JaysJeep Posted November 7, 2016 Share Posted November 7, 2016 Hello everyone! I joined the Comanche Club last week when I purchased an '88 Comanche. She's a beauty. But I'm having an issue that I can't explain. When it's in 2wd, it goes great. But when I put it in 4wd, the rear driver side wheel seems to move slower than the rest, and just skids along. It almost looks like it is trying to go backwards. Everything that I can think of that would explain it, would also manifest in 2wd. So I'm super confused. Any thoughts? Link to comment Share on other sites More sharing options...
88whitemanche Posted November 8, 2016 Share Posted November 8, 2016 Maybe because your thinking that 4wd means all wheels need to move, when your in 2wd unless you have an lsd/locker, of some sort means that both wheels spin at the same time...if your open diff one wheel will have power as the other would just roll because it's not the wheel that receiving the power... Link to comment Share on other sites More sharing options...
87MJTIM Posted November 8, 2016 Share Posted November 8, 2016 I hope you're not driving in 4wd on drive pavement. You probably have an NP231 tcase. This is a part-time 4wd, not full-time. If you have an NP242, that is full-time 4wd. Link to comment Share on other sites More sharing options...
A-man930 Posted November 8, 2016 Share Posted November 8, 2016 You're doing this with the wheels in the air aren't you? Link to comment Share on other sites More sharing options...
DirtyComanche Posted November 8, 2016 Share Posted November 8, 2016 Mismatched gear ratio between the front and rear axle... Or it could be other things, but I'd start with that. Link to comment Share on other sites More sharing options...
schardein Posted November 8, 2016 Share Posted November 8, 2016 You're doing this with the wheels in the air aren't you? :agree: Link to comment Share on other sites More sharing options...
Pete M Posted November 8, 2016 Share Posted November 8, 2016 Mismatched gear ratio between the front and rear axle... Or it could be other things, but I'd start with that. that was my first thought too. Link to comment Share on other sites More sharing options...
AeroNautical Posted November 8, 2016 Share Posted November 8, 2016 Mismatched tire sizes, too! Link to comment Share on other sites More sharing options...
JaysJeep Posted November 8, 2016 Author Share Posted November 8, 2016 Maybe because your thinking that 4wd means all wheels need to move, when your in 2wd unless you have an lsd/locker, of some sort means that both wheels spin at the same time...if your open diff one wheel will have power as the other would just roll because it's not the wheel that receiving the power... I understand awd vs 4wd. It doesn't have lockers. It's an open diff. And the wheel isn't just rolling like a normal open diff would. It's stopped/going backwards. Link to comment Share on other sites More sharing options...
JaysJeep Posted November 8, 2016 Author Share Posted November 8, 2016 It seems like the general consensus is the mis-matched gear ratio on here and among other people I've talked to. I'm going to get it up today to look at it. I'll let you all know what I find. Link to comment Share on other sites More sharing options...
schardein Posted November 8, 2016 Share Posted November 8, 2016 Maybe because your thinking that 4wd means all wheels need to move, when your in 2wd unless you have an lsd/locker, of some sort means that both wheels spin at the same time...if your open diff one wheel will have power as the other would just roll because it's not the wheel that receiving the power... I understand awd vs 4wd. It doesn't have lockers. It's an open diff. And the wheel isn't just rolling like a normal open diff would. It's stopped/going backwards. You didn't answer the question, are you doing this with the wheels in the air? It is possible someone swapped axles and you have mismatched gear ratios. Is your truck an original 4wd or was it converted from 2wd (check the VIN, does it have original 4wd emblems?) An odd thing I have seen to make a wheel lock up is a rusted parking brake cable that is seized inside it's sheath. In this situation, the truck could back up ok (the rear drum brakes are designed to be more effective going forward than reverse) but as soon as it tried to go forward the one rear wheel would lock up. The only thing I can think of that would make a tire appear to go "backward" would be driving a full locker or spool on dry pavement. In a tight turn, the inside wheel can't travel the distance the outside wheel is taking, and will appear to skip (often making a chirp-chirp-chirp sound). It's not really going backward, just trying to catch up to the outside tire. Link to comment Share on other sites More sharing options...
A-man930 Posted November 8, 2016 Share Posted November 8, 2016 Let's be clear about something: mismatched gear ratios would not, in any universe, cause one wheel to turn backwards in relation to the others. Your initial post: But when I put it in 4wd, the rear driver side wheel seems to move slower than the rest, and just skids along. It almost looks like it is trying to go backwards. "skids along" implies you're observing this while driving. But your other post: And the wheel isn't just rolling like a normal open diff would. It's stopped/going backwards. Implies you're looking at it on a lift with the wheels off the ground... With an open diff you can't count on the left and right side wheels to be rotating at the same speeds. As mentioned, things like brake drag will influence what you see. Not recommending this, but I've personally used my hands to stop one wheel of an open diff hanging on a lift above my head at 40+mph. Does the truck drive in 4wd ok if you drive in a straight line on dry pavement? or does it buck and pop at you? Link to comment Share on other sites More sharing options...
DirtyComanche Posted November 8, 2016 Share Posted November 8, 2016 Let's be clear about something: mismatched gear ratios would not, in any universe, cause one wheel to turn backwards in relation to the others. Never tried it, huh? Link to comment Share on other sites More sharing options...
A-man930 Posted November 8, 2016 Share Posted November 8, 2016 Had 3.07s in the front and 3.54s in the rear for a year or so and might have put her in 4wd a time or two... No. Would one axle turn slower? sure. But not backwards. Link to comment Share on other sites More sharing options...
gogmorgo Posted November 9, 2016 Share Posted November 9, 2016 Because the axles only have to turn "on average" at the same speed, one wheel could be rolling at the same speed as the two on the other axle, and the other could be turning much slower, or possibly even backwards, to make up for it. It's a lot like dragging a vehicle in park, one wheel turns forward at the speed of the vehicle, the other wheel goes backwards. Link to comment Share on other sites More sharing options...
A-man930 Posted November 9, 2016 Share Posted November 9, 2016 I think its safe to say that the OP does indeed have different ratios front vs. rear. Pop the covers and start countin'! Let us know what you find. In the meantime I'm gonna stop arguing theoretical stuff here since I've never actually witnessed this scenario in person and we don't even know if the guy is describing a phenomenon he's observing with the car in the air or driving, straight line or in a turn, gravel or pavement, etc. Link to comment Share on other sites More sharing options...
A-man930 Posted November 9, 2016 Share Posted November 9, 2016 Ok so I might eat my words here... In this scenario: driving in a straight line, np231, numerically lower front diff, equal tire sizes, transfer case putting up with this abuse, and superior tire traction on the front. The truck would be dragged by the front diff, which due to the 50/50 split in the t-case, would impede the speed the rear propshaft wants to turn. IF one of the tires achieved greater traction than the other then you have a scenario similar to what gogmorgo described (dragging a vehicle in park). I stand corrected. I love this forum! Link to comment Share on other sites More sharing options...
JaysJeep Posted November 9, 2016 Author Share Posted November 9, 2016 To clarify: I've tried to put it in 4 wheel drive twice, both times in a dirt lot. I drove maybe 5 feet in a straight line and observed the described scenario. I didn't get a chance to get it all jacked up to see what it does in the air. Hopefully I'll have time Saturday. Keep the ideas rolling! I'll keep everyone updated when I can count the gears. Link to comment Share on other sites More sharing options...
yxmj Posted November 9, 2016 Share Posted November 9, 2016 You won't have to count....when you take off the cover it will be stamped on the ring gear Link to comment Share on other sites More sharing options...
JaysJeep Posted November 9, 2016 Author Share Posted November 9, 2016 I also found this. https://youtu.be/RNgjS5mHI0E Link to comment Share on other sites More sharing options...
JaysJeep Posted November 10, 2016 Author Share Posted November 10, 2016 Okay. I got the truck up tonight. Put it in 4wd, then taped a line on the wheels and side of truck. I blocked the two wheels on the passenger side, so that spinning the rear driver side would make the front drivers wheel spin too. I rotated the rear wheel one complete revolution, then observed the position of the front wheel. The front wheel had rotated 1 1/8 rotation. Conslusion: Different gear ratios. Some bozo must have replaced one of the axels and mixed it up. I'm surprised someone who knows how to swap and axel would make that mistake. Now I'm going to figure out the ratios. Anyone know what the ratio is supposed to be on the '87 4.0L longbed? Link to comment Share on other sites More sharing options...
87MJTIM Posted November 10, 2016 Share Posted November 10, 2016 A 4.0 auto would have come from the factory with 3.55 in front and rear. A manual would have come with a 3.07. It looks like you one of each. Math: (3.55-3.07)/3.55= 13.5% That is close to 1/8th (12.5%) Was the truck originally 4wd? Is the front axle CAD or non-CAD? (Is there a "box" on the passenger side with vacuum lines connected? Yes=CAD, No=non-CAD) Was it originally auto? manual? Swapping from one to the other along with one axle may be the problem. Edit: All 4wd MJs came with the CAD front axles. Link to comment Share on other sites More sharing options...
yxmj Posted November 10, 2016 Share Posted November 10, 2016 Why waste time scratching your head and guessing.Take off the diff covers...see what the actual ratio is and then you will know for sure...why speculate when the answer is right there :dunno: . :MJ 1: . Link to comment Share on other sites More sharing options...
JaysJeep Posted November 10, 2016 Author Share Posted November 10, 2016 Why waste time scratching your head and guessing. Take off the diff covers...see what the actual ratio is and then you will know for sure...why speculate when the answer is right there :dunno: . :MJ 1: . Well, taking off the covers would require refilling and resealing the covers, which seems like more work than counting a different way. Link to comment Share on other sites More sharing options...
JaysJeep Posted November 10, 2016 Author Share Posted November 10, 2016 Rear wheel after 1 rotation Link to comment Share on other sites More sharing options...
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