Do 285's make the Allison shift funny?

04GMC8100HD · July 25, 2003

I was just wondering, because I plan on putting a set on my new truck when it comes in. I also plan on a wester's PCM, will this correct any shift problems I may have with the 285's?

Randy

c5vetteman · July 25, 2003

The Allison web site states that 285's may prevent the tranny from shifting into fifth gear. Also, I read on this forum that GM issued a TSB to dealers not to do any drivetrain warranty work on Allison tranny's with 285's mounted on the vehicle.

This bums me out because I am looking forward to getting a Duramax, but I can't stand the look of the 245's!

JimWilson · July 25, 2003

I don't know if Lyndon (Wester) has cracked the code for the allison yet. Might want to send him an email and ask ([email protected]).

04GMC8100HD · July 25, 2003

I talked with Lyndon this morning and he wasn't aware of any problem with the allison and larger tires, he said that it would just relearn by itself, but if a problem did arise he thought he could take care of it.

Randy

c5hd · July 25, 2003

I've seen new Duramx/Allisons lifted at the dealership. Have to have at least 33s on them. No that it answers your question, but you'll probably be fine. I would make sure that you dealership is mod friendly.

Misbavn · July 25, 2003

I have a'03 CC Dmax/Alli and have been running 285's since day one. My dealer took the 285's off my trade (02 1500 Ext Cab.) and swapped them onto the Dmax. I have had the truck two months and 4K miles with no problems.

ScramblerHD · July 26, 2003

purchased my 03 HD D-Max in Feb. it had 285's from the dealer and I have 10000 on it now with ZERO problems. go for it

04GMC8100HD · July 26, 2003

Thanks Guys!

Randy

Moonlight · July 26, 2003

No problems here. 03 2500 with 315/70R17's ... does take awhile longer to shift into final gear (about 50 mph) but I haven't noticed any problems at all.

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