Buddy of mine has a strange problem with his tranny...he lives over 5 hours away though so ive been trying to help him diagnose it over the phone.
Its a suncoast IV with an LB7 valve body, 05 LLY trans/C1-C2 rotating assy, and an LB7 front pump (with pressure mods)...kind of a mutt.
It has weird issues in reverse. Basically when you shift it into reverse theres a 2 second pause, then a big clunk.
What is strange is that when you watch it with a Tech 2, in neutral, the turbine speed sensor reads the same as input speed (normal), 680rpm. Then you shift it into reverse, input speed stays at 680rpm (normal), and turbine speed drops to 0 rpm (normal).....BUT then 2 seconds later when you hear/feel the CLUNK, the turbine speed jumps up to ~570-580rpm and jumps around a bit. Remember the truck is still not moving at this point...so something inside the trans starts slipping a LOT 2 seconds after you shift into reverse. The truck still backs up under its own power and acts more or less normal in all forward ranges.
Another weird thing is when you shift into reverse, the "previous gear" on the Tech 2 says "7" (normal), but after the CLUNK, "previous gear" goes to 255.
The other thing that happens right before the clunk is the PC solenoid A current goes to .5 amps.
When you are in neutral PC solenoid A is at .09amps. Shift into reverse, stays at .09amps. Then 2 seconds later, it jumps to .5 amps just as you hear/feel the CLUNK.
The other thing is that when you shift into reverse, shift solenoid C changes status with the CLUNK as well.
Also, he said when you shift into reverse, after the CLUNK, you can hear something clicking/ticking/tin metal noise in the trans....as if something inside the trans starts spinning after the CLUNK happens......even though the truck is still stopped with his foot on the brake.
When the trans is cold, the clunk is not really noticible, but when you shift into drive, the truck seems like it wants to walk through the brakes? Then as the trans gets warm the walking-thru-brakes in drive issue goes away and the reverse CLUNK issue becomes apparent.
He tried a known-good TCM so bad TCM is ruled out. The TCM has an 01 operating system in it as far as I know.
He says it has thrown P0701 several times, but its not regular and doesnt happen often.
I asked him if he had checked line pressure in neutral and reverse, and to see if it changes with the CLUNK, but he hasnt had a chance to check that yet.
Ben
Its a suncoast IV with an LB7 valve body, 05 LLY trans/C1-C2 rotating assy, and an LB7 front pump (with pressure mods)...kind of a mutt.
It has weird issues in reverse. Basically when you shift it into reverse theres a 2 second pause, then a big clunk.
What is strange is that when you watch it with a Tech 2, in neutral, the turbine speed sensor reads the same as input speed (normal), 680rpm. Then you shift it into reverse, input speed stays at 680rpm (normal), and turbine speed drops to 0 rpm (normal).....BUT then 2 seconds later when you hear/feel the CLUNK, the turbine speed jumps up to ~570-580rpm and jumps around a bit. Remember the truck is still not moving at this point...so something inside the trans starts slipping a LOT 2 seconds after you shift into reverse. The truck still backs up under its own power and acts more or less normal in all forward ranges.
Another weird thing is when you shift into reverse, the "previous gear" on the Tech 2 says "7" (normal), but after the CLUNK, "previous gear" goes to 255.
The other thing that happens right before the clunk is the PC solenoid A current goes to .5 amps.
When you are in neutral PC solenoid A is at .09amps. Shift into reverse, stays at .09amps. Then 2 seconds later, it jumps to .5 amps just as you hear/feel the CLUNK.
The other thing is that when you shift into reverse, shift solenoid C changes status with the CLUNK as well.
Also, he said when you shift into reverse, after the CLUNK, you can hear something clicking/ticking/tin metal noise in the trans....as if something inside the trans starts spinning after the CLUNK happens......even though the truck is still stopped with his foot on the brake.
When the trans is cold, the clunk is not really noticible, but when you shift into drive, the truck seems like it wants to walk through the brakes? Then as the trans gets warm the walking-thru-brakes in drive issue goes away and the reverse CLUNK issue becomes apparent.
He tried a known-good TCM so bad TCM is ruled out. The TCM has an 01 operating system in it as far as I know.
He says it has thrown P0701 several times, but its not regular and doesnt happen often.
I asked him if he had checked line pressure in neutral and reverse, and to see if it changes with the CLUNK, but he hasnt had a chance to check that yet.
Ben
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