[wertyu78]

I have an 86 CJ7 with the TF99 Dana 300 and dana 44 rear end.

I have 35 inch tires on it and have not regeared. Acceleration is poor, as well as gas mileage.

What do i need to do to regear?

[buzzbrick]

If you search 're-gear' you'll get all you need to know; this subject comes up a lot. Chances are good that if you have to ask, you'll probably (almost guaranteedly) want to just have a shop do it. There's lots of ways to mess this one up and completely trash your gears.
As for a quick summary of needed parts:
-gears (in your case likely 4.56 or 4.88)
-carriers (you'll need both front and rear axle)
-gear install kits
-diff cover gaskets
-silicone RTV
-gear oil

[curbcrawler]

I ran the exact set up, year, tanny, tire size, the rare for that year d44 rear end, every thing you have. I used 4: 11 gearing that helped alot but on the highway 70mph I was at 2800 on the tach. Any lower gearing 4.56 or lower would make your engine scream at high way speeds assuming its a i6 258. If you dont go hwy speeds go with 4.56 or lower. I fixed my problem by installing a 5 speed manual tranny.

[CJATE]

i am very happy with my 4.56 on 35's at times wish was lower, but I would not do 4.10's

mine is fine on the highway (but i try not to put it there)

[80cj]

The OP has an auto tranny. 4.10 gears may be sufficient considering that the auto tranny's torque converter will help getting started from a dead stop or on hills and still yield decent gas mileage and highway RPM.

[curbcrawler]

Originally Posted by 80cj

The OP has an auto tranny. 4.10 gears may be sufficient considering that the auto tranny's torque converter will help getting started from a dead stop or on hills and still yield decent gas mileage and highway RPM.

My thoughts and experience exactly. the only time I wanted for more gearing was in loose sand then I would just shift the transfer case into low range. I swapped in a manual 5 speed eventually, to get more on the top end. 70mph at 3000 rpm was killing my gas milage not to mention the i6 does not like high rpms.

[80cj]

Another thought is that there is a 4.27 ratio available for the D30 and D44. This could be a good compromise for 35's.

[80cj]

Originally Posted by curbcrawler

I ran the exact set up, year, tanny, tire size, the rare for that year d44 rear end, every thing you have. I used 4: 11 gearing that helped alot but on the highway 70mph I was at 2800 on the tach. Any lower gearing 4.56 or lower would make your engine scream at high way speeds assuming its a i6 258. If you dont go hwy speeds go with 4.56 or lower. I fixed my problem by installing a 5 speed manual tranny.

Hmmm curbcrawler... did you correct your speedo? According to this chart, 2800 seems a bit fast. Although the chart is set for 65 mph, 5 mph more should not result in the 2800 rpm you saw.
4Lo.com :: Gear Ratio & Tire Size Chart

[curbcrawler]

Originally Posted by 80cj

Hmmm curbcrawler... did you correct your speedo? According to this chart, 2800 seems a bit fast. Although the chart is set for 65 mph, 5 mph more should not result in the 2800 rpm you saw.
4Lo.com :: Gear Ratio & Tire Size Chart

I used a GPS. 2800 is exactly what I got at 70 mph. In review of my specs. I conscidered the true diameter of my tire, I run 35"BFG ATs which measure out at 33-34" in diameter not 35" as claimed by the manufacturer, that could account for extra rpms. According to the chart he would have be at 28oo and some with a true 35" tire at 65. Still, not real great.

[Mike Romain]

Originally Posted by 80cj

Hmmm curbcrawler... did you correct your speedo? According to this chart, 2800 seems a bit fast. Although the chart is set for 65 mph, 5 mph more should not result in the 2800 rpm you saw.
4Lo.com :: Gear Ratio & Tire Size Chart

That chart is off. I have a GPS also and use measured 'mile' markers so know my speedometer is right on.

At 65 mph, I am turning 2300+ rpm with 33" tires, 3.31 gears and 1:1 tranny gear. The chart says I should be turning 2191 rpm. Hmm unless my tires are actually 32. Ok, nevermind....

[80cj]

I did some calulations using the rotational velocity formula at this web site:Gear Design Equations Formulas Calculator Velocity Speed MPH

The rotational velocity (engine RPM) for a true 35" tire at 70 MPH would be 2755 RPM. Considering that your 35's are a little less than 35" true diameter, it looks like your 2800 RPM figure is in a very close ball park.

[curbcrawler]

Originally Posted by 80cj

I did some calulations using the rotational velocity formula at this web site:Gear Design Equations Formulas Calculator Velocity Speed MPH

The rotational velocity (engine RPM) for a true 35" tire at 70 MPH would be 2755 RPM. Considering that your 35's are a little less than 35" true diameter, it looks like your 2800 RPM figure is in a very close ball park.