Th400 to TH700r4

[MIKE_JAMES]

I have a 1985 4wd pickup, has M1008 inside the drivers door does anyone know if its possible to swap the factory the factory th400 for a th700? have had a lot of conflicting stories from the local experts, including "just get a 700 with a K stamp on the case" to " your truck is to heavy for the 700, it wont last a month" , any comments appreciated

[tpitt]

Mike,
You can do it, but unless you have a well built 700, I don't know if its worth it. The flexplate is different, as is the tailshaft. You would have to change shafts or use a transfercase set up for a 700. Advance adapters may have everything you need. I did this on my 87 Suburban, and ended up changing it back to a 400. I thought I had bought a good 700R4, but I got taken.

Now for a round trip plane ticket and expenses paid, my wife and I can bring you everything you need. tpitt

[Heartbeat Hauler]

There is some swap info on this site. Hope it helps.
http://www.rowand.net/Shop/Tech/Auto...issionSwap.htm

JP

[moondoggie]

Good Day!

I have no idea how difficult a 400 to 700R4 swap might be, but if you do it you'll notice two things for sure: 1) your truck will run a LOT quieter at highway speeds; 2) your mpg will pick up enough that you'll notice, even if you don't keep records.

Make sure your 700R4 is built stout. I know it can be done, but don't know the particulars. My local tranny guy said that if you saw what holds a 700R4 in OD, you wouldn't pull a boat trailer with no boat on it in OD; if he built it, & you didn't allow it to "hunt," it would last forever. This is supported by Jet building 700R4's guaranteed to 520 lb/ft.

Good Luck & Blessings!

[Truck]

There is some swap info on this site. Hope it helps.
http://www.rowand.net/Shop/Tech/Auto...issionSwap.htm

JP

Link didn't work for me..can you repost it

Truck

[Truck]

Got it to work, try this:
http://www.rowand.net/Shop/Tech/AutomaticOverdriveTransmissionSwap.htm

Great write and info..


Truck

[bowtieluvr]

Mike,
Been there done that. Now have 10,000 on my rebuid 700r4 conversion. Mine was an '86 K case 700r4 auto. I also replaces the np205 with an np241 with a much lowe low range about 2.7x:1 compared to 1.9x:1 with the 205 (I dont remember the tenths digit in the ratio. Went from 14-15MPG to 17-18 MPG with a high near 20MPG with 4.10 gears. Much nicer vehicle to drive ('85 GMC K3500)than before. I got the TV linkage from a van at a "pull your own part" salvage yard. Never regretted the change. Also the np241 is IMHO a better way of going. Is very strong with the addition of the C Clip retainer readily available which prevents the tailhousing C-Clip from failing to correcly hold the shaft located. Again this is a great swap.

[Heartbeat Hauler]

Here it is again. I hope it works this time:
http://www.rowand.net/Shop/Tech/AutomaticOverdriveTransmissionSwap.htm
JP

If this doesn't work go to Rowand.net and check out tech tips.

[bowtieluvr]

All,
At end is the link to information for the C-clip transfer case saver made by Gilly's. Also should have noted that during my conversion it was recognized that my valve body had the hydraulic lockup valve in place. These, as was the case with mine, are sometimes used in conjunction with the lockup solenoid to control lockup however in my situation I did not want to run wiring and configure a way to properly control lockup. Instead I just followed the directions in my TransGo kit to provide hydraulic lockup only. This Involved dropping a check valve into the lockup solenoid snout(supplied in kit), and using proper spring in the hydraulic lockup valve train in valve body for application(diesel). This effectively makes the lockup solenoid act as always locked up as the check ball does not allow fluid past and pressure builds behind it, all lockup function is then controlled by the hydraulic lockup valve train only. This is basically the way many diesels were from the factory as they did not have ECM/PCM/TCM as I am told. Works very well but sometime wish I could unlock at will. And yes you need a new Flex-Plate picked mine up at autozone $40-$50 was surprised at the high quality(pineer I think) Link to transer case saver http://www.drivetrain.com/gillies/Tcasesaver.html

[coxfmly]

Mike, Why dont you install a Gear Vendor unit instead?

[MIKE_JAMES]

Sorry about the delay, thanks for all the replies to tpitt I was thinking about coming over if all the parts were "off the shelf" but if you did come this way remember our dollar is getting back to about half of yours= cheap holiday! Bowtieluvr,did you have to swap the transfer case? I do a lot of highway travel so mpgs and revving are what im trying to help but weekends are for fun in the rough. coxfmly, what is a Gear Vendor unit.Thanks to all

[bowtieluvr]

Mike,
I think your CUCV should have a np208. To swap from a th400 to a th700 you will need to either replace the transfer case to transmission adapter(th400 uses 6 bolts th700 uses 4) and the input planetary gear wich will have a 32 count female spline for th400 to a 27 count female spline input planetary gear to accept the th700, Or you could replace the whole unit for one that was used on th700, Or you could use the advanced adapters kit which requires the th700 be torn down to replace the output shaft with a 32 spline unit. If your case is aluminum it is most likely np208. If it is something else let me know I will give you other options.

[MIKE_JAMES]

Hey, just answered my own question, googled gear vendor unit and found some interesting info, no need to change out the th400 or the np208, these things bolt in behind the transfer case and accordin to the blurb they double the gears and final drive is .78, not quite as good as the th700 but looks to be cost effective, has anyone tried one of these units?

[ambulancechser]

Mike...Greetings from alberta...it's interesting to run into another mike james,especially on-line.
Try this www.usgear.com
This particular aux gear box mounts in between the trans and x-case.this allows use in 4-wheel drive and low range.You also get to keep a rather rugged t-400 trans.Personally i'd avoid the 700r.to many horror stories out there.The cost of a built 700-r4 would come close to the us.gear box.
The ultimate in rugged is this WWW.stak4x4.com
also available with an overdrive gear. cheers.