need more out of 4th gear

[lefty]

hey guys i have an 85 CJ7 with the AMC 258 i6 / 4.2l engine. T-176 tranny and danna 20 rear end. first three gears work great but forth gear has nothing. it keeps at the speed i enter it at and barely accelorates at all. is this normal or do i have an issue that needs to be addressed? the jeep runs down the road at 60 to 65 pretty good but thats all done by pushing the first three gears. is there anything i can do to get more out of 4th gear?

 

[CJ]

Sounds like you have the dreaded 2.77 gear ratio, what is your diff. ratio?

 

[mtnwhlr]

It says you have 36" tires what gears are you running?

 

[lefty]

as far as i know the gears are stock

 

[lefty]

bought the jeep 3 months ago with all the receipts of the things that have been done to it but there is nothing about any gear swaps.

 

[CJ]

as far as i know the gears are stock

What is the gear ratio? Stock gears vary, -->> http://www.jeep-cj.com/forums/f99/how-determine-your-gear-ratio-10217/

 

[mtnwhlr]

as far as i know the gears are stock

There is your problem mine is under powered with 31"s I can't even think how bad it would be with 36" tires.

 

[lefty]

ok i will pull the cover and see whats in there because everything has been sprayed by that undercoating stuff so im pretty sure i can read a tag if there is one. so lets say for instance that i have the dreaded 2.77 gear ratio lol. i take it im looking at a gear upgrade? whats would be the best gears to go with for speed?

 

[mtnwhlr]

With that much tire I would go with 4.56

 

[CJ]

You don't have to pull the cover, just follow our guide. Let us know.

Look here again -->> http://www.jeep-cj.com/forums/f99/how-determine-your-gear-ratio-10217/

 

[lefty]

the driveshaft rotates 5.5 times in 2 turns of the wheel. while spining one wheel the other wheel spins in the same direction sometimes but not all the time.

 

[CJ]

Without an exact measure I cant give you a gear ratio - but I will say it sucks for your tire size.

 

[CJ]

With 36" tires I agree - 456 gears or higher are necessary!

On my CJ with 31;s I run 4.56,,,

 

[lefty]

how do i get an exact measurement? 5 and 1/2 times with two rotations of the tire is pretty much dead on from the looks of it

 

[CJ]

how do i get an exact measurement? 5 and 1/2 times with two rotations of the tire is pretty much dead on from the looks of it

You need to pull the cover and count the ring and pinion teeth.

 

[lefty]

OK will do... thanks for your time

 

[Old Dog]

how do i get an exact measurement? 5 and 1/2 times with two rotations of the tire is pretty much dead on from the looks of it

sounds like the dreaded 2.73 gears to me. That would be pretty normal for your year cj.
I agree 4:56's would work well.

 

[BusaDave9]

how do i get an exact measurement? 5 and 1/2 times with two rotations of the tire

You need to pull the cover and count the ring and pinion teeth.

sounds like the dreaded 2.73 gears to me. That would be pretty normal for your year cj.
I agree 4.56's would work well.

I wouldn't even bother removing the cover. I think Old Dog is right. You have about 2.73 gears. If he's wrong it's not by much and it really donesn't matter anyway. What matters is the gearing you need. I have 36 inch tires and 4.88 gears. I wouldn't want to go much lower but I don't drive much on the highway. If this is a daily driver I would agree with the others and recommend 4.56 gears.

Here's a chart to help find the right gears. Shoot for the green. The numbers in the middle are RPM at 60 MPH

 

[lefty]

Thanks guys. So looking at the chart if I went with 4.56 gears at 60 MPH I would be at 2766 rpm if I'm understanding this correctly. What gear would I be in according to the chart? As the jeep is now I'm shifting from third to fourth at around 60 at about 2700 rpm.

 

[Old Dog]

The chart would be for 4th (1:1) gear.
If I were you I'd measure the height of your tires, most do not measure what the sidewall size says it is.
Here's a link to another gear calculator to play with http://www.grimmjeeper.com/gears.html