Time for a solenoid?

[rydplrs]

I have an 02 gmc 2500hd 4x4. I have noticed it doesn't 'coast' if I let off quite often. From research it looks like the f solenoid is leaking by. I just got the truck, and haven't changed the fluid and filter yet. It was previously owned by a city, so maintenance was probably good, but drivers probably not.

I don't want to replace the fluid, just to do it again if I do the solenoid after.

Am I on the right track?
Does fluid and filter have a chance of solving it?
How much will I spend on the solenoid, and how hard is the job? I always treated transmissions as sealed units. So I have no real experience with what's what inside, but I'll spot a solenoid, and know f is closest to the shifter linkage.

 

[Mike L.]

F trim is lock up solenoid. What do you mean " won't coast "? If F trim was leaking you would have some TCC issues.

 

[rydplrs]

Won't coast, if I let off doing 20 or more it will self brake. I have to stay in the throttle even going down hill to maintain speed. I have driven Allison transmissions with 6.0 and 8.1 gas engines and they didn't do that. Once it gets down to first the engine decouples from the transmission, and it rolls as I would expect.

What is tcc?

 

[rydplrs]

It's not like it's in tow haul mode, it's just a little drag. Also after getting off the highway running empty, then driving 30-50 my tranny temp climbs to 200, when it got that high I put it in tow haul and it dropped to 160. I haven't driven long distances at medium speed to know how it heats up that way.

 

[Mike L.]

It's not like it's in tow haul mode, it's just a little drag. Also after getting off the highway running empty, then driving 30-50 my tranny temp climbs to 200, when it got that high I put it in tow haul and it dropped to 160. I haven't driven long distances at medium speed to know how it heats up that way.

If F trim was bad it wouldn't do this. Who are you listening on the forums that said this?

 

[Awenta]

Like from the engine slowing it down? That's normal for a diesel, they drag more.

Temperature drops in tow haul because pressure is lowered.

Not saying nothing is wrong. Just don't know what you're expecting. Maybe post a video?

Sent from my SM-N910V using Tapatalk

 

[rydplrs]

Yes the engine slows it down. I think it's more then normal, if I'm braking hard with 5-700lbs in the bed I have to use a lot of brake, because it seems to be trying to still push the truck, like it's not downshifting fast enough to keep up. Its more noticeable as a feeling in the controls, then it is something to catch on video. At first I thought a brake was dragging, but they have checked out fine.

The tranny temp seemed excessive, considering I drive like an old man, and the temp was only in the 70's. What's it going to get to when it's 95 outside?

I did not realize tow haul lowered the pressure, I knew it would lock the converter, eliminating a friction based heat source.

I do not know how long the truck was parked before I bought it. It was atleast 6 weeks while bidding was open.


The Allison dealer opens in about an hour, I'll just get fluid and a filter and see what that does for me, it's not the end of the world if I have to do it twice.

 

[rydplrs]

If F trim was bad it wouldn't do this. Who are you listening on the forums that said this?

Google searching other forums. I know not to take one thread as gospel, so when the answer seemed to trend, at f leakby, not failure, I decided to post it here to hash it out before tearing into it.

 

[duratothemax]

Like from the engine slowing it down? That's normal for a diesel, they drag more.

Temperature drops in tow haul because pressure is lowered.

Not saying nothing is wrong. Just don't know what you're expecting. Maybe post a video?

Sent from my SM-N910V using Tapatalk

It actually has nothing to do with being a diesel....

Its to do with the Allison being a clutch-to-clutch transmission, and the way the Allison TCC lockup schedule is programmed. There is nothing overrunning or freewheeling in the trans; its always locked positively in one gear like a manual transmission. The only "give" in the trans is the converter, when its unlocked. When the converter is locked, its going to feel just like a manual when you get into the throttle, and when you let off the throttle....

Even at lower speeds with the TC unlocked, you still get a bit of that "dragging" feel...again, because its a clutch to clutch trans. And the Allison keeps the converter locked 100% of the time on the highway, it doesnt unlock and "coast" when you let off the throttle.

Its not going to feel like any older 4-speed automatic, because it isnt an older 4-speed automatic.

 

[duratothemax]

I have an 02 gmc 2500hd 4x4. I have noticed it doesn't 'coast' if I let off quite often. From research it looks like the f solenoid is leaking by. I just got the truck, and haven't changed the fluid and filter yet. It was previously owned by a city, so maintenance was probably good, but drivers probably not.

I don't want to replace the fluid, just to do it again if I do the solenoid after.

Am I on the right track?
Does fluid and filter have a chance of solving it?
How much will I spend on the solenoid, and how hard is the job? I always treated transmissions as sealed units. So I have no real experience with what's what inside, but I'll spot a solenoid, and know f is closest to the shifter linkage.

Im 98% sure your truck is fine and theres nothing wrong with it.

I think you just arent used to the way an Allison feels, compared to all the other automatics you've driven. Its a big heavy-duty clutch-to-clutch trans. Its not going to feel like a car...or even an older 4-speed Dodge or GM truck trans for that matter either.

 

[duratothemax]

I have driven Allison transmissions with 6.0gas engines and they didn't do that.

You definitely have not driven a 6.0 with an Allison.

And what 8.1's have you driven? 8.1 Suburbans and avalanches dont have an Allison.

Driving a duramax/allison is going to feel different than driving an 8.1/Allison....and its going to feel WAYYYYY different than a 6.0/4L80.

 

[minerigger]

8.1 2500 did

 

[duratothemax]

8.1 2500 did

Yeah I realize that.............

Thats why I said 8.1 Suburbans and Avalanche's

 

[minerigger]

10-4. I know you know that Ben...you've forgot more about these trucks than I know

 

[rydplrs]

The 6.0 and 8.1 were both in early 2000's 2500hd trucks. The 6.0 was a 4 door, the 8.1 was an extended cab. They both belonged to friends of mine, and I drove them 1000-1500 miles each. I'm pretty sure the 6.0 was an Allison, because it had the same brake pedal kick if you start it with your foot on the brake. I know the 8.1 had an Allison.

It probably is just me getting used to it, and driving it has helped with smoothing it out a little. I put on just under 1000 miles in the 10 days I've used it. It only had 120k before.

 

[rydplrs]

It actually has nothing to do with being a diesel....

Its to do with the Allison being a clutch-to-clutch transmission, and the way the Allison TCC lockup schedule is programmed. There is nothing overrunning or freewheeling in the trans; its always locked positively in one gear like a manual transmission. The only "give" in the trans is the converter, when its unlocked. When the converter is locked, its going to feel just like a manual when you get into the throttle, and when you let off the throttle....

Even at lower speeds with the TC unlocked, you still get a bit of that "dragging" feel...again, because its a clutch to clutch trans. And the Allison keeps the converter locked 100% of the time on the highway, it doesnt unlock and "coast" when you let off the throttle.

Its not going to feel like any older 4-speed automatic, because it isnt an older 4-speed automatic.

Thank you.

 

[duratothemax]

I'm pretty sure the 6.0 was an Allison, because it had the same brake pedal kick if you start it with your foot on the brake.

Im pretty sure it did not have the allison.

"same brake pedal kick"?????? Thats called hydroboost. (ie, brakes that are power assisted by hydraulic pressure from the power steering pump, instead of vacuum assist) All 2500/3500 trucks have hydroboost regardless of engine or trans.

That has absolutely nothing to do with the transmission

 

[Mike L.]

The 6.0 and 8.1 were both in early 2000's 2500hd trucks. The 6.0 was a 4 door, the 8.1 was an extended cab. They both belonged to friends of mine, and I drove them 1000-1500 miles each. I'm pretty sure the 6.0 was an Allison, because it had the same brake pedal kick if you start it with your foot on the brake. I know the 8.1 had an Allison.

It probably is just me getting used to it, and driving it has helped with smoothing it out a little. I put on just under 1000 miles in the 10 days I've used it. It only had 120k before.

The 6.0 was not an Allison. It does not have enough balls to run it. You never looked under the truck to verify.

 

[rydplrs]

No, I never looked.


The fluid and filter fixed everything right up. The engine drag was more then expected because the tranny wasn't shifting smooth, and was in the wrong gear so to speak. It shifts smoother, and consistently now and the temp doesn't exceed 170, was pretty stable at 160, but I could get it up a little more working it after a highway run.

It also quickly returns to idle when I let off at medium speeds, which it wasn't doing before.