3T40/TH125C skips second gear

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Points
0
Location
New Jersey
Website
www.edsofvineland.com
Any Pict's pointing up? A few of the servo & feed tube would be nice. How was the "Push" test of the servo itself? There are many available updates to make this trans stronger and if you get to that point then we can assist more. The pan appears to have a significant amount of "Loose" burnt clutch material. If there is nothing indicated at the servo level then you may try removing the side pan to examine the valve body, they are known for "chewing" the roll pins and spitting out important valves, usually it's the pressure regulator itself but I have seen others spit.
However, since you have a more then fair amount of loose material in the pan, you would be justified in removal and overhaul also. There has to be some burnt clutches inside and it's cheaper to repair it now then after it destroys hard parts. Post results, Transman
 

ShortysTRM

Newbie
Joined
Jul 17, 2009
Messages
13
Points
0
Servo cover:


Crack or tear in servo, probably been there since new, but I thought I'd post it:


Servo:



There was definitely resistance when I pushed up on the servo, but I doubt it was excessive or too little. It was pushed back like a weak shock absorber with slow rebound. The cover bolts were all tight, although one had noticeably less torque on it. There was a good bit of sediment on top of the servo piston (I guess that's what it's called?) but I guess it's to be expected since it's just below the band and acts as a horizontal surface for it to collect on. I thought for sure the band was going to be shot, but it was surprisingly springy. That's as deep as I've gotten so far. Today is my Saturday in terms of work schedule, so I can go back and do whatever you need me to tonight.
 

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Points
0
Location
New Jersey
Website
www.edsofvineland.com
Was the "Bullet" in place? the bullet looking object in the hole near one of the bolt holes, held in place by the servo cover itself?
The little crack in the servo is no problem of itself but may be there because the servo is bottoming out without fully forcing the band on (extremely worn band). Do you see the servo traveling far enough to bottom out on the bore? Post back, Transman
 

ShortysTRM

Newbie
Joined
Jul 17, 2009
Messages
13
Points
0
The bullet fell out before I could see anything about its positioning, but it was definitely there. I did notice that the band seems to have a "dent" where the servo normally presses, and that it seems like it can be moved from side to side a fraction of an inch. That may be normal, though. I can't really tell whether or not the piston is bottoming out. I used a piece of plastigage to see if it was, but couldn't get an accurate result. My servo pin has two grooves, which means it's the shortest available, but I'd imagine all 3t40 come with that from the factory.

The side cover appears to be a PITA to get off, but I may go for it sometime.
 

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Points
0
Location
New Jersey
Website
www.edsofvineland.com
The "dent" is a locator for the servo, to make sure it pushes on the center. It should wiggle a bit inside. Use heavy grease to see if you are bottoming out. Put a blob on the servo and push it in, see what kind of mark or if it makes a mark of it touching (hard to explain but easy to see). They do make a 3 groove pin but if it's worn that far then it won't help to change it now.
If you want to remove the back pan & VB to check, OK but if you are going to remove the whole side cover then remove the trans because at that point you may as well overhaul the trans. To remove the back cover you may need to drop the front bolts of the frame to allow enough movement (not always needed). Post back, Transman
 

ShortysTRM

Newbie
Joined
Jul 17, 2009
Messages
13
Points
0
I really don't know if I can get the side cover off without removing the trans mount, and even then I figure I can only get to the valve body with the trans in the car. Everything I've seen so far is spotless, but there has been a lot of friction material loose inside the trans. It makes me think that the band itself may just be worn beyond rango of the factory servo pin. Is there enough friction lining on the band that it would pay off to try a longer pin? I've got the shortest of the 3 in the car now. The pin with one band is slightly longer, and the pin with no bands is longer still.

I'd just go ahead and drop the transmission, but it appears to be a big task regardless of whether it comes out the top or bottom of the engine bay. I don't have very many tools to work with besides a typical engine lift and unorganized hand tools. Honestly, the car is on ramps right now :-[ I don't have the money for all the tools needed to overhaul it, but I could afford the clutches and bands.

Guide me, oh wise one lol I have been at a standstill since I pulled the servo and I can't work on my other cars while this car is in the garage. I have the car's factory service manual, as well as a GM Automatic Transmission Manual from Hayne's [which is MIA at the moment] if either of those might help...
 

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Points
0
Location
New Jersey
Website
www.edsofvineland.com
I believe the band is gone at this point and overhaul is necessary, you gave it a try but it's inside now. This may be a bit much for you. The removal of the trans is down, partial frame removal. The car will have to be supported high enough that the trans can come out after removal AND the engine will have to be supported while the trans is out. You can make a hanger from 4X4 across the fenders with chain bolted to the engine (SAFETY FIRST). Mike dropped the whole support assy. Engine & trans as a unit but it is an extremely big job in a home garage. I understand money is tight but consider the size of this job before you attempt it. I can assure you that the overhaul is simpler than the removal with only a few special tools needed, the bushings can be taken to a local machine shop for pressing for a very minimal fee. Post what YOU wish to do and we will help (step by step) if needed. Transman
 
Top