Is there a benefit in changing from a 4 speed to a 5 speed when re-gearing
 

My current XJ is a 2.5 liter 4 speed with 3:55 gears and a 3 1/2" lift. This is not a DD and I am wanting to go to at least 31"x10.50 tires, maybe more I don't know. We mainly use the little XJ for pleasure riding fire roads and the such, no extreme rock crawling. I want to re-gear just to make life a little easier on the 2.5 liter when I go larger tires. My current thought is to go 4.10 maybe 4.88 depending on final tire size.

I have a 5 speed in a 84 XJ and am considering swapping it into my 86 4 speed XJ. My question is: Is there any benefit in doing the swap? Is there any major issues in doing the swap?

Just a little something I'm kicking around for a winter project this year.

I appreciate all your opinions and thoughts.

Happy Jeepin'
TexasTaz38

You shouldn't have any trouble changing it all over. What really counts is the final drive ratio of the transmission. The 5 speed I think has a 25% overdrive, where the 4 speed has 1:1 final ratio. So yes, you will need the taller gears with the 5 speed on the 31s

As 4.3L XJ stated, the difference between the two transmissions is overdrive in the 5 speed. Overdrive allows you to cruise at interstate speeds at a lower RPM due to a lower numerical gear in the transmission. So if you go to a 4.10 axle gear, then the engine will see it as a 3.07 in overdrive (.75x4.10). I don't think it will hurt the engine. There is minimal load cruising at a steady speed. If fuel consumption on long trips is a concern, make the swap. If your highway RPMS are high, then make the swap. But the 5 speed will not make any difference in any other area of driving. First gear through fourth gear should be the same or very similar between the two transmissions.

What 5 speed transmission is in the 86 model? If it is a Peugeot 5 speed or an ax5 it is probably weaker than the 4 speed you have in it now.

Just leave the 4 speed for what you do............

The 5 speed is actually in a 84 v6 XJ. Haven't even looked under it to see what 5 speed it is.

I doubt our XJ would ever see over 65mph. We trailer it to the mountains and just run around up there for the most part. Speed limits are in the 55 - 60 mph range.

I still plan to re-gear and go a little bigger tire, more cosmetics than anything else. I thought if I went the 5-speed, I could go a little deeper gear, i.e., 456 and still have an acceptable road rpm range. The deeper gear to help facilitate low rpm torque for just crawling along sight seeing.

Cruiser, your probably right. If it ain't broke, don't fix it. lol

Thanks for all your thoughts.

TexasTaz38

Did you know some 4 cylinder Cherokees and Comanches came with 4.56s?

Just do it.

Yea, seen that in print but have not found any for salvage. I think they had to have the tow package and an automatic transmission, isn't that right?

Would really like to find one and just grab the drive train, do the CAD elimination and bolt them in. That would be toooo easssssyyyy. Everything comes along after I've done something else. lol

Happy Jeepin'
TexasTaz38

Yeah. Gonna be rare. I was mostly emphasizing that 4.56s with the 4 speed and big tires would be just fine.