700r4 swap

[Leevon]

So the TH400 in my "new" '87 Silverado is having issues.  I think the pump is shot because it whines really bad when it's cold and takes time to engage.  It's fine when warm, but my guess is it's just a matter of time.  I would like to swap in a 700r4 and have been doing my homework here and on other boards.  I have a few questions.

1)  The truck is TBI/ECM-equipped and currently has a TH400.  I have read that the torque converter lock-up function on '87 and later models is controlled by the ECM, but I also see the majority of people wiring up the lock-up function as a retro-fit.  Is mine ECM-controlled if so will it be plug and play?  I will be using an '87-92 700r4. 

2)  The TBI unit has a bracket that looks like it has the factory set-up for the 700r4 option.  If this is the case do I just need to get a factory TV cable and plug it in?  Of course I have been studying the critical adjustment procedure. 

3)  I read that '80 and up crossmembers have the 700r4 position already drilled in the frame?  If this is the case then I'll just need to move the crossmember back, shorten the driveshaft and possibly change the yoke to 30 spline? 

4)  EDIT:  I just thought about the VSS system.  How does this interface and will any 87-92 trans accept the VSS cable?  I'm lost on this one. 

Sounds pretty straight forward, like possibly the easiest 700r4 swap.   Any thoughts?

[Dragon]

Might be off on this cause its late, but I would think you could do a Stand Alone Conversion that wouldn't require using a Control Module(ECM)
Here is Painless Wiring's Conversion Setup:
http://www.painlessperformance.com/webcatalog/catviewsearch.php?SearchField=700R4
You ofcourse would still need the proper TBI TV(Throttle Valve) Cable(Very Simple adjustment, and Would Highly Recommend a New GM Cable if you can get you hands on one.  Old ones will have a tendency to be stretched or frayed, so a new one is an Afforable Piece of Insurance!)..

If you want to do a complete Factory Setup and Use an ECM, I would suggest going the easiest route, and just swap in an Underhood Harness(with its ECM, although yours ECM should be the same, just swap the PROM chip from the 700R4 truck) from a truck that came with a 700R4.

BTW: just enter in Painless' stock number on Summit Racing's website, and it will show you their price

[Captkaos]

The TH400 didn't have a lockup converter, only the TH350C and the 700R4 did.  Since you have and 87 with the ECM, you can use it to do the control. 

The TBI should have the brackets/holes to mount the TV cable, it is REQUIRED for proper use on the 700R4.  You need all of this from the donor.

All trucks from 82 and up should have the holes for the 700R4, but if they don't it's just a matter of moving it back and drilling new holes.  Same goes for the 73-80 trucks...

Is you current setup cable driven, if so, the VSS is built into the speedo, you just need to hook it up and it will get the signal.

[Leevon]

I found out today that the tranny is from a '91 diesel van and the story is that the motor went bad which is why it was parked.  We agreed on $225, and I'm picking it up tomorrow.  Thanks for the help guys!

[Captkaos]

You will need a new converter.  Diesels converter stall at a different speed than a gasser.

[Leevon]

Picked up the 700r4 tranny yesterday.  Found out today it is an '85 model %@#@*&% after checking the tag. Needless to say I have been trying to contact the seller.  I did not get the feeling he was shady, so let's hope he will give my money back.  Shame on me for not checking the numbers at time of sale.  Frustrated. 

EDIT:  He returned my call and is going to take care of it, he has a another trans that is in a running '89. 

I have been doing a little research and I would like to use the ECM to control lock-up.  I read a thread by a guy with an '89 pickup that had a TH400 and he swapped in a 700r4.  His engine harness had the correct pigtail right down by the tranny.  He plugged it in and pulled the chip from a 700r4 truck and it functions perfectly.

I have not looked yet to see if I have the wiring pigtail, nor do I think I'll get that lucky, but I am assuming it would be straightforward to tap the correct wires or pin on the ECM if necessary.  Has anybody done this? 

[stevens]

Do they make a short shaft 700r4? And would it be the same size as a short shaft th350?


78 p/u 355  Big ten