Allison 6sp: C5 Toast again ?

[Gutruk]

In addition to my current converter heat/ damage issues as per other recent post today, I also noticed my c5 clutch pack is toast again in centre discs/plates. It was stuffed when we overhauled it and upgraded all the other clutches with stage 5 PPE gear. Very odd then we thought so we replaced the discs and plates taking care to set clearance spot on, it was slightly tight with same plates back in it and new discs so we got one smaller plate to help that.
Could my converter overheat issue that was obviously taking a lot of oil as cooler flow was minimal be affecting the c5 circuit of have I got something else going on here ? No previous codes for it and never has been in past.. I am getting suspicious of two problems right now, that c5 should be like new..
Thanks for any input..

 

[IOWA LLY]

It was stuffed? I don't understand what that means.

What exactly did you set the clearance to?

Did you verify that you don't have a cracked apply piston? Don't have a damaged or missing seal on the apply piston? Something is very wrong for you to have damaged C5.......



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[Gutruk]

Sorry - stuffed over here means its burnt in center discs! outers ok. It was like this when we rebuilt it too.

Clearance set to 0.098"

Yes all good, closely inspected due to seeing this burning disc issue. New seals in, old ones ok too.
Yes we both thought that but hard to diagnose ! for it to burn in only a few days I am thinking a control issue bit no codes to guide me.. 1st and reverse have always been a decent engagement, IE:not soft

 

[IOWA LLY]

0.98 is too loose in my opinion. I'm not sure if that is loose enough to cause your issue or not though. Never tried running one that loose.

I've seen oem transmissions as tight as 0.057" on C5s.

The fact that you had issues with C5 before your rebuild concerns me. I would be replacing the piston just in case it's cracked where you can't see.


Only time I've seen burnt C5s was in a truck that would drop to almost 0 psi of main line during shifts sometimes. Turned out to be a sticky lube valve in the stator housing if I remember correctly.

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[Gutruk]

Ok I will tighten it up, the discs were burnt and worn down smooth towards centre of the pack only, outer discs and plates ok, I assume more heat in centre as it wont dissipate as quick as outers. We replaced all discs and plates with same size and the measure was about 0.078" which was under spec so we added one thinner plate to get it into spec but you say this isn't an issue eh..
I will check or replace piston, we did spray it with solvent to see if it had issues but all good.
odd as trans never threw a code or anything prior but it was hesitating into 1st eventually due to worn and burnt discs I assume.

 

[THEFERMANATOR]

I would STRONGLY reccomend removing the valve body, and air checking EVERY clutch circuit BEFORE putting it back together this time. Something is DEFINATELY not right if you're burning up the C5 clutches. Also make sure your valve body is flat. I had ALOT of weird shifting issues after I built my trans(worked fine in my donor with 162K miles on the clock). Took the valve body apart, layed it on a flat block, and HOLY CRAP at the warpage in it. Took me over 30 minutes with a flat block and a piece of about 80 grit just to get it down close to flat, then had to smooth the finish off after all the rough sanding. Ended up swapping valve bodies to get it to where I was happy with it.

 

[Gutruk]

Ok thanks for tip, I will read up on the air check process..

 

[Tothemax]

Check line pressure. I've had bad Tcm tunes cause high line pressure that I believe to have leaked to c5 clutch driving causing them to drag

 

[Gutruk]

Ok will do, assume at the port ? I have borrowed EFI live & scan tool as well. Done datalog run and on clutch was 232 psi, off clutch was zero. I was hoping I could analyze each clutch with EFI it but seems not..
I did note that as I pulled up in Drive to a stop that the off clutch would show 28 psi until I went into park and back into drive, where it went back to zero. maybe that's a trim thing .. not sure as only learning !
I agree that c5 appears to be dragging somehow

 

[THEFERMANATOR]

The value you see on datalogs is a hypothetical pressure. The lmm has no pressure sensors in it, and the tcm has no control over the actual line pressure other than the g solenoid that dumps 100 psi of main at idle and low throttle input situations. You'll have to get an adapter, and put a gauge on it at the pressure port(little brass plug near the spin on filter) to actually check line pressure. Stock should be 240-245 without lockup, and 140-145 while in lockup, and you should see a 100 psi drop at idle when the tcm turns the g solenoid on.

 

[Gutruk]

Ok thanks on it...

 

[IOWA LLY]

Check line pressure. I've had bad Tcm tunes cause high line pressure that I believe to have leaked to c5 clutch driving causing them to drag

No way did a tcm tune cause your line pressure to be excessively high......

As ferm already said the TCM doesn't control mainline pressure. On 2001-2010 anyway. On 2011 and newer it does. However the mechanical side of things will only allow something less then 300 psi on a stock transmission. (seems to be some controversy on how much exactly) No matter what the tcm says to do. And 300 psi is not nearly enough to cause issues with C5.

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[Tothemax]

No way did a tcm tune cause your line pressure to be excessively high......

As ferm already said the TCM doesn't control mainline pressure. On 2001-2010 anyway. On 2011 and newer it does. However the mechanical side of things will only allow something less then 300 psi on a stock transmission. (seems to be some controversy on how much exactly) No matter what the tcm says to do. And 300 psi is not nearly enough to cause issues with C5.

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Yeah the one I had the c5s die in was a 2011 it would max out my gauge at 450psi as soon as it was in gear and stayed pined down the road. The stock Tcm fixed it. And I had tried 3 tuned tcm's a40 and a50 and they all maxed the gauge out. They had been tuned by dmaxtunner.

 

[Mike L.]

Yeah the one I had the c5s die in was a 2011 it would max out my gauge at 450psi as soon as it was in gear and stayed pined down the road. The stock Tcm fixed it. And I had tried 3 tuned tcm's a40 and a50 and they all maxed the gauge out. They had been tuned by dmaxtunner.

What was done to the trans? The TCM can not raise pressure above what the pressure regulator spring allows.

 

[Gutruk]

I will post a pic or two of c5 when i get it out today. Maybe i should inspect regulator valve while i have it out as well? All we did to this was add a shim froms transgo kit.

 

[IOWA LLY]

Yeah the one I had the c5s die in was a 2011 it would max out my gauge at 450psi as soon as it was in gear and stayed pined down the road. The stock Tcm fixed it. And I had tried 3 tuned tcm's a40 and a50 and they all maxed the gauge out. They had been tuned by dmaxtunner.

No way that was a stock transmission.

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[IOWA LLY]

I will post a pic or two of c5 when i get it out today. Maybe i should inspect regulator valve while i have it out as well? All we did to this was add a shim froms transgo kit.

The transgo kit doesn't come with any mainline pressure regulator shims. What shims exactly are you referring to?

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[Mike L.]

No way that was a stock transmission.

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The blow off valve in the stator support activates at 400psi. If the trans is stock without the ratio tek aluminum defeat plug; you can not see 450psi.
Seems there is always trans problems with pink slippers tuning. Kinda like his rods.

 

[Tothemax]

What was done to the trans? The TCM can not raise pressure above what the pressure regulator spring allows.

it had a suncost kit with ratio tek kit for the 11 up allison

 

[Gutruk]

C5 is melted ...
This is valve that was replaced, wasnt transgo kit ...