I'm looking into swapping my turbo 350 out of my 81 and putting in a 700R-4 from bowties overdrives. I've never done tranny work like this and i need some info and pointers to installing it. I've read i will need to shorter the Drive shaft some, anyone know how much that costs? Anyone know how to match the shifter to the tranny? Is everything pretty easy to do yourself? Any feedback on this will be very helpful. Thanks Guys!

 

I put a 700r4 that I had built to my specs, in my 79'. I did have the drive shaft shortened and balanced. Can't remember exactly how much, but I think it was under $100.

I modified the cross member by removing the welded in factory unit, and put in a bolt on one from Bowtie Overdrives. This made a real nice conversion, and allowed me to re&re the tranny w/o removing the motor.

As far as the shifter goes, I was lucky to find a relacement console shift indicator on e-bay which was new to replace the TH350 indicator which doesn't provide for the O/D position.

You'll also need to pcik up an adaptor for your carb linkage, (depending on what you're running) for proper geometry, connection and operation of the Throttle Valve cable. Bowtie will also have something that'll work for you.

Good luck.

 

I shortened the driveshaft about 2 3/4" and it was about perfect. Cost was around $100. But keep in mind, this was changing from a TH400 to a 700r4. I also had to buy a Corvette yoke from Bowtie and an offset U-joint.

The worst job probably was standing on my head installing the new brake light switch with the lockup cutoff.

The other job is to fabricate a new mounting pad on the tranny crossmember. The odd thing about the 700R4 is that although the tranny is almost 3" longer than the old TH400 the mount ends up around 3" closer to the engine. The good part is that the crossmember didn't require any mods other than welding on a plate. I'm glad I didn't spent the $200 (for Bowtie's crossmember) for a mod this simple.

I'm still working on some vibration issues but it is definately a good swap.

 

if i got the crossmember would i need to do any welding?

 

hey yellovette, for the carb, is that the TV cable that they have on bowties? which one would i need? Did you take a torch to the old crossmember? And for everything else all the exsisting stuff worked?

 

jdmick, did you get that lockup switch from bowtie? im not very familar with what a yoke is? i feel retarded but could you explain please and why would i need it?

 

The largest problem with any car, let alone Shark generation vettes is the exhaust system being run throug the cross member, it's a dumb design from the git go....requires system cutting to remove the tranny....unless a stick shift, then the muncie MAY be able to be removed without cutting exhaust pipes.......

next time round, I"M fabbing up my own cross member and it's going to be easy as hell to flip in and out with about 4 bolts MAXXX....

NO exhaust work.....

 

i used the BTO cross member,the BTO shift detent kit,the lockup brake relay and tv cable/bracket. it was not technically hard but is a lot of work. the TV cable is matched to your carb and buy the necesary bracketry.....i decided to use already engineered componetnts instead of trying to fabricate my own stuff.....i sourced my 700r4 locally

 

I just read about K-case tranny? could someone fill me in on this? Thanks guys for being patient with me here.

 

Yes, Bowie supplied me with the lockup switch. They also sold me a 2400 rpm stall converter, shift detent plate for the overdrive, brake light switch with the lockup disable terminals, trans temp guage and pressure guage. Yes it all adds up.
The yoke is the front part of the driveshaft assembly that slides into the back of transmission. The size is different from a TH400 to a 700R4. Good luck.

 

you guys are awesome! can someone fill me in on a detent plate?, im not sure exactly what it is.

 

The K case is the heavy duty case. I find them in trucks.

 

ahhh ok thanks!

 

The shift detent is the plate that stops your shifter in the right places. It is why you need to press the button in to get out of park etc. The overdrive transmissions need an extra slot because of the extra gear.

BTW, like Bob says, get a TV cable mounting assembly from Bowtie that is matched for your carb. It makes installation and tuning a snap. My buddy/tranny guy also got a vacuum lockup disable switch for me. It disables the 4th gear lockup under load (when vacuum drops) so it's like having another gear between third and locked up fourth.

 

the shift detent can be replaced by taking the side console covers off and drilling out the spot welds.....what is your rear end ratio???? if its 3.08 the 700r4 is a good choice if its 3.90 then the 2004r is a better choice you need to determine your rear end ratio before you got to far....i think i paid about $740 for everything i needed less the trans cost and new torque converter.....you will need a new one and make sure you nail down the stall speed right the first time.....i have a 2500 stall speed but a 2200 would be fine

 

Bit busy here & haven't read the replies, so I may be repeating what others have said. Somewhere in the archives I did a post called something like "200-4r swap - lessons learned" which covers fitting a BTO 200-4r into an L81. It's an easy job, but why do you want the 700? If it's for the lower gear then fine, if not then I'd recommend the 200 as the ratios are evenly spaced, the driveshaft doesn't need shortening & it's an easy swap. The TV Made EZ kit is needed, the shifter concversion kit is worth having, the installation kit is excellent (the pressure gauge makes TV cable setup a piece of ****), the BTO x-member WILL be needed for an '81 (and it allows true duals to be fitted), a trans fluid temp sender & gauge are very useful (& will convince you that fitting a SMALL trans cooler is a good idea), a 2200rpm stall converter is great on the street, a rear ratio of 2.87 (if that's what you've got) is OK in OD (not great, but it does the job) & I was impressed with the service from BTO, which is saying a lot as I'm on the other side of the Atlantic from them! Don't think I've forgotten anything? Downsides: the x-member is painted with rubbish paint, I got mine powdercoated. If they haven't changed the design then the ears don't line up correctly to get the bolts through the tabs on the chassis (the bolt that runs horizontally at each end of the x-member). These can be filed to line up, but then the next problem occurs - when you tighten the nuts on the bolts the ears start collapsing inwards as there's nothing to stop them. I made up 2 tubes & forced them between the ears & they did the job. No other problems as the instructions are so good. One thing not mentioned was regarding the dipstick/filler tube. I found it easier to fit it once the trans was in the car, but there was a gotcha. There's a tab on the tube that lines up with a mounting hole in the bell-housing, so a bolt holds it in place. Rather, it should line up! Test fit the tube before fitting the trans and make sure the holes line up as trying to bend the tab once it's all in the car is near impossible.
Fitting a 200-4r into my '81 was THE best mod I've done to it. By far.
Here's a pic of the stock x-member next to the BTO one (so you can see what I mean about the ears):

Here's a pic of it all in place:

Don't bother getting the converter cover as it's made for a 153 tooth flexplate & ours are 168 teeth. You can make up spacers for it (as I did) or you can modify the Th350 one to fit. I have it on good authority that a hammer is all that's needed

edit: If you've still got the computer in place then the wiring can easily be modified so that the computer decides when to lock up (as it does with the stock trans). If it's not in place (or not asking for lockup) then you can do what I did: I took the 12v coming from the TCC switch on the brake pedal & connected it directly to pin D(?) on the trans. This gives lockup whenever the trans is in OD & it unlocks (for safety) when the brakes are used. It's a lot easier than messing about with computers, vacuum switches, realys, etc & I can't see why I'd want it unlocked when in OD? The one "problem" with these OD trans is that they don't shift out of OD as speed drops. Mine will drop all the way down to 40mph (1000rpm) in OD, so I manually shift into "3" at speeds below about 55mph. I've got a 2.87 rear ratio & the motor turns 2000rpm @75mph. With the converter locked there isn't much acceleration in OD (it's an L81!!!!) & when more throttle is used it downshifts into 3 (or 2) anyway, so I can't see why I'd want the option to unlock the converter in OD? Just in case I do want it unlocked, I've adjusted the TCC switch on the brake pedal so that it cuts power to the trans as soon as the pedal is touched, but have never needed to do it (apart from checking it works).

 

hey yellovette, for the carb, is that the TV cable that they have on bowties? which one would i need? Did you take a torch to the old crossmember? And for everything else all the exsisting stuff worked?

I used a stock TV cable. I think they're all the same.

As far as the old cross member, I didn't want to use the torch under the car, so I used a combination of tools, reciprocal saw, die grinder w/ cutting wheel, and finally to remove all traces of the previous welds on the side rails, I found that my air chisel was awesome.

The Bowtie crossmember bolts on with one through bolt, attached to brackets which I manufactured, then bolts on underneath the side rails. I drilled the side rails of the chassis, then made a backing plate which went inside the rails where the cross member bolted through.

It all took me aaround seven evenigs' work and off and on with the crossmember about a hundred times, but in the end it turned out a great fit, which also looks good in the black powder coating.

 

The TV cable setup is the most important thing on this install. If it is right you will love it, if it is wrong you will have nothing but problems including wrecking the trans. The BTO website will lead you to the right bracket for your carburetor. They have pictures showing everything. I did not have that when I did mine so I had to do a little engineering and make my own bracket. It wasn’t that difficult.
trans install.
I also would recommend installing a trans cooler. The OD trans are heat sensitive. trans cooler installed.

 

i left the pan off when i did my TV cable install so i could visually see the plunger at WOT....this was a really simple way to get it right the first time