Goin with a 700r4

[TugOwar]

Well, the 68 GMc has been out of commision with a blown th350 for over half a year now, waiting for me to get a better job.

Got the job, now just have to do the work.

Anyway, it came to my attention that the th350 that was in the truck when I got it is a short tailshaft, which means someone modified the driveshaft at some point and I have a sneaking suspicion thats the cause of the vibration I never could nail down.

So in weighing my options and deciding I wanted a new one piece driveshaft I've decided to just have one made now instead of one now and another down the road sometime. I'm going to go ahead and attempt the 700r4 conversion.

Picked up a used one this afternoon for $75. Even if its no good at least I now have a core to work with.

I'm looking for any information you guys who have done this have to offer.
This is a 3/4 ton GMC, it has the big heavy crossmember that bolts at the top and bottom of frame. Any suggestions about how to set up the trans mount? Can I even use this crossmember or do I have to use something else?

The trans I got today doesn't have a torque converter with it. I'm assuming any converter I get HAS to be from a 700r4?

The lock up mechanism, I know nothing about this. Its just a 12 volt current right? It can just be toggled on and off right?

I know I have to get a bracket for the tv cable at the carb end.

Anything else you guys can think of that would be of help.

I appreciate any input as I feel like I may be getting in over my head with this but I'm committed now.

In case you're wondering, I searched the FAQ as well as this forum and found no information about making this swap. Maybe I'm not searching right or something.

[krue]

Your truck should have come factory with a short tailed th350, that's what mine has. The long shaft was a 73+ tranny (I think). www.700r4.com has a good tv cable kit. The xmember will have to be moved back (you may have to drill some new holes in your frame). Good luck with it.

[bigvinnie]

this link should answer a few questions....

http://67-72chevytrucks.com/vboard/s...ad.php?t=33266

[TugOwar]

Excellent! Thanks very much for the resources and info guys. I'll keep you posted.

[farside847]

Off question: How are you planning to jack up the new tranny into position, do they make tranny jacks?

[TugOwar]

Just going to set it on top of my floor jack, maybe with a couple wooden blocks for added height, and lift it into place.

And yes, they make jacks especially for transmissions. Worth the money maybe if you change transmissions on a regular basis, but for ocassional swaps/changes the floor jack works fine.

Far as that goes, someone with good fabricating skills could build a bracket of sorts to bolt the trans to that would sit on the saddle of the floor jack.

[rauto13]

I just did the 700R4 swap, used the original tranny crossmember, just moved it and redrilled holes, I also used braided stainless cables from Lokar for the TV cable & a new throttle cable, I really like the swap, I hade a shop rebuild the tranny, do some upgrades and install it for me.

Also on the one piece driveshaft, I found a one piece aluminum driveshaft out of a mid 90's chevy long bed, although I have not measured it, it looks to be close. Maybe any easy swap, may need to be cut down, not sure yet.

On the torque converter, I am fairly sure you would need one out of a 700R4, I would make sure and get the lockup converter, the shop explained everything about how it gets better mileage and helps the tranny run cooler.

[TugOwar]

Thanks for the reply rauto. Glad to hear you're liking the swap.

I may have to go junkyard hunting for a driveshaft like you mentioned. Even if it needs to be shortened and reballanced thats still cheaper than having one made from scratch.

I stopped by the local transmission shop this afternoon and he told me the same thing you did about the TC. If I had thought about it more I would have realized it has to be a locker.

I asked if he had a used one around for sale. He said nope, they get snatched up pretty quick for use as cores. A new one,he said,is about $130.00. I guess it's pic-n-pull time. lol

Went by autozone and picked up front & rear seals, filter and new tv cable.

[nvrforgotten52]

hey,
i did the 700r4 conversion a while back on my 69. its not that bad. here is a link to help you with the manual lock up switch. you dont need to spend 90 dollars on a kit from jegs when you can do it yourself for a few bucks.
http://www.smokemup.com/tech/700r4.php

good luck,

david

[TugOwar]

nvrforgotten52, thanks for the reply and the link, very helpful.

A guy I work with who is also my neighbor came over a few minutes ago and told me he found me a TC for the 700. Half an hour and $15 later I have a TC.

[woodridge]

You need to make sure you have the correct converter, there are two different input shafts used in the 700's. One will not install at all the other will but you will have park and 6 neutrals. Count the splines on your input shaft and the small set of splines in the converter and make sure they are the same.

[TugOwar]

Originally Posted by woodridge

You need to make sure you have the correct converter, there are two different input shafts used in the 700's. One will not install at all the other will but you will have park and 6 neutrals. Count the splines on your input shaft and the small set of splines in the converter and make sure they are the same.

Ok, does anyone know the difference in the number of splines on the 2 input shafts? Is it a dramatic difference or like just one or 2?

I count 30 splines on the input shaft of the trans. Counting the small splines down inside the TC ain't as easy as you might think. Its DARK in there for one thing, and when I set it down to look inside the fluid strats to pool in the bottom so ya gots to be quick! lol

Anyway, couldn't round up a flash light so I tried to set it under the flourescent shop light but guess what, my head makes for a pretty nice "flourescent eclipse"!

So I had a brainstorm and used the digi cam with flash turned on to take a pic down inside. It worked but not as well as I had hoped.

Here a couple of the better pics, reduced in size. I count 30 one time and 31 the next. What can you see?

[TugOwar]

will do that tomorrow woodridge, thanks for the heads up.

[woodridge]

Not a problem, as easy as these trucks are to work on it's still no fun to have to pull a tranny right back out or be ready to do an install on sat afternoon and have the wrong parts.

[VetteVet]

The 82 83 and early 84s had 27 splines and the 85 and ups had 30 splines.

[TugOwar]

Thanks Vet