Jump to content

Gear Ratio advice


Recommended Posts

I know this has been discussed a million times but I just found out what my gear ratio is and I know nothing about this. It is 3.08. I am not sure but I think that sucks and wanted everyone's advice.

 

My truck originally came with 225 tires and I recently added 235's. The engine barely runs as I go down the highway. But if I am going 60mph and climbing a hill, I could easily downshift.

 

What is optimal for highway use on 235 tires and is the ratio easy to swap on both axles with new parts or would I need to get them at a junkyard? I have a d44 on the rear and no idea on the front.

Link to comment
Share on other sites

Ideal ratios, are somewhat dependant on your engine as well as tranny combination. Then, we will need to know what is your final tire size you will be running.

 

If your feeling such a difference going up one size in diameter, I'm going to guess you have a 2.8L or a 2.5L engine. Even then, your engine is likely tired to feel such a difference for such a small change.

 

You say you have a D44, it would sux to loose that, so a gear change or a hunt for another with better gears would be tops on my list. 4 Cyl trucks got you better gearing, but not always the D44. XJ's seem to be a bit more common here if for D44's at the rear. BUT, they will not swap directly in, but over all not too hard to make them work.

 

CW

Link to comment
Share on other sites

If you have 3.08s you must have a 5-speed. The 4.0L automatics came with 3.54 gearing, and for street use with 235s that's probably a good choice of ratio. You can get a front axle in that ratio out of any wrecked Cherokee or Comanche with an automatic and 4.0L. However, although any year front axle will bolt into your truck, there are differences in hubs, rotors, calipers and knuckles from year to year so it will be important to know what you're getting and make certain that ALL of those parts are compatible.

 

Also, later model front axles and any from a Cherokee with Selec-Trac won't have the front axle disconnect. That's actually an advantage (one less thing to fail), but you'll have to plug the unused vacuum port.

 

And you'll probably have to bite the bullet and buy new gears for the rear axle, since Dana 44s are getting hard to find.

 

If you think you might move up to 30x9.50 tires, I would suggest 3.73 gears. However, it's unlikely you'll find that ratio in a junkyard Cherokee or Comanche.

Link to comment
Share on other sites

Tough call. Are you planning on anything bigger in the future? Small lift and 31s maybe? It costs so darn much to change ratios in an axle that it almost seems a waste to change the 44 to only 3.55 or 3.73. :(

 

How much highway travel does the truck see? How much longer do you think the truck will be on this duty? How much money do you have available for this endeavor? How new are the brakes in your current axles? Any major work done to them recently?

Link to comment
Share on other sites

Sorry about this. I see now I left out a lot of important information. Yes it is the '87 4.0 5 speed. 3.08 is how it was geared from the factory. I don't quite understand why they would have geared it the way they did.

 

I don't see ever going to tires larger than the 235 (I don't know how many inches that translates to). The truck atually has an easy life. I don't intent to ever get rid of it and it is not my primary driver. In other words, it is a toy. The only problem is I am an idiot when it comes to cars so any time I need something repaired, I need to take it somewhere.

 

I am sort of hearing people say it is a PITA to change the gearing in the front/rear unless I get lucky at a junk yard? Are the parts not available new?

 

I would bet that is the worst gear ratio they put in these. Would you agree?

Link to comment
Share on other sites

Sorry about this. I see now I left out a lot of important information. Yes it is the '87 4.0 5 speed. 3.08 is how it was geared from the factory. I don't quite understand why they would have geared it the way they did.

 

I don't see ever going to tires larger than the 235 (I don't know how many inches that translates to). The truck actually has an easy life. I don't intent to ever get rid of it and it is not my primary driver. In other words, it is a toy. The only problem is I am an idiot when it comes to cars so any time I need something repaired, I need to take it somewhere.

 

I am sort of hearing people say it is a PITA to change the gearing in the front/rear unless I get lucky at a junk yard? Are the parts not available new?

 

I would bet that is the worst gear ratio they put in these. Would you agree?

 

Its only a pain because its time consuming and the result is costly. Generally NOT a job the shade tree mech can accomplish.

 

In reading your uses of your MJ, I have another suggestion. You could find a complete vehicle with better axle gearing, and swap in both axles. Then sell your D44 to fund the whole project!! Now, the D35 gets a bad rap, sometimes rightfully so. But in stock trim, IE your 29" 235's tire size make this make sence. The D35 is quite likely all the axle you will ever need. Personally, I would look for a pre 1989 vehicle so you can get the stronger non "C" Clip axle with bigger brakes. A set with 3:55 gears will be a nice upgrade, its harder to locate a set with 3:73's, but if you want to jump to 4:10's look for 4 cyl auto vehicles.

 

CW

Link to comment
Share on other sites

My Cherokee has 3.07 gears with a 4 litre and AX15 5 speed. I can smoke the tires in 1st, 2nd and 3rd. 4th I can't, but driving like that I'm already doing 70 by the time I hit 4th. I can put down a skid mark in 1st for well over 300 feet.

 

More commonly, I shift early. It has no trouble cruising 20mph in the alley in 3rd, 30mph on side streets in 4th and 40mph on the main drag in 5th. That's with 235/75R15 tires, which are roughly equal to a 29x9.50.

 

My Comanche has the 4.0 with an AW4 4 speed automatic and 3.55 gears. That combination worked good with the 235/75R15 tires that came with it when I bought it, but sucks on the freeway now that I run 33x12.50s. Cruising around town is not that bad, though, and I can still peel out from a still stand in a straight line -even if only for 20 feet or so. Will be going to 4.10 at some point in time. The current 3.55s will end up going under the Cherokee when it gets bigger tires.

Link to comment
Share on other sites

In other words, it is a toy. The only problem is I am an idiot when it comes to cars so any time I need something repaired, I need to take it somewhere.

If you're not set up to do the work yourself, and you don't plan to go larger than 235/75R15 for tires, I'd suggest you leave the axles alone. I have over 280,000 miles on a stock 1988 Cherokee with the 3.08 axles. I have moved up in tire size since it was new. It has seen a lot of miles with 235/75s, and when I was using it off-road I ran it with 30x9.50s. That was far from ideal on the trail, especially rock crawling, but it was quite livable on the street. At the moment, while I'm getting some other tires mounted, the XJ is wearing a set of 31x10.50s from my MJ.

 

Sure, more gear would be better, but 235s aren't enough bigger than stock tires to make it absolutely necessary to change gearing. To do the swap, any way you might approach it, you're looking at several hundred dollars. IMHO it doesn't make economic sense for your situation.

Link to comment
Share on other sites

Thanks guys. jamminz.gif

 

If I recall correctly, Dana put a tag at the diff to indicate which gears were installed. Because I live in Indiana, they would be rusted beyond recognition. If I did find some axles, how would I know if they 3:73 verses 4:10?

 

Is it safe to say that 3:73 is perhaps the best for all around use?

 

Also, my diff has limited slip. Is that comon or would I most likely be giving that up?

Link to comment
Share on other sites

3.73 can sometimes be found in a Grand Cherokee with the towing package. But only the front axle would work, the rear would be set up for a 5 link coil spring suspension. 4.10 is very common on 4 cylinder (2.5 Litre) Comanches and Cherokees with a 5 speed stick shift. And yes, you would most likely be giving up your LSD. 4.10 is also a common ratio for the much stronger, but a bit narrower Ford 8.8 out of mid/late 90s Exploders, and these can come with LSD also.

 

But in my opinion, for s stick shift 4.0 with 29" tires, 4.10 is way too high a ratio. If you really do want to go up, I would not go higher than 3.55. That can be found in any 4.0/auto. If you get a rear axle out of a hard to find Comanche you would not have to weld on new perches. If you can find an impossible to find metric tonne one, it would have a D44 in the rear. Also a lot of 91 and 92s have a D44 under them. Best choice in my opinion is to get the HP Dana 30 front axle out of an XJ with ABS. High pinion, but stronger u-joints. Get a rear 29 spline 8.25" out of a 97 or newer XJ, cut off the perches and shock mounts, and have new perches welded on in the correct location. If you need more traction, spend $300 on an Aussie locker for the rear, or $230 for the front. Or both :eek:

Link to comment
Share on other sites

Thanks guys. jamminz.gif

 

If I recall correctly, Dana put a tag at the diff to indicate which gears were installed. Because I live in Indiana, they would be rusted beyond recognition. If I did find some axles, how would I know if they 3:73 verses 4:10?

 

Is it safe to say that 3:73 is perhaps the best for all around use?

 

Also, my diff has limited slip. Is that comon or would I most likely be giving that up?

There is usually a tag on the front differential. There usually was NOT a tag on the rear differential.

 

Everyone's idea of the "ideal" gear ratio is different. And a lot depends on how you plan to use the vehicle. If you plan on a lot of high-speed highway cruising, you might want a ratio that'll keep the RPMs down somewhat and yield (maybe) better gas mileage. If the truck is a weekend warrior and won't see a lot of highway use, more gear makes it more driveable at lower speeds.

 

For comparison, based on 235/75R15 tires, here are the RPMs in 5th gear for 65 MPH with different gear ratios:

 

3.08 ==> 1724

3.54 ==> 1988

3.73 ==> 2095

4.10 ==> 2303

 

To put that in perspective, my 1966 Rambler American with a 3-speed manual tranny, 3.08 gears and small-ish tires ran 2500 RPM at 60 MPH, and 3000 RPM at 72 MPH. And it would cruise happily at 72 MPH all day. You can easily run 4.10s with the 235s and not be concerned that you're "burning up the engine."

Link to comment
Share on other sites

But in my opinion, for s stick shift 4.0 with 29" tires, 4.10 is way too high a ratio. If you really do want to go up, I would not go higher than 3.55. That can be found in any 4.0/auto. If you get a rear axle out of a hard to find Comanche you would not have to weld on new perches. If you can find an impossible to find metric tonne one, it would have a D44 in the rear. Also a lot of 91 and 92s have a D44 under them. Best choice in my opinion is to get the HP Dana 30 front axle out of an XJ with ABS. High pinion, but stronger u-joints. Get a rear 29 spline 8.25" out of a 97 or newer XJ, cut off the perches and shock mounts, and have new perches welded on in the correct location. If you need more traction, spend $300 on an Aussie locker for the rear, or $230 for the front. Or both :eek:

 

Hey! Sounds like my truck! :D

Link to comment
Share on other sites

But in my opinion, for s stick shift 4.0 with 29" tires, 4.10 is way too high a ratio. If you really do want to go up, I would not go higher than 3.55.

Just an FYI for terminology... A 4.10 ratio is a lower ratio than 3.55. When talking about gears, the higher number means lower gear ratio. :thumbsup:

 

From my experience, 3.55 gears would be the optimum ratio to run if you are not going any larger than a 235. The high rev from the 4.10's wll not damage the engine, but it is quite annoying...I have been there--done that, and it sucks.

Link to comment
Share on other sites

hey i got a 88 comanche 4.0L with a d 44 and d 30 and the gears are 3.08s and i have 31X10.5 all terrians. yes i know that is very $#!&ty indeed. but any ways i am getting some 32s or 33 super swampers in a little while and i don't travle very fast mabe 55 60 mph tops and i want some 4.10s or 4.88s would this be to high of a ratio?

Link to comment
Share on other sites

hey i got a 88 comanche 4.0L with a d 44 and d 30 and the gears are 3.08s and i have 31X10.5 all terrians. yes i know that is very poo indeed. but any ways i am getting some 32s or 33 super swampers in a little while and i don't travle very fast mabe 55 60 mph tops and i want some 4.10s or 4.88s would this be to high of a ratio?

FWIW, 31x10.50s with 3.73 gears turn EXACTLY the same RPMs in 5th gear as a stock XJ or MJ on stock tires with the 3.55 gears. That's a decent combination for street use and light trail use, but not really enough gear for moderate to serious off-road use.

 

IMHO, "ideal" ratios would be 3.73 for 30" tires (which was the plan when I bought the 3.73 gears), 4.10s with 31s, 4.56s with 32" tires, and 4.88 gears for anything larger than 32".

Link to comment
Share on other sites

well the i thin i will get some 4.88 gears then but what will the top speed be? just wondering

 

 

Well above the legal limit. :D

 

I've got 4.10s and 33s and while it's ok, I'd like to have a bit lower gear. 4.56 make for a good compromise. :thumbsup:

 

Oh, and 4.88 is a lower gear ratio than 3.08. Higher number = lower ratio

Link to comment
Share on other sites

well the i thin i will get some 4.88 gears then but what will the top speed be? just wondering

 

 

Well above the legal limit. :D

 

I've got 4.10s and 33s and while it's OK, I'd like to have a bit lower gear. 4.56 make for a good compromise. :thumbsup:

 

Oh, and 4.88 is a lower gear ratio than 3.08. Higher number = lower ratio

 

 

I have 4:10's in the TJ with a 5SPD and am currently running 33AT's. The thing goes like a rapped ape!!! But its newer, with less miles and has to be producing more power than my MJ. The MJ has 4:56's with an AW4, and again, 33" tires. But this time MT's. While its no slouch, its not nearly as peppy as the TJ. :D

 

There is allot of personal opinions going on here. Your best commonality IMHO is actual engine RPM's at speed. As Eagle has listed for you. Target a bit more RPM for a bit more power but lower mileage.

 

CW

Link to comment
Share on other sites

Well, everyone grab your chest because you may feel some chest pains coming on. I asked about how much it would cost (at a dealer) to change the ratio. $1,200 per axle. :ack:

Yea...the gear sets alone are $500 +/- each at the dealership. You can get both axles done in the aftermarket for $1200 easily...and probably less.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...