Odd allison problem

[felix225]

Have an 05 duramax that has more than a couple issues. The truck will lose all gears with the harness plugged in anytime you try to put it into reverse or drive. The nsbu switch is indicating perfectly on my laptop though.

Now, this is usually where I read codes and see whats going on, but to get the truck home, unplugged the round harness and it goes into mechanical limp and feels good and strong in reverse and pulls decent in fwd, until it was warm. Put the truck in park and tried to put it back in gear and it feels like it is in neutral while in reverse and it feels like it has a trans brake when put into drive..

I am going to have to replace the internal harness (leaking) anyway, and wondering if anyone has ever had this issue or knows of anything in the valvebody may be sticking to cause the no reverse and trans brake feel in drive with nothing plugged in when the truck has warmed up slightly?

 

[Mike L.]

Codes? Without them we have nothing.

 

[felix225]

I understand needing codes for the problem with it going into range inhibited, that's not what I am asking about though.

With the round connector unplugged, the trans should be in a mechanical limp mode giving me reverse and 2nd (or whatever the default fwd gear is) and it will, when its cold, but if it warms up and you put it in park and then try to use reverse or drive (all while being unplugged in mechanical limp mode), reverse feels like its in neutral and drive acts like it has two fwd gears engaged at the same time. Let the trans get cold and it will pull fine. There is something mechanically going on, but I don't know hydraulic flow of the manual valve and cant find much info on the hydraulic flow for the various gears.

I will be pulling the valve body soon to check out the shift valves and test the solenoids as pulling codes means nothing at the moment when it has such an odd issue without being plugged in.

 

[Big Block 88]

I see what you are saying, but if you have any codes odds are mike can tell you what the issue is. I wouldnt pull the vb till you know what codes you have.

To say "codes mean nothing" perhaps you shouldnt pull the vb or work on the trans at all

 

[Mike L.]

Ohming a solenoid might tell you something about the electrical health of the windings, but it won't tell you anything about the mechanical part. You will need a solenoid dyno to be sure.

 

[felix225]

The original problem my friend had was when he would drive it, it would lose reverse after the trans got warm, going into range inhibited, but would still give him drive (limp mode) if he put it park and tried to go back into gear. So after driving it like that for over a year, he decided to take it to a shop..

Well, when the truck got to me, it had been to two different shops and the owner doesn't know exactly what was done. The first shop claimed to have replaced the harness and the psm, but it still has the old harness plug coming out of the trans and its leaking pretty badly in the pin area. The second shop claims that all the mechanical parts are in good shape, but I have no paperwork or anything else to go by.

When I pulled the codes the first time, it had any and every code you could think of, and Im sure that has a lot to do with the trans being unplugged, reprogrammed and everything else. I will being pulling the current tcm programming out to see what has been changed with the tune in it and make sure the tcm can read/write along with testing the various outputs as well.

My main reason for disregarding codes is the fact the trans is losing reverse and engaging in drive (feel it lurch, watch turbine speed drop to zero) but refuse to pull (like its in two gears) all while unplugged, taking all electrical out of the equation and it only does it after its slightly (above 120*) and put into park and back into gear.

I was hoping there may have been something tale-tale that would give me something to look into, but Ill just feel my way through it and see what happens.

 

[onebaddmaxxx]

Yeah.....clear the codes, force it to limp then tell us the codes. Mike will be at least able to give you a direction to look at

 

[Mike L.]

Times have changed. Seat of the pants diagnosis will get you no where. It worked 20 years ago but not now. Good luck.
If you decide to throw some codes at us we can help. But telling us it does this or that from time to time means absolutely nothing.

 

[felix225]

I will try to make some time tomorrow to work on the truck and see if I can pull codes and basic visual stuff.

I appreciate the information and will hopefully have something more to give you guys something to go on to get me in the right direction.

 

[felix225]

I finally had time to check the truck out again. Dropped the valvebody, checked all the solenoids (ohmed good), checked all the valves and springs, everything moved free in the bores. Solenoid filter was clean, put a new internal filter (other one was aftermarket with wrong o-ring), suncoast filter lock, new internal wiring harness (old one was leaking through the pins), new pressure switch manifold , and new spin on filter with a fresh fill of Shell Spirax S6 fluid.

Did a read on the vcm/tcm and everything read good, moved the shifter to reverse and drive, range inhibited on both.

Pulled these codes the first time
[] P0700 - Transmission Control System (MIL Request) (Pending) (History) (Current) (Immature)
[] P0500 - Vehicle Speed Sensor A (Pending) (Current) (Immature)
[] U0101 - Lost Communication with TCM (Pending) (History) (Immature)
[] P0722 - Output Shaft Speed Sensor Circuit No Signal
[] P0875 - Transmission Fluid Pressure Sensor/Switch D Circuit

Cleared the codes and these came back the second time
[] P0700 - Transmission Control System (MIL Request) (Pending) (History) (Current) (Immature)
[] P0875 - Transmission Fluid Pressure Sensor/Switch D Circuit (SES) (Pending) (Old) (History) (Current) (Immature)

 

[Mike L.]

P0875 is the reverse pressure sensor on the pressure switch manifold. Could be a bad o ring on the manifold.

 

[felix225]

I am planning on dropping the pan again tomorrow after I check the TCM connections. I will double check the manifold O-rings are in place, as it was a new one, I didn't pay much attention to them before I installed it.

 

[felix225]

Checked the TCM connections, everything looked good, pulled the pan and checked continutity on the tan wire off of the pressure switch manifold and pin 4 on the TCM, ohmed out perfectly and no ground shorts. Pulled the pressure switch manifold off and all the O-rings are in place and look just like new. Not really sure where to go from here, almost like the valvebody itself is somehow the problem but not sure where.

 

[felix225]

Tore the valve body all the way down, lapped the mating sufaces on both halves, ran a bore brush through all the valve bores, cleaned everything three times and put everything back together. Same codes 700 and 875.

On a side note, does anyone have a close up picture of the gain and reverse gain valves that the B and A trim solenoids work. I think there may be an issue with them, but I have nothing to compare them with, but they look like someone took a grinder to them (shiny, kinda rough with flat spots in various areas on them). I ran some emery cloth over them to smooth them out some, but didn't want to take to much off of them.

 

[felix225]

On a side note, anyone happen to have extra a and b trim gain valves laying around? Be happy to buy a set, or know where to get them, as I haven't had much luck sourcing them.

 

[jc1843]

I would replace the pressure switch manifold- only about $40.

 

[gmac32]

I have seen some with the wiring going bad in the harness going down to the tranny

 

[felix225]

Ive tested the wiring harness (external) and it reads perfect from the trans to the tcm, the pressure switch manifold is new, the internal wiring harness is new, new internal filter with filter lock, and I went through the valve body, which is when I discovered the A and B gain valves didn't look right. The rest fo the valves are a dark grey color and the gain valves are too, except in the large area that fits into the bore of the valve body, they look like bright aluminum, and are gouged up (like someone tried to grind them down), with the exception of a few tiny spots where the grey is still on it. they are not smooth at all either..I have ordered a new valve body and will post results when it comes in (sometime next week) and get it swapped out, I will also post a few pictures of the gain valves and what I am talking about too.

 

[othrgrl]

Would you happen to be the guy that called looking for an LLY valve body today? I have never had to replace a valve body, except one with valve bores reamed out to run some over sized trim valves (BD valve body IIRC). Have you tested pressure at the test port to see what it is putting out and compared to factory tolerances?

 

[felix225]

I went through GM for the valve body..but let me recap to say why I came to the conclusion..

Truck had been to a shop before it came to me. The owner drove it to the shop for a range inhibited problem causing a no reverse condition and when the guy got done with it, it would no longer move on its own anymore.

Originally, I tested the internal wiring harness (leaking through pins, so replaced), PSM was throwing codes for 3 different pressure sensors (replaced), internal filter was aftermarket and had green o-ring on it (replaced with allison filter and installed filter lock).

Tore the valvebody down and the GAIN valves (valves that go against the and b trim solenoids) didn't look right. the cylindrical area that goes into the valve body oppposite the button head side that the solenoids are on were shiny aluminum looking, with grind marks on it, rough, with small flat spots, similar to if you were to try to grind something down on a bench grinder.

I have tried to find just the two gain valves, but couldn't..so went with the next option.