5.13 or 5.38

I can't decide. I'm putting new tires on the heep and I want to go with 37" MTR's. With that I'll need new gears. I have 35's with 4.88's and I feel like its lacking especially on the freeway and on winding hills and such.

I've searched back and I see recomendations on the 5.13's and 5.38's.

With the 5.13's on
1) the freeway (70mph) I would be spinning at 3445 RPM (w/ overdrive= 2283)
2) around town (25, 35mph) I would be pushing 1231 & 1723 RPM

With the 5.38's on
1) the freeway (70mph) I would be spinning at 3613 RPM (w/overdrive= 2394)
2) around town (25, 35mph) I would be pushing 1290 & 1807 RPM

The recommended RPM range for a v6 was 2200-3200 on the freeway. But as I read in past threads that the I6 likes to run a bit higher RPM.

This will be my daily driver so what would your opinion be as far as gears go?

Oh, in addition to this I'm going to go ahead and pop some ARB's in there at the same time to avoid having to pull everything apart more than once. I already have an air system running of my air conditioning, would that work for operation of the ARB's. I have an incab switch to flip then I would imagine I would have to hit the switch for the ARB's but I'm not sure if it would put enough pressure to active the lockers...

Thanks for the help.

-Kevin

What axles are you using? I asked this same question and was told to go with the lowest gears I could get for the axles I had. For the hp44 & hp60 5.38 gears are the lowest so that's what I went with and matched that up with 5.43 gears in my Ford 9". At 70 mph with the AW4 auto trans and overdrive I'm at 2,500-2,600 RPMs & at 80 mph I'm at just under 3K. I have power once again. I moved up from hp30/44 with 4.56 gears and 35's to now hp44/9" and 37's. A lot of people are very scared of lower gears on the street, but with an overdrive tranny it will be fine. 5.13 gears aren't bad either, but 5.38's are better for 37's. Just keep in mind that you do lose a some strength when going with lower gears because you lose some gear to pinion contact, but 5.38's will be fine.

It's when you go to 5.89 gears in the regular dana 44 is when you are getting mighty low. I drove a CJ7 buggy I sold some time ago with dana 44/9" with 5.89 gears and no overdrive in the SM465 tranny and the 37" MTRs I now have on my XJ and it was o.k. I didn't have my tach hooked up, but I got it up to 85 or so being that is was full width and 103" WB like my XJ. I drove great. After that it sat in my garage until I sold it. I drove it from Truckee to Citrus Heights about a hour to 1-1/2 hr drive.

Troy

I've cut a HPd44 up front and a Ford 9" in the back.

I called up Drivetrain warehouse and they have the 5.13's instock. But I think I'm going to end up on the 5.38's. I'm extremely light on the go pedal for less strength in the gear pinion I dont think will be THAT big of a concern. If I'm not getting traction I'll choose another route rather than hammering down.
My tranny has been set up to be the same as the AW-shifting so I have control over what gear I'm in and I think that my help a bit.

Thanks for the help.

You didn't mention what tranny (year) you were running. Looking at the numbers below it looks like you're basing your OD numbers on a .66:1 ratio (or somewhere around there). That wouldn't be correct on any of the XJ tranny's I know about.

I would still say a minimum of 5.38. I've got the older AW4 (.705:1) and I'm running 5.38's and 35's. Couldn't get me to ever go higher and cruising 70+ isn't a problem. 2700-2800 @ 75.

Later,
Lincoln

I have 5.13 in my 44/9 with 36'' swampers. I-6, aw4 auto.

I like it and am very happy with it. I don't drive much over 65 or 70 and I wonder what it would be like with 5.38's. I bet I would be very happy with them. But, on the rocks the 5.13 are awsome so, I think that you would be happy with either decision.

It is kind of a flip of the coin.

Big Red said:

Just keep in mind that you do lose a some strength when going with lower gears because you lose some gear to pinion contact, but 5.38's will be fine.
Troy

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can you back this up any i was under the impression that the gear mesh is practicly the same with verry similar contact patches i've never heard of anyone having problems with deep gears breaking because there too week. i on the other hand have heard that people thought they set up there gears right and ended up breaking them.
i don't have a pinion in my hand but the only thing that would make sense to me for failure is that the minimum diameter of the pinion is reduced by trying to put fewer teeth on the pinion thus making it weeker similar to spline count on a shaft

Few teeth the lower you go in gearing. With a Ford 9" this isn't that big of a deal, but the dana 44 can lose quite a bit when you go deeper. I still like the idea of going as deep as you can with a hp44 or hp60, rather than get 5.13's and then find out you would like just a little more gear reduction etc. The move to 5.38s from 5.13s isn't really worth the cost and time so do it right the 1st time when getting the stock axle and building them up. Many had 3.50 gears and the move to 5.38s is a huge jump

wrecked said:

I've cut a HPd44 up front and a Ford 9" in the back.

I called up Drivetrain warehouse and they have the 5.13's instock. But I think I'm going to end up on the 5.38's. I'm extremely light on the go pedal for less strength in the gear pinion I dont think will be THAT big of a concern. If I'm not getting traction I'll choose another route rather than hammering down.
My tranny has been set up to be the same as the AW-shifting so I have control over what gear I'm in and I think that my help a bit.

Thanks for the help.

Click to expand...

Match the 9" gearing with 5.43s if you get 5.38s in the hp44. The Ford diff has different gear ratios then the dana axles, but within a few % is fine. Many Toyota guys match 5.29 gears in their Toy 8" with 5.38 gears in their Waggy dana 44 front axle.

Troy

bj-666 said:

can you back this up any i was under the impression that the gear mesh is practicly the same with verry similar contact patches i've never heard of anyone having problems with deep gears breaking because there too week. i on the other hand have heard that people thought they set up there gears right and ended up breaking them.
i don't have a pinion in my hand but the only thing that would make sense to me for failure is that the minimum diameter of the pinion is reduced by trying to put fewer teeth on the pinion thus making it weeker similar to spline count on a shaft

Click to expand...

I believe it is because they are smaller. I know with bikes, alot of us BMXers have switched over to a 25 tooth front sprocket and a 9 tooth rear sprocket(cog/driver).
The rear 9t driver has to be made of titanium because it each tooth takes on so much more stress as there are less teeth.
I would imagine that its the same concept. Less teeth taking on the same stress= more likely to break.

As for my tranny I believe its the AW5 maybe AW4. It the 1-2,3, overdrive, N, R, P out of a '90 Limited. How much will that change the RPM range?

wrecked said:

As for my tranny I believe its the AW5 maybe AW4. It the 1-2,3, overdrive, N, R, P. How much will that change the RPM range?

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AW4 would be what you have. They changed OD around 91 (?) and went to a .75:1 OD.

Regardless, I would do 5.38's. You'll still be under 3K at 80mph.

Also the pinion will break before the gears will on a good setup. Goatman will argue that, but I've seen more pinion breaks than actual gear failures. The only gear failures I've seen in a 44 were bad setups or they weren't broke in slow enough and you could see the damaged teeth from getting hot.

On that note do a search for Goatman and gears. He's running 5.13's and a stroker with 37's and thinks it's about right. Pre stroker he wanted deeper. He's running the same OD ratio I am.

wrecked said:

I believe it is because they are smaller. I know with bikes, alot of us BMXers have switched over to a 25 tooth front sprocket and a 9 tooth rear sprocket(cog/driver).
The rear 9t driver has to be made of titanium because it each tooth takes on so much more stress as there are less teeth.
I would imagine that its the same concept. Less teeth taking on the same stress= more likely to break.

Click to expand...

the differenc is the cut of the gears hypoid gears are designed in a way to eliminate weakness with varying gear ratios