Well lost overdrive today. Was towing my trailer back from weekend trip and was doing 65 in OD like I have for 146,000 miles. I got a couple of sudden bumps, like a serious miss and boom, no overdrive. I push the OD button to disengage overdrive and everything runs normally. I mean no other changes. Pulled the trailer the rest of the way home, about another 100 miles.
Any ideas??
Before I get trashed for towing in overdrive, I have 410 gears and a transgo shift kit to increase overdrive engagement. There was not searching for gears, everything was fine. I was under load when this happened. Right now everything is cool and still no overdrive.

 

I'll support you on the OD thing! There's no reason not to tow in OD. I tow 7500# and always tow in OD.

 

Sounds like the OD sprag let go, maybe a snap ring but I've always thought that it would still work with the snap ring gone, would just hang on the downshift (this is assuming a 4R100, the 4R70W is a different thing) Either way it looks like you're gonna have to pull the box. Before you do anything drastic, have a dealer look at it for codes and something really easy. It's pretty hard to say from just a desciption, but the OD sprag would do that. How's reverse, is it smooth or kinda bumpy?

G

 

Thanks for the responce. I have the 4R70W. There is no problem with reverse, when I got home I parked the trailer with no problem. It backed up my steep driveway and I was able to park next to the garage without any trouble. There is no other problem except no overdrive.

I read a couple of posts about a servo letting go in the valve body. Anyone know anything about this? Any other suggestions?

 

I'm just not good enough with the 4R70W to really help you. Sorry I couldn't be more help. I'll ask friend who works on them more than me, maybe he has an idea.


G

 

My 4r70w let go pushing it up the grapevine in the summer heat. It downshifted out of OD and when it went back in it made a huge bang. Went another 200 MI before it started shifting a little funny. another 500 mi ( I was in the middle of a trip to Northern CA from So CA ) and I knew I was in trouble. sprag did let go as well as a bearing in the rear. Had to rebuild ( upgraded parts) and all is well.

 

Thanks guys for the responce. Anyone else have any ideas?

 

I guess no-one here can help me. I'm going in. Tomorrow I'm going to pull the pan and see if there is something obviously wrong in the valve body.
If not then it transmission shopping I will go...

 

Good luck WLF, I hope it's something minor for your sake. If not you might be looking for a built up or race duty unit. Sorry, but it's the only upside I can see to the crapped out trans scenario.

Let us know how things turn out for you.

 

LE PEW,
Thanks. You can bet if I have to replace the trans, it will get something special. I really can't complain, just under 150,000 hard miles on this drivetrain.
We shall see.

 

Maybe a perfect excuse for an 04???

 

Well the valve body checked out OK. I found a piece of one of those snap circlip rings on the magnet. It came from somewhere up in the top of the trans so I guess it needs a rebuild.

I found three different performance transmission makers. If anyone knows of a good performance transmission place, please post it. The shop down the road will install (switch the transmissions) for $350. I don't have a lift so I guess thats a fair price.