t-case gearing

Ive got a 69-5 with 35" tires and a v8 and warn OD, 4.88 gears. In low range it is the lowest geared jeep I have ever driven. I am used to driveing intermediate year jeeps with the stock 3.54 gears on 33's though, I have driven 4cly wranglers with the 4.10 gears, but even with the 35's this jeep is soo much lower. Im wondering if OP had put the 3.15 tara low gear set in the t-case. Is there any way of telling from looking at the case externally?? I dont want to take anything apart. It has a m21 muncie 4spd, which from my understanding doesn't have the best gearing. Thanks.

 

Are you sure it's an m21? Is it possible it's an sm420?

 

yes, I ran the number on it. Came up a 69 m21 4spd. All alum. case and side shifted, no top cover.

 

No external mods needed to put the Tera Low gears in the case so externally you won't be able to tell. You could drop the pan and look inside. That's easy enough to do.

 

If you dropped the pan, what would you look for to tell you it had the tera low gears in it?

 

what would I be looking for when I drop the pan.??? I wouldn't have a clue. I just refilled it and the trany with gear oil, what a pitty. If you could tell me what I would be looking for, I will drop it anyway.

 

The easiest would be to pull the back of the OD and count the "main drive gear" teeth. The teralow's will be 26 tooth rather than 29-and you have to use them with a 26 tooth OD bowl gear. I think you would just about need a stock intermediate gear for reference to tell if you just pulled the pan-they do look different, but not that much different.

And on the M21: I wouldn't put too much faith on the case numbers. The internals get swapped all the time. If it is a M21, you have a 2.20:1 first gear. An M20 will have a 2.52 or 2.56:1 (early).

 

Mmm. I'd guess you'd count the teeth on the gears. There's a table on the Novak site that describes the transfer case gears. Or maybe they are marked somehow ... perhaps Nick knows of an easier way.

<edit> Ah - too late. Duffer has it.

 

And jeepcj, I'm glad I am not the only one left running the sbc/muncie thing. The 3.15 gears did help a bunch, but 3.54 diff gears with that drive train is still pretty high, especially with 33's. My 4.10's work reasonably well and still give you about 3.07 on the road with the OD engaged.

 

Perhaps, but I would be extremely surprised if someone went to all the work to fit a stock set of the older 26 tooth gears in there that offer nothing in the way of an upgrade. If there are 29 teeth on the bowl gear, it will be a moot point-something that you may be able to count with the cover off and a good light. A white grease pencil will mark it.

 

Calculate the engine RPMs for a given speed. That will give you the reduction ratio.

I'd use a measured mile (1/4 mile?) and a stopwatch, or maybe a GPS. Set your hand throttle to 1000 RPM and see how long it takes to travel a mile in top gear, low range. Or measure your speed with a GPS. Measure your tire diameter. So, at 1000 RPM, 1000 / (reduction) * tire diameter * pi / 12 / 5280 * 60 is your speed in miles per hour. Set that equal to the measured speed, and solve for the reduction. Divide by your axle ratio, and that's your TC ratio.

 

wow, that sounds complicated timgr. I think I will just be content knowing it is geared very low. Even on the street it is low. With the OD off, I am in 4th gear around 35 mph. I dont have a speedo in it yet so I dont really know how fast I am going exactly. I just keep up with traffic. Maybe it's just because Ive never driven a 4.88 geared vehicle before. I Was just hoping there was an easy way to tell. thanks guys

 

Another thought. Put the transmission in high (4th gear, 1:1 ratio), transfer case in low. Mark the balanced or pulley on the motor and the rear output yoke on the transfer case. Either disconnect the rear driveshaft from the transfer case or jack up the rear of the jeep (use jackstands to support it) then turn the motor over by hand and count the crankshaft turns to 1 transfer case output rotation. That would also tell you the low range of the transfer case. The Tera and jb conversion gears are much cleaner machined gears than the stock spicer gears and are "gray/silver" looking compared to the stock spicer gears but may be harder to I'd for most. Most of the jb and Tera gears are marked but may not be real visible.
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are you sure you have 4.88's and not 5.38's?

 

thats what it sounds like to me.
35 to 45 mph in 4th gear describes the slug.
it is wound up at 45.

 

nick mill, That sounds like an idea that I could do! Unclbill, yeah I counted the teeth about a year or so ago, I can't remember what it was, seems like it was something like 11 and 39, I looked in the back of a quadra tec mag at the ring and pinion section for the ratio. I like the idea of nicks, so that works the same way as counting the drive shaft to tell your ring and pinion?

 

Do you know for sure what T case you have? I think it was around 1966 that they changed from a small index hole to a larger one. The Tera kit will not fit into the older smaller hole ones. I am thinking that you can see and measure the hole on the side of the case to tell which you have. If you have the smaller one, then you know for sure there is not a kit in it. I think if you go to the Tera site, they will explain what I am talking about.