Th350 to 700r4

[robert passmore]

I have a 1981 and swapping out TH350 for a 700r4. Being that it is a ‘81 and the 700r4 wasn’t produced yet, the holes on the frame for the transmission support bracket for the 700r4 weren't a thought. I’ve read that the 700r4 is 2” longer from the bell housing to the transmission mount than the Th350. Do I need to drill new holes in the frame or is there another mount out there that utilizes the same holes but is offset to accommodate the 2” difference? The upper transmission mounting bracket on the passenger side will be difficult to drill inside the frame channel with the cab on the frame. Any thoughts are appreciated.

 

[hogdaddy]

I think I had to redrill 2 of the 4 if I recall. I am unaware of any aftermarket crossmembers.
On my 1986 I did not have any issues drilling. It's possible I only used 3 bolts? I can go look at it tomorrow.

 

[robert passmore]

Thanks for the reply. I’ve got an 84 that I did the swap and simply used the same transmission support and moved it back a couple of inches to the predrilled holes. The difference between the 81 and 84 is that the 84 frame was predrilled for both the TH350 and the 700r4. 700r4 wasn’t around in 81.

 

[hogdaddy]

This looks nice especially routing exhausts and looks like it uses lower frame rail.

G Force RCC10-3 Transmission Crossmember, 1973-1987 Chevy C10

This crossmember is a stock replacement designed to allow a dual exhaust system to be routed under the crossmember, allowing ease of header connection, while keeping the exhaust above the frame rails. Great for stock chassis and lowered trucks alike. As a direct replacement; most transmission...

www.speedwaymotors.com

 

[Turbo4whl]

As stated you will need to add some holes. You can use the TH350 cross member, you will need to add a notch in it to clear the 700R4 trans pan. Yes the 700R4 did use a slightly different rear cross member.

You can use an angle drill for the upper holes. Use a short Uni-bit. A pain, but doable.

 

[robert passmore]

Thanks. I’ll post back with what I decide to do.

 

[Ricko1966]

You also depending on year's may have to swap the transmission tail shaft housing and install a speedometer gear. You will have to run a TV cable with proper geometry,and figure out how to control converter lockup. The 9 inch turbo 350 is close enough in length to 700r 4 your driveshaft will work. Look up 6 inch 9 inch and 12 inch th350 so you can udentify them .I'm sure all 81s had a 9 inch but you should check who knows what's happened in 40+ years.

 

[BadBowtie]

I installed a 1973/74 stock transmission crossmember (non-catalytic converter) on my 1983 Silverado, an original 700R4 truck. I threw away those left & right upper side braces all together. I didn't have to drill any extra holes in my frame.

The 1973/74 straight transmission crossmember accepted my 700R4 mount without drilling. It also was perfect for running my 3" pipes right off my longtube headers. It allowed a perfectly straight shot back, rather than that awkward left side twist.

Finally, there is both a long tail and short tail TH350. One does not require a shorter driveshaft, nor moving the transmission crossmember back.

Add a transmission cooler up front. The biggest one you can fit- Trust me.

 

[Ricko1966]

I installed a 1973/74 stock transmission crossmember (non-catalytic converter) on my 1983 Silverado, an original 700R4 truck. I threw away those left & right upper side braces all together. I didn't have to drill any extra holes in my frame.

The 1973/74 straight transmission crossmember accepted my 700R4 mount without drilling. It also was perfect for running my 3" pipes right off my longtube headers. It allowed a perfectly straight shot back, rather than that awkward left side twist.

Finally, there is both a long tail and short tail TH350. One does not require a shorter driveshaft, nor moving the transmission crossmember back.

Add a transmission cooler up front. The biggest one you can fit- Trust me.

There's 3 lengths 6,9,and 12 a 200r4 will go where a 6 came out,a 700 will go where a 9 came out and a 12 you're going to look at it and go who put this f#ck!n 12 inch th350 in here,I can't swap anything.