Grab A Gear !!!

[DriVer]

I remember this trucker’s slang and I thought that it would be appropriate for the discussion that I would like to present. On the CB you might hear occasionally one trucker saying to the other “Grab a gear there driver!” and I just want that to be our theme for this discussion.

At so many shows across the US where corporate reps and ambassadors have had an opportunity to speak with owners about brake problems one of the constants that is related by owners is the following. When asked if the owner knows exactly what select shifting is, they will almost always respond, “Yes! I do that, I just reach up on the dashboard and click off the switch.” Well, the only thing that does is bring in about 10% or less in effective compression braking because by selecting off on the OD switch you are going from OD to direct. The difference between OD and Drive is so small as to be ineffective when used in compression on grades. Doing that shift is typically beneficial when getting the engine to begin revving up at the bottom of a grade and perhaps when slowing down when exiting an Interstate off ramp.

Select shifting is accomplished when the driver grabs the shifter and manually begins to choose gears. On grade when approaching something less than a 5% grade quite often a 3rd gear selection will hold you back quite nicely without too much input on the brake pedal. If the grade changes to more that 6% to 9% selecting 3rd gear will offer you little if no forward resistance and your speed will quickly exceed the posted speed limit.

Realizing that a grade of 9% or more is present and immediate shift to 2nd gear is warranted. As you observe your vehicle descending the grade you will see that the tachometer is going to spin up into the 4000 RPM range and that’s OK. You will also observe that your vehicle may only achieve 55 to 60 MPH on descent however that’s not a hard and fast rule.

Depending on the grade you may really get going and you are going to have to bring in some brake. For example I recently negotiated a 10% grade and on this grade even 2nd gear isn’t enough alone to hold you back and you are going to have to scrub some speed. The most effective technique to scrub speed would be to apply a moderate amount of pressure to your brakes for no longer than 2 to 3 seconds and then release the pedal. If you’re still going too fast, repeat the process as many times as required to slow down to a desired speed. The key here is to apply the brakes like you mean it and then getting off the brake pedal for as long as possible to allow the rotors to cool.

A driver getting on the brake gently and continuously controlling forward speed using the brake will overheat the entire system, melt sensors, damage pads and warp & crack rotors.

Descending a grade in 2nd gear will often slow a vehicle too much and you might wind up going slower than 45 MPH. If this happens, simply shift “up” to 3rd and your vehicle will speed up having reduced the gearing and bringing in less engine compression. Again your braking strategy should be moderate pressure on, get off the pedal, repeat the process until the desired speed is achieved.

The chart that is referenced below is located in the Chassis Guide under transmissions. You can download the 2009 Chassis Guide using the links provided in the stickies at the top of the page. Look for “NEW” 2009 Chassis Guide.

Below is a chart showing acceptable speeds for the various gears of your transmission. This will apply in all driving conditions including inclines and declines when manually selecting gears. Shifting out of overdrive on downhill grades allows the engine/transmission to be part of the braking process and is highly recommended by Workhorse. This practice will provide better engine/transmission cooling and minimize wear to the service brakes. Although the AllisonTM transmissions have a built in range inhibitor feature in the TCM (transmission control module) that restricts the transmission from shifting into certain gears if it may damage the transmission or engine, it is best to observe the speed limitation as shown for the Hydra-Matic 4-speed transmission.

Beginning in 2005 the Grade Braking feature was added to all chassis utilizing the AllisonTM transmissions. This is a selectable feature that uses the engine and transmission to control vehicle speed during downhill grades. This feature is enabled by a toggle switch labeled GRADE BRAKE, physically similar to the overdrive switch. Once engaged the green grade brake symbol will illuminate in the instrument cluster, see adjacent picture. When the driver depresses the brake pedal the transmission will downshift and assist with controlling the vehicle speed. The Grade Brake switch is installed by the body manufacturer and generally located in close proximity of the head light switch.

It has been proven that owners with 2005 and newer chassis exhibit fewer brake problems due to the Grade Brake feature. For all you drivers out there that own a 2001 to 2004 chassis don’t be afraid to” “Grab A Gear!”

[wa8yxm]

I will say this about the Allison Grade Brake feature

I LOVE IT!

[Daysu47]

Is the Allison Grade Brake feature available aftermarket??

[RickNB]

Great post Driver and this applies to all heavy vehicles and has been used by truck drivers for years. Another thing we can learn from truck drivers is to bleed off speed in stop and go traffic with the gears before actually reaching the stop sign/light etc if the timing is right a complete stop may not be necessary and the brakes do not need to be touched, this might not be the case for overheated brakes but sure saves on pad wear. Truckers use this method for a couple of reasons one to reduce brake use/wear and the other is so they do not have to do a cold start with a heavy load saving on fuel as well. Just to reinforce this it has nothing to do with the current WH brake problems but should be used regardless. "Grab a Gear guys"
Have fun
Rick

[adj]

Thank you DriVer.

[RovinOn]

My Coach is an 05 and has the Allison Grade Brake ,,,, love it!

[DriVer]

Quote:

Originally Posted by Daysu47 Is the Allison Grade Brake feature available aftermarket??

I believe so. Give Brazels RV Performance a call and ask to speak with Jon.

[JonBrazel]

Here is a direct link to our website with information regarding our Allison GradeBrake retrofit: Brazel's RV Centralia Washington

[Duner]

Quote:

Originally Posted by DriVer ...... I just reach up on the dashboard and click off the switch.” Well, the only thing that does is bring in about 10% or less in effective compression braking because by selecting off on the OD switch you are going from OD to direct. The difference between OD and Drive is so small as to be ineffective when used in compression on grades.

DriVer, just to be clear ....
Switching the OD switch to OFF takes you from 5th gear to 4th gear.

[abarkl]

My '01 Workhorse W22 chassis doesn't have an OD switch. What difference does it make?

[DriVer]

Quote:

Originally Posted by Duner DriVer, just to be clear .... Switching the OD switch to OFF takes you from 5th gear to 4th gear.

Yes absolutely!

In my comments I referenced "direct." When one shifts from OD at .71 to 1 to Drive, the ratio is 1 to 1 which is often referred to as direct.

Thanks for reading the article!

[DriVer]

Quote:

Originally Posted by abarkl My '01 Workhorse W22 chassis doesn't have an OD switch. What difference does it make?

abarkl, I'm not sure who your coach builder is however in my experience I have seen and heard where the OD switch was intentionally left out of the OEM's build.

Bummer!

The "OD Switch" allows you to manually switch from overdrive OD to 4th gear or Drive at the click of a switch. I'm not sure why they would have done that. Surely it wasn't due to the cost of the switch.

[Fred and Bonnie]

Driver, great article, one word of caution. I got a "Check Transmission Temp" warning when decending a significate winding grade in second gear, traveling about 30 MPH. Obviously I upshifted and increased my speed to 35 MPH. Receiving this warning and not knowing the transmission temp was the push to install the ScanGaugeII indicating system.

Fred

[DriVer]

Quote:

Originally Posted by Fred and Bonnie Driver, great article, one word of caution. I got a "Check Transmission Temp" warning when descending a significant winding grade in second gear, traveling about 30 MPH.

Fred, We have seen that in a publications where there is a BIG concern about load vs RPM vs speed. I expect that we want to maintain both an effective RPM level and maintain a moderate vehicle speed. This improves the circulation of the transmission fluid and the flow of air going through the cool pack.

The SGII's "TFT" (transmission fluid temperature) parameter is invaluable in displaying this type of information. I keep a TFT reading open at all times.