'86 Comanche Rear Axle Ratio 3.54 Or 3.55?

[tleed]

My '86 Comanche was a V6 automatic. The engine is dead, may it rest in peace. I'm trying to ID the axle ratio. I turned the back wheel and it comes up to approximately 3.5 revolutions of the driveshaft for every 2 wheel revolutions. Apparently that rules out all the ratios that are 3.31 and down and 3.73 and up.

 

But in my reading, I've seen 3.54 and 3.55 axle ratios as factory options for that year. But I've seen more 3.55's. Is the 3.54 a misprint, or were both axle ratios actually available for that year? If they were both available, is there a way to distinguish the two besides pulling the differential cover? When I was under there counting revolutions, I didn't think to look for a tag...

 

I'm contemplating an axle swap from a Ford Explorer in the hopes that it will stand up to the 5.7 liter LS1 I'm prepping to transplant into it. Anybody know if 3.54 and 3.55 ratios fairly common in those Fords?

[Pete M]

essentially they are the same ratio.  the differing numbers are from different size axles that have slightly different numbers of teeth on the gears.  :thumbsup:

[Pete M]

for example:

ratio --> teeth count

4.11:1 ---> 37/9,

4.10:1 ---> 41/10,

4.09:1 -->  45/11

 

 

all are, for all practical purposes, the same ratio

[tleed]

Well, if I'm trying to match a front axle ratio to a rear axle ratio, is the difference material? I'm anticipating using an NP229 transfer case. I'm a little leery that the mysteriously magic and kinda expensive viscous coupling in that case will burn up with slightly mismatched ratios. (And please don't turn this thread into a transfer case discussion with that disclosure. I'm really trying to focus on axles here.)

[Pete M]

the difference is minute compared to differences in tire tread thickness.  won't matter at all. :D

[tleed]

I like that response. And apparently 3.55 Ford 8.8 gear sets are plentiful in the aftermarket.

[Eagle]

Well, if I'm trying to match a front axle ratio to a rear axle ratio, is the difference material? I'm anticipating using an NP229 transfer case. I'm a little leery that the mysteriously magic and kinda expensive viscous coupling in that case will burn up with slightly mismatched ratios. (And please don't turn this thread into a transfer case discussion with that disclosure. I'm really trying to focus on axles here.)

They are the same. The reason you see references to both is that the 4WD trucks had both. In the same truck.

 

Remember, the front Dana 30 has a smaller ring gear and a smaller pinion gear than either a D35 or an AMC 20 (since you have an '86, the AMC 20 was the optional, heavy-duty rear axle). Because of the size difference, it isn't possible to make both with exactly the same number of teeth on both gears. So we get "mismatches" to the second decimal: 3.54 / 3.55, 4.10 / 4.11, etc.

 

They came that way from the factory. That slight difference doesn't matter.

[Pete M]

3.73 or 4.10 would give even more punch :D  also very common in the explorer 8.8s.

[HughMann]

You can safely run 3.50's and 3.56's at the same time so 3.54 and 3.55's are fine.

[Incommando]

I have had jeeps with 4.27's in the front and 4.30's in the rear from the factory so that much difference is for sure acceptable.

 

It sounds like maybe that '86 is 2wd. If it is then there is no added expense to a ratio swap and no real reason to stay at 3.55. ( OOPS EDIT: I see in the sig it is a 4x4. Staying with 3.55's saves re-gearing the front) I,too, think that a swap in ratios would best be made now. If you are changing engines there is no good reason for trying to stay within the stock parameters.

 

When looking for an 8.8 search for a V6 Explorer over a V8. Both 8.8's are the same but for some reason junkyards often price the axles from V8's higher. There is a $20 difference in the closest PnP here.

[HughMann]

I have had jeeps with 4.27's in the front and 4.30's in the rear from the factory so that much difference is for sure acceptable.

 

It sounds like maybe that '86 is 2wd. If it is then there is no added expense to a ratio swap and no real reason to stay at 3.55. I,too, think that a swap in ratios would best be made now. If you are changing engines there is no good reason for trying to stay within the stock parameters.

 

When looking for an 8.8 search for a V6 Explorer over a V8. Both 8.8's are the same but for some reason junkyards often price the axles from V8's higher. There is a $20 difference in the closest PnP here.

I was looking at Car-Part last night and the price diference between a V8 8.8 with 3.55's and the V6 with 3.55's was at least $100.

 

also some bronco's came with 3.50's up front with 3.55's out back from the factory.

[benjy_26]

Personally, I'd get myself a 3.73 or 4.10 8.8 and re-gear the front. I meam, if you're regearing one axle anyway, might as well improve the situation all around.

[tleed]

Funny you should say that about the V6 v. V8 axle prices. I just had my local junkyard tell me this morning that they're two different axles But that guy also told me they're both 8.8. I guess the books show different part numbers or something. Sounded funny to me, but I didn't know enough to argue at the time. Now I suppose I don't want to argue with that.

 

I found a limited slip disc brake 3.73 225k-mile Ford 8.8 axle for $200. Looks like I can re-gear it to 3.55 for about $200, which doesn't sound too bad for an axle with new gears. I'm building this engine for low-end torque more than high hp. I'm not a drag racer and I'm thinking I'd rather stick with the 3.55 for mileage purposes. I'm thinking a 5.7 LS1 is plenty to push that ratio with an NV3550  5-speed. I had a Miata with 4.11 gears. That thing would wind into the heavens, but it was so buzzy at 75 it drove me crazy…almost.

[Pete M]

and how big were the tires on that miata? :D don't discount tire size into that equation.  I've got 3.92 gears and roughly 29" tall tires in my Dakota R/T and never thought the rpms were that high on the freeway.  with 30 or 31" and 3.73 gears it should be juuuuuust fine.  :D 

[Eagle]

and how big were the tires on that miata? :D don't discount tire size into that equation.  I've got 3.92 gears and roughly 29" tall tires in my Dakota R/T and never thought the rpms were that high on the freeway.  with 30 or 31" and 3.73 gears it should be juuuuuust fine.  :D

3.73 gears with 31x10.50 tires is exactly the same as stock tires with 3.55 gears. I think 3.73s are the optimum ratio for 325/75 and 30x9.50 tires, but even for 31s IMHO 4.10s are a much better choice. With a 5-speed, the engine will NOT be "buzzing."