Tires and Gearing info

[madizell]

It works. Now, if you can give us some insight on auto transmission function...

My take is that we are both potentially right at some point or other. Whether a converter is locked or not locked, I believe is about impossible to tell just by listening or looking at the tach -- it takes familiarity with how the system works and then you have to observe until you have a sense of what you are observing. This is assuming we each even have locking converters, as not all of them lock up. This also assumes that if they do lock, they lock at the lowest numeric converter ratio (i.e., 1:1) which is what I assume.

Converter lockup and 5th gear selection (or overdrive if you must) are completely separate things, so it is possible of course to have a converter lock in most any gear as long as engine speeds and strain are constant. How many rpm you will see increased on the tach due to a converter spooling to high ratio depends on the converter design, gear selected or in use, and your final drive ratio, so it would be best to stay within brand and engine/transmission combos, as well as performance situations, for comparisons. How my Nissan works is no real indication of how a Toyota works, or a Ford or Chevy, except that auto transmissions work the same in theoretical function no matter which brand you have.

Best situation would be to have a gear enunciator, as found on the Audi Quattro and other similar systems, where it can literally tell you which gear is engaged.

 

[IllianaXJ]

Also for reference: 2001 Jeep Cherokee 4.0L automatic, 4.88 gears. RPMs ~2400 @ 65 mph, 2500 @ 70 mph.

Here's a good link to calculate estimated RPMs with your engine/trans/tcase/gear combo:

http://www.grimmjeeper.com/gears.html

 

[biere]

An unlocked torque convertor is going to slip as you add in more power, such as the supercharger coming on line.

When I used to modify vehicles I sometimes saw a locked torque convertor slipping because its stock clutch setup was not strong enough to hold the power I was putting through the system. Basically I had not built the system to handle all the power.

It sounds about right with the torque convertor unlocking but as mentioned not having it in front of you makes it a bit of guesswork anyway.

My jeep has the diesel and 5 speed mercedes automatic and it locks and unlocks depending on what it thinks is best. I wish the autostick had a function for me to unlock the torque convertor because going from locked 5th to unlocked 4th by downshifting with the autostick is a big rpm jump but you have to use the throttle to make the torque convertor unlock and that can be difficult to do.

 

[Redline]

SOAZ, you seem to like the 4.88s on you 3rd Gen pretty well?

I was trying to talk myself out of re-gearing but now I'm back thinking it’s what I need to do to get the engine spinning where it needs to be.

4.56 gears are what I thought I wanted, but I'm giving very serious consideration to 4.88s. It's only 150-RPM more at 65-MPH and it will surely pull hills, weight gain, altitude, and the Chaser better.

Big decision.

 

[SOAZ]

SOAZ, you seem to like the 4.88s on you 3rd Gen pretty well?

I was trying to talk myself out of re-gearing but now I'm back thinking it’s what I need to do to get the engine spinning where it needs to be.

4.56 gears are what I thought I wanted, but I'm giving very serious consideration to 4.88s. It's only 150-RPM more at 65-MPH and it will surely pull hills, weight gain, altitude, and the Chaser better.

Big decision.

I read all of the calculations of RPM's etc and I made my decision half off that and half off of speaking or reading up on what others have done.

For me, it was the way to go. I'm not as offroad committed as Scott so 5.29's would have been annoying for my daily driving and highway driving.
I really wanted to get some low gearing back. Going up some steep hills in Colorado loaded down made me sure of that!

For me it was the perfect medium. I miss going 90 on occasion and I could even use a little lower gearing when going down a couple steep decents.

I think that I would have hated to spend the money on anything less than 4.88's.
Of course you have a whole different decision to make and none of my info really applies I guess. :sombrero: :safari-rig:
Good luck and remember you can't really go wrong.