I have an '02 Allison that is shifting oddly.

Upon light acceleration, there is a quick surge, or spike, in engine RPM just after the transmission changes gears. This can be heard and felt. It is even noticeable when towing a boat, which weighs in at only about 5,000lbs.

It is more noticeable when not towing. It doesn't happen all the time, but definitely more so when tranny is up to operating temp, which is usually about 150 degrees.

Anybody experience this before?

It's called shift flare. Very common. Mine did it all the time. I don't know if it is a real problem... just a nuisance.

Hoot,

You say yours "did it all the time", does that mean it quit doing it at some point in time, or that you don't own the truck anymore?

Look at his sig. You can see he traded his in for a Dodge.

I still contribute as much as I can with somewhat of an objective approach even though I drive a goat now.

As far as my GMC Allison experience....

It did it often during the first couple shifts, the whole time I owned it. Not every time in every situation. I never considered it a serious issue. I think most Ally's do it once in a while. It ain't easy keeping control of rpms the way the computer controls the shifts, in every situation.Edited by: hoot

Mine still does that...has since new.

Has anyone taken their Alli into Chevy to see what they say about this shifting flare?

I plan on doing so, but thought I'd get prepared first.

Mine seems to do it. Mainly when the truck is first started. (cold)

I am taking mine to a tranny shop for a Suncoast. Shall see if the flair is still there. Mine only does it under light acceleration, and it was a rather common condition on past threads, so I never considered it a problem. Now the slippage I get with my current power levels THAT is a problem.

I have a Suncoast.....not a full on devil went down to Georgia version but an upgrade. It still has a funny flair shift when cold, it is probably something to do with the fact that the engine isn't allowed to make full power until everything is up to temp.


The ally is very sensitive to changes in input power.

You guys have to get use to the TCM being a bitch. It moniters your driving habits while you are driving( like how are you driving now, not how did you drive yesterday) If you do a lot of hyway driving , your TCM will learn nothing.( not the way to brake in a trans mod). If you drive agressively the TCM will bump the pressures, and then for a couple of days you might drive easy in stop an go traffic and all of a sudden you stand on it and the Ally slips, you say WTF. Well, it's normal, I know it sucks.


mike

Figures. I don't drive mine, hard. Do occasionally step on it for passing. I have had some wacked stuff happen.
Mike, can anything be done to keep the presures up, all the time? (TransGo, Co-Pilot?)

I saw a lot of flare before getting my stage 3 upgrade....might have been attributed to TCM and some slippage. I experienced it both when the truck was stock and especially when I started the performance upgrades. Now, haven't noticed flare...upgrade is about a month old. But once in a while there is a very slightly firm shift. The firmness only happens after getting in to it for a period of time and then trying to drive like a 90 year old. The firmness goes away pretty quickly....TCM probably adjusting.


Overall, life with an upgraded tranny has been all http://www.dieselplace.com/forum/smileys/Big Smile.gif http://www.dieselplace.com/forum/smileys/Big Smile.gif http://www.dieselplace.com/forum/smileys/Big Smile.gif s. I just wish I'd had the money to do it sooner.


Wayne

I understand the TCM tells the ECM to cut the throttle during a shift, then re-apply the power after the shift. Also unlocks the converter during the shifts, then relocks the converter as part of the process. If you happen to be moving the throttle position to ask for more touque the re-apply of power will be very noticable. Works the same but opposite when coasting in tow-haul mode (convertor locked) as it down shifts. Throttle up, down shift, then reduce throttle, all with no foot feed pressure. More noticable as the load increases.


Interesting stuffhttp://dieselplace.com/forum/smileys/Big%20Smile.gif