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700R4 transmission in a HMMWV

dhaumann69166

Active member
234
77
28
Location
Hyannis, Nebraska
Has anyone gone the route of just changing the input gear on the t case? The input shaft from a NP208 is the same as the NP218. NP208’s came in both 27 and 32 spline so if you put the 27 in your 218 the 700r4 is direct bolt on. There are two different lengths of the input shafts. Can’t remember if it’s the long or short you need but I know it was the newer 208’s.
You can buy TC lockup wiring kits from Summit Racing for around $100. It’s a pretty basic 4 wire setup so if you want to save some money you can build your own wiring. A little time on google and you will find step by step on how to do it yourself.
http://www.monstertransmission.com/700R4-External-Lock-Up-Kit_p_4988.html#.WrxpiyJMHDs
https://www.summitracing.com/parts/tci-376600
 

davykeith

Member
50
2
6
Location
Ellisville, MS
UPDATE: 700R4 installed and running down the road

UPDATE report: Got my 700R4 in with a few hitches but overall not that big of a deal. I had my mechanic install a 700R4 with heavy duty clutches and spline (rebuilt by Action Automotive out of Missouri but I'd be careful if you decide to order from them very long story so PM me) along with a 241c transfer case. Problems encountered.
Flexplate aka Flywheel. Had to find the correct flexplate as the one in my HMMWV wouldn't line up.
The TV bracket. For the amount of talk about this I was thinking this was going to be some kind of major problem but it wasn't. Strangely enough I already had a bracket already in place on the back side of the engine underneath the cover bolted onto the engine that evidently used for the TH400 in some capacity. My mechanic opened the hole up on the bracket to receive the square lock housing (the thing you adjust to have proper placement of the cable that will kick the trans down a gear WOT). My mechanic had fitted it to the metal linkage control arm going to the throttle but after evaluating this closer I discovered that at the end of the kick down cable there was little plastic housing fitting that clamped right on to the throttle body so I ditched the multi bend control arm linkage as it was at an awkward angle. I'm still tweaking it because I need more cable wire length (and less cable plastic housing). Going to cut out some of the plastic cable body to lengthen my cable.
Shifter. I retrofitted my three speed shifter to cover Park, Reverse, Neutral (neutral switch eliminated so it would start in park), Drive and 2cd gear. I don't have 1st gear but meh I didn't have to pay $500 for a 4 speed shifter. This involved fabricating extensions on the bottom of the shifter to provide a greater range of points that the shifter could be moved to achieve all ranges mentioned above.
Dip stick. It was preventing my dog house / inside engine cover from closing. Got a torch and bent it to fit. Looking at maybe taking the 700r4 dipstick and trying to make it work as my bending skills are very lacking.

Front Driveshaft. Had to be shortened about 1.75 inches (I think). Interesting note is that the universal joints on the rear drive shaft were all out of alignment. I was told by my mechanic this will cause all kind of driveline vibrations. I had the driveline shop cut and re weld to align them. This was a bit costly at about $275.

Spacer bracket. Had a bracket fabricated that holds the transmission in place as the one that was on there wouldn't line up to bolt up to the transmission. I was told that holes could have been drilled in the cross member if you didn't want to fabricate the bracket.

After a few miles, I noticed the output shaft of the transfer case that has the yoke for the front drive shaft was leaking. I put a $10 seal in it with several hours of cursing and screaming. Get a yoke puller or similar type tool and a seal remover and don't try to do it on the cheap.

Extended range report. I drove it about 300 miles this past weekend to and from Mobile, AL. Everything worked as it should. At 70 MPH I'm running 2650 RPM. At 80 MPH I'm running 3200 RPM. Yes I know 2800 is sustainable RPM so don't be a debbie downer I just wanted to see what it would do. Gas mileage improved from 11.5 MPG to 12.5 MPG. I think I could get better if I held her at a steady 60 or 65 on the interstate but the whole point of going to this 4 speed is so I can cruise at 70.

Next projects: I want to install a temperature gauge to monitor the temperature of the transmission oil. I also want to install a lockup for highway use. I'm looking at this one that works off the brake light but I'm not sure how I'm going to do that as this system is 12 v and well brake lights are 24 v. I'm open to suggestions on this.TCC-BOSCHCOMPLETE.JPG
 

Bocephus

New member
104
1
0
Location
Iowa
That was an awesome write up davykeith! I'm still in the sourcing phase of trying to get a decently priced 700r4, then I plan to start the conversion on mine. I might hit you up with any questions!!!
 

Dock Rocker

Active member
980
71
28
Location
Jackson ms
Next projects: I want to install a temperature gauge to monitor the temperature of the transmission oil. I also want to install a lockup for highway use. I'm looking at this one that works off the brake light but I'm not sure how I'm going to do that as this system is 12 v and well brake lights are 24 v. I'm open to suggestions on this.View attachment 725635
A 12 volt micro-switch behind the brake pedal will do just fine to unlock the TC. You can just skip the 24 volt switch all together. I would just put a riv-nut in the floor and screw it in behind the pedal.

https://shop.advanceautoparts.com/p...s-vJr8i76H1T0a1Wqq8aAhkBEALw_wcB&gclsrc=aw.ds





Sent from my iPhone using Tapatalk
 

davykeith

Member
50
2
6
Location
Ellisville, MS
That was an awesome write up davykeith! I'm still in the sourcing phase of trying to get a decently priced 700r4, then I plan to start the conversion on mine. I might hit you up with any questions!!!
Feel free to do so. I'm enjoying the heck out of mine. My complete rebuilt transmission and xfer case was $1,800 shipped. I don't even want to tell how much I paid to have it put in but I didn't want to try and do it myself as I don't have a lift. My luck I would have squashed my head with the trans falling on me and whatever I paid would be peanuts compared to the hospital bill. You have to put things in the right perspective.
 

gray1027

New member
19
1
3
Location
Pensacola, FL
Neutral safety switch with 700r4 conversion??????????

I know this is an older thread, but I have converted my 1989 HMMWV m998 from its 3l80 to a 700r4 and everything has gone perfect by using the info on this site. BUT, I went to start as to finish filling with trans fluid and nothing. I know it is the neutral safety switch coming from the engine harness making it not start, as it will in gear, but what do you do about that NSS?

Thanks in advance
 

davykeith

Member
50
2
6
Location
Ellisville, MS
I know this is an older thread, but I have converted my 1989 HMMWV m998 from its 3l80 to a 700r4 and everything has gone perfect by using the info on this site. BUT, I went to start as to finish filling with trans fluid and nothing. I know it is the neutral safety switch coming from the engine harness making it not start, as it will in gear, but what do you do about that NSS?

Thanks in advance
Got to bypass the neutral safety switch.
 

infidel got me

Well-known member
1,685
32
48
Location
Newberry, Florida
Daveykeith, I installed a 700r4 in a customers humvee last year. The only problem that I had were --

No flywheel-- was not included in kit-- was supposed to be included

Dipstick tube had to be modified

Transfer case was a pita to get back in -- close to gas tank, but didn't rub.

Everthing else lined right up, no driveshaft issues, no drilling, etc...

Maybe it was because you changed t.c. case
 

JoeJrTheBarber

New member
268
19
0
Location
Chicago, IL
I bit the bullet a few weeks back and got a 700R4 package from Mike Reid of Dirty Boyz Off Road. Package came with a stage II trans, convertor, cables, etc.
As soon as its in the truck I will give ya guys a full write up about it here.
 
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