Allison 5sp: Hanging in 4th gear sometimes

[Whitetail Addict]

My trans is hanging in 4th gear at times. Most of the time it is when I can't get ehough speed built up initially to get to 5, like after pulling out of a stop sign. Then when I can it hangs in 4 sometimes up to 70-75mph. Usually 1/4 throttle it will shift fine, if I go more it usually won't shift. Sometimes I have to go to 3/4 throttle to get it to shift. Sorta like it has to go out of grade brake mode.
My tune has throttle response increased and I didn't know if this was related to the throttle position sensor, also wonder if I should change the torque table, I am using the stock torque table with a modded McRat tow tune. I am new to the tuning and trying to learn what to change exactly. Thanks for any help.

 

[Noreaster]

My trans is hanging in 4th gear at times. Most of the time it is when I can't get ehough speed built up initially to get to 5, like after pulling out of a stop sign. Then when I can it hangs in 4 sometimes up to 70-75mph. Usually 1/4 throttle it will shift fine, if I go more it usually won't shift. Sometimes I have to go to 3/4 throttle to get it to shift. Sorta like it has to go out of grade brake mode.

Thats funny I was going to post something similiar tonight. Mines acting similiar mostly when its cold. I won't do it if the temp is 1/4 the way up the gauge.

 

[Mike L.]

Make sure your fuel filter is fresh first. Next take the tune out and see what happens.

 

[Whitetail Addict]

I didn't check the gauge to see if it is heat related, that is something I will keep an eye on. Any info I can gain might help me diagnose it.

 

[Whitetail Addict]

Make sure your fuel filter is fresh first. Next take the tune out and see what happens.

Thanks Mike, the filter has about 8k mi on it. Probably due for a new one. What affect does a restricted filter have that would cause this symptom?

 

[Noreaster]

I only have 2k on fuel filter.
Could a tranny filter cause it? Im due for a spin-on & sump filter change.

 

[Noreaster]

What affect does a restricted filter have that would cause this symptom?

When the filter is dirty it doesn't like to shift when hard into throttle, have to let off to get it to shift.

 

[Whitetail Addict]

Thanks Noreaster, when it hangs up it won't shift until I let off. It has done it since it was tuned, with three different tunes, but that is probably due to it calling for more fuel through a restricted filter.

 

[Noreaster]

On my Predator I can compare the desired fuel vs. the actual

 

[Mike L.]

Thanks Mike, the filter has about 8k mi on it. Probably due for a new one. What affect does a restricted filter have that would cause this symptom?

When fuel filter is restricted you must press the throttle quite a bit more to attain same speed as with a good filter trying to get the same amount of fuel to the engine. Problem is, throttle position sensor is telling the TCM you are deep into the throttle and to extend the shift point. Bigger problem is you can't get going fast enough to shift at the programmed speed sensor strategy to shift because of lack of fuel to get to that speed. Hope you understood this. If not I will try better.

 

[Whitetail Addict]

When fuel filter is restricted you must press the throttle quite a bit more to attain same speed as with a good filter trying to get the same amount of fuel to the engine. Problem is, throttle position sensor is telling the TCM you are deep into the throttle and to extend the shift point. Bigger problem is you can't get going fast enough to shift at the programmed speed sensor strategy to shift because of lack of fuel to get to that speed. Hope you understood this. If not I will try better.

Yeah Mike I do understand it. I appreciate the in-depth explanation, that sounds like my issue.
Will that also cause the backshifting or gradebraking I am experiencing when I hit the brakes in 5th?

 

[Noreaster]

Well the trucks still doing it when cold until it gets up to temp. Doesnt matter how fast or slow you go it won't shift to overdrive. Desired to actual fuel is right on so fuel filter is not the problem.

 

[Whitetail Addict]

Noreaster, I know that the truck will extend shifts if the engine operating temp is down, like a cold morning. But that usually goes away within the first few miles.

Update on my truck- I haven't got to the dealer yet to get the filter, was planning on it today but I didn't get to it.
Something I did notice today while driving is the one time it hung in gear I had to sorta kick it down (like you would a carbureted vehicle to kick off the choke) when I lifted it up shifted. Just as you explained Mike. Then the next time I hit the brake pedal, on maybe a 5% grade, it went into grade brake mode. Does this still sound like the filter?

 

[Noreaster]

Dealers are usually pricey on filters $45, could try Napa $35 or order on them from Bline filter for $18 http://www.blinefilter.com/store/in...=13989&zenid=7bcafd903afef87261b8ebd0f4c810af

 

[Whitetail Addict]

Thanks for the tip Noreaster. I can get a discount at the dealership though. Also I am sort of a stickler for using GM products for some reason. It definately costs me more, but I guess its piece of mind.

 

[The Neens]

Let us know how it acts with the fresh filter...If you have any tuning questions, give me a shout...

 

[Whitetail Addict]

Thanks for the offer Neens....I will do that.

 

[Noreaster]

Thanks for the tip Noreaster. I can get a discount at the dealership though. Also I am sort of a stickler for using GM products for some reason. It definately costs me more, but I guess its piece of mind.

Racor makes all the filters, Ac Delco, Napa, etc get blank filters & put their name on them.

 

[Noreaster]

It doesn't matter what I do, it won't shift to 5th unless its 150degs.

 

[racinmike77]

are you sure that its not your converter being kept unlocked to build heat?