SC IV Reverse TC lockup?

[Chevytech122]

Anyone heard of any issuses where the converter tries to lock in reverse? After the rebuild i backed it out of the garage and road tested fine. Now when its up to temp and you put it in reverse it feels like the converter tries to lock. The truck shakes, doesn't stall out. 1st gear is fine though, no shake. all forward gears shift fine, converter locks like it should. Any thoughts?

 

[Mike L.]

Anyone heard of any issuses where the converter tries to lock in reverse? After the rebuild i backed it out of the garage and road tested fine. Now when its up to temp and you put it in reverse it feels like the converter tries to lock. The truck shakes, doesn't stall out. 1st gear is fine though, no shake. all forward gears shift fine, converter locks like it should. Any thoughts?

If the converter controls are suspect, the TCC ( converter clutch will lock in any gear.) I suspect the C1 clutch might be too tight which will cause a bind up in reverse. Basicaly you will be in forward and reverse at the same time.

 

[Turbo Buick 6]

If the converter controls are suspect, the TCC ( converter clutch will lock in any gear.) I suspect the C1 clutch might be too tight which will cause a bind up in reverse. Basicaly you will be in forward and reverse at the same time.

Mike, can you make a trans break doing this

 

[JoshH]

Mike, can you make a trans break doing this

Trans break or trans brake?

 

[Turbo Buick 6]

Trans break or trans brake?

Maybe a trans brake that will break the trans and make for a broke trans

 

[Chevytech122]

Mike, this is the LLY trans that was in travis's truck for somewhere around 15,000 miles that ben put together. he put all the clutchs together. i was waiting on the P3 torrington bearing. so all i did was put that last bearing in, the park pawl spring in, and the c1/c2 drum. the rest was already together again from 3 weeks ago when ben was here. it is the LB7 valve body, im just curious if maybe something on the valve body is causing this because thats basically the only difference since it was working fine in travis's truck.

P.S. Thanks for the parts, the different torrington for the p3 sun gear that i needed is the bigger one. GM and the allison dealers listed 2 for that and i needed the bigger of the 2 that no one had in stock!

 

[Chevytech122]

Also i forgot to add that i have a tech 2. It shows the selected gear, commanded and current gear all as reverse... not sure if it would still try to be in forward and reverse. It tries to creep backwards when its shaking too. And you let off the brake and it does go backwards as it should.

 

[mainer]

john,

did you guys have the c1's apart when u were searching for the source of the metal shavings?

i wouldnt think that anything should change when reusing the clutches already in it as far as clearances go unless it got put back together wrong

 

[SmokeAintBroke]

john,

did you guys have the c1's apart when u were searching for the source of the metal shavings?

i wouldnt think that anything should change when reusing the clutches already in it as far as clearances go unless it got put back together wrong

We never took the c1/c2 drum apart. Everything in the front half of the trans looked good. It was obvious where the metal shavings were coming from once we took the tailshaft housing off. Because the trans in foreward gears works so good, I dont think that it is a mechanical "clearence" issue. It seems more hydraulic related. But who knows.

 

[Chevytech122]

Playing around tonight if you let off the brake, reverse acts normal. Really wierd...

 

[duratothemax]

yep...im confused.

We never took the front drum apart, so there should be no issues with C1 clearance. It only seems to do it when the truck is up to temp I guess?

If you put it in reverse and let off the brake (dont try to hold it back) and let it just coast back under idle, its fine...its only when you try to hold it "stopped" in reverse that it shudders?

I have not seen the truck personally do it, so its kinda hard to describe it and im trying to help John and travis diagnose it over the phone.

To rule out something electrical I was going to have John disconnect the TCM and see if hydraulic-default works "normally" in forward and reverse on the trans.

Could it be the TCC valve is dragging making the converter clutch partially apply? But we wouldnt see the effect in 1st gear because 1st gear lockup is hydraulically blocked out on the 5 speeds? I was also going to have John sit with the truck in drive (1st gear) and then manually command 2nd gear with the tech 2, but hold his foot on the brake......if the truck starts to shake and shudder I guess that might mean a draggy converter clutch valve??? I have no idea.

There are no other drivability issues as he said and ALL of the forward gears work/shift perfectly, as does lockup when in tow/haul etc...

ben

 

[Mike L.]

If there is metal in the trans it might be sticking the converter flow valve.

 

[duratothemax]

that could very well be possible because we are using the original LLY pump (that had the metal run through it from the lunched bearing).

Its a kind of a bastard trans.

02 LB7 bell housing, LLY main case and tailshaft housing, LLY internal parts/drum/etc, LB7 valve body, LLY complete pump assembly/converter flow valve, main regulator, etc..

we did not take out/clean the converter flow valve or main regulator valve/shim, we basically just swapped bell housings... the converter flow valve is the stock one; back when I built it for travis's LLY, we did not use the suncoast converter flow valve.

Maybe it will unstick itself, hopefully...I wish I had the truck right in front of me because there is a bunch of things I would like to try as far as better diagnosing it...

ben

 

[SmokeAintBroke]

I know i just talked to you on the phone ben, but when i got in the driveway after work i put it in reverse again just to see if it is still doing it. It seems like it shakes harder sometimes than others too. I need to get a tech 2 at lunch tomorrow, get the trans warm and play around with it. Isn't there a reason why we didnt install the suncoast valve? Kinda wish we had taken that apart... Also, this is john posting with travs computer haha.

 

[duratothemax]

ok another update...

now it sometimes wont engage drive or reverse. Once it goes into gear its all fine. Sets a P0701.

Its an LLY pump in an LB7 bellhousing...I wonder if that messed something up? Stock LLY cutback valve, shimmed main regulator.

Or, a bad PSM??? We are going to start out by removing the snake oiler and checking mainline pressure...

any other ideas?

 

[Mike L.]

After you check mainline, check for cracked sump filter at the neck and make sure it's not plugged. I assume your spin on is fresh.
A bad PSM can cause this or a bad temp sensor ( in the PSM ).
A stuck lube regulator valve in the stator body can cause this also.
P0701 indicates that the TCM is not seeing hydraulic action in the PSM.

 

[clayt171]

Sorry, PSM?

 

[Mike L.]

Sorry, PSM?

Presuure Switch Manifold on the valve body.

 

[duratothemax]

Mike do you think this could be related to the reverse "lockup" problem?

Like I said, we did not disassemble the LLY pump at all when we put it back together with the 2002 bellhousing. Maybe the metal that was run through it from the bad torrington bearing previously was sticking the main regulator valve, lube regulator valve, or converter flow valve.....or all of them. We would have disassembled it to check, but when we pulled it out of the original truck, there were no drivability issues or weird converter or engagement issues, so we assumed the metal shavings hadnt made it into the pump??

 

[Chevytech122]

Mike,
The internal filter and external spin on filter are both brand new. Not saying the internal isnt cracked. If i pull the pan i want to change it anyways. Also, would there be any other driveability issues with a stuck lube regulator? My original thought was PSM... i want a little more direction before i start throwing parts at it. After all, its not a customer pay job haha...