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Old 10-10-2006, 03:58 PM   #1 (permalink)
SaintC
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Is the TH400 a direct bolt on replacement for the 700R4?

Hey guys,

My 84 truck has a 700R4 tranny that has lost 3rd and 4th gear. I have a TH400 that came from a 78 Chevy Van 30 that I know to be in good condition. I am going to rebuild my 700R4 myself just because I have always wanted to. Can I install the TH400 in my truck in the meantime? Is it a perfect fit...same everything, or at least an easy drop in temporary replacement? It took me around a year to get my truck back on the road...so I would assume this transmission is probably gonna take me a couple of months to get done.

Thanks
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Old 10-10-2006, 04:27 PM   #2 (permalink)
chevydiesel
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The TH400 will physically bolt in, but the mounts for the transmission might be different (tailshaft).

I don't know whether the spline count on a 700 is the same as a 400 on the output shaft or not, check that.

The TH700 requires lockup (electric) and a detent (TV) cable. The TH400 has no use for these, but will require a vacuum regulated source to shift properly (if at all). This is done on a 6.2 with a VRV, it will install in place of the TPS on the side on the injection pump currently (that controlls the TH700 lockup converter).

If it were me, I'd find a core builder 700 and build, or take the truck off the road for awhile, may not be worth the trouble for a 400, a TH350 would be easier for sure, same length, and spline counts, etc.
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Old 10-10-2006, 04:32 PM   #3 (permalink)
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Ahhh drat!

Excellent info...I sure do appreciate it. Not the news I was hoping to get...but very helpful nonetheless.

thanks so much
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Old 10-10-2006, 09:47 PM   #4 (permalink)
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I just went the other way, got rid of the THM400 for a 700R4. JUdging from what I had to do, you would be doing the opposite.
Crossmember had to be modified (in my van, in your truck you can probably just slide it forward on the frame some)
Flex plate swap (Holes that mount the TC in different location)
You would have to lengthen your drive shaft
as well as get the aforementioned vacuum pump and regulator to get the THM400 to shift for you.
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Old 10-13-2006, 02:27 PM   #5 (permalink)
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No thanks...I have no interest in going with a permanent 3 speed. My truck whines enough as it is at higher rpms...

All this info has convinced me that the effort is not worth it.
I will rebuild my 700 when time permits.

ok...onto the rebuilding.
Who has rebuilt a 700?
What rebuild kit did you buy?
Did you use any particular book or dvd?
I have already purchased several aftermarket items to improve the tranny...including the corvette servo, plate, shift kit, something else.

On ebay...oregon performance sells the master rebuild kit, and the book...not sure how long i want to go around town with a 2 speed...but darn it...I do not have time to rebuild a tranny at the moment...nor the funds to pay someone else. life...gotta live it
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Old 10-13-2006, 06:25 PM   #6 (permalink)
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I ripped into mine, but I put used parts in it and it wasn't the best (which is all right since it wasn't really supposed to be the best). If I had spent the money on the proper parts I could have made a really nice tranny. I didn't use a manual or anything, just common sense. There isn't much to rebuilding an automatic other than making sure everything is assembled in the proper order, keeping everything very clean, and making sure you replaced everything that wears out...

As far as rebuild kits go, get the one that includes the most stuff. I priced out all the stuff to rebuild it but then figured out I could have a manual (which I wanted) for a lot less money. The rebuild kit I would have bought included all the clutches and steels, seals, etc. I would also get a new pump if I were you... You can probably get by just fine with the one you've got, but I would replace it anyway. You will want a shift kit, Transgo or B&M would be fine. If it were me I would also want to replace the torque converter if for no other reason than it is probably all full of junk from when the trans burned up. Some types of planetary gear arrangements are better than others. The one with 5 gears is the best, but it is rather expensive. There are many, many other things that I don't know about that you will want to do... Others who know more about it than I do will fill you in I am sure.

You will find that it does get expensive to put one of these together... You can easily run up a bill of over $1000 in parts alone.

By the way, there are pictures of when I did the 700R4 that used to be in my truck in my Garage. EDIT: I just remembered the Garage is supposed to be down tonight, not sure if it is or not.
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Old 10-15-2006, 01:04 AM   #7 (permalink)
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I am definitely looking for a cheap way to go. This truck gets sporadic use, so I am really looking at just getting the truck back on the road.

The master kit runs around 100-120. I wouldnt mind getting a book, as sometimes the book can give you tips that save you lots of frustration at times.

Probably get to this project in a month or so. Argh.

And..very cool pics. I want to take pics of projects, but I always end up regretting that I didnt.
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Old 10-15-2006, 09:05 AM   #8 (permalink)
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You'll probably need more than the master kit. Just keep that in mind... Seems to me there were several kits available (something like the master kit, the super master kit, and the super super master kit, whatever that all means. Just get the one that includes the most stuff (it's also the most expensive, but it is worth it and I think the most expensive kit I could buy was $175).

Don't worry about putting off the tranny rebuild... Taking the tranny out is a really nasty messy job when you are working in the driveway without a hoist or a transmission jack... Believe me, I did it three times... Each time I had it out, worked on and put back in within the space of a day or two. The first two times were with used transmissions I bought (each of which failed with 25 miles of installation). The third time I got some miles out of the tranny I put in, which was the best parts of two junk transmissions put together...

Glad you like the pics! Always good to have an idea of what you are going to see when you take the thing apart.
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Old 11-16-2006, 03:35 PM   #9 (permalink)
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Quote:
Originally Posted by chevydiesel;1344719;
The TH700 requires lockup (electric) and a detent (TV) cable. The TH400 has no use for these, but will require a vacuum regulated source to shift properly (if at all). This is done on a 6.2 with a VRV, it will install in place of the TPS on the side on the injection pump currently (that controlls the TH700 lockup converter).
This is interesting to me because I have a th400 and a 350 gasser in my truck. I just got the diesel and am reading up here to learn about them. My tranny has a leak that can't be fixed. So, I was thinking I might go with the 700... but knew it mean new mounts and shorter drive shaft.. but that might be less work than everything you mention if my 6.2 has this strange stuff of which you speak. How can I tell?
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Old 11-16-2006, 06:29 PM   #10 (permalink)
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Quote:
This is interesting to me because I have a th400 and a 350 gasser in my truck. I just got the diesel and am reading up here to learn about them. My tranny has a leak that can't be fixed. So, I was thinking I might go with the 700... but knew it mean new mounts and shorter drive shaft.. but that might be less work than everything you mention if my 6.2 has this strange stuff of which you speak. How can I tell?
Look on the injection pump (in the engine valley). If it is set up for a 700R4 it will have an electric switch on the passenger side of the injection pump (on the end of the throttle shaft). If it is set up for a TH400 it will have a valve with some vacuum line connections instead.

Also, most J-code engines (no EGR valve in the intake) were set up for a TH400 while most C-code engines (with EGR) were set up for a TH700R4.

By the way, there really is no transmission leak that can't be fixed... Where is it leaking? The TH700 really isn't the best transmission to put behind one of these engines unless it is built up to take the torque...
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