TH400 going out in my 89 C2500

[BigBen]

Im going to preface this with I don't know that much about automatic transmissions so I'd like some input on what to do. The transmission in my 89 C2500 has recently started sounding like something is rattling around in it and it drives like there is too, so sounds like it's time for a new transmission. When I bought this truck I wasn't planning on it being my daily but it now is, and I was wondering how possible it is to swap the TH400 for a 4-speed automatic. Ive heard of 200R4 and 700r4 swaps, but i've also heard that a 4-speed swap wont work because the column shifter doesn't have enough space near the transmission to move around (I'm assuming this is just for manual transmission). The upside of just putting a new TH400 in it is that they're cheaper and easier to find, but the way I see it putting a transmission with an overdrive gear would end up paying for itself as I mostly drive on the highway and I live in CA with the cheapest gas being $5/gal. The only thing I am worried about is a lower towing capacity with an overdrive gear, but I think you can install a kickdown switch? Would appreciate some input.

 

[movietvet]

Hopefully @NickTransmissions can chime in.

 

[Sean Buick 76]

The best swap would be a 4L80E as it’s a strong trans with overdrive but it also requires a $300-$600 controller to operate. You would need to have the driveshaft shortened with this swap but it is the same spline count on the output shaft.

The second best swap would be a 700R4, not as beefy but no computer needed just a toggle switch for the lockup converter. Different spline count on the 700 but you can just swap in a driveshaft from a truck of the same wheelbase that came with one.

 

[BigBen]

The best swap would be a 4L80E as it’s a strong trans with overdrive but it also requires a $300-$600 controller to operate. You would need to have the driveshaft shortened with this swap but it is the same spline count on the output shaft.

The second best swap would be a 700R4, not as beefy but no computer needed just a toggle switch for the lockup converter. Different spline count on the 700 but you can just swap in a driveshaft from a truck of the same wheelbase that came with one.

Currently 20 and pretty broke so 700R4 it is, did some research and looks like GM trucks with the long bed are the only ones with the same wheelbase, but I found one at my local pick n pull so looks like I have a day planned out ahead of me.
https://www.picknpull.com/check-inventory/vehicle-details/1GCDC14Z8LZ104940
You guys see anything wrong with this? I cant afford a new transmission so I'll take the risk of a junkyard one.

 

[movietvet]

The one you have on there now is used.

 

[Sean Buick 76]

Be sure to get the TV cable and brackets from the donor truck as well. These are needed to control the trans manually based on throttle position. Then be sure to get them setup right so the line pressures in the trans are correct.

 

[BigBen]

Be sure to get the TV cable and brackets from the donor truck as well. These are needed to control the trans manually based on throttle position. Then be sure to get them setup right so the line pressures in the trans are correct.

Went to the pick n pull to check out the transmission before it closed, looks dented so ill wait until I can find one in better condition I guess. Im heading back tomorrow with some tools to get the driveshaft, but ill make sure to get the brackets and the TV cable while i'm there too (Didn't know I needed those so appreciate it). Here's some pics of the transmission, I don't know what these ones should look like but i'll guess that divot isn't supposed to be there.

 

[BigBen]

The one you have on there now is used.

Yeah I get that but its cheap. I figure worst comes to worst I could have rebuilt it but I don't have the time for that right now. Ill save up some more money while i'm looking for another one since the pick n pull one didn't work out.

 

[movietvet]

That pan dent does not look bad enough to pass on the transmission.

 

[NickTransmissions]

Went to the pick n pull to check out the transmission before it closed, looks dented so ill wait until I can find one in better condition I guess. Im heading back tomorrow with some tools to get the driveshaft, but ill make sure to get the brackets and the TV cable while i'm there too (Didn't know I needed those so appreciate it). Here's some pics of the transmission, I don't know what these ones should look like but i'll guess that divot isn't supposed to be there.

Replace the TV cable with a new one - do not pit that old-ass decrepet cable on to your vehicle/trans. Also you'll need the bracket.

Take that pan off and inspect the underside and what's at the bottom of the pan. If nothing alarming or damge is observed put it back on with a few bolts and yank it. Put a diff pan on it later.

Lastly, make sure you do a pressure test before trying to drive it so you can confirm/deny TV cable set up and adjustment are good.