YJ Dana 35

[Nightpath]

Howdy all,

Thinking about going 3.07 for gears. A bit better for off the line and off roading (light), and way more common than the 2.73 in my current axle (pretty sure it's chewed to now anyways).

Will a YJ D35 axle slide in the same as a D35 from a XJ? Both have drum brakes and the like, and I'm pretty sure the YJ isn't C-Clip.

[eaglefreek]

Spring perches are different, but I don't by how much. Not sure on the shock mounts.

[Nightpath]

That can all be cut and welded I think but from what I've read they should be the same.

Getting pretty excited. 3.07 is exactly what I want for an axle.

[eaglefreek]

Are you doing  the AW4 swap? I had 3.07's with  225/75/15 tires and OD was useless below 75 with the 3.07's. It kept going in and out of OD. I had to switch to 3.55's.

[Nightpath]

Yeah, the AW4 is what I'll be using with teh 4.0 / 231.

Would tire sizing help any? Or would 3.3x gears be better? Trying to avoid the MPG gobblefest taht my XJ saw (with its 3.54)

[BenM]

I'd go with a 3.54 with an overdrive transmission in an Eagle. 3.31 gears if you can find them are good as well.

Road RPM with stock (195/75R15) tires and an AW4 (.75 OD) @ 65: 2.73/1686; 3.07/1896; 3.31/2044; 3.54/2186; 4.10/2532

Road RPM with stock (195/75R15) tires and a T5 (.86 OD) @ 65: 2.73/1933; 3.07/2174; 3.31/2344; 3.54/2507; 4.10/2904

Road RPM with stock (195/75R15) tires and a 998 or T4 @ 65: 2.35/1935; 2.73/2.248; 3.07/2528

Tire sizing doesn't do too much in the confines of the stock Eagle. It's about 150 RPM less with 235/75R15 tires with 3.07 gears and an AW4. With 195/65R15 tires (which seem to be very common) it'll go up just a bit to 2013 RPM, about 117 RPM.

Make sure you swap your speedometer gear to match. You have to calculate tire diameter (between 25" and 29") from the P-sizes.

[Nightpath]

Using this calculator seems to be good for me : http://www.csgnetwork.com/multirpmcalc.html

So with the AW4 + 3.07, and a P235 75 R15 tire, the RPM would be a bit less with OD, probably 1730-1760 or so. Does this seem a bit low for highway RPM? Seems when I check it at most ranges with the AW4 ratios that it keeps it at too low of an RPM.

A bit lower gear, like 3.31 would seemingly be better without gutting myself.

[BenM]

With the AW4 on the highway you would still be in a low comfortable cruising RPM at 3.54. I think the Eagle moves around a little better at around 2250 RPM on the highway. Below 1900 RPM is best left to Spirits, Gremlins, and Pacers.

Looking at the stock Cherokee, which took a lot from the Eagle, they were set up with 3.54 for the AW4 and 3.07 for the T5, and I had no problem getting 20 MPG in one with the AW4 so long as I kept it under 60, but the Eagle should fare better at 65-70 because it's not a big square brick. The limit on the Cherokee and Wrangler is really the aerodynamics.

The big 235/75 tires will hurt city fuel economy, it's more mass on the outside of a larger diameter wheel and the engine has to break the inertia of them each time you start, and if you want to stick with them I'd lean more toward the 3.54. If you were planning on the smaller sizes then the 3.31 would make more sense.

Unfortunately, you are going to be hunting for 3.31 if you go that way. They were only offered in '81 on Eagles and are rare in Jeeps.

I've been using http://www.grimmjeeper.com/gears.html, it's nice to compare, but the "copy" buttons seem backward to me. It's got most common transmissions in it.

[carnuck]

I put the 235/75/15s on my wagon and it killed in town economy with the 2.72s. I haven't driven much since swapping in the 3.08, but the off the line power is MUCH better. This is with 2.72 gears and 727/NP229. Now a little known fact: The AW4 with Renix EFI has a .70 O/D and the HO is .75 which was done because of the change in cam timing to move the HO powerband up the RPM range. That was actually a secondary "feature" because the main reason for the cam timing change was to get rid of the EGR valve by changing the overlap and reducing the VE (Volumetric Efficiency) of the cylinder filling.
   Less pressure = less ping.

Cam Brown used a YJ Dana 44 axle in his original "Flying with V8 Eagles" wagon back in the late '80s/early '90s. If they are SOA, it was 3/4" offcenter but worked fine by notching the centering holes slightly. XJ diff is a bolt in for spring pads and all 5 speed 4.0L were 3.08 so only shock mounts needed modding. I'm thinking I should make a shock mount plate that goes between the springs and axle (like my Comanche had) so no welding needs to be done on the axle. (I wonder if Priya's hubby would object to that? )