I had a 2005 LLY-equipped Silverado w/Allison.

When I would go over speed bumps (even at very slow speeds), the torque converter would cut out and I'd get no power to the wheels.

The 48RE has no such shortcoming.

So there you have it - one instance where the reliability of the 48RE exceeds that of the Allison. Frankly I'm surprised this doesn't get mentioned more in 48RE vs Allison discussions. It was a PITA and a little dangerous.

 

Thats the first time Ive read something bad about the Allison.

 

Ever? I've read a bunch of negative, from Allsion owners.

 

There were some problems with the five speed Allisons but I have not heard any problems with the six speed Allisons ( 06 and up) Dodge dropped the ball as far as I am concerned when the came out with the 48r everone else had a five speed and they proudly announced a four speed.
Jim O

 

Jim,what kind of problems,and which series 5-speeds?eh

 

Another disadvantage I have read, the Allison must have the power cut off via computer to the engine in order to make each shift. Modern street bikes with aftermarket computers also use this type of system to speed shift without using a clutch while at WFO. The computer kills the ignition (or fuel with a diesel) and the shift happens, then power is restored.

Problem is if the timing is not perfect, the diesel will destroy the trans in short order. Can anyone confirm this about the computer controlled Allisons?

I will keep driving my handshaker regardless.

 

A Duramax guy posted similar information in a thread on GM vs. Dodge recently. I think the defuel/timing problem for the Allison is only an issue in high performance applications.

 

The allison is programmed like a medium duty tranny. It defuels during shifts which gives far superior durability for the transmission but means that the truck isn't quite as fast. Any time the clutch packs are slipping is bad. If you keep fueling, they will slip a lot more and wear out faster. You can also shock load certain parts if the programming is not great.

The allison is not a perfect transmission by any stretch, however it is pretty good. I would definitely pick one over a 48re.

 

is that seriously the best complaint you could come up with?

It does that because a clutch to clutch automatic, like a manual, is always locked firmly into one gear. You cant have a "runaway" or freewheel condition with the allison. So when you make shifts between gears (up or down), you actually feel the truck changing speeds like a manual trans. Like if you were going 30mph in 3rd gear with a manual trans, and then suddenly put in the clutch, downshifted to first, and then side stepped the clutch. You get jerked forward in your seat and the truck immedaitely slows down. The allison has a VERY low 1st gear ratio; the jump from 1st to second is fairly large. So when you are driving around and come to a stop, the trans wont actually downshift from second to first until 1mph or so.

Because otherwise if it was programmed to downshift to first when speed drops to 5-7mph, you'd get that jerk-forward engine braking effect, and that would result in lots of useless complaints from people like you who dont understand the trans.

So heres what happends when you are going over your speed bump and you get that deathly life ruining terribly awful funky sensation of no power for all of 1 second:

You slow down to 6mph as you come to the speed bump, and the trans stays in second gear. You then slow down to 3mph and roll over the speed bump. Because the springs are stiff, the wheels catch a bit of air. You are braking when you hit the speed bump so when the wheels become airborne for that split second, the wheels actually suddenly stop for a split second. So the computer suddenly sees the speed sensors go from 3-4mph to 0mph (even tho the truck is actually still moving at 3-4mph), and it says "oh crap he stopped, I gotta downshift to first now". So just as you let off the brake and go to accellerate again, the trans is right in the middle of that 2-1 downshift. When you press the accellerator pedal again to speed away from the bump, the engine is still in defuel mode (to make the shifts smooth) because the trans hasnt completed the shift.

So you get that sensation of no power for 1/2 a second or so, and then the trans completes the 2-1 downshift, and you suddenly get power back, and the engine revs way up but the truck doesnt move out as fast as you are used to because 1st gear on the allison is geared so low.

So GM has two options. Program the shift strategy and shift points in the TCM so it downshifts earlier and causes the engine braking slow down effect that jerks you in your seat, but you dont get the loss of power sensation. Or program it so it downshifts later, and is a smooth downshift, but then you get the sensation of no power for a second. Either way people are going to whine and complain, so they are between a rock and a hard place.

There. Make sense now?

ben

 

so does your handshaker if you think about it. :

ben

 

Yep, that's the best complaint I could come up with. It was otherwise a great transmission and I'd give a kidney to have it hooked up to my current powerplant.

Thanks for the explanation, it makes sense.

 

I had a duramax loaner when my GMC was in for warranty repair and I noticed this also. It was an 03 and it seemed really sluggish anytime I stopped or almost stopped. I know guys that love this trans but I'll stick with a manual til I need an auto.

Hey Duratothemax, are you really getting 'air' at 3 mph over speedbumps? I'd suggest keeping both hands on the wheel!

Kurt