4L80-HD in an 87 TBI?

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Motor_Head_Jr.

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Got a question about a truck i'm building, It's an 87 3/4 ton picked it up cheap because it had a blown motor. I replaced the Engine with one I had out of an 87 Blazer that I replaced with a 454. Now this 350 I put in this truck runs great timing is good but the transmission is shifting like the throttle is full open, I mean you gotta know it's coming or you'll get whiplash. The transmission is a 4L80-HD. I was talking to some people about possible causes and the best I can come up with is that the 4L series transmissions run off a TPS to control the fluid pressure in the valve body kind of a built in slip eliminator my question is, where is this located on the 4L80-HD and is it even compatible with the TBI PCM from 87 or can one be modified without it turning into a mickey mouse project. Also the engine I pulled from this truck originally still had fresh paint in the valley below the intake, was thinking that the slamming this transmission is causing could have been the reason most of the cranckshaft was in the oil pan?:confused: Any help is much appreciated.
thanks, Aaron
 
anytime you start switching engines and transmissions in a vehicle with a computer you have to install the computer and wire harness that matches the engine and transmission you are installing. Your best bet is probably to contact a company like the one below which are very familiar with your trani.

http://www.rosslertrans.com/4L80E STreet and strip HD transmission.htm
 
On a detailed look at the transmission turns out I was misled by the parts house, the transmission is not a 4L80-HD it's a 3L80-HD which is a turbo-hyrdamatic 475 so does anybody have any ideas on what would cause a hard shift like this, the transmission seems to shift fine from gear to gear but it hits so hard going into reverse and drive that it actually kills the engine. Not sure where to go from here thoughts point to a check ball missing or stuck in the valve body or a torque converter that may be locked up?? Best I can figure by the ID tag on the transmission it is the original one from the truck and i replaced the engine with one from the same year truck so i can't see the computer being an issue should have done some more research to begin with I guess. Thanks
 
Lockup torque convertor in the lock state would do that. If you drive and come to a stop does the car stall? Why would a check ball be missing, thought this came from a running vehicle?
 
When I bought the truck the engine in it was blown. It appears that the engine was a fresh rebuild, it still had shiney paint in the valley underneath the intake.

I never had a chance to look at the transmission until I put another engine in the truck, but the guy I bought it from said the transmission was also a fresh rebuild. I was thinking that a check ball was left out in the rebuild??

Yes the truck dies when you come to a stop most of the time and it dies most of the time when shifting from park to drive or reverse.

How would I check to see if this is a lock-up torque converter and how would I know if it's locked up?
 
Thanks for the article, this transmission has no wires running to it except for the speedometer, I'm gonna try a torque converter swap. The truck has zero stall right now so I'm thinking that the torque converter is siezed up. will update on the progress.

Thanks for the help
 
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