I have an 87 convertible with I'm told has a 700R4 trans. Gets about 25 mpg on the highway & turns about 1100 rpms at 65 mph. I just bought an 80 vette which I don't know what trans is in it but turns about 2500 rpms at 65 mph. My question is, can I swap a 700R4 into the 80 without alot of mods ? Has antone done this ?

 

The 200R4 works better as an easier swap candidate. It has been done many times and there are kits available to fill in the gaps between factory parts and what is missing. Use the search feature on the forum. Lots of information to be found.

 

You have a turbo 350. It has no overdrive. The 700 trans has been swapped many times into C3 cars with little problem. I am doing one for a forum member this fall along with a 383.

 

So what is involved beside getting the 700R4 ?

 

These are some of the parts you'll need to swap out your transmission to a 700r4.

http://www.bowtieoverdrives.com/cata...php?ITEMID=115

http://www.bowtieoverdrives.com/cata...php?ITEMID=377

http://www.bowtieoverdrives.com/cata...php?ITEMID=221

You will have to have your drive shaft shortened.

 

Thanks for the info !

 

You need to do some research and find out all the details involved in swapping an overdrive transmission into your NON-overdrive car. There are trade-offs in selecting which O/D transmission you wish to install. In general, it is easier to swap a 700R4 into a THM-350 application....or a 200-4R into a THM-400 application. But, you can get either one into either car with a bit more effort.

If you do a significant amount of highway driving in your C3, having an O/D tranny is a real treat....IF your rear axle has a 3.23 or steeper gear set in it. If you have a 3.08 or less and you install an O/D tranny, the upper gear will be of little use to you anywhere except the highway. For suburban driving, you would need to set the shifter one gear lower to prevent low-rpm 'chugging/lurching'.

You also need to determine how you are going to control the lockup clutch. IMO, sticking a simple toggle switch on it is NOT a good idea, unless you ONLY intend on using it on longer highway runs. It would be best to install a lockup controller module that will properly manage the lockup and prevent misuse and early failure of the L/U clutch.

 

Hi, I've just swapped a 700 into a sbc powered '51 Stude, different car but same engine. It has 3.55 gears and is a perfect match, although we're changing to a 3.73 LSD shortly. Yes don't use a 700 with tall gears. The trans is amazing, I built it with a shift kit, vette servo, 3/4 valve and a lock up kit. I'd never go back to a 3 speed auto, the gear spread is crap.
Go for a post '87 700, they're a better trans although the 200 is an easier swap in a vette like others have said. Just getting a 200 in England is not that easy.

 

I am about to make the same swap.

 

I did make this swap in my 81... After the 'Rebuilt' th350 the PO had installed lost 3rd gear ...

Paired with a 383 stroker... It drives fantastic!

My rear gears are still the 2.72's or 2.73's the 81 automatic came with... I had originally planned to swap those out almost immediately, but for the time being I enjoy cruising the freeway at a nice lower rpm... And getting the mileage to boot!

Had to adjust the shift linkage mounting bracket by simply drilling a new hole in it that matched the pan design ... I opted to let the trans guy modify my existing trans mount(didn't know a 82 trans mount might have been a bolt on plug n play)... So he cut off and rewelded the mounting plate to fit ... Then had to clearance and box/strong back the mount to accept the position of the speedo gear housing... Add a T.V. Cable... And have the driveline shortened... Still using my stock shifter, downside is I can't manually drop it to first... But that's hardly needed when I typically only see first at a stop or in a low speed or full throttle scenario...

All in all... Replacing every single component inside the 700r4 'donor' case, adding his special touch to the internals to make it strong enough for my engine hp and driving style... I was $4k out the door. Roughly $2 k in parts etc, and $2k in R&R and fabrication etc.. Plus, having a warranty through his shop should anything go amiss is well worth a little more investment...

He set up hydraulic lockup in 3rd as well as 4 th... Eliminates all friction/wear of the moving parts and helps keep temps down... The lockup is controlled by driveline rpm... So, he set it to match with a future gear change in the rear I had planned on doing...

The motor has got tons of torque and hardly raises an eyebrow to me 'lugging' it anywhere... It always loves to pick up Rpms and mph at any change in throttle pressure... It'll roast tires at any stop accompanied with full throttle.. But typically just hooks up and GO's!

Tried getting some quick vids showing trans shift points and lock ups in relation to Rpms... Here's a slow even progression through the gear ranges...


Then I foolishly tried to get one of me giving her a lil bit of the skinny pedal... I won't do that again without someone else in the passenger seat to film for me... She got a bit squirrely, had to let up from the throttle to get her under proper control, then hit the skinny pedal again...


Love this car! And couldn't be happier with my choice of adding overdrive !

Next decision will be... Keep this gearing for freeway cruises? Or go bigger rear gears... And if so... How big? Lol. Mines a daily driver... And absolutely a blast to drive anytime... Anywhere!

 

I just had a conversation with a friend who rebuilds transmissions for a living and he seems to the the 200r4 is a better transmission hands down..And I also read its a much easier swap due to length and size... I had a 700r4 in my 84 and never had issues with it myself but when I had the tranny rebuilt in my dodge truck a few years back I was talking with the builder about the 700r4 in my vette and he did say he sees a lot with the same failure but I cant remember what it was.

 

The failures common to 700r4's are the 3-4 shift... And snapping of the spur gear if dropped into gear at too high of an rpm...

My Trans builder put the trans-go shift kit in to help with the 3-4 shift, and warned me to always be at a low idle when going into gear...

From what I've researched/read and heard... The 200r4 was primarily built for v6 applications and a 700r4 would be better suited for a higher hp motor application...

I have zero complaints about mine.. And recommend anyone does their own research about what is best for their application...

Mine, I went with a pre 1987 block... Tried hard to find one from 85-86 to no avail... Ended up with a pre 86, hence another reason why we replaced ALL the internals...

My advice, for whatever it's worth... Find a reputable builder, and spend some money letting him use all the tricks of his trade to get you what YOU want. ;-)

 

[QUOTE=76yellow;1587299688]I have an 87 convertible with I'm told has a 700R4 trans. Gets about 25 mpg on the highway & turns about 1100 rpms at 65 mph. I just bought an 80 vette which I don't know what trans is in it but turns about 2500 rpms at 65 mph. My question is, can I swap a 700R4 into the 80 without alot of mods ? Has anyone done this ?
I have a chance to pic up a TPI set up cheap (computer, harnesses, etc) I want to put this in my 80. Good idea, bad idea ? Whats involved ? I've tried searches but haven't really found alot. Anybody done it to an 80 ? I still want to do the trans swap. I have a 200r4 sitting in my shop. I also have to find out what all is involved for that swap. How do I find out what rear end gears are in my stock 80 L82 Automatic ?

 

Very common. You'll need a crossmember modification, throttle linkage adapter and shortened driveshaft. Optional, but worth doing is adding a detent to the stock shifter (or buying an aftermarket shift plate) which will allow you to access first gear. The stock shift pattern for a TH350/400 will get you PRN432, not PRN4321, but will be usable.

If you want to do it, go ahead. They're great for torque and will improve driveability. If you're not intending to do a lot to the car, it will support the stock setup pretty well. It may be easier to go to an aftermarket controller though (like a FAST EZ-EFI TPI retrofit kit). The stock computer uses chips and may need a bit of reprogramming to go into the 81. The L98 ECM does control the torque converter in a 700R4 pretty well though.

The GM Heritage center (search for it) could list it. If they've been changed though, the easiest thing to do is jack the rear of the car off the ground and watch the driveshaft as a helper spins the wheel. The number of driveshaft revolutions is your gear ratio. IE, 3.55 = 3 and a half turns, 3.70 = three and 3/4 turns (roughly) etc.