Chugging / shuddering in OD, tranny issue?

[cardude]

I have a 94 suburban 6.5l TD. I got it not to long ago and I am noticing a shudder when it shifts into OD. its not consistent though, and it seems like it happens at other times very infrequently. I do notice it more when it shifts down into OD around 2K rpm.

any ideas? could it be the OD gear bands going bad or an rpm issue with the torque converter, or possibly something else?

any help / ideas appreciated
Chadd

[Robyn]

The final shift you feel at about 45 MPH is the lockup.
If the shudder happens at this point then the TCC may be heading south.

Try holding just a light touch on the brake pedal and run the gears. This will keep the TCC from engaging.
Once 4th has engaged then let the TCC engage at around 50 MPH if the shudder happens then its got to be the converter clutch.

The factory programing uses Pulse width modulation during engagement of the TCC to keep it nice and smooth.

Sadly this is a mistake and most reprograming kits and some of the Chip makers (Heath) take this out and let the clutch just lock up "Boom"

Far better for the clutch rather than the bump bump bump slide umph crap.

My Dahooooley hits at 45 MPH and you know its in, whump its there.
If the boot is hard on the skinny pedal its even more agressive.

If the tranny has a buttload of miles its probably time to get the box worked over.

Freshen the box and add a new converter. Be sure to get a good shift kit installed.


Best

Robyn

[DaveBr]

Check out this thread
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=33598

[More Power]

Does your 1994 6.5TD have EGR?

[zoelhebert]

i had the same problem a gm tech told to try some lub modifier thats what he call it , its realy additive they use in rear diff from ac delco you can buy it at a gm dealer or a ac delco suplier it comes in a 2 oz or so bottle sory i dont now the right name for it ,it work in my truck, if dont work you need a new torque convert

[DmaxMaverick]

i had the same problem a gm tech told to try some lub modifier thats what he call it , its realy additive they use in rear diff from ac delco you can buy it at a gm dealer or a ac delco suplier it comes in a 2 oz or so bottle sory i dont now the right name for it ,it work in my truck, if dont work you need a new torque convert

If an additive improves ANYTHING, the tranny is due for overhaul. The additive(s) only improve conditions, allowing the tranny to work a while longer. If the TC is shot, it's shot. Additives may help, but they are temporary. Failure is inevitable.

That said, I have "extended" many tranny lives with an additive. My personal favorite is "Trans-Medic" (Gunk product). I have tried many, and it has worked best. YMMV

[JohnC]

Check the engine mounts, especially the one on the crossmember...

[GMC Hauler]

I have a 94 suburban 6.5l TD. I got it not to long ago and I am noticing a shudder when it shifts into OD. its not consistent though, and it seems like it happens at other times very infrequently. I do notice it more when it shifts down into OD around 2K rpm.

any ideas? could it be the OD gear bands going bad or an rpm issue with the torque converter, or possibly something else?

any help / ideas appreciated
Chadd

If the trans has only shuddered a few times, flush the fluid, install a shift kit, and maybe this. It's easy while you are already there:

http://www.sonnax.com/announcements/34994-01K.pdf

You will only spend under $200. It has extended my trans life for more than 30K, many of them towing heavy. The shuddering has not returned.

The way i see it, 30K is worth $200. Since a trans normally lasts 100-200K, and a new trans is around $2000, 10K miles are worth $200-$400. Since I am passing 30K with no sign of impending failure, my investment has paid off.

Skip the additives.

Robin is right somewhat. The programming that heath and Kennedy do lengthens the pulse width modulation time for controlling line pressure. Heath does not add that much. I looked at the data from a laptop based OBD 2 reader with a stock PCM and heath's performance PCM (ver 2.0). it adds some, not much. That alone did not make the booming shifts.

Many will remember that I made a electronic shift enhancer that raises line pressure, much like Heath's and B&M's external kit. They can add a lot of line pressure. They do make the shifts BOOM, like Robin described. The shifts were somewhat scary, when the vehicle jumps under a full power shift while towing.
Now, i have the above recommended mods installed, and the shifting is far better than before. Notice that i still have the Heath 2.0 PCM installed, and is working with the mechanical shift kit. I removed the electronic shift kit.