Downhill braking in reverse.

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Downhill braking in reverse.

August 31, 2015, 01:32:45 am

Hello Everyone, Our 98 320 is in the yard!
We'll conclude our transaction in the morning then off to the tire shop for new Toyo's. I found it just a little alarming that it was all I could do to stop the coach idling in reverse down our drive. Putting it in neutral solved the problem but can't guarantee that will always be a viable solution.
Have been told by other 320 owners that a lot of this is attributable to the tremendous low end torque of the M11 combined with a very low gear ratio in reverse on the 4000 Allison.
Both 320's I've driven seemed to challenge the brakes in drive at idle so this seems somewhat plausible . Was wondering if anyone else had had similar experience and if so could point me towards a possible improvement such as slack adjusters incorrectly set or idle being turned up a little to much. Thanks ,Tom
PS will replace the old 280 photo as soon as my computer programmer gets home from work tomorrow.

Re: Downhill braking in reverse.

Reply #1 – August 31, 2015, 06:20:59 am

An easy fix, first lower the idle rpm to 650 or less, and have the brakes repaired by a shop that knows what they are doing.
A very solvable issue, much more important than new tires.
Good brakes Should not be difficult.
Good luck

Re: Downhill braking in reverse.

Reply #2 – August 31, 2015, 06:41:28 am

Your brakes need adjusting. Also as Dave said, check your idle speed but I am sure it is your brakes.

Re: Downhill braking in reverse.

Reply #3 – August 31, 2015, 06:52:44 am

Definitely find someone who understands the brakes on your Foretravel. Note: Many shops don't really understand them. Try to find someone in your area who maintains fire trucks with disc brakes; they have a better chance of fully understanding your brakes. You definitely should not be experiencing this type of problem.

Re: Downhill braking in reverse.

Reply #4 – August 31, 2015, 07:13:39 am

Thanks. We're supposed to take Mom to see her ailing brother in Indiana next weekend. I am going to want this addressed along with tires and fluid /filters before we roll.

Re: Downhill braking in reverse.

Reply #5 – August 31, 2015, 07:30:14 am

Some cummins shops work on our brakes.

Re: Downhill braking in reverse.

Reply #6 – August 31, 2015, 07:51:05 am

Quote from: D.J. Osborn – August 31, 2015, 06:52:44 am

Definitely find someone who understands the brakes on your Foretravel. Note: Many shops don't really understand them. Try to find someone in your area who maintains fire trucks with disc brakes; they have a better chance of fully understanding your brakes. You definitely should not be experiencing this type of problem.

I have learned the hard way that just because the company works on fire trucks does NOT mean they know what they are doing on the brakes on your RV. There solution is to just replace the complete system.

Find the manual here on the forum, down load it. It explains how the brakes are to be repaired and have them read that before you let them work on your brakes.

Good luck

Re: Downhill braking in reverse.

Reply #7 – August 31, 2015, 08:48:35 am

If brake pads are in good shape and slack adjusters are correctly set and brakes properly lubed, I don't see anything else that will make brakes work better. More than likely the idle is set too high. Can M11 idle be user set, to lower the RPM's? I would think that at low RPM, the torque converter would be designed to mostly slip and keep coach in place with minimal brake pedal.

Re: Downhill braking in reverse.

Reply #8 – August 31, 2015, 09:43:59 am

The ratio difference between 1st and reverse isn't that large no the 4000's series.

First, make sure slack adjusters are not too loose.

Second, turn OFF the retarder and do a couple of stops from highway speed using only the brakes. Do these fairly close together.

My experience is that braking effectiveness drops over time because the brakes tend to "glaze" up because they don't get hot due to the retarder being so strong.

I noticed a difference is slow speed stopping after a few heated stops. Also, the parking brake works better.

Re: Downhill braking in reverse.

Reply #9 – August 31, 2015, 09:58:55 am

Yes the idle is user adjustable with the cruise control buttons.

Re: Downhill braking in reverse.

Reply #10 – August 31, 2015, 10:27:29 am

With cold brakes and a steep driveway, it is quite possible the torque at idle will overcome the service brakes. This is our case with a steep driveway where I have to go down in neutral. I can lock up all six on the flat at higher speeds when they have had a stop. All the coaches develop lots of torque at idle speeds, especially if it's a little high.

The rear cans are smaller than the front and in normal driving, the engine and retarder/Jake help slow the coach down. At idle, just the opposite happens especially if the idle speed has been adjusted up to lessen vibrations in the interior.

Use the online Meritor manual to check adjustment before assuming your condition is normal.

Pierce

Re: Downhill braking in reverse.

Reply #11 – August 31, 2015, 12:06:20 pm

Thanks Pierce! Both Keith Risch and Paul Yasbek assured me were fine. Keith walked me through the process of finding idle switch under dash. Wallah! three bumps down and it holds fine and shakes at idle like the 280 used to. Now tires!

Re: Downhill braking in reverse.

Reply #12 – August 31, 2015, 12:27:29 pm

On a 98 m11 celect plus I think the idle adjustments are in a switch under the left dash.

Set at 600.

Deglaze the brakes. Almost constantly as they glaze and are cold blooded by nature.

Verify which D2 valve is in your coach. Needs to be the 110 to 125 or so one.

Mine had a 90 psi range at low and the braking effect was noticeably less.

So I turn off the retarder a lot during drives and when the road is clear fore and aft I use the brakes hard several times from 60 to 70 down to 40 or so. Hard. Do it again.

If still not strong brakes verify the D2 pressure and keep stopping until they deglaze and reach operating temps.

We are under loaded I think on these brakes. They were made for heavier vehicles. We do not warm them up enough.

Probably why Foretravel put the retarder on the coaches. Ensures panic stop ability on cold and/or glazed brakes IMO.

Coming into a city type area I turn off the retarder and warm the brakes up a bit before I need them.

I have learned to drive in medium crowded conditions without the retarder. Warmed up the brakes are very strong.

But the retarder on and off switch and the handle have been relocated to the middle of my console and are always in my mind if an emergency stop is needed and the brakes may not be enough or warmed up enough.

I would think that the lower D2 pressure from gumming up of the valve over time and/or the use of the lower pressure valve itself and the constant use of the retarder cause the braking issues you are seeing.

Only really shows in reverse.

The disk brakes seem to race grade hard metallic pads on them. Need to be warmed up and no surface rust on the rotors and need hard use and high pressure air from the upgraded valve to stop.

And a 600 rpm idle helps.

I prefer the disk brakes without the retarder for most use but be careful as their action is very dependent on their being warmed up and no rust or corrosion from sitting around.

Bob

Re: Downhill braking in reverse.

Reply #13 – August 31, 2015, 01:42:52 pm

I agree with caflashbob and disagree with those indicating you need brake work.

I seldom use the retarder when driving, except when descending a steep hill.
I find the brakes come on too hard with retarder on for normal driving (I brake easy).
When approaching a traffic light at the bottom of a hill, I find that it takes a lot of brake pressure to bring my coach to a stop, so at 5mph, I select "neutral", then reselect "6" when light turns green. I find this makes it more comfortable to keep the coach from creeping when stopped at the light.

I do use the retarder when in heavy traffic on a freeway because of the sudden stops that happen.

Backing down a hill in reverse is frightening, and I engage "neutral" for this also.

Also, check the brake caliber rods (two on each caliber) because they can get dirty and prevent the brakes from releasing. Also check for uneven brake pad wear caused by a stuck caliber.

Re: Downhill braking in reverse.

Reply #14 – August 31, 2015, 01:56:53 pm

I back down a steep hill every time I put the coach away. Brakes work fine and no need for neutral to be selected.

Re: Downhill braking in reverse.

Reply #15 – August 31, 2015, 03:33:08 pm

Quote from: John S – August 31, 2015, 01:56:53 pm

I back down a steep hill every time I put the coach away. Brakes work fine and no need for neutral to be selected.

Believe the idle adjustment is critical.

Re: Downhill braking in reverse.

Reply #16 – August 31, 2015, 03:51:35 pm

The retarder allows for the brake pads to last nearly forever. But like mentioned above by Bob and me....use them once in a while.

After sitting for a while, I make sure to use the brakes hard a few times to get them hot and clean the rust off the rotors. My parking brake holds on my driveway....which is steeper than any public road i've ever seen.

Re: Downhill braking in reverse.

Reply #17 – August 31, 2015, 04:43:12 pm

Quote from: TAS69 – August 31, 2015, 03:33:08 pm

Believe the idle adjustment is critical.

It is easy to adjust the idle with the cruise control buttons. Then test if your brakes work.

Re: Downhill braking in reverse.

Reply #18 – August 31, 2015, 05:17:37 pm

Ours is under the dash. Easy as pie.

Re: Downhill braking in reverse.

Reply #19 – August 31, 2015, 08:26:38 pm

I also use my retarder like Wyatt

"I seldom use the retarder when driving, except when descending a steep hill.
I find the brakes come on too hard with retarder on for normal driving (I brake easy)."

If the d2 controller has the max pressure setup the brakes get slightly touchy at low speeds.

Re: Downhill braking in reverse.

Reply #20 – August 31, 2015, 09:19:02 pm

Funny, I love the retarder at low speeds- often use it by itself with joystick. Yes, brakes and retarder together touchy at low speeds.
But I only take off retarder in heavy rain where hydro planing or skidding is more likely. Never know when you will need to panic stop so like to leave it always on.
If I want a smooth stop in town I will often reach down and pull retarder 2/3 to full on with joystick w/o touching brakes. If I need a more aggressive stop I can add service brakes smoothly as needed. (Remember, retarder pretty much already fully on).
Try it, you may like it. Then again, maybe not. Different strokes!

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