Low gears in a low-pinion D44 front

[tsm1mt]

I've had good luck running 4.88s in my front axle for the last 8 years, but there's a new rig underway and that means changes.

I just recently discovered the availability of 5.86 gears for a standard-rotation D44.

I was a little worried about going to 5.13s or 5.38s, but 5.86 is even more suspect.

Rear will be a 9", so no worries about the pinion strength there.

5.86 and 35s work out nicely, putting top speed in the 100mph range, though maybe 5.38s would give a little more margin and I wouldn't have to push the engine so hard - but I've seldom been in a spot where the course was straight enough long enough to hang on to 100mph.

Would YOU consider 5.86s? Have you run 5.38s with good results in a race truck with a D44 front end?

I've gone through a few sets of balljoints, and only one axle shaft that bent when the housing broke in half.. otherwise, the front has held up fine with stock components inside.

[AngerIssues]

5.86 and 35s work out nicely, putting top speed in the 100mph range, though maybe 5.38s would give a little more margin and I wouldn't have to push the engine so hard - but I've seldom been in a spot where the course was straight enough long enough to hang on to 100mph.

Would YOU consider 5.86s? Have you run 5.38s with good results in a race truck with a D44 front end?

I've gone through a few sets of balljoints, and only one axle shaft that bent when the housing broke in half.. otherwise, the front has held up fine with stock components inside.


What kind of revs would you be hitting at 100 mph with 5.38's? That seems pretty darn fast for that ratio. I'm at 4.88s / 4.86's and although i don't really push my motor TOO hard, getting up to and beyond 100 is high enough in the revs for me (not to mention I don't like to look at the tach and my wb is probably longer than yours). You said it, there aren't many spots you can hang on for long at that speed, that is for sure. I can think of very few in SCORE, for example.

I personally wouldn't go that low. I am very happy with my gearing. How many speeds you running, 3? Anyway, I seldom wish I was lower-geared. I also have the two-speed trans-case if the rubicon pops up or things are going painfully slow for some reason. That would be very rare also.

ken

[tsm1mt]

What kind of revs would you be hitting at 100 mph with 5.38's? That seems pretty darn fast for that ratio. I'm at 4.88s / 4.86's and although i don't really push my motor TOO hard, getting up to and beyond 100 is high enough in the revs for me (not to mention I don't like to look at the tach and my wb is probably longer than yours). You said it, there aren't many spots you can hang on for long at that speed, that is for sure. I can think of very few in SCORE, for example.

I personally wouldn't go that low. I am very happy with my gearing. How many speeds you running, 3? Anyway, I seldom wish I was lower-geared. I also have the two-speed trans-case if the rubicon pops up or things are going painfully slow for some reason. That would be very rare also.

ken

3spd 727 auto for the transmission.

With 5.38s, 35s, at 6000rpm I'd be doing 116mph (leaving out slippage in the converter, the fact that the tires are a little shorter than a true 35, etc)

A change to 5.86s puts it at 106mph.

4.88s, like I run now, 128mph at 6000rpm with 35s. (I currently run 31s, which is 113mph)

I want to do a few long distance desert races, but mostly I run CORR-like events.

Occasionally, even smaller/tighter courses.

I can remember running 80-85mph at times last year, so my thought is, if I'm not going to use the top end of 3rd gear, why not lower the ceiling?

Lower gears = better acceleration, and if I don't need the top speed, then gear down.

The valves were floating at 6300rpm before I overhauled it this winter - with heavier springs in place, maybe there's more RPM in it. As it was, I'd hold it at 6300rpm for long stretches, and it held together just fine.

My biggest concern with going too-low on the gears is going too-weak on the gears.

To that end, I was contemplating 3.08s and just leaving it in low range, but then I'm always paying the price of the losses in the gears, along with an inability to actually have a "real" low range for a short/tight area.

[AngerIssues]

What "type" of racing... I guess would have been a great point.

We RARELY ever get anything that flat in SCORE, can't run on any pavement that fast anymore, and except for an occasional dry lake bed, if you are going more than 85 you have a really odd spot in the course - at least that is my thinking.

I don't push my motor that hard, but we run 300, 400, 500 and more miles.

Great point about "if you don't need the upper end"... why not go lower.

I've been very happy with 4.88's. I have no interest in going lower, nor have I had any breakage issues (beyond what one might expect for what we do).

I've gone through 4 or 5 transfer cases now... but never during a race until Primm. I might have to go to the NP 205 that is cast...and heavy as I understand it - but no chains?

[tsm1mt]

What "type" of racing... I guess would have been a great point.


My concern is more the strength of the gears than the overall choice of the gearing.

4.88/31s works fine, though I'd like to be a little lower. Going to 35s won't help that situation. :)

Wide open desert to race on is hard to come by around here, but there's a track built with the intention of racing CORR/WSORR available. On the groomed course, 80+mph is attainable.

The majority of my competition are 2wd trucks, and they're running 6.x gears in their rear 9"-ers with 35" tires.

We RARELY ever get anything that flat in SCORE, can't run on any pavement that fast anymore, and except for an occasional dry lake bed, if you are going more than 85 you have a really odd spot in the course - at least that is my thinking.


Glad to hear that - I have hopes of heading south at least once, and while I don't mind holding the engine between 5-6k for an hour, I'm not sure about doing that for a few hundred miles.

I've gone through 4 or 5 transfer cases now... but never during a race until Primm. I might have to go to the NP 205 that is cast...and heavy as I understand it - but no chains?

Yep, the 205 is all gear driven, no chains to stretch or jump a tooth or anything like that.

It also has a nice 2:1 (1.96:1) low range that gives a decent top-speed when in low range (vs most of the ~2.7:1 cases).

Depending on just how much power you're pushing and your choice of transmission, you might also get away with a Bronco Dana 20, or the earlier full-size truck Dana 21 single-speed case (divorced, IIRC).

The Bronco 20 is still gear driven, but lighter than the monster 205.

[straightaxle]

Yes, I would worry about the strength of the pinion gear a little, but most of our problems have been with the spider gears. They have more stress on them than the pinion. All the ring and pinions that we have changed have been because of the spider gears falling into them. I would say you would probably be fine.