i wanna know what i need to do a 700r4 to th 350 swap in my 91 rs

 

hey well.... i have an 83 z28 and i just did a 700r to a 350 swap and only things i had problems with is i had to swap the tail shafts ( easy 4 bolts) and i had to use the 700 tranny mount on the 350 and i had to dril a whole in the mount about 1 inch behind (towards the rear end) the exhisting stud and put my own bolt thru it all for the cross member to bolt up. thats it works great!!!!!!!!!!!!!

 

what tailshaft off the 700r4 and what about all the wires and **** from the 700r

 

i dont think mine has any wires going to it. just the shifter cable. mine doesnt have a NSS either. and mine is the long tail shaft 350, which has a spacer/adapeter followed by a 700r4 tail shaft housing. that way it can use stock cross-member and have provisions for torque arm and the same speedo drive (mech. or elec.).

 

I was unsure about that tailshaft deal. So basically its bolt up if you get a long tailshafted th350 and change out your origininal tailshaft?

 

not quite. first i must say that i did not do this conversion to my car, the previous owner did. but from what i've looked at and read on here i've been able to find out what was done. basically my setup is a long tailshaft (or output shaft) TH350. If you buy a swap crossmember like the spohn ones with crossmember mounted torque arm mount then it will be a "bolt-in" swap just like it is. I dont know about driveshaft length or speedometer hookup in that configuration though. But back to mine, long tailshaft TH350, remove the original tailshaft HOUSING (not the tailshaft, just the housing). Appearantly they have the same output splines so you can reuse the same yoke that connects the drive shaft to the transmission. You have to buy an adapter plate, I thought I had a pic of mine but i dont. it slides on and then you slide on your 700R4 tailshaft housing, bolt them all together and now you're TH350 has the necessary provisions to mount your torque arm, you speedometer housing will still be in the 700R4's tailshaft housing so u just have to hook that back up, and you can reuse your stock crossmember bc it now lines up just as it did before with the mount on the tailshaft. As far as i know, the driveshaft fits too. As i said i believe the spline counts on the tailshaft are the same, but the length i'm not so sure. it must be close since the torque arm mount works out.

note: since i dont have a pic of the adapter/spacer plate, i can tell you that its like 2 or 3 inches wide, just so you know how much longer the original tailshaft is on a longtail 350. hope this helps. and if i have said something in error, someone who knows, please correct me. goodluck with your swap.

 

Thanks. That makes sense. I meant to say tailshaft housing. That makes the whole swap seem more realistic. Im still debating if I want to loose overdrive.
Whats your cruising RPM's? Thats my only kicker for the swap. But most likely, i'll stick with the 700 if i can get my hands on one

 

well the rpms aer going to vary depending on your ring&pinions and rear tire size. I have 4.10s and a 26.6in tall tire. at 55mph i'm turning about 3500rpms. I hate it. This car is not a highway car. A taller tire and less gear would bring them down, but I'm looking to get an overdrive transmission in mine (700r4 or t56). Most ppl that i've seen put th350s in their car if its going to be a mostly or all drag car. if its a daily driver or drive alot to car shows and other stuff where highways speeds are involved, then you'll probably want an overdrive. it all depends on what you're going to do with the car and like i said your rear gears adn tire size. There are calculators online that can tell you approximately what your rpms will be given a particular setup.

 

The th 350 has 3 different length tailshaft housings they are 6", 9", and 12" the 9" is the best suited for the swap. As far as this being the only problem you may feel a vibration when you get the car up to speed or about 1800 to 2500 rpm. The vibration is likely coming from the driveshaft at the tranny. The torque arm will not stop the vibration by it self. The the 700r tailshaft housing is too short for the 350 with the 9" housing. The difference is about 1.5 to 2" and that will cause the driveshaft to vibrate under acceleration and higher speeds, or basically when the drive line is under stress. Another option other than the spacer is to buy a bracket that will bolt to the 350 tailshaft housing and then will allow the torque arm to bolt up correctly. You could also buy a torque arm relocation cross member for the 350 or a whole new torque arm altogether. Summit, Jegs, and Sphon all have these in various price ranges. The spacer would be the cheapest, then the bracket. A whole new torque arm setup or cross member will cost about 275.00 to 350.00...

 

ok so i must have the 9" tailshaft th350. that makes a little more sense. So in my description, you have to use the 9" tailshaft. or do one of the other options listed by palmerracing83.

 

figured i'd post some pictures i just took of my setup. so ppl could see what i was talking about. Not the best pics, but you can see it. The one pic you can see there's a silver colored block/plate that mounts between the tailshaft housing and the back of the trans. Which has provisions for the cross-member mount, so you can use the stock x-member and tailshaft which allows you to use stock speedo stuff and torque arm mount. And the other pic just shows roughly how wide it is; sandwiched just past the round dome cover for the governor stuff and the tailshaft housing. not the best of pics, but its the best i could do right now.

 

AH, now i see. i'm looking at this swap now.. but where am i gonna find the block that adapts it?

 

sorry, i cant help you there bc i really dont know. I didnt buy it. and I dont think its custom made, but idk it could be. never did a search on the web. but i have talked to a few other ppl about it and they had never heard of it.

 

Here is a good pic of the spacer.

 

well correction i just did a search and b&m makes a kit (30299) but it doesnt look anything like mine. but according to this thread it works fine:
https://www.thirdgen.org/forums/tran...y-pic-b-m.html

you can even buy it from jegs for $96. looks like hurst makes one too.
and after another search, it looks like this place sells or used to sell the spacer. i'm really not sure if theyre still around, but you can try it if you want.
http://www.teckpak-fitzall.com/teckf...witch_kits.htm

 

much better pic thats exactly what i have, or close enough. where'd u get yours?

 

I didnt go that route, but kept it as a option. I ended up with a 4X4 trans that I wanted to build. I ended up buying a longer tailshaft and housing. I used the B&M or Hurst kit for the torque arm. I used the stock driveshaft and crossmember.

I was luck enough to find the conversion parts. I wanted the 4x4 trans because some of the hard parts are suppose to be stronger. I used a kit from Dana at Probuilt.

Best bet is if it is a 6" tailshaft, find a new driveshaft/crossmember. Unless you are lucky enough to find the parts and need to rebuild the trans anyway.

 

so with a 9" tail shaft, and that b&m-30299 kit i'm good?

 

Yes.

I suggest getting a flexable dipstick tube with double o-rings. The stock 700r4 will not work with the th350.

 

cool cool. thanks.

 

I don't mean to knock what you are doing, but I have always wondered why people replace a 700R4 with a TH350.
Why are You doing it?

 

cheeper for me. Its a highschool budget build, and since my dad gave me the big FU today, its getting pushed further down the calender till completion.

 

A th350 or 400 are a lot stronger than a th700r4. I've blown 700r4's left and right. Switched over to a three speed and no problems.