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Cheap re-gear/more speed on 31's?

H

HenryKrinkle

NAXJA Forum User
Location
WI
I understand this topic may come up a lot, so please bear with me if you can. I have an '88 that is a solid runner with no lift. I trimmed fenders and got 31" BFG's on. The problem is it is REALLY slow. I am planning a trip with lots of fast freeway driving. I'd like to keep the tires, so short of going smaller there, is there anything I can do? The rear axle is not a D44, so I'd rather not dump a lot into building up. I think a re-gear without a locker is the best idea, unless there is a street-friendly locker that is real cheap (doubt it). If you think I'm right about the straight re-gearing, could you point in the direction of a good supplier with reasonable prices?
Any help is much appreciated.
Thanks
 
I'm assuming you've got a 4.0 with the AW4 automatic. In this case, your cheapest (but not neccesarily fastest) route is probably going to be the junkyard. Look for a 4-cylinder XJ with manual transmission. Chances are it has 4.10s (check, but this should be the case); either take the entire axles or open up the diffs and grab the gears at your discretion.
 
Is yours a 4 cyl. or 6 cyl.? Is it an auto or manual? You can scrounge the junkyards for lower geared axles and do a swap. Typically you can find that the 4 cyl. rigs had 4.10 gears, 6 cyl. manuals had 3.07 gears and, 6 cyl. auto's had 3.55 gears.
 
If you are going to pay a shop to re-gear both axles, then parts/labor will cost more than buying two used axles from a salvage yard with the gearing you want.

3.07--used with 4.0L engine / manual transmission
3.31--only available on older (pre87?) 2 door XJs with "Fuel Economy" package
3.55--used with 4.0L engine / automatic transmission
3.73--found in some XJs with the towing package
4.10--used with 2.5L engine usually, and older XJs with the "Off-Highway Vehicle" package.
 
Here we go again...:doh:

4.10s were only found in 2.5L / AX5 XJs. Meaning if it has an AX4 it does NOT have 4.10s (and yes there were 2.5L / AX4s). I've never heard of the "off-highway vehicle" package. Not saying it doesn't exist, but who here owns or has seen one? If it was an elusive 2.5L / AW4 it had 4.56s.

I've seen a few examples of either of these first hand. I've PERSONALLY pulled a D30/8.25 set from a rolled '94 2.5L/AX5 XJ that had 4.10s at a JY. I've also PERSONALLY popped the covers off TWO sets of D30/D35s from 2.5L/AW4 XJs that had 4.56s at a different JY.
 
For one trip on the highway, I wouldn't do anything. Maybe run the trans in "3" while you're cruising. That will essentially have the same effect on your highway travel as regearing.
 
Mine's an I6 4.0 auto- so I'm at 3.55. I will need to do the front and rear, correct? Junkyard or used may be an option, but I'll already have to do the swap in a cold garage (WI), so I might have to just order them. I have a Haynes manual, so I'll start reading there.

Anyone happen to have a link with a good write-up on this?
 
gw204 said:
For one trip on the highway, I wouldn't do anything. Maybe run the trans in "3" while you're cruising. That will essentially have the same effect on your highway travel as regearing.
Click to expand...

"3", huh. I guess I never really thought of that:wierd:. The trip is about 1k miles, anyone think that would be a bad idea? I'll do a transmission flush before hand. Thanks for the tip! That would really simplify this whole thing for me!
 
gw204 said:
For one trip on the highway, I wouldn't do anything. Maybe run the trans in "3" while you're cruising. That will essentially have the same effect on your highway travel as regearing.
Click to expand...

Except that it's going to hurt fuel economy (like any XJ needs worse mileage), will change the torque converter behaviour, and cause the tranny to run at higher temperatures. Will it work? Sure. But it's not a solution.

HenryKrinkle said:
Mine's an I6 4.0 auto- so I'm at 3.55. I will need to do the front and rear, correct?
Click to expand...

Yes. Both ends will have to be done.

Junkyard or used may be an option, but I'll already have to do the swap in a cold garage (WI), so I might have to just order them.
Click to expand...

If you're not comfortable with setting gears up yourself, axles may be a better bet. Just something to consider.

Check the search for more info regarding doing it - there's been a lot written here about regearing.
 
i have seen two xjs at the junkyard with 2.5L AW4. one was two wheel drive with 4.56 D35 and the other had 4.10 D35 and missing the front axle.
 
casm said:
Except that it's going to hurt fuel economy (like any XJ needs worse mileage), will change the torque converter behaviour, and cause the tranny to run at higher temperatures. Will it work? Sure. But it's not a solution.
Click to expand...

Not necessarily all of the above. Different scenario, but I think it applies... My brother and I just towed my old 8000 lb. boat 300 miles with his '08 GMC Sierra HD. We ran the trans in both Drive and "3" at times. In Drive we did record slightly better economy, but "3" resulted in fewer shifts/more power and lower trans temps (he has a factory trans temp readout).

My '00 4.0/AW4 locks the TC in 3rd when I run in "3" so it won't hurt anything other than your wallet... The increased fuel consumption won't cost nearly as much as 2 sets of gears and installation.
 
gw204 said:
Not necessarily all of the above. Different scenario, but I think it applies... My brother and I just towed my old 8000 lb. boat 300 miles with his '08 GMC Sierra HD. We ran the trans in both Drive and "3" at times. In Drive we did record slightly better economy, but "3" resulted in fewer shifts/more power and lower trans temps (he has a factory trans temp readout).
Click to expand...

Sure, and I see where you're coming from on that. However:

My '00 4.0/AW4 locks the TC in 3rd when I run in "3" so it won't hurt anything other than your wallet... The increased fuel consumption won't cost nearly as much as 2 sets of gears and installation.
Click to expand...

Long-term, the savings of doing the gears makes more sense from the financial, livability, and wear-and-tear standpoints. I'm in a 2000 on 4.10s with 31" tyres, and ran 3.55s for about a year after putting the 31s on; the 4.10s have more than paid for themselves by now just in fuel savings. While the cost of recouping the gears (or axles) won't be made back on his 1000-mile trip, it'll be a good start at offsetting it, and will have him taken care of for the foreseeable future given the tyres he's running.
 
4 cyl. D30 and a Ford 8.8 thats 4.10 axles for less than half the cost of regearing. Takes a bit of work to get the rear axle to fit but 31spline axles, LS and disks would be worth it to me.
 
i would regear to either 3.73 or 4.10....i would look for a Ford 8.8 with either of these ratios and LSD ('97+ will have disc brakes)....then get the new carrier, ring, and pinion for ur front D30 (grab some '96+ front shafts too for the larger u-joints while ur at the pnp)
 
so is a ford. 8.8 a direct swap then?

If so i'd like to go this route someday when I get ready to lift my new to me Jeep. It'd be a lot cheaper to get 4.10 gears that way.

What vehicles would I be looking for to find the 8.8 and 4.10's?
 
A 8.8 is not a bolt in swap. You need to flip the spring perches from SUA to SOA. Ruff Stuff has 8.8 install kit that comes with perches, u-bolts, shock tabs. As far as finding an 8.8 with 4.10s look for 1997-2001 (those years come with disks). I have heard you want one from a 2 door.
 
The 8.8 is a popular swap. It is NOT a direct bolt in. You need to cut and move the spring perches to fit the XJ. Then you have to adapt the brakes system to work with the rear discs. Search "Ford 8.8" and you'll get a lot of hits. If you don't want to "waste money on your current axle, it wold probably be cost effective to do the 8.8.

You can drive the AW-4 long distances in "3" without hurting it. The TCU sees the shifter position, and locks the torque converter just like it would in drive. No extra heat generated.
 
Thanks everyone for the advice. The 8.8 with discs swap will hopefully happen sometime down the line, but for now I'm very glad to just put her in 3. Now for that damn cracked exhaust manifold....:roll:
 
HenryKrinkle said:
Thanks everyone for the advice. The 8.8 with discs swap will hopefully happen sometime down the line, but for now I'm very glad to just put her in 3. Now for that damn cracked exhaust manifold....:roll:
Click to expand...

I recently installed an 01' intake manifold (equal length runners) and an APN style header on my 98' that has 4.10's and 33"x12.50's and I always felt like I should have gone with 4.56:1 gears but I had such an increase in power and torque after the intake&exhaust install that I'm really happy with the setup now. I've got more power, torque and a few more mpg's to boot.

I got my header for $180 from rockauto.com and my intake manifold from a local junk yard for $35 and since your going to have the manifld off anyway to do the exhaust it just makes sense to do the intake. It's not regearing but it is a substantial increase in power, performance and mileage incease. Also it's in your budget and something you can do yourself, it is a pain in the ass but well worth it.

Good luck on whatever you decide.
 
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