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1990 G20 700R4 Remove and Replace
#675360 November 22nd 2014 12:01 am
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This is my first post besides my introduction so please bear with me. The transmission on my new-to-me 1990 Chevy G20 Coachmen Conversion van blew up on me yesterday. I lost all gears and a ton of fluid. I was lucky enough to find someone on Craigslist that has a '90 700R4 with 83k miles on it. Mine has 184k miles on it.

The van in question has a 350 in it.

So I'm in the middle of removing the transmission now and I have a couple of questions:

1) Do I have to remove the exhaust Y-Pipe in order to get the transmission out? Just looking at it, obviously it would be a lot easier to do with it gone but I'm worried I'm going to strip or snap the studs on the manifold and end up with another nightmare to deal with. It looks like if I jack the transmission up I may be able to clear the Y-Pipe.

1a) If I do have to remove the Y-Pipe, what is the best way to tackle the rusty studs/nuts without breaking anything?

2) What else should I do while the transmission is out? I'm assuming the rear main seal. Anything else?

3) The "new" transmission is also from a '90 2WD V8 Chevy truck of some sort. Is there a way to identify the torque converter and compare it to the one I have? Any way to determine if my torque converter is still good?

4) I assume I can use a compressor and an air nozzle to blow old fluid out of the cooler lines, correct?

Thanks in advance for any help with my questions! I hope to get this done this weekend and be back on the road by Monday. I already have the front end up in the air, the drive shaft dropped, inspection cover removed, and the top 4 bellhousing bolts removed. I sprayed the studs on the exhaust manifolds where the Y-pipe attaches with PB Blaster in anticipation of having to remove them...

Re: 1990 G20 700R4 Remove and Replace
oobnuker #675365 November 22nd 2014 1:03 am
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I know some trucks have different gears to our vans. Might want to find out what ratio the new tranny has compared to the one your taking out. Dont want to be doggy on the bottom or screamin on top. Oh my does that sound like my ex-wife. Well Id do a little checking before you shell out the $$$


SUNSHINE VANS-VAN DIEGO
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Re: 1990 G20 700R4 Remove and Replace
frscke1 #675372 November 22nd 2014 10:10 am
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Ok. First of all I would be extremely apprehensive to install an unknown auto trans in, even if it was free. Its too much work to have to pull it back out and you would have some cost even just for fluid, etc. Your van could already be on its second trans at that many miles. The "New" one could be on its way out at 83K. The one in my 1992 V6 van went out at 98K.
Just to clarify, the 700R4 has been renamed 4L60, this was used until 1992. 1993 and up has a 4L60E that is electronically controlled by the computer. Your 4L60 has a TV cable, the 4L60E does not have this cable.
The Y-pipe does have to come down. Usually, some of the studs break off. You can cut the end of the stud off at the flat of the exhaust manifold flange with an angle grinder or die grinder with a cutoff wheel. Then just drill the stud out with a 3/8 bit and use 3/8 bolts and nuts. The studs are soft and drill easy. Wear safety glasses/goggles when drilling/grinding overhead. Those shavings seem attracted to your retinas.
I don't usually recommend a lot of new parts if the old ones are Ok. But, always use a new trans input seal for the torque convertor. Its so much worn to replace it later and often it is damaged when the used trans was being removed and the torque convertor was hanging on it.
As far as a replacement trans. There may be different lengths of the tailshaft. Also, you may need the speedometer gear from your old trans to keep your readout correct. There may be different number of clutch packs for a v8 versus a v6 (the v8 trans would be stronger than a v6 trans).
You definitely should clean your lines/cooler. They make a special can of stuff for this. You could definitely do a somewhat compromised job with compressed air. I have heard of people using a garden style sprayer with clean fluid to clean these lines. Switch what line is your input several times to be sure to get them clean.
Unless your used trans is known to be good and very inexpensive, I would look at having your existing trans rebuild by a reputable shop. With you doing the pulling and re-install, it might not be that much more than a used one. This is what I have always done. After you buy a used one, pay for fluid, pay for new input seal, pay for tow home after if fails on you out of town, you have a lot of money invested in a big ? Then, you still will have to pay for rebuild, new fluid again, etc. Sometimes the cheaper route turns out to be more expensive.
While you are under van and dirty, change your fuel filter unless you have done it recently. Dirty filters kill the in-tank pumps. It is in the back, behind rear axle on pass side. Spray threaded line with penetrant oil first.



1992 Chevy G20, 110" wheelbase, Mark III conversion, L31/4L80e swap, Express wiring harness.
Re: 1990 G20 700R4 Remove and Replace
oobnuker #675434 November 23rd 2014 1:07 am
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I appreciate the comments and completely understand the apprehension regarding using an unknown transmission...BUT, I did it anyway. I grabbed the transmission this morning.

Just got finished taking the old one out. I just realized that there are two differences between the two units.

One, the "new" transmission has a gear driven speedometer vs. the electronic unit on mine. The tailshafts and housings are otherwise identical in length, etc. What does it take to get the speedometer working?

Two, on the new transmission, the linkage attachment point on the transmission is cocked at a different angle than the original. Basically the original transmission is perfectly vertical in Park where the new one seems to be rotated 45 degrees or so. What do I need to do there?

PLEASE - I don't mind being told "I told ya so", but throw in something constructive while you're at it. I'm in a bind and doing the best I can. The van is not only my only source of transportation, it is also my current "home". I need it up and running ASAP.

Thanks for any help!

Re: 1990 G20 700R4 Remove and Replace
oobnuker #675567 November 25th 2014 12:56 am
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Got it going finally. Everything was pretty straight forward. As far as my questions go in case anyone finds this and needs an answer - One, it doesn't seem like an easy task to switch from mechanical to electronic speedometer. There are some adapters that are made available that seem like the best approach and they are not too expensive. So for now, I have no speedometer. And for question Two, all I had to do was take the yoke or whatever it's called from my transmission and attach it to the new one in order to get things lined up the way they were.

One of my biggest headaches was the exhaust - I broke two studs, two came out, and two I was able to get the nut off of. So cutting the studs and drilling and getting everything lined up was kind of a nuisance. The REAL headache was a U-Joint of all things. I've never replaced a U-Joint before so I wasn't exactly sure what to expect. I found that the U-Joint on the transmission side of the driveshaft was nearly worn through - as in NO bearings left, just slopping around in the cup and the posts were almost worn in half. I went to AutoZone and got the U-Joint specified by their system and went on my merry way. When I looked at it, it looked REALLY big and impossible to get in there so I spent an hour scouring the internet for info on installing U-Joints and found plenty of info about pressing them in, using a vice, etc. So in my feeble mind I decided that maybe if I hit it hard enough and squeezed it long enough in a vice, I'd be able to make it fit... Yeah, NO. I ended up finally taking it to a machine shop. The guy there used his caliper to measure the ID of the yoke and the OD of my supplied bearing cups and decided that it was impossible and NOT the right part. So off to AZ I went. After getting a bunch of huffing and puffing and eye rolling the manager finally disappeared for about 15 minutes and somehow came back with a different part number for me. VOILA! Whatever he looked up or how ever he found it, it was the right part.

Trans blew Friday afternoon, started taking things apart and getting a feel for the layout of everything Friday night. Got the transmission out of the vehicle 10pm Saturday night. Got all the drilling and crap done on the exhaust Sunday and got everything back in and buttoned up by Sunday night except for the U-Joint and the remainder of my exhaust which had been pieced together by the previous owner. I figured I'd get up today, slap the driveshaft together and be on the road.

And I finally am.

Re: 1990 G20 700R4 Remove and Replace
oobnuker #675713 November 27th 2014 2:38 am
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A 700R will run you 800.00 to get rebuilt, you can get them used for under 100.00 and lets say 100.00 in trans parts that gives you 4 attempts. Not that you want to do that but 600.00 in your pocket is a good feeling. I think if you take off the tail shaft there is a gear for the cable control and a magnet for the sensor control and I do believe these can be swapped but look into it before you remove the drive shaft and rear trans mount. AND if you remove the tailshaft you can replace the rear seal and brass bushing in there for under 20.00 but you will need a trans shop to press in the bushing.


Munzvan@aol.com / Runnin Wild Truckers / I never met a van I didn't like.
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Re: 1990 G20 700R4 Remove and Replace
Munz #675722 November 27th 2014 11:00 am
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I am glad to hear the new, used trans worked out. Sounds like maybe it should have had speedo problem worked out before installing. However, all these things depend on your personal situation. If you have only one vehicle, then you need to do what is necessary to get it back on the road ASAP.
Personally, I think all the guys running carbs and three speed trannies are crazy with all the cheap, fuel injected engines and OD trannies out there to swap. But, we all have our own preferences and situations.
Like my dad used to say about mufflers, "If you can't see straight through it, how's the exhaust supposed to get out".



1992 Chevy G20, 110" wheelbase, Mark III conversion, L31/4L80e swap, Express wiring harness.

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