4wd question

Moderator: sandaltered

4wd question

Postby jeepnut » Tue Aug 04, 2015 6:45 pm

My question is I have 4.56f/6.50r gear with a 78 3/4f and 108 7/8roll out 1 to 1 on chain drive. It is binding a little and the front wheels rotate backwards when I jack it up overdriven I believe. I want to change the front tires to correct the binding do I need to go bigger or smaller. I had the formula at one time but no longer have it. Thanks.
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Re: 4wd question

Postby 357Bronco » Wed Aug 05, 2015 8:03 pm

This was a popular topic on here in the past. I always figured if the tire was spinning backwards when jacked up it was being pushed and I would say it was underdriven. In your case I would say you need a taller front and/or a shorter rear. If a front was overdriven ( more revolutions ) it would spin forward when jacked up. If you pump up your fronts and lower your rears there should be less back spin, you could do that ( or the opposite ) as an experiment before trying new tires.
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Re: 4wd question

Postby sandaltered » Thu Aug 06, 2015 5:50 am

Yes, you're overdriven. Your front tire is rolling further than it should compared to the rear in each rotation of the driveshaft. So when you jack it up, it corrects itself by turning backwards. It looks like you're only about 3% overdriven. That's not horrible. 76.4 would be the proper rollout for no overdrive. But that's cutting it a little close.

Is it difficult to push on concrete?
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Re: 4wd question

Postby jeepnut » Thu Aug 06, 2015 11:10 am

Yes on concrete, but I also noticed at Michigan it would not roll down the hill in staging . it's also a bit hard to pull in 4wd. with everything off the ground it all seems free no binding so I didn't think it was related to anything else.
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Re: 4wd question

Postby Snowball » Thu Aug 06, 2015 12:28 pm

Yes have a question about stager wanting to know if it will hurt anything by running 31x10.50x15 on 8 inch in front and 33x12.50x15 on 10 inch wheels on back with 3.55 gears trying to get the front spinning a little faster all help is appreciated thanks
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Re: 4wd question

Postby sandaltered » Thu Aug 06, 2015 3:56 pm

jeepnut wrote:Yes on concrete, but I also noticed at Michigan it would not roll down the hill in staging . it's also a bit hard to pull in 4wd. with everything off the ground it all seems free no binding so I didn't think it was related to anything else.


That's a little strange. You're not that far off by my calcs. My Jeep struggled too in 4WD. I think my chain drive ended up bound up. My calculations usually agree with everybody else's. I can't imagine it not rolling down the staging hill at WMSD. Did you ever unlock your front hubs and try rolling down again?
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Re: 4wd question

Postby jeepnut » Thu Aug 06, 2015 8:43 pm

No Mike I didn't
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Re: 4wd question

Postby 357Bronco » Sat Aug 15, 2015 10:39 am

This always seems backwards to me. Mike can you check my gearing with your program? 101.5" rear roll out, 97.5" front roll out. 4.11 rear gear, 3.92 front. When I jack up the front after driving forward, the tire spins backward about 3"s or so. I also wanted to take some gear out of the truck at some point, I have 3.73 rear and 3.50 fronts, hoping that combo would work, seeing as though I own all the parts.Thanks, Scott.
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Re: 4wd question

Postby sandaltered » Fri Aug 21, 2015 6:59 am

I calculate ideal at 3.95. So your 3.92 is about 1% overdriven. So that should work good.

For the gear change to 3.73 rears, no overdrive would be 3.57. That 3.50 gear would be 2% over. Still not bad. Should work just fine.
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