as mine. I bet there's corrosion in the brake valve. I'll post back as I case the issue. BTW, my unit has a step cover that is air operated. This failed to work a while back. I took out the solenoid that operated it and found some corrosion in there. I took it apart, put it in my ultrasonic cleaner, and presto - all is well. I'm looking for something similar with respect to the brakes.

The odd thing is, we changed the air dryer fairly regularly. So I would have expected the brakes to be mint inside. Oh well. We shall see.

Found this on the Internet;

1.) Insufficient Brakes

-Brakes need adjusting, lubricating or relining.
-Low air pressure in the brake system (below 60
psi).
-Brake valve delivery pressure below normal.
-Wrong size actuators and/or slack adjusters.
-Failure of part of a dual air system.
-If remote mounted brake valve, check linkage.

dale1 · 09-15-2020, 06:17 AM

Greetings. same issue with mine. it takes much more peddle than normal. last trip, during hard braking, something popped, steering wheel shook slightly and then it started braking normally. nerve racking. Talked with truck driver friend. he stated the air modules in the wheels likely sticking, need lube, or need replacing.

I would like to know your findings. if i get a resolution. i will do the same. dale

shootist · 09-16-2020, 10:49 AM

Pretty sure the rears engage with release of air and the fronts on mine with air pressure applied engage. That is the one thing on the coach I still pay to have worked on. I'm just not schooled well enough yet to put lives at stake. Fortunately brakes are common to trucks and shops don't have the adversion to that part of a class a.

Xmcdog · 09-16-2020, 10:54 AM

Quote:

Originally Posted by timex

Check at the base of the pedal where it pivots. I've seen on trucks where the metal shaft that the aluminum brake pedal pivots on corrodes causing it to not move freely. It in turn can't push down the piston on the air brake valve. If the pedal moves freely then I would have a truck mechanic look at the air brake valve. Good Luck.

This is a common problem here where an excessive amount of salt is used on the roads. Snow melt drips off boots and corrodes the piñ and treadle.

Use a good penetrating oil to free it up. Pull the pin, polish, oil and replace.

wolfe10 · 09-16-2020, 10:54 AM

Quote:

Originally Posted by shootist

Pretty sure the rears engage with release of air and the fronts on mine with air pressure applied engage.

NOT CORRECT.

Front brakes are air applied.

Rear brakes have two separate "cans":

For service brakes, same as front-- air applied.

For parking brake, spring applied, air released.

twinboat · 09-16-2020, 11:00 AM

Quote:

Originally Posted by shootist

Pretty sure the rears engage with release of air and the fronts on mine with air pressure applied engage. That is the one thing on the coach I still pay to have worked on. I'm just not schooled well enough yet to put lives at stake. Fortunately brakes are common to trucks and shops don't have the adversion to that part of a class a.

Spring ( parking brakes ) release with air.

Service brakes, the ones you use to stop while driving, apply with air pressure on all wheels with brakes.

This is basic air brake operation and worth a few hours of your time understanding it.

twinboat · 09-16-2020, 11:06 AM

If the brake pedal hinge pin is not seized, the next place to look is under the rubber boot, below it.
There is a plunger that goes thru the base plate that can also seize. Lifting the boot, you should be able to spin that plunger in the base plate.

shootist · 09-16-2020, 05:37 PM

Quote:

Originally Posted by wolfe10

NOT CORRECT.

Front brakes are air applied.

Rear brakes have two separate "cans":

For service brakes, same as front-- air applied.

For parking brake, spring applied, air released.

That's what I tried to say, fronts work by applied air, no park brake, rears are applied by release of air. Did not know the air applied the rears while driving. I did know I wasn't up to speed to work on them, thanks guys.