88ComancheGA Posted April 20, 2020 Share Posted April 20, 2020 I have two MJ's. Both Renix 4.0 engines. Both appear to be fully stock. The 88 4WD is rough body and some floor rust, but has good engine, trans, transfer, and axles. The 87 2WD has great body with no rust and only minor body damage and sold interior, not sure about engine at the moment. My plan, move all the 4WD components from 88 4WD to 87 2WD. My main question, why do i have to change out transmission? What is the main difference between the two trans? Also, since this will be my first swap, what are major pitfalls to look out for while doing this? I found some old discussions on this topic, from years ago, wanted to see if there was any new tips or tricks? Thank you for any help offered. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 20, 2020 Share Posted April 20, 2020 The 2wd transmission will not accept the transfer case. So you have to swap the 4wd transmission also. Are both trucks same bed length? If so, drive shaft from the 4wd should swap over (unless one auto and the other is manual). Also what axle in the rear do you have - D35 or D44? That may affect the drive shaft, also. The front axle and drive shaft should swap over without any issues. Link to comment Share on other sites More sharing options...
Eagle Posted April 20, 2020 Share Posted April 20, 2020 The difference is that the 4WD transmission has the output end set up to have a transfer case attached to it. The 2WD transmission has a long tailshaft with a splined end that accepts the front yoke of the driveshaft directly. It's easier to swap the transmissions than it would be to try to take the 2WD transmission apart in the vehicle and reassemble it as a 4WD tranny. Link to comment Share on other sites More sharing options...
Pete M Posted April 20, 2020 Share Posted April 20, 2020 are both trucks the same type of trans? (auto or manual) Link to comment Share on other sites More sharing options...
88ComancheGA Posted April 20, 2020 Author Share Posted April 20, 2020 Hello. Here are answers to the questions. Thanks for the help. The 4WD has the following Rear is Dana 35 (42968) dated 02/24/87 Front Dana 30 (40869) dated 07/24/85 The 2WD has the following Dana 35 (42106) Dated 11/15/85 Both beds are the same, 6 ft short bed. Both are manual 5 speed trans Overall seems to be the parts are interchangeable? Any thoughts or concerns? Link to comment Share on other sites More sharing options...
JMO413 Posted April 20, 2020 Share Posted April 20, 2020 1 minute ago, 88ComancheGA said: Hello. Here are answers to the questions. Thanks for the help. The 4WD has the following Rear is Dana 35 (42968) dated 02/24/87 Front Dana 30 (40869) dated 07/24/85 The 2WD has the following Dana 35 (42106) Dated 11/15/85 Both beds are the same, 6 ft short bed. Both are manual 5 speed trans Overall seems to be the parts are interchangeable? Any thoughts or concerns? You should be good to swap everything. You will have to use the 4wd transmission. You will have to check the rear gear ratio in the 2wd and see if it matches the front. If it's doesn't you'll have to swap the rear also. Link to comment Share on other sites More sharing options...
Pete M Posted April 20, 2020 Share Posted April 20, 2020 be sure to start a build thread and include lots of pictures! Link to comment Share on other sites More sharing options...
omega_rugal Posted April 21, 2020 Share Posted April 21, 2020 7 hours ago, JMO413 said: You will have to check the rear gear ratio in the 2wd and see if it matches the front. both should be 3.07 but is better to check, just in case some PO had messed with it Link to comment Share on other sites More sharing options...
88ComancheGA Posted April 21, 2020 Author Share Posted April 21, 2020 Looks like both rear ends are identical. I attached a picture of both rear end tags. Both are Dana 35C with 3.08 gear ratio as both have 4.0 IL6 with 5 speed manual gear boxes. And I know over time someone could have messed with the gears, but overall everything looks very stock on both vehicles. Based on the rear tags, any concerns or items to look out for as I make the swap? Thank you for the feedback. Link to comment Share on other sites More sharing options...
omega_rugal Posted April 21, 2020 Share Posted April 21, 2020 yes, 3.08... i wonder why Jeep even bothered putting such ratios on 4WD models, the 3.55 would be the bare minimum for off-roading Link to comment Share on other sites More sharing options...
87MJTIM Posted April 21, 2020 Share Posted April 21, 2020 1 hour ago, omega_rugal said: yes, 3.08... i wonder why Jeep even bothered putting such ratios on 4WD models, the 3.55 would be the bare minimum for off-roading It was the '80s. Every (cheap) effort to increase MPG was implemented. (See front axle CAD.) Also, the 3.07 was offered only in the 5 spd Jeeps. Autos and 4 cyl/4 spd. came with 3.55 and higher ratios. To meet Fed CAFE standards, off-roading wasn't a thought. Link to comment Share on other sites More sharing options...
omega_rugal Posted April 21, 2020 Share Posted April 21, 2020 i thought the OD was meant to make up for the low rear ratios, the CAFE is killing the planet instead of saving it... Link to comment Share on other sites More sharing options...
Pete M Posted April 21, 2020 Share Posted April 21, 2020 3 hours ago, 88ComancheGA said: Looks like both rear ends are identical. I attached a picture of both rear end tags. Both are Dana 35C with 3.08 gear ratio as both have 4.0 IL6 with 5 speed manual gear boxes. And I know over time someone could have messed with the gears, but overall everything looks very stock on both vehicles. Based on the rear tags, any concerns or items to look out for as I make the swap? Thank you for the feedback. you can do a quick and easy check of the ratio by spinning one tire around exactly twice while counting the number of times that the driveshaft rotates. just past 3 rotations is 3.08. Link to comment Share on other sites More sharing options...
BeatCJ Posted April 22, 2020 Share Posted April 22, 2020 7 hours ago, omega_rugal said: yes, 3.08... i wonder why Jeep even bothered putting such ratios on 4WD models, the 3.55 would be the bare minimum for off-roading At least it's not the 2.73 gears that were original in my '81 CJ-5 4 Speed. On most trails, finesse was out of the question. Swapping to 3.55 axles was huge! Link to comment Share on other sites More sharing options...
omega_rugal Posted April 22, 2020 Share Posted April 22, 2020 2.73 in a vehicle that was meant to be driven on rough terrain, what were they thinking, but look with those gear i STILL get terrible gas mileage Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now