4:88s, not so popular, but gonna try it

GrayBeard

New member
Well, after debating for several months and reading all the post for and against regearing for the JLUR with 37's, I've decided to pull the plug and buy a set of Spicer 4:88's. I also pull a 3000 lb trailer, plus normal off-roading gear at times.

I figured why not, somebody needs to try it and see if there is a noticeable difference and if so worth the cost.

Luckily, I have a friend at a dealership, who is able to give me a break on installation with cooperation from the dealership, in exchange for publicity for a very Jeep friendly dealership.

So, I'll let you know, what I think of the change.

Gears are shipped and scheduled to be arriving next week 🤞. I also ordered a Rancho Front Diff Skid Plate at Eddie's post recommendation, however they're listed as "Back Ordered".

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GrayBeard

New member
Hmm, if I had to regear, I’d probably go with 5.13 as 4.88 is too close to 4.10 but, I’d be willing to bet you’ll be happy with it. Hell, I’m plenty happy with 4.10 [emoji41]


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Thanks, thought long and hard over 5:13 or 4:88. I guess cause I unfortunately I do more highway/city driving than off roading [emoji852] plus pull the trailer figure 4:88 would work best for me. Plus 37s is the biggest I'm going.

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13_gecko_rubi

New member
Thanks, thought long and hard over 5:13 or 4:88. I guess cause I unfortunately I do more highway/city driving than off roading [emoji852] plus pull the trailer figure 4:88 would work best for me. Plus 37s is the biggest I'm going.

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The thing is with 4.88s you'll still be dropping into 7th a lot esp towing. With 5.13s you'd stay in 8th. I always tell everyone whatever you thought was good for a JK, go one deeper. That's because 8th (double OD) is only 0.67:1. I've told several people do 5.13s for 37s and got a lot of "no way". Every one that has listened said thank you. If I was building a mainly wheeling JL I'd use 5.38s for 37s.

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NFRs2000NYC

Member
So you're saying 5.13s will bring a 37" wrangler closer to the performance of a stocker on 410s? No concerns over a weaker pinion due to the size?
 

JeepJL

New member
Hmm, if I had to regear, I’d probably go with 5.13 as 4.88 is too close to 4.10 but, I’d be willing to bet you’ll be happy with it. Hell, I’m plenty happy with 4.10 [emoji41]


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I was super happy with the 4.10s also until I changed my exhaust and realized how much the tranny was hunting for gears or only using max of 6th on the interstate. I didn’t even realize it until I could hear the motor with the aftermarket exhaust. Goes to show how smooth and soft that transmission shifts. Needless to say I wasn’t ready to re-gear quite yet due to limited options so I put the factory exhaust back on and now I’m back to not needing to re-gear. [emoji13]


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JeepJL

New member
The thing is with 4.88s you'll still be dropping into 7th a lot esp towing. With 5.13s you'd stay in 8th. I always tell everyone whatever you thought was good for a JK, go one deeper. That's because 8th (double OD) is only 0.67:1. I've told several people do 5.13s for 37s and got a lot of "no way". Every one that has listened said thank you. If I was building a mainly wheeling JL I'd use 5.38s for 37s.

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I was a huge fan on 5.38’s on 37s with a JK. I got the same thing, Thank you for those that did it. They were amazing on the highway, would pull hills in 5th all day long. That 3.6 was made to run scary hot and high RPMs. [emoji1360][emoji1360]


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Hooligan_JL

New member
I will have 37’s soon and also pull a 3,000 pound expedition trailer. Very interested to know how things work out for you. I wasn’t planning on regearing as everything I’ve read seems to indicate that the 8 speed can handle it very well. Please update once done.


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Jesse_01

New member
We are running 5.13 & 37" Cooper's. Around town there is lots of hills, it never see's 8th. Mainly 1-6. Oh the highway it down shifts awfully early from 8 to 7 on the slightest grade.

If a person wants see 8th even on slightest grade you would go 5.38.

If I could regear again, I would go 37" & 5.38.

Here is your ratio & tire comparison to stock

IMG_2561.jpg


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13_gecko_rubi

New member
We are running 5.13 & 37" Cooper's. Around town there is lots of hills, it never see's 8th. Mainly 1-6. Oh the highway it down shifts awfully early from 8 to 7 on the slightest grade.

If a person wants see 8th even on slightest grade you would go 5.38.

If I could regear again, I would go 37" & 5.38.

Here is your ratio & tire comparison to stock

View attachment 7939


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Ya if I were to do it myself I would do same and go to 5.38s. In future may have to do fabbed 9s on the JL just so i can get into the 6.xx ratios for 40s :)

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wayoflife

Administrator
Staff member
I'm sure it's just me and based on personal experience but I would never run 5.38's in a 44. The numbers may be right but the pinion is just too small or at least, for my taste and from what I have seen.
 

wayoflife

Administrator
Staff member
I'm sure it's just me and based on personal experience but I would never run 5.38's in a 44. The numbers may be right but the pinion is just too small or at least, for my taste and from what I have seen.
 

wayoflife

Administrator
Staff member
I should also note that of the JL's I've seen running 5.38's and 40" tires, none have seemed to perform that great. I don't know if it's a shift point issue or what but for instance, Tom from PSC was having a hell of a time keeping up, even on the highway when climbing grades. I could literally hear his JL bogging down and then hunt for gears all the time. Granted, he was running heavier axles and pushing 40's but I would have thought the 5.38's would have more than made up for the difference. It was almost as if he were running an old JK with a 3.8L - ask me how I know. :rolleyes2:
 

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