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Tractor Talk Discussion Forum

OT: 1986 Chevy Truck transmission swap

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Brad in WI

11-01-2006 02:34:57




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I have a Chevy K10 4X4 with a 700R4 overdrive transmission. The transmission has seen better days and I want to replace it with something that is more afforadable than a $800 rebuild. What other trannys will work with this setup with very minimal work to alter the drivetrain. All the truck will be used for is hauling around larger parts for the tractors from the boneyards. The truck is also equipped with a 350ci engine.

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jdemaris

11-01-2006 05:54:47




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 Re: T400 easy swap in reply to Brad in WI, 11-01-2006 02:34:57  
T400 is a pretty easy swap and is the most rugged auto. trans. GM had at the time.
I have two 83 diesel Blazers that I converted year's ago - from the 700R4 to the T400s (3.08 axles). I have a mechanical governor in one (no modulator), the other's all use a vacuum simulator valve (VRV) to mimic throttle/vacuum reponse like a gas engine has. So, changeover in a gas engine truck is easier than my swaps. You can buy adapters to go between the transfer case and trans - but finding a donor vehicle is easier. I have one if you need it - but I'm in New York. I've got a low-miles 4WD 89 Suburban with an excellent T400 trans, torque converter and 241C transfercase. I recently let my son take the engine from it, and I'm going to take half the frame for a K5 Blazer motorhome project.
My 86 diesel Blazer was recently changed over -same deal (3.08 axles) In the case of my 87 3/4 ton 4WD Chevy Suburban and 89 GMC Suburban (both diesels) - the dealer would not sell them with the 700R4 - since they were both bought as tow vehicles -they both came with T400s and 3.73 axles. The lack of overdrive should not be an issue - unless you've got axles over 3.73. My 87 Suburban made it to the 500,000 mile mark with orignal engine and T-400 trans - with a lot of towing and 75 MPH highway speeds. The 14 bolt SF rear-axle went twice - but that's a different story. Also, since all of mine are diesels - the RPM range is more limited than your gas engine. A 6.2 diesel has an optimal high RPM range of 1800 - 2200 RPM. Your 350 gasser will handle the higher RPMs better - so if I had no problems - you shouldn't either.

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MeAnthony

11-01-2006 04:18:14




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Brad in WI, 11-01-2006 02:34:57  
I had the same problem with an '83 GMC 4x4 diesel. Found a place locally(Jackson, MI) that sold swap kits. For $150, I bought the parts to make a turbo 350 out of a '65 Chevy two-wheel drive work.

I agree with Allan, though. For a daily driver, with today's gas prices, you might not gonna like a 3 speed. But if it's just an every-now-and-then kind of thing, it might be your cheapest option.

Here's a link to an online outfit that also sells the swap kits.

Good luck,
Anthony

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Allan In NE

11-01-2006 03:38:32




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Brad in WI, 11-01-2006 02:34:57  
Brad,

You've got a tiger by the tail as the '83s thru the '86s were the worst of the bunch, unless it has already been replaced at one time or another.

A 350 or a 400 tranny will fit in there, but believe me, you don't want that "engine screaming" type 3-speed box, let alone the hassle of changing the pickup over.

The "cheapest" route is to get a used transmission out of a salvage yard which came from a '91 or '92 pickup before GM went to the electrics.

Trouble is, you might have to do the job 2 or 3 times to find a good one.

I don't envy you; they are an old-fashioned nightmare. Good luck,

Allan

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Brokenwrench

11-01-2006 06:33:14




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Allan In NE, 11-01-2006 03:38:32  
The problem with a 91-92 700 is after 87 they went to computerized lockup. The easiest swap would be to find an 86 or older 700, and if lockup don`t work, pull the solenoid down and put a check ball on top of it. That way it`ll mechanically lock up with third. But..... like Allen said, good luck finding a good one. The 87-92s run an auxillary valve body, and a different pressure switch set up. I don`t believe electrically it`d be a clean swap.
Regardless of what you do, if you go to another 700, you have to have a working torque converter clutch lock up system. If you don`t, it won`t be long and you`ll burn up the 3-4 clutches and the 2-4 band. Another point is that the 700 lives and dies by the throttle valve cable. On the 350 trannys the cable is just a kickdown cable. The 700 relies on the cable to boost pressure as you accelerate. Alot of 700`s met their doom cause nobody hooked the cable back up or it was adjusted improperly. Hope this helps Brokenwrench

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Allan In NE

11-01-2006 06:51:48




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Brokenwrench, 11-01-2006 06:33:14  
Yeah,

There is just so many things that I take for granted.

I re-wire the vacumm switches from the firewall to the to electrical plug and also "re-switch" the valve body's pressure switches to grab when in third and/or fourth.

Also, I put in the positive TV pressure control from a shift kit so that the silly Throttle valve can't stick anymore.

Guess the average Joe isn't gonna think about stuff like that. :>(

The point I was making tho, was that GM finally got 'em "toughened up" by 1991 and 1992.

Allan

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Brokenwrench

11-01-2006 07:34:31




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Allan In NE, 11-01-2006 06:51:48  
With all the older chevs still out there, you could probably market a conversion kit to suppliment your farming operation. I agree the last of the 700`s were the best. They did the same thing in the front wheel drives. The 4T60E was notorious for breaking reverse shells. In 96-97 they started running a hardened shell. Then in 98-99, they scrapped the whole works and went with the 4T65E. Oh well, it keeps food on my table. Stay warm in that fancy new setup of yours. Brokenwrench

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frankiee

11-01-2006 07:18:49




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 Re: OT: 1986 Chevy Truck transmission swap in reply to Allan In NE, 11-01-2006 06:51:48  
Transmissions are a confusing thing.
I was the one that on a prior post put the carb and intake on the 93 Suburban to replace the TBI
Works good.
We went 150 miles south yesterday to get another vehicle and my dad said ( Who said it was going to be real bad on gas?) I said I did. He thinks it is better then the TBI. I still dont believe it but if it is worse then not by much that I can tell.
The only problem with it is it has a harsh 1 to 2 shift. The rest of the shifts a smooth.
We can live with it because it is now just a yard vehicle and maybe an emergency vehicle if the other "new to us" vehicle breaks down.
It would be nice if I could figure out why the harsh shift though. I have the MAP hooked to ported vacuum. The other alternative would be to live with it as is or put a THM 400 3 speed we got in another junker we have here in it.
I dont need the exercise right now to tranny swap so I think I will figure out how to calm that shift in my spare time.
Any ideas?
P.S Alan
We found the correct center head for the 93. No drilling involved. Thanks for the heads up. My father had just given it away with a bunch of other scrap not 9 months ago. We bought it back for $20 with a q-jet on it.
Thanks for the help

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Bob

11-01-2006 07:27:38




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 Re: OT: 1986 Chevy Truck transmission swap in reply to frankiee, 11-01-2006 07:18:49  
1.) WHY did you connect the MAP sensor to PORTED vacuum????

2.) The "center head" is an "intake manifold", at least to the restof the world!



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