Chevy and GMC Duramax Diesel Forum banner

Need opinions from the Alli Gurus

4K views 37 replies 8 participants last post by  ChevyDMax89 
#1 ·
Alright, I'm gonna try to explain what's going on the best way I can. I've already searched previous threads and have not come across my exact problem. There is two issues that I'm having and I'm not sure if they pair with each other or could be completely different problems. The first one started a few months ago and is a drivetrain screech every so often. I thought it was something caught in the brakes at first so I wanted to see if it would go away on its own. But its still there and can happen at any time (accelerating, braking, turning, etc.) and its a screech noise definitely sounds like metal on metal. The other problem started a few weeks ago which is the transmission when driving and it it goes to lock the TC in 5th, it sort of jerks when locking, sometimes harder than others. Sometimes hard enough where it feels like someone is bumping my rear bumper, other times it goes in rather smoothly... At first I thought it was just because of the weather getting abnormally cold the past few days for Florida but it will even do it when its warm now. I do not see any jump in RPM when going to shift, and it goes thru all the other gears just fine, and I've also never limped it. Therefor I don't think its "slipping", but what would cause that bump when locking the TC in 5th??!! Is this problem and that drivetrain screech related? Can a TC going bad make that sound?
 
#3 ·
Maybe when you're bored tonight...
 
#4 ·
Sub'd
 
#5 ·
Are you having similar issues?
 
#6 ·
Try and get a vid of the screech...or sound clip. Could be a zillion things, but at least start by looking into your wheels and brakes and anything around the driveline touching a moving part.. hanger, dust cover, loose exhaust and take a good look behind the rotors for rubbing backing plates. Not sure about the TC issue, but again start with the simplest, fluid level etc.
 
  • Like
Reactions: ChevyDMax89
#7 ·
Fluid level is good and I change the spin on every other oil change. Also switched to Transynd last year so that's all fresh. Doesn't smell burnt. Pissing me off though, it does it daily now. I'm thinking the hard lockup and the screech might go hand in hand....
 
#8 ·
Converter usually should lock in 6th not 5th no? unless you're in tow/haul then it's 2nd
 
#9 ·
No, it locks in 5th and then switches to 6th while locked. You are right about tow/haul though, it locks in 2nd.
 
#13 ·
I'd assume because of the better throttle response.
 
#14 ·
But the fuel mileage must be horrible lol.. Okay so update on my issue.... turns out the trans IS slipping going from 3rd to 4th. It will revv up a few hundred RPM sometimes before it shifts. Not all the time, but sometimes. Its weird the harder I am on the throttle, the BETTER and firmer it shifts... but just normal driving and babying it, it shifts worse
 
#15 ·
Tow haul helps save your stock trans with slightly quicker shifts. Also with turbo baking (activated in tow haul) it's really nice barley using the brakes in traffic. Haven't noticed terrible mileage but it's a 7200lb truck, I'm not too concerned with mileage lol.

And now that you describe your problem that way, my truck started doing that same slip at part throttle...changed the fuel filter and it fixed it. Or turn down your tunes.
 
#17 ·
Mike L, come on man just read some of what I said and give some sort of opinion !!! I'd appreciate it...
 
#18 ·
Bumping
 
#19 ·
Hey Jimmy... Getting the creative juices flowing, Why don't you try average throttle driving from a stop all the way into 6th with the Tow/haul mode on and off.. First try it not on andif you feel the clunk ok..maybe its the TC locking up... Then try it w/ Tow/haul mode on from the start since the TC will already locked up and say you dont feel it then it was just the TC locking in from the start.. Make sense?
 
#20 ·
Since the trans is slipping from 3-4th sounds like your already on the road to a rebuild though..sadly
 
#21 ·
I see what you're saying but with tow/haul engaged, the TC will lock in 2nd and not even get into 6th, right? I've tried this and I don't feel it when tow.haul is engaged, so it is only doing it when locking in 5th....
 
#22 ·
Well regardless your problem is with 5th not 6th.. So, if you don't feel it with tow/haul mode engaged when it goes into 5th then it has to be nothing more than TC locking up..IMO.. Maybe our conversing will get someone else to chime in.. Im far from a tranny guru but just trying to get the juices flowing here...
 
#23 ·
Yeah I definitely see what you're getting at. I've also been told that what I've been feeling in 3rd going to 4th is slippage now so that stinks. It will jump RPMs sometimes when going from 3rd to 4th. Ohhh the joys of owning a truck haha. One good thing is I may be getting my hands on a 6 speed Alli and T-case with only 20k miles on them this Saturday. Hoping the transaction goes smoothly... That way I'll at least have a backup tranny if something happens.
 
#24 ·
Very nice... and BTW, on my street tune 3/4 throttle i get some rumbling/vibration when going from 3-4th...Its identical to driving over very small rumble strips. Your not the only one with problems, its just a matter of how much people want to share.:)
 
#25 ·
And not on any of the other tunes? That's really odd. Wonder what that could be? driveline issue maybe? U-joints?
 
#26 ·
Honestly Im thinking its slippage.. Haven't taken the time to watch RPM's etc but sure feels like thats the problem..
 
#28 ·
Did some google reading on torque converter chatter.. Interesting.
 
#30 ·
Prob mine since Im blabbing about rumble strips..lol.... Prob nothing that Kory's new LML TCM tuning couldn't fix though..:thumb
 
  • Like
Reactions: ChevyDMax89
#31 ·
Chevy I haven't read if your tuned or not, or really can't seem to see what the actual issue is that your having. I've read that you think it's slipping, it could be a shift flare. Rpms flare up on 3-4 shift. A high tune will do that on stock trans sometimes. If your stock tuned then yea your trans is pretty much shot.

I think it'd help if you could reexplain what is going on.
 
#32 ·
Here it is in a nutshell:
Basically I've been feeling a rather hard TC lockup in 5th. When it goes to lock in most of the time, it locks harder than what it used to, sometimes almost feeling like someone bumps my rear bumper. It shift thru all other gears fine and even into 6th and stays locked (which is what its supposed to do until let off throttle) Also, I'm getting a jump in RPMs sometimes going from 3rd to 4th. One more thing is this noise that sounds like metal scraping or a bearing squeel of some sort. I'm 90% sure its driveline related, not brakes or hoses or belts. That led me to think the noise and converter acting up go hand in hand. Maybe I have a TC bearing thats worn out or going bad causing all this?
 
#35 ·
Jimmy, how's the new Trans?

And how many miles has your truck been tuned?
 
#36 ·
Hey Bama! The Suncoast trans feels great!!! Very pleased so far. Firmer shifts and lockup, and no more slipping!! I tuned the truck right around 150k miles and it now has 178k... So almost 30k miles tuned, which isn't much, considering I was never really hard on it or towed heavy loads. The previous owner before me did though, but the truck was stock, so I'm sure 150k+ miles of towing a big heavy dump trailer had a lot to do with the original trans being a little tired, especially after I tuned it.
 
#37 ·
Sounds good man. I tuned mine at 40k, and just rolled 100k. I usually run opt stock tune, and I do like that skinny pedal, but I don't do many wot runs. Still, built Trans is the plan.....one day:grin2:
 
  • Like
Reactions: ChevyDMax89
#38 ·
I've got the factory trans that came out of my truck for sale by the way!! You should buy it and build it when you're ready :)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top