Here is a news flash, Ford and Dodge also have a lock-up torque converter and tow/haul mode. There is no additional braking in an Ally other than engine friction, just like any other diesel that doesn't have an exhaust brake.

 

I drove a trailered 1 ton Duramax with the Ally. All it does in tow mode is downshift if you depress the brake and not touch the gas pedal. On steep grades, the RPMs go so high that it made me uncomfortable, like 3000+. Slowdown with engine braking was not very good, although it was present. Just not sufficient for the truck and a 6000 lbs trailer, I still had to use the brakes. The truck was not equipped with an exhaust brake.
-P

 

you can turn a dmax ~5000rpm on stock internals without it blowing up. You have nothing to worry about with grade braking at 3000rpm

besides, the TCM will make the trans upshift if rpms go above 4900 in grade braking mode.

 

My 2003 Dmax would downshift only. Have seen 4,700 rpms on downhill.

My 2007 Dodge 48re doesn't downshift as aggressively in Tow/Haul, but it is there. But, I like the 48re shifting better than the Allison which felt "mushy" to me.

 

I just took two 07 duramax to my farm to haul hay....One is sitting on the side of the road and wont go over 30 miles an hour....Truck is nice very comfortable....I know everything mechanical can break but with 3,000 miles it is a little disapointing....WHATS UP WITH THE FACT YOU CANT IDLE FOR MORE THAN 10 MINUTES.....JEEZ....they say they will not run if you do idle for more than 10 mins

 

my old man has a 05 and when in tow mode on the trans it down shifts soon and the engine rpms go up that is probably what they are talking about. no need for an exhaust brake it almost stops too fast

 

They are wrong.

 

The GM's and the Ford's both have a tranny brake that downshifts when you tap the break and the shifting strategy is changed. The shifting is pretty rough and scary on the GM's in tow/haul.

 

not sure what you mean by scary. Scary rev limit? You are not going to blow up a dmax by overrevving it. Sled pullers run 4500rpm with stock valve springs, stock everything and they have no problems. The computer will not let you hurt anything.

As far as rough, thats because the allison does not free wheel and is always locked in gear, ie, you actually feel engine braking just like downshifting a manual.

If I come off the highway and I throw it in 1st, it will slow the truck down (albiet, when its unloaded) with hardly any use of the service brakes. The 2-1 downshift slows the truck so fast that it will bark the tires and throw you forward in the seat.

the allison's grade braking strategy i s much more advanced than the fords. The fords is a simple "hit the brake, downshift". The allison's is completely dynamic, if you hit the brake and are decellerating at X rate, and have been going x speed for more than x seconds, etc.... Downside of this is that sometimes it waits forever to downshift, which ill admit is really annoying. Then again, you can always move the shifter down and it will downshift right away, unless a downshift would cause the engine to overrev, in that case it will wait until youve slowed to a speed that is safe to do a downshift.

 

Tranny brake huh. You may want to do some research on automatic transmissions, and how lock-up torque converters fit into the picture. Tranny Brake

 

grade braking with the Allison doesn't equal a exhaust brake in braking a load. My neighbor has a 32' GN tripple we use moving cattle. At over 20000 lb gross its a good load but going down 6-8 percent grades the rpms are high and didn't do the job on his 3500 SRW GMC DMAX/A. He installed a EB and it will hop the wheels in 3rd on dry pavement when empty. It slows the same load better than my EB/Cummins with the same loads.
I also RV in the summer, with three other friends, and one has a 2500 DMAX/A that pulls a 9450 gvwr 5er. My 2500 '03 2500 Cummins HO 3.73 with the NV5600 and a Jacobs pulls a 11200 GVWR 5er and they alway make be bring up the rear. The Jacobs slows my much heavier 5er to slower speeds without brake input than his grade braking and constant brake riding when comming down Monarch Pass,CO or the million dollar highway between Durango to Silverton to Ourey, CO.
The DMAX in the 4500 trucks have a EB option. GM doesn't recommend a EB for just the 2500/3500 DMAX as lifter jacking is a problem for the hydraulic lifter engine.
JIM

 

What else would you call it? It is a brake that uses the capabilities of the transmission to slow the vehicle down. Call it an engine brake, tranny brake, whatever you want, but it still slows the truck down right? Do a little research on your own.. .....there are many ways of making the converter stay locked up! Some of them are even factory as like it was said before.....both Chevy and Ford have it. You can add one to about any automatic truck with a little inginuity and about 5 dollars worth of parts.

 

the turbo vane position can be programmed in conjunction with the grade braking allison, using aftermarket software. It becomes an exhaust brake of sorts. the combination with the allison is a heck of a grade brake.

 

Even when locked up, other automatics can free wheel because they have overrunning clutches. The allison and aisin both use clutch-to-clutch operation, and are the only types of transmissions that are always positively locked into one gear like a manual trans.

 

i've got an 07 duramax sitting in my driveway. I dont believe the tranny slows it down even close to the exhaust brake that i have on my 07,pulling the same size loads. The braking feature on the tranny is barely noticed when you are draging 16k behind you. I must say tho the motor has improved over the 06 and far as the idle over 10 min, thats a bunch of bull i've idled this truck over 10 min this week. This one even has me thinking that with all the trouble i've had with my 07 ctd that i would replace with an 07 duramax, But what do I know I just tow for a living