4x4 700R4 to 350 swap - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-20-2003, 02:06 PM
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Red face 4x4 700R4 to 350 swap

I have a 87 k5 Blazer 4x4 350 TBI with a 700R4 trans and my trans is acting up. The fluid is black and it has bubbles in it. It kinda smells burnt but I'm not sure. It has a funny shine to it but it sinks into the napkin normally. I read that was a test for the fluid??? The radiators clean and green. 2 days ago, all the gears went out but 1st gear. I had been driving for about an hour and it stopped shifting while in city traffic. I had reverse but that was it. 1st and reverse seemed to jerk/slip. I parked it and took a train home. I came back the next day to give it a good checkout and drving test and it worked OK, enough to get 30 miles home. Even OD was working but it still has a slippage or jerking problem when I first take off. It may be throught all the driving ranges but more noticable when you first take off. Can just bad fluid alone do that?

Some other possibly related things (you be the judge):

I've had a bad squeel when I start, after I have stopped nad when the truck is warmed up. When this happens, my alternator drops to 8-9 volts when I stop. To me, It sounds like a very bad belt squeel or alternator bearing but I don't know transmissions. Its so loud when you under the hood, its hard to tell where its coming from.

The blower motor and blower motor switch went out and I used the fan and switch off my 89 s10. The air in tube on the fan housing was on the other side but a little garden hose and duct tape got my truck warm again. Don't know what that effected, if anything.

The 350 TBI sounds like its got a vaccum leak but I can't find one. It has a miss and previously I changed the plugs, cap and rotor but no change...ya that was just guess work.

I also had to pass my emissions test and put the tailpipe back on. For some reason it seems hold or sufficate the motor a little. Not just sound going out the back now but a little lack in power so it seems.

I passed emission test OK and I'm getting 17 MPG so thats usually an indication its running pretty good.

Right now I was going to change the fluid just to see if maybe its bad fluid thats causing the slip. I bought the truck 8 months ago and only check the fluid once so i dont remember what it looked like. What can I look for in the old fluid to know if theirs damage or what can I check while I have it open. I'm definitly not a trans guy so be gentle with me.

I was also checking a built up 350 trans I have in my garage. I was thinking about just swaping the 700R4 for the 350. I measured them and the 700R4 case seems to be 2 inches longer without counting the shaft. I'm new to 4x4s but it looks like the tranny case bolts to the transfercase then there's another shaft coming out the back for the drive shaft. I have a 82 jimmy drive train with a blown trans but I noticed, that 350 is almost the same as the good one. It has a 2 inch spacer to, I assume, make it the same length as the 700R4. But the shafts from the car trans, the good one, and the 4x4 trans (jimmy) have different shaft coming out of the case. I haven't counted the splines but one is bevaled and the other is straight at the tip. Also, the car th350 has the speedo gears in it and the truck one doesn't. Where did the speedo go on the truck one? So, I'm getting confused as well as confusing you by now. Sorry for writing a book but I'm pulling my hair out trying to get my daily driver on the road again. Any help would be greatly appreciated!!!!

Thanks
DAVE

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Old 12-20-2003, 08:22 PM
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Cool

Frist the TBI vacuum leak... it is very common for the gasket under the TBi unit to blow out a piece or it gets sucked into the engine.

Second, the 700 to T-350 conversion.

There is a spacer needed to keep things lined up for mounts and drive shafts since the T-350 case is shorter than the 700 as you noticed.

THe 2wd , 6 inch output shaft on the T-350 can be shortened slightly and used with the spacer to replace the 700 tranny. The splines are the same. Many folks use a chop saw and grinder to shorten the T-350 shaft.

make sure you use the correct square cut O-rings in between the spacer, tranny and transfer case adapter.
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Old 12-21-2003, 03:28 AM
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700r4 swap

Thanks for the info. Crosley on the trans swap. I can see that theres about and inch or less that would need to come off the T350 6 Inch shaft to work. I have that spacer off an old burned up t350 from my 82 jimmy. Does anyone know the exact amount I need to take off or a good guess?

I opened the 700R4 and checked the fluid and pan. It was black but didn't smell burnt. There was a lot of metal flake in the pan. I don't know how much is normal, if any, and I assume that means something is worn down bad. I put in 5 quarts of fluid and it runs about the same. Still has a bit or jerkness when you take off but seems a tiny nit better. How long do you think I can run that trans for before it finally gives out and what are the signs to watch out for. I need to get a few hundred miles out of it before I have vacation coming but I don't want to get stranded in winter either.

Any info would helpful!!!

Thanks,
DAVE
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Old 12-21-2003, 10:46 AM
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Cool tough call

Hold the tranny a little closer to the screen so I can listen to it....

How long your tranny will last is something I compare to a heart attack or stroke. An often heard phrase at the hospital is : " He was fine yesterday".

Same thing with a tranny, people tell me :" it drove yesterday, today it won't move"

My point is ; there is no way to know how long a unit will function.

Second point......... there is some room for a slight difference in the length of the output shaft as it engages into the 4x4 adapter. Cut the shaft to the correct length the best you can.

THe company I work for has distributors in Mexico. Every couple of months we get a T-350 in the shop that has the shaft cut down for 4x4 use. "Crude" is the key word on how they cut these shafts off and use them for years down there.


Quote:
Originally posted by Davesblazer87
How long do you think I can run that trans for before it finally gives out and what are the signs to watch out for. I need to get a few hundred miles out of it before I have vacation coming but I don't want to get stranded in winter either.

Thanks,
DAVE
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Old 12-22-2003, 08:59 PM
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Answer to the question

Well, I know how long it will last..exactly 47 miles. I was doing good on the highway in overdrive and I stopped for gas. Soon as I came to a stop...voooooom all engine no trans. It did move about 1 mph in drive so I finished her off by flooring it to finding a parking spot.

I've been con'd before by high price tranny guys. I told this guy that it was working, I lost everything but first and reverse. Next day it worked fine and then I lost it all. He said, "Its the sun gear, the planetary gears...its toast..need a whole new transmission..$995". I'm just learning about tranny's but does this sound right. From what I red, to really know, you have to check the preasure and inpect pumps and gears. Technically, if there was enough gunk in there and a valve stuck open, you'd loose preasure and have no movement. There's no way I'm spending a thousand bucks on a transmission. Not with you guys around to help me rebuild my first tranny..well try anyway!!! I know I know..a 700R4

Also, does anyone know it a 700r4 out of a camero will work in a 4x4 replacing the 700r4. I thought they were all the same. You can just pull the tail and put in the truck spacer...good to go. Again the tranny Pro told me, "you can't do it, they are all different". If its really true then I have no choice but to start sawing my t350.
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