Im hoping I can get some expert advice. I have an LML here that did a trans build a couple months back and have been having a frustrating intermittent issue with TCC lockup. The issue im having is during lockup, the TC will lock-unlock and then lock again for good. If i do 20 runs from 1st to 6th at 25%-40% throttle, it will give me this lock-unlock-lock issue twice on average and usually between 130-170 degrees. Using T/H seems to inhibit the problem. This is the 12th Allison that Ive built but my first LML build.
The build is as follows: Ratiotek PRX no shim w/ blue spring, new g3s, Goerend DK. Pressure manifold is new I have confirmed that there is no pressure tuning present, mechanical line pressure gauge shows 250 base pressure and 315 boosted. Ive also been monitoring TCC PC solenoid command with a scanner, 50% of the time I see it ramp up to 60ish then dip down to 25ish then ramps all the way up to 152. The other 50% of the time it ramps straight up to 152. I see no co-relation between the ramp up and the lock-unlock-lock issue.
No codes present at this time, just the lock-unlock-lock issue.
First thing i did was swap in a TCM from another truck, which did not fix the problem.
Second thing I did was swap in a new DK converter to rule out the possibility of a defective TC, which did not fix the problem. Also pulled the bell housing off to check the ring seals while i had the trans out, they were OK.
Customer used the truck to haul his camper without issue all weekend in T/H.
Third thing we tried was pull a couple data logs to see if it was tune related, tried a couple TCM tunes but didnt help.
Fourth thing i tried was throw some more parts at it(imagine that), new pressure manifold and EPC solenoid thinking maybe the EPC solenoid was slow to react causing a dip in line pressure pulling lockup somehow. It made sense at the time but not so much anymore. After re-installing the VB I lost reverse after pulling it out of the shop and a test drive around the block. The truck finally threw a code. p0878 pressure switch 4 high voltage. Cleared the code thinking it was due to an empty VB. code did not come back so i left the new pressure manifold in it.
Customer used the truck to haul his camper without issue all weekend in T/H again.
Fifth thing i tried, thinking that i have a cross leak in the VB being that this problem is more prevalent between 130-170, I took both halves to work and checked flatness on a granite inspection table. I found the main VB half to be .004-.005 out of flatness and the surface finish was very poor, bad enough that I thought I could see the cross leak on the steel seperator plate. So I pulled the dowels out and honed both halves to remove the factory tooling marks and got them flat within .001. Slammed the VB back in the trans, but again, same problem. We then pulled 15 data logs, only two of the logs witnessed the lock-unlock-lock issue. Parked the truck in the yard, shut it off and then decided to back it into the shop. p0878 came back again, cleared it and got it backed into the shop. I then removed the electrical connector to find ATF in the plug connection. I then replaced the harness with a brand new one thinking i found the problem, but again same thing, lock-unlock-lock and now the damn thing is losing reverse sometimes.
I have another LML lined up to borrow the valve body out of this afternoon to see if I can isolate the VB as the problem or not. If this was my personal truck my next step would be to ghost ride it into a tree but its not so Ill have to fix it unfortunately.
The build is as follows: Ratiotek PRX no shim w/ blue spring, new g3s, Goerend DK. Pressure manifold is new I have confirmed that there is no pressure tuning present, mechanical line pressure gauge shows 250 base pressure and 315 boosted. Ive also been monitoring TCC PC solenoid command with a scanner, 50% of the time I see it ramp up to 60ish then dip down to 25ish then ramps all the way up to 152. The other 50% of the time it ramps straight up to 152. I see no co-relation between the ramp up and the lock-unlock-lock issue.
No codes present at this time, just the lock-unlock-lock issue.
First thing i did was swap in a TCM from another truck, which did not fix the problem.
Second thing I did was swap in a new DK converter to rule out the possibility of a defective TC, which did not fix the problem. Also pulled the bell housing off to check the ring seals while i had the trans out, they were OK.
Customer used the truck to haul his camper without issue all weekend in T/H.
Third thing we tried was pull a couple data logs to see if it was tune related, tried a couple TCM tunes but didnt help.
Fourth thing i tried was throw some more parts at it(imagine that), new pressure manifold and EPC solenoid thinking maybe the EPC solenoid was slow to react causing a dip in line pressure pulling lockup somehow. It made sense at the time but not so much anymore. After re-installing the VB I lost reverse after pulling it out of the shop and a test drive around the block. The truck finally threw a code. p0878 pressure switch 4 high voltage. Cleared the code thinking it was due to an empty VB. code did not come back so i left the new pressure manifold in it.
Customer used the truck to haul his camper without issue all weekend in T/H again.
Fifth thing i tried, thinking that i have a cross leak in the VB being that this problem is more prevalent between 130-170, I took both halves to work and checked flatness on a granite inspection table. I found the main VB half to be .004-.005 out of flatness and the surface finish was very poor, bad enough that I thought I could see the cross leak on the steel seperator plate. So I pulled the dowels out and honed both halves to remove the factory tooling marks and got them flat within .001. Slammed the VB back in the trans, but again, same problem. We then pulled 15 data logs, only two of the logs witnessed the lock-unlock-lock issue. Parked the truck in the yard, shut it off and then decided to back it into the shop. p0878 came back again, cleared it and got it backed into the shop. I then removed the electrical connector to find ATF in the plug connection. I then replaced the harness with a brand new one thinking i found the problem, but again same thing, lock-unlock-lock and now the damn thing is losing reverse sometimes.
I have another LML lined up to borrow the valve body out of this afternoon to see if I can isolate the VB as the problem or not. If this was my personal truck my next step would be to ghost ride it into a tree but its not so Ill have to fix it unfortunately.
