Allison 5sp: Head scrathcer of the day

[THEFERMANATOR]

My BURB's tranny has been working great until yesterday. Out of the blue it started flaring the 1-2 shift SEVERELY! When it goes to shift it would feel like it would hit neutral with no defuel, then bind, and slam into 2nd. Checked it for codes and found none, fluid level is dead on, fuel filter just changed, as well as spin on which had very little sheen on the magnet(had to be one of the cleanest spin ons I have ever changed on any ALLISON). Took it out today and still no codes, TAPS show as converged, but it would hit a wall and slam into 2nd. Reset the TAPS and made no difference. Then on my way home to park it, it started shifting like the TAPS had reset and smoothed itself right out after a few shifts.

When it was doing this it would ONLY happen on the 1-2 shift, 2-3 was perfect as well as the 3-2 and 2-1. Didn't matter if I was in tow/haul or normal mode when it was acting up, it shifted the same way. I'm wondering if my TCM isn't going on me as I have always had problems with TAPS going screwy, and the DVT's not working with this TCM. The big kicker is I'm laid up right now on crutches after hip reconstruction surgery. And problems with the BURB is the last thing I need right now.

 

[Mike L.]

Sounds like a ripped C4 piston.

 

[THEFERMANATOR]

Or a delaminated C4 clutch was my guess. Just drove it to the store and everything was fine with it. Shifted like normal. When it was doing it it would do it on every 1-2 shift, but not the 3-2 shift. In about 2 months when I'm back on my feet I will probably pull it out and check it. Trans has been in for over 2 years now and about 20K miles with 0 problems, then out of the blue this happens. The only other thing that comes to mind is it did it when I switched my headlights on, so I will go out tonight and try it again with my headlights on.

 

[Kappa9012]

what causes a ripped piston like this? doesn't sound like the burb is turned up to much, so why would it fail randomly?

 

[Mike L.]

Or a delaminated C4 clutch was my guess. Just drove it to the store and everything was fine with it. Shifted like normal. When it was doing it it would do it on every 1-2 shift, but not the 3-2 shift. In about 2 months when I'm back on my feet I will probably pull it out and check it. Trans has been in for over 2 years now and about 20K miles with 0 problems, then out of the blue this happens. The only other thing that comes to mind is it did it when I switched my headlights on, so I will go out tonight and try it again with my headlights on.

Delaminated clutches will turn up in the sump filter with a lot of red lining material that is not burned at all.

 

[Mike L.]

what causes a ripped piston like this? doesn't sound like the burb is turned up to much, so why would it fail randomly?

According to my Allison contact it was a manufacturing defect and they had a lot of them. The rip was as big as your index finger nail. The rip was consistent and they all were identical.

 

[A. Stock Lbz]

According to my Allison contact it was a manufacturing defect and they had a lot of them. The rip was as big as your index finger nail. The rip was consistent and they all were identical.

Is this common in the 6 speed to? I have a similiar problem with the 1-2 shift only.

 

[THEFERMANATOR]

I have ZERO clutch material present in mine that I can see, and I have ALTO apply pistons in it. Drove it a few more times and it hasn't messed up again. I'm beginning to think I'm having TCM issues as this is the same TCM that 2 years ago I was having a click on the 3-2 downshift that stopped when I flashed back to an 01 OS. I have a spare that I will try and put on it next week. Being laid up SUCKS!

 

[THEFERMANATOR]

what causes a ripped piston like this? doesn't sound like the burb is turned up to much, so why would it fail randomly?

One thing to keep in mind is with the TRANSGO trim valves your running full line pressure to the C3, C4, and C5 pistons where stock only ran 125 PSI from the trim valves. The only clutches that ran full line pressure were the C2 and C1 clutches(not all the time either). Then throw in a lot of guys running 270+ line pressure VS the stock 245 when unlocked, and no kickdown, and you can see why the apply pistons could fail. I know I'm running stock line pressure, and the white spring(roughly 170 during lockup) in mine.

It seems to be shifting fine now, but I will probably still tear it out when I am able to again.

 

[Max Attitude]

According to my Allison contact it was a manufacturing defect and they had a lot of them. The rip was as big as your index finger nail. The rip was consistent and they all were identical.

I wonder if this is the problem mine has? Shifts hard 1-2 sometimes but not always. When I put spring clamps on it wasn't near as bad. Mine is all stock. Sorry, not trying to hijack.

 

[THEFERMANATOR]

Gotta get out and swap the TCM and see if that is it. One time it will shift perfectly, and then out of nowhere it will give me a zinger. I have been having problems with it off and on ever since I put this TCM in with a random no defuel on the 2-3 shift at low throttle inputs. One time it will shift great on the 1-2, and then the 2-3 will bang. Then it will do it on the downshift, but not the upshifts. Ether I have something sticking in the trans, a bad TCM, or it has become my wife(which is most likely since I do call it wife #2).

 

[Mike L.]

One thing to keep in mind is with the TRANSGO trim valves your running full line pressure to the C3, C4, and C5 pistons where stock only ran 125 PSI from the trim valves. The only clutches that ran full line pressure were the C2 and C1 clutches(not all the time either). Then throw in a lot of guys running 270+ line pressure VS the stock 245 when unlocked, and no kickdown, and you can see why the apply pistons could fail. I know I'm running stock line pressure, and the white spring(roughly 170 during lockup) in mine.

It seems to be shifting fine now, but I will probably still tear it out when I am able to again.

Pressure has nothing to do with the defective pistons. I have seen more stock pistons ripped than built transmissions.

 

[THEFERMANATOR]

Mike wins the bet. Tore it out today and found a nice small tear in the C4 apply piston. One thing I noticed was both the C3 and C4 lip seals of the apply pistons are rock hard. You can't hardly push them down to compress them. I wouldn't expect to see rubber this hard on a 3 year old apply piston. And then there was the unexpected damage to find, my C2 clutches are FRIED! The colonel couldn't make chicken as crispy as my C2's are. A couple of them don't even have friction material left. I did not expect to see that with an ALTO pack with 7 frictions and a wave plate. I'm only pushing about 400 to the wheels to. And it was shifting great on the 3-4 just yeaterday.

 

[THEFERMANATOR]

Not much of a tear, but enough that it sure made it shift BAD! It was wierd because if you drove it easy it would shift great one day, but if you shut it off and got back in it within an hour it would bang. If you let it sit over an hour it would be fine so long as you didn't get on it.

 

[ironmax]

I hate that dam seal. I replaced C3 apply at 30k after build. Then the c4 after another 28k.

 

[Chevy1925]

Not much of a tear, but enough that it sure made it shift BAD! It was wierd because if you drove it easy it would shift great one day, but if you shut it off and got back in it within an hour it would bang. If you let it sit over an hour it would be fine so long as you didn't get on it.

looks just like brians did when he went through that headache on his old twin'ed truck. his would shift fine under easy throttle but try to go WOT and it would hang like a SOB

 

[THEFERMANATOR]

looks just like brians did when he went through that headache on his old twin'ed truck. his would shift fine under easy throttle but try to go WOT and it would hang like a SOB

Yep, mine would shift fine if I babied it, but as soon as I got onto it just a little it would have a huge delay and then bang in. Then the TCM would freak out and go to shifting like crap for a few shifts then return to normal. But then the next day it would shift bad at part throttle and fine when I got on it some.

 

[Mike L.]

That looked like a stock piston.

 

[Evan@InglewoodTrans]

Sure does

 

[THEFERMANATOR]

That looked like a stock piston.

It was from an ALTO kit I bought from SUNCOAST in 2011.