ābsinth77

So I am going to pull my 700r4 transmission I built last year and install my race built th350 from another drag car I own and have gotten the 18 5/8" out put shaft that comes out of the 9" tail housing TH350 trans. I know the c4 700r4 out put shaft is 3/4" shorter then the car versions used in all others so will have to cut shaft to fit. Also I know the 700r4 vette tail housing will bolt right up to the TH350 transmission case because I have done so myself in my garage. I just don't know if the vette tail housing will still fit right into C beam torque arm after putting on TH350 trans? My post is strictly about anyone who has done this or helped another do it along with any photos or advise. I searched all prior posts with little help overall for information. I like the vette community on this site but unlike maybe 90% or more of the posters I am a master mechanic (technician) as well as certified transmission builder working Ohio's top engine and transmission race shops over last 20 years. The problem is that the popular adapters sold 15-20 years ago are unavailable now which means custom build job is needed. To be frank about my quest I certainly encourage all respondents to avoid posting anything about why not keep my 700r4 or anything related to 700r4 is a better tranny. I am not interested in those thoughts but only the responses of those who have done the TH350 swap. So let me clarify that my vette is carbed gen II 421 stoker small block with 581 HP running 10's and still street-able so I know my car is set up right to take it. Why I am changing is because rebuilding the clutch pack multiple times a race season is very time consuming and annoying when I can just rebuild once new clutches over winter before race season in my TH350 for cheap. Also most important is that I will be doing all the work which is my labor for free. After all is said is done I will upload a video on YouTube for those to see the build and work done if maybe other's also want to see how to do too. Thanks and please help my quest.

JoBy

Tail excluded the TH350 is shorter than the TH700R4.

The C-beam would have to be 2 3/8" longer than stock automatic c-beam.
The manual transmission C-beam is only about 1" longer than automatic.

Cutting and welding in a piece to make it longer should be fairly simple.

rklessdriver

The spacer you need is still made.

http://www.fitzall.com/supportDetail.php?7Q-35B-22

The TH350 ends up being 5/8" l9nger but the C Beam bolts up fine with at most a litte enlarging of the front bolt holes. Mine needed nothing and bolted right up.
Will

ābsinth77

Thank you for the schematics. I did not really consider altering the C beam and was only focusing on the tail housing. I have been thinking about making an extra crossmember to help hold the tranny and keep some of the crazy torque off of the tail housing area to keep it safer also. I will now consider this option as well. Tack så mycket.

ābsinth77

I used the link. So this is the infamous spacer needed then? I will only need to use this with the original 700r4 tail housing and then it will bolt into C beam pretty much fine, unless the holes need oblonged a bit? I can't believe after 2 months of online searching that I wasn't able to find this! B & M and all other companies told me the spacers and adapters were obsolete. I just chalked it up to the c4 not being popular enough for any modified parts any longer. I've modified many parts for cars over the years but something like this is too hard to dream up easily so thanks a million my friend!

rklessdriver

That is all you need. Its a very easy conversion. That is not a C4 specific spacer.... any 2WD 700R4 can be replaced with a 9" output TH350 using it...

You really dont need any additional trans mounts either. My 84 went 8.70s@155mph with the stock C Beam. Best of 1.24 60ft..... The C Beams will flex and bend over time but my car had a TH350 in it from the time it was a mid 10sec street car in 2009 till it was an 8 sec car by 2013.... I stayed with the IRS and TH350 for 2 yrs after the car was an 8 sec car before converting it to a straight rear and powerglide. I replaced 1 C Beam over that time.
Will

ābsinth77

Just wanted to update the post and say I have all the parts needed now and will begin the build soon. As mentioned I will be uploading a YouTube video for those who may want to know more about this swap. Thanks for the responses and great info!

ābsinth77

ābsinth77

Whole kit at http://www.fitzall.com/7-35C.php $259

Spacer kit at http://www.fitzall.com/7Q-35B.php $85

ābsinth77

pologreen1

Nice!

ābsinth77

Just to clarify this photo shows a TCI speedo gear for a 700r4 housing that I used to confirm the proper meshing together of the gears on the output tailshaft and housing gears that I then turned the output shaft by hand to see the gear's square hole turning properly as confirmation. The final C4 sensor of my 1990 will be used.