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Old 07-22-2005, 05:30 AM
Greg Clark Greg Clark is offline
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Join Date: Jun 21, 2001
Location: Chattanooga, TN
Posts: 5

’91 GW transmission swap

I recently began contemplating installing an overdrive automatic to replace my TF727 and NP229 (driver’s side drop).
When brainstorming this task, a few questions come to mind:

1) I was intending to swap in a TH700R4 with NP208; what, when, and where was this combination available on GM products from which I can steal my parts?
2) When using the AMC motor to GM transmission adapter, along with the GM bell housing, can I anticipate any firewall clearance problems? Can I anticipate other undercarriage clearance problems when making this swap?
3) How much longer (dimensionally) is the proposed transmission/transfer case than the stock arrangement? How will this effect drive shaft lengths?
4) Will the stock u-joints bolt up to the NP208?
5) Will this swap affect cruise control operation/connection?
6) Can the TH700R4 be selected/shifted to lock out the overdrive for towing?
7) How to accommodate speedometer cable adaption?
8) How to accommodate the transmission cooler connection?
9) How to accommodate the original floor mounted low range shifter to the new parts?
10) How to accommodate the dash mounted 4x4 selector to the new parts?
11) Can I use some of the Chevy mounting brackets/parts to mount the parts into the Jeep? Which one’s?
12) How to accommodate the factory transmission shifter to the new transmission? How can the factory shifter be adapted to arrange selection and indication of overdrive or drive on the factory steering column shifter?
13) What vintage transmission and rebuild part considerations do I need to make when selecting/rebuilding the TH700R4?

What have I forgotten to consider?

As mentioned above, I was intending the TH700R4 with NP208 but would consider a Dodge NP241 with another transmission if the right combination can be identified to me and all the above questions can be answered.

Thanks in advance for any and all help.
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Old 07-22-2005, 05:41 AM
joe joe is offline
Join Date: Apr 28, 2000
Location: PNWet, USA
Posts: 22,392

Originally posted by Greg Clark:

What have I forgotten to consider?
Are you planning an axle ratio swap also? If not an OD tranny will be useless in a stock geared 91 with the 2.73 or 3.31 gears(only stock gears avail from factory). These rigs are pretty much overdriven axle wise as is. Add an OD trans and in OD you'll be so low in the motors power band the trans will constantly be shifting itself back into high gear(3rd) anyway.
"Don't mind me. I'm just here for the alibi"
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Old 07-22-2005, 07:17 AM
Joe Guilbeau Joe Guilbeau is offline
Bleedin' Gasoline
Join Date: Apr 17, 2002
Location: San Antonio, Texas
Posts: 2,137

I had heard that the Chrysler 518(A)??? is essentially a 727 with overdrive. The output yoke is longer...
Joe Guilbeau<br />1983 Cherokee Laredo WT (SJ-17), 360/229/727/D44/D60 4.10 Gearing, 8-lug hubs, Edelbrock Performer w/EGR Intake, Mallory Unilite Series 47 Photo-Optic Infrared Trigger Vacuum Distributor, Mallory Surge Protector, Mallory Promaster Coil, Holley Pro-Jection TBI 502-Analog, FlowKooler High Output Water Pump, Staggered 4-Core Custom Industrial Radiator, HD Fan Clutch, Dual Electric Fans, CS130 Delco 105-Amp Alternator, Oil Bypass Mods at Rear of Block and Distributor Oiling, Superlift 4\" Suspension, Rancho RS5000\'s, Hi-Tech 31\" Re-Treads, Aero 33 Gal Tank w/Skid Plate, Custom Rear \"Longhorn\" Bumper
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Old 07-22-2005, 07:52 AM
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mdill mdill is offline
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Join Date: Nov 22, 2000
Location: Richfield MN
Posts: 7,076

the 518 is a 727 with a Overdrive bolted to the
back end. The issue is there are no AMC bolt pattern 518's,the OD unit is pretty long and the
valve body differences make it a non starter as
far as using the unit boted to the back of a AMC
727. I have a NOS 518 OD unit and a AMC 727 core
but have not had time to look try and see what
would all have to change to make it work but I don't think it is going to work without more time
and $'s than I want to spend.

I think a 700r4 with great after market support would
be the mos practical.

Mike D.
Home of ADHD project list

1977 J-10 Honcho 360-T15-D20
1977 Cherokee WT 360-Th400-NP241 true-trac(s)
1979 Cherokee 4 Door 258-T-18-D20
1981 Cherokee Chief WT 360-727-NP208
1972 K20 Suburban 350 SM465 205
And the other stuff that gets driven
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Old 07-22-2005, 08:20 AM
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JeepinPete JeepinPete is offline
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Join Date: Dec 09, 2003
Location: Quakertown, PA
Posts: 2,190

If you have 3.31 gears, and are running stock tires, then adding a 700R4 will give you gearing very similar to what newer trucks are running. For example, I have a '01 Durango. It is running 265/70/16 tires, and 3.55 gears. Run the numbers, and it turns 1612RPM a @60mph. A Wagoneer with 3.31 gears, 235/70/15 tires, you would be turning 1672rpm @60mph. Whether the 360 has enough to push a Wagoneer and the speed in another question...

'55 Willys Wagon, the original FSJ
Sitting on a '77 Cherokee frame, Dodge D60's
Isuzu 6BD1, NV4500, NP241
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