Allison grade braking problems

[Drive a mile, walk the rest]

I have more questions and doubts about grade braking. Why bother with grade braking? The duramax does not have a jake brake, so I don't think that it is generating a significant amount of braking horsepower. Why do you want to wear out a $4000.00 transmission to save $40.00 brake pads? It might be good for TOW/HAUL mode with an after market exhaust brake, but it doesn't make any sense if you are empty.

My allison will downshift into first gear and slide the rear tires for about twenty feet and then upshift again. Why do you want to "grade brake" at such low speeds? It would be impossible to overheat the brakes before you stopped. All this does is spill a lot of coffee!

I have noticed that the transmission does not want to upshift after a grade brake related downshift. It will stay in 4th gear at 65 MPH with light throttle. It will not upshift until over 70 MPH.

The "normal grade braking" that is described above may prove to be extremely dangerous on snowy mountain. Imagine descending a 7% grade covered with packed snow and heading into a corner at the end of the cliff. Gently apply the brakes and get a transmission downshift to 3000 RPM? Gee, I can hardly wait for winter!

Does anyone know how to use the grade braking only in tow/haul mode? How about a complete disable? How about a 6.5 and a 4L80e?

[mdrag]

Check out Kennedy's website and choose TECH TIPS, then DURAMAX TIPS for a thorough explanation of how the grade braking feature works:

www.kennedydiesel.com

Also illustrated instructions for the high idle and OD lock out mods.

[Drive a mile, walk the rest]

mdrag,
Thank you for showing me the kennedydiesel webpage. The duramax techtips are very informative.


I learned that the grade-brake is designed to use up an expensive transmission in an attempt to save very inexpensive conventional brakes.

I learned that the grade brake will disengage after the vehicle has lost traction. It will be the drivers responsibility to regain control of the vehicle after the skid.

I learned that there is no way to turn off the grade braking. It is on in tow/haul and normal mode.

I still have a few unanswered questions.
1) Why won't the transmission upshift after a grade brake downshift?
2) Does anyone know how to disable the grade brake?

The kennedy diesel information has generated one new question. What happens if the truck is in 4 wheel drive? The front and rear wheel speeds will be the same. How does the grade brake know that the vehicle is slipping?

[hoot]

1) It will upshift if you accelerate.

2) You minimize grade braking by not using tow/haul.

If grade braking disengages under loss of traction...

1) You may have been going to fast in the first place

2) Your driving expertise takes over. That's what I would prefer. Would you rather have the truck go into autopilot and land it for you too?
Don't forget you have antilock brakes that really work well.

[mdrag]

DAM WTR,

I don't recall any information or previous posts indicating that the grade braking feature was going to cause the Allison problems, such as premature wear etc.

Where can I learn more about this problem?

mdrag

[kerry witherspoon]

Well grade braking do you need it if towing yes but does it eliminate the need for common sence no. Idrive a duramax and also semi most problems i see are people in to big a hurry.Also on my duramax grade braking has never lost me rear wheal traction on ice.

[56Nomad]

Sorry about a dumb question.....

I carry a 3800 Lb camper in my 3500 truck.
When I've come down very steep grades, I've
just shifted to 3rd or 2nd if necessary to keep
from going too fast downhill.

I've never really used my grade brake...other than
to see that it functionally works.

What is wrong with down shifting to a lower
gear on the Allison-vs-using the grade brake??

[CanadaKev]

Dam,wtr,
You wrote.

"My allison will downshift into first gear and slide the rear tires for about twenty feet and then upshift again. Why do you want to "grade brake" at such low speeds?"

The grade braking feature, does not downshift into first, even in T/H. If yours is downshifting into first, then something is wrong. Get it checked out. In Normal, which I presume you normally ;) run in, the grade braking feature only does a 5th to 4th downshift. But if you read JK's info., then you know that. Again, if you are seeing (grade braking)downshifting in Normal mode then something is wrong. Get it checked out.

I have never heard of anyone sliding the rear tires using the grade braking feature. Again, if this is happening to you, it is not normal. Get it checked out.

56Nomad,
No such thing as a dumb question ;)
Except for maybe Wilky's :D
Manually downshifting the tranny is perfectly fine. That's what its for.
Do you not use T/H when you have the camper on?
It isn't neccesary. But if you did, you would find it doing basically the same thing as you've been doing manually. All your doing is keeping your revs up, and letting the tranny slow you down. In T/H the grade braking does exactly the same thing.
Kev

[DDD70]

T/H grade braking?
One word Fantastic!
While in Montana ealier this fall
was on a Highway (?) east of St Mary
the down hill grade must have been 5
or 6 miles long and I use the T/H
braking.A Cruise bus was loaded behind me.
When we stopped the drive asked me if
I had a Jake brake because he watched
me coming down the grade and only saw
the brake lights twice.Told him what we have
on these trucks.Said he used the Jake
all the way down.I run just under 19000
don"t know his weight.He was impressed and
so was I.JM$.02W

[Maverick]

DAMWTR,
My truck is in 4wd and T/H most of the winter pulling freight up and down mountain passes. Grade braking works excellent and at almost 109,000 miles at 20-30K GVW, my Allison shows no sign of wear. The brakes will heat up and fade under certain conditions. I have done it already. Grade braking works! I have NEVER had the truck kick out on me under any condition. If you are driving down a 15% in 2wd with only your old bloodhound in the back on snow packed road while in T/H, I would expect your truck to come around. You gotta drive with common sense. Was your previous vehicle a Ford?

[ 11-19-2002: Message edited by: Maverick ]</p>

[IndigoDually]

I wish that the grade braking would work at even lower speeds. I have a hill that I frequently travel down between 10-20 mph and I have to shift into 1st manually and I use the trailer brakes to keep my speed down. It is a pain when the system releases at 20 mph just when I need it the most.

Drive, if you are haveing the upshift problems have you just gotten to the bottom of a hill and are climbing back up? That is the only time with a trailer that I could not get an upshift. I am not familiar with the O/D disable because it is new from the factory in '03 but do You unintentionally hace 5th locked out and this is why it's stuck in 4th? I would like to hear more about the circumstances of the wheel lock-up and sliding situation. I'm not doubting, just interested.

John

[CanadaKev]

John,
I agree. It would be nice to have it continue down into first. I too, have to downshift into first manually to continue the transmission braking.

I use the T/H grade braking feature in conjunction with an exhaust brake. The two work extremely well together, and really save the trailer brakes. No more over-heated trailer brakes smile.gif
Kev

[hoot]

Judging by these posts...

Grade braking gets the thumbs up!

[SoMnDMAX]

56 Nomad, manually selecting the gear you want to be in will work, but you're not getting the full effect. When tow haul is selected and a downshift happens (grade braking), the torque converter is locked up. When you manually downshift (tow haul off) the effect of the downshift is less, due to loss thru the torque converter.

Grade braking has released every time for me when vehicle speed has reached 20 MPH. Never has it stayed engaged below that speed. I agree with Kevin and John, sometimes it'd be nice if it would stay engaged a bit longer, but for me, I'm very happy with how it works.

As for the rear of the truck trying to pass you, I had it happen. Just my luck, the day I picked up my truck from the dealer we had a snowstorm. On the way home, I thought I'd give it a try, not knowing what to expect... Well, to make a long story short, I learned a lesson that day- &gt;&gt;&gt;Do NOT use grade braking on icy roads when the truck isn't loaded!!!&lt;&lt;&lt; redface.gif :eek: Nothing was damaged, except a pair of underwear... :eek:

DAMWTR, I'd have your truck checked out. Going by your description, there's something wrong. Best to take your dealer for a ride. On a side note, you can tow with the grade braking off if you do not like it.

[ 11-20-2002: Message edited by: SoMnDMAX ]</p>

[Drive a mile, walk the rest]

WOW! You guys are great! Thanks for all of the great posts. It will take a while to respond, but here it goes.

HOOT,
1) It does not upshift. Not always.
2) I don't use T/H when empty.
1) I loses traction at 10-20 MPH on a gravel road.
2) I am an experienced driver. That's why I'm concerned.
My truck is not right. Who is the best dealer in SW Washington or NW Oregon?

MDRAG,
More shifts means more clutch engage/disengages means more wear. Mine shifts way to frequently. It is not right.

KERRY,
I agree, people go down the hill too fast and they don't have enough brakes left when they get to the bottom.
I lose traction at low speed. 10-20 MPH. It shifts into 1st and they break loose. That not right.

56NOMAD and SNMNDMAX,
I like grade/braking when towing heavy. But the computer can't see the hill coming like a driver can. You can pull the shifter down to 2nd or 3rd before you start gaining speed. Try T/H and see if you like it.
Pulling down into 2 or 3 should provide the same amount of braking. The "loss" in the torque converter is turned into heat. Personally, I would rather have that 5% loss used to cool the engine rather that heat the transmission.

CANADAKEV,
I agree. I am going to get checked out.

DDD70,
I agree. At 19K GVW, grade braking would be a blessing. I get too much of a good thing when I am empty ;)

MAVERICK,
20,000 TO 30,000 GVW? No wonder you get brake fade! At that GVW you must have a lot of weight on the drivers to help hold them down.
I am using common sense. That is why I am so concerned. I don't use T/H when empty. I get too many downshifts without it.

INDIGODUALLY,
I have a 2002. It does not have an O/D lockout. It will stay in 4 after a grade brake downshift for miles. Up hill or down hill, throttle or no throttle. I have to get to 70 MPH to make it upshift.
The wheel slip happens at 10 to 20 MPH without T/H. It should not be downshifting. I am assuming that something is wrong with my truck.

HOOT and SOMNDMAX,
I think that I would be happy if it would work right. Thanks to everyone for telling me how it is supposed to work!

Does anyone know a good mechaninc in the SW Washington or NW Oregon area?

[IndigoDually]

Good Answers!

It sounds like your converter is not unlocking or disengaging and dragging the truck down. As CanadaKev and I have said ours release at 20 mph and the truck is freewheeling without any assistance. There's a issue somewhere.
Don't feel that you are alone, I am going back and forth with the mfg of my motorhome over punchlist issues. My last motorhome I got all of the problems fixed after 2 yrs and it was then stolen and totaled. Now I am starting over wit hanother that is turning out to have more issues than the last one. Hang in there.

John

[SoMnDMAX]

I need to clarify this statement I made- "When you manually downshift (tow haul off) the effect of the downshift is less, due to loss thru the torque converter."

The reason for the loss is the fact that typically the torque convertor isn't locked up in second, third, or fourth gear when tow/haul is off. The torque converter absorbs some of the engine braking that could be had.

[conradv]

Since we're on the Allison, I have a question

When driving down an icy, curvy road, say at about 40 mph max, with the T/H Off, how does the allison interact with the ABS system with the truck in 4wd as compared with it in 2wd when you hit the brakes? (I'm talking about normal winter hill braking, not nutso-slam-on-em-as-hard-as-you-can....)

[SoMnDMAX]

Seems to be fine, drives like any other vehicle. No suprises that I've found.

[56Nomad]

Back to the top.....

OK, I tried the tow haul mode. I just bought a
"Weekend Warrior" trailer and was towing it home.
I figure the trailer weighed in at about 5500 lbs
and I'm going downhill on a 6% grade at just under 60 mph.

I didn't want to gain any more speed.... so instead of
downshifting to 3rd from OD, I hit the Tow/Haul button.
The dash green lite showed the Tow/Haul mode was on,
but there was no change in my RPM's so I had to use my
brakes to slow. Still nothing happened. This was only
grade on my trip back home, so I couldn't test it again.

Whats up...... maybe, my load wasn't heavy enough? :confused: :confused:

[Maverick]

I notice that most of the grades that I grade brake on I have to hit the brakes twice. It will down shift on the second braking. The truck needs feed back from your brake pedal, speed, cal. of grade, and inertia to figure out if it wants to downshift or not. Maybe you didn't get on the brake pedal hard enough to show the computer that you were trying to slow down. My 3500 grade brakes easily as it does it everyday. My 2500HD does not(wifes driver). It seems my truck learns my driving habits and acts accordingly.

[ 12-10-2002: Message edited by: Maverick ]</p>

[Stage 1]

My experience (like Mavericks above)w/ grade brake has been positive w/03' 3500 towing 12 to 13K pounds. Towed about 2,000 miles, much of it through the mountains of VA and WV w/great success. On down grades used the T/H mode, along w/OD lockout activated. Applied the brakes and truck started to grade brake, when speed increased the truck downshifted to a lower gear. Manually applied truck brakes very little on down grades of 5 to 7%. I am very happy w/trucks capability to grade brake w/12K pound trailer being towed.
My towing experience through mountains was totally outstanding!! :D

[IndigoDually]

Nomad, You have to lightly apply thr brakes to let the truck know that You intend to slow down. It won't just downshift on it's own, it waits for input from the brake pedal to activate and the accellerator to disengage.

John

[Bob E.]

Stage1 said that he started downhill and felt the grade brake start in when he braked, then increased speed, braked and then the downshift kicked in. Being a newbie, maybe I don't understand what the grade brake is, but isn't it a downshift? Our 2500 downshifts every time you hit the brakes, so if we're already getting the rpms up pretty good, we're reluctant to hit the brakes and downshift again, for fear of a strain on the tranny. Is an exhaust brake the answer, or am I missing something? Is this tranny working correct, downshifting every time we hit the brakes?

[Maverick]

Say you are doing 60mph and come to down hill grade. You are coasting and apply the brakes. Nothing will happen except you may slow down abit. Apply brakes again and the truck should down shift to 4th gear. If coasting and picking up speed, apply brakes again and it will down shift to 3rd. At this momment you should be around 3500-3600 rpm. If you apply the brakes again, nothing will happen. You will just slow down faster. The engine is in it maximum grade brake mode. Grade brake will not neccesarily happen every time you hit the brakes going down hill. It takes speed, the % of the grade, and brake pedal pressure to make it all happen. If in T/H and you coast to approx 50 mph it will down shift to 4th on its own without even touching the brake pedal. If at 50mph you turn T/H off it will up shift to 5th. Its just the way its designed. If in T/H and you accel to a speed lower than 60mph it will not shift to 5th either. It will stay in 4th. You can turn T/H off and shift up (5th) then turn it back on again and cruise in T/H below 60mph in 5th gear. If you look at your tach it has a broken red line up to 4750. Above 4750 it is solid. The broken area is the grade brake area. It is designed to grade brake up to 4750rpm. If rpm should try to go high while grade braking it will up shift as not do damage to the motor. I have grade braked my 3500 above 4,000 rpm with no problems. All of the above are characteristics of my truck and should be very similar to every D/Max Allison equiped truck. Hope this helped.

[ 12-11-2002: Message edited by: Maverick ]</p>

[CntrlCalDmax]

If I'm driving along on a fairly level area and come to a down hill, it takes a couple of brake applications to activate the grade braking. If I'm driving through a up and down foothill or mountain area the TCM seems to figure this out and the grade braking becomes much more agressive. It will apply sometimes by just taking my foot off the accelerator. Once on more level ground it becomes less agressive. I think GM put a lot of time in designing this program. I have been very happy with it expecially with the exhaust brake.
Leo