Allison Slipping

have a 3000(06) MH w/cat350 with 35,000 miles....for the past 15,000 on occasion it slips and races 4-500 rpms between 3rd and 4th...Allison has reset the computer for adaptive learning 5 shifts fine for several hundred miles then it slips, then it goes back to normal shift...Allison replaced brain last week...did fine for 400 miles, now its slipping again probably 10-15 times during 500 mile trip...Has transynd from plant....fluid level is correct when hot by sensor and dipstick(slight foaming at very top)...any suggestions...with a very cold ambient (20degrees) temp, it hard shifts from neutral to drive on the first shift...after that its ok...Idle is at 700 during hard shift...don't know if these are related but I'm *** tired of returning to Allison just to have the same problem re-appear. The coach wt is 31,000 lbs with additional 10,000 lb tow capacity. I tow a yukon xl ( 5700 lbs).


Update...I'm in Ocala and it is now slipping from 3rd to 4th every time unless I baby the shift....Does anyone have experience with Florida Detroit Diesel-Allison. located at 224 SW 52nd Avenue. I haven't called them yet.....
Re: Allison Slipping

Sure sounds like a problem internal to the transmission. The occasional slip that the adaptive controls corrects is not unusual, but slipping every shift from 3-4 is not. If the unit is still in warranty, you really should take it to Florida DDA or some other Allison authorized dealer or distributor location. F-DDA should do you a good job, but it's been a long time since I've had any contact with them. Good luck.

One thing to keep in mind is when changing the weight of the vehicle (like adding or removing the tow vehicle) can cause adaptive to have to re-adapt to the new weight. However, the constant 3-4 slip you describe doesn't sound good.
Re: Allison Slipping

It tends to act different when I drop the yukon and go no-tow..harsher shifting for awhile and then It smooths out(adaptive I guess) however the slipping is with or without the tow vehicle....I'm gonna call Florida DDA in Ocala tomorrow Morning...thanks for the help....
Re: Allison Slipping

That part makes sense. It adapted to a heavier vehicle(more total weight, more clutch pressure sooner to prevent slippage). Drop the Yukon, shifts harsher for a bit as it adjusts to a vehicle 5000 plus pounds lighter.