Grade Brake Problem?

Richard 34A · 01-01-2008, 02:36 PM

I just came back from a trip involving going over the Grapevine grade just north of Los Angeles. I used the Grade Brake feature that is standard in my 2005 Workhorse chassis Sightseer.

I used the grade brake per the owner's manual and all seemed fine. (Owner's manual: "press and release the brake pedal once.") The transmission down-shifted one gear, to fourth, with the engine running at 3,000 to 3,200 RPM and I also had to do some additional braking so as not to gain too much speed. All went well for some time, and then I noticed that the engine seemed a lot quieter and realized that the tachometer showed only 1,200 RPM and I was definitely gaining too much speed. The green icon was lit on the dash but the grade brake never engaged again; I gained far more speed then I would normally drive and felt lucky that I was near the bottom of the grade when this happened.

Any ideas what happened, why the grade brake seemed to disengage, and why I never was able to engage it again? I did try it later on flat ground and it seemed to work fine; i.e., it down-shifted one gear.

Thank-you,

Richard 34A · 01-01-2008, 02:36 PM

I just came back from a trip involving going over the Grapevine grade just north of Los Angeles. I used the Grade Brake feature that is standard in my 2005 Workhorse chassis Sightseer.

I used the grade brake per the owner's manual and all seemed fine. (Owner's manual: "press and release the brake pedal once.") The transmission down-shifted one gear, to fourth, with the engine running at 3,000 to 3,200 RPM and I also had to do some additional braking so as not to gain too much speed. All went well for some time, and then I noticed that the engine seemed a lot quieter and realized that the tachometer showed only 1,200 RPM and I was definitely gaining too much speed. The green icon was lit on the dash but the grade brake never engaged again; I gained far more speed then I would normally drive and felt lucky that I was near the bottom of the grade when this happened.

Any ideas what happened, why the grade brake seemed to disengage, and why I never was able to engage it again? I did try it later on flat ground and it seemed to work fine; i.e., it down-shifted one gear.

Thank-you,

KIX · 01-02-2008, 04:40 AM

This answer is PURELY a guess. Could the RPMs have gotten to a high enough point that the grade brake disengaged to "save" the engine? Maybe more speed control by the driver is required to prevent engine overspeed.

FrankO · 01-02-2008, 05:16 AM

If you hit the gas pedal while GB is engaged it disengages until you rehit the brake pedal again. As Kix said if the RPMs get too high you need to hit the brake to bring the RPMs down again.
This a great feature.
Frank O.

Richard 34A · 01-02-2008, 02:48 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KIX:
This answer is PURELY a guess. Could the RPMs have gotten to a high enough point that the grade brake disengaged to "save" the engine? Maybe more speed control by the driver is required to prevent engine overspeed. </div></BLOCKQUOTE>

Hello KIX;

The owner's manual makes no mention of the grade brake disengaging at a certain RPM, but it could be possible. 3,000 to 3,200 RPM for a gas engine doesn't seem excessive to me and I was applying brake pressure to help maintain overall speed.

Due to the grade, I didn't apply throttle, which would then disenage the grade brake. Even stranger, though the green icon for the grade brake was lit up on the dash, pushing the brake pedal did not re-set the grade brake to 'on'.

Hopefully someone here has had this happen and can tell me what went wrong; even if I accidentally disengaged the grade brake, I should have been able to set it again and have the transmission drop down into fourth. I think next time I will simply turn off the overdrive, which also accomplishes what I needed; I panicked and forgot about the overdive switch. I can tell you that I had white knuckles by the time I got to the bottom of the grade! Lesson learned...

Richard 34A · 01-02-2008, 02:57 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by FrankO:
If you hit the gas pedal while GB is engaged it disengages until you rehit the brake pedal again. As Kix said if the RPMs get too high you need to hit the brake to bring the RPMs down again.
This a great feature.
Frank O. </div></BLOCKQUOTE>

Hello Frank O;

I think it's a great feature also, but something made it not function correctly. I was applying brake pressure to help maintain speed control and once I realized that it had disengaged, I tried to reset it but to no avail. It is functioning though, as I tried it later on a flat road and the transmission immediately down-shifted to fourth.

It did get kind of scary for a few moments but luckily I was near the bottom of the grade. Next time, I'm turning off the overdrive switch and starting down the grade no higher than fourth gear! (The Grapevine is a long grade but designed for freeway speeds if anyone here hasn't been on it. It's not a slow, curvy, mountain road and nor was I driving too fast to start with.) A fully-loaded motorhome going down a long grade almost feels like it doesn't have brakes if you really use the brakes hard... they seemed to overheat, or lose effectiveness rather quickly in my situation.

FrankO · 01-02-2008, 03:33 PM

Richard,
I am by no means an expert at any of the systems in my MH but I do know that once you turn the switch on the dash the system stays on (light stays on). Unlike the cruise which does totally disengage and turn off when you hit cancel or hit the brake. I think that I turn off the overdrive before turning on the Grade Brake.
Unfortunately I won't be driving mine again until April. I will experiment then but you will probably get better advice from this forum before then.
Frank O.

Tom N · 01-02-2008, 04:39 PM

When you problem developed why didn't you downshift with the shift lever??

-Tom

Richard 34A · 01-03-2008, 02:34 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tom N:
When you problem developed why didn't you downshift with the shift lever??

-Tom </div></BLOCKQUOTE>

I could have, and should have: I simply 'spaced' due in part, to my surprise that it had disengaged and knowing that I was near the bottom of the grade anyway. And it would have been even easier for me to simply turn off the overdrive switch...

Tom N · 01-03-2008, 05:24 PM

In late Oct I drove ~500 miles on the Blue Ridge Parkway. Never turned my grade brake off. It worked great and I did little braking.

-Tom