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-   -   FJ40 Ring & Pinion gearing question (http://www.risingsun4x4club.org/forum2/showthread.php?t=8013)

Mendocino 08-25-2008 08:20 PM

FJ40 Ring & Pinion gearing question
 
I am considering changing my 4.10 R&Ps for 4.88. I am currently running 35s and my 700R4 tranny has an underdriven (.7 to 1) 4th gear. With the current set up I can do ~75 on the highway at about 2200 RPM. I will eventually go with larger tires, but want to know what I can expect to loose in top speed with the 4.88s. I would appreciate some comments from those of you with 4.88s and similar size tires.

What gears are preferred? Precision or Yukon, or ? Where should I purchase the gears?


:thumb:

Hulk 08-25-2008 11:54 PM

Those are both good brands, Jeff. I put Precision gears in my 80. I purchased here: http://www.justdifferentials.com/ They have gears for 40s as well.

Just send a PM to ringpinion.biz on Mud. His contact info:
Carl
JTS Parts & Accessories
carl@justdifferentials.com
509-888-AXLE (2952)

Uncle Ben 08-26-2008 07:25 AM

Quote:

Originally Posted by Hulk (Post 84339)
Those are both good brands, Jeff. I put Precision gears in my 80. I purchased here: http://www.justdifferentials.com/ They have gears for 40s as well.

Just send a PM to ringpinion.biz on Mud. His contact info:
Carl
JTS Parts & Accessories
carl@justdifferentials.com
509-888-AXLE (2952)

Precision is Randy's Ring and Pinion House brand and Yukon is Drivetrain Warehouse's brand. They are made in the same factory! Precision seem to be made under higher tolerance as they are very consistent in fit. As Matt suggested either set is a good choice but personally I use Precision Gear.

Mendocino 08-26-2008 10:55 AM

Any comments on the gear ratio fellas?:confused:

Uncle Ben 08-26-2008 04:01 PM

Quote:

Originally Posted by Mendocino (Post 84386)
Any comments on the gear ratio fellas?:confused:

4:88's are as low as you can go with a c-clip type Cruiser diff. '56's are great all around for strength and install ease. 4.11 Toyota fine splines are very strong!

subzali 08-26-2008 04:28 PM

When I ran the gear ratios I found that for 35s I was going to try 4.56 gears, but I had plans for lower tranny/t-case gearing so I wouldn't have to do 4.88s (I wanted to avoid high rpms at highway speed). I didn't want sickly slow final crawl ratio either, I figured 80 or 90:1 was good 'nuff for my needs. Course now my plan is to stay with small tires and 4.11s for a while, so...

Rzeppa 08-26-2008 05:41 PM

Iron Pig Off Road (Lance Williams) is a TLCA member business that sells Yukons. Ihaven't heard anything bad about either Yukons or Precisions, and until Kevin's post I didn't realize there might be any difference.

As for ratio, you might simply go by tire size ratio. Stock (from the factory, 73-75 vintage) 7.50x15s bias plies were *around* 30" diameter, although a lot of them were changed out to 235R75 radials which are around 29". So 35"/30"*4.11=4.795 which is darn close to 4.88s to put it back close to factory. Of course an SBC and 700R4 isn't stock, so that's just a little perspective.

Mendocino 08-26-2008 06:06 PM

Thanks fellas. I ran the numbers with my tranny first gear, t-case, tire size, and R&Ps. Overall I think the 4.88s make the most sense.:thumb:

Uncle Ben 08-26-2008 06:36 PM

Quote:

Originally Posted by Mendocino (Post 84431)
Thanks fellas. I ran the numbers with my tranny first gear, t-case, tire size, and R&Ps. Overall I think the 4.88s make the most sense.:thumb:

Jeff, Keep in mind there is more to final gearing than just math! Physics is a huge chunk of the pie! If you are running a 2F or some anemic 4 popper in a rig then low gears are your only choice. When you double or even triple your hp and torque you have to take into factor the strength. You don't need as low a gear with more power so you can get by with a higher pinion tooth count (stronger) and still pull hills that would kill a tractor engine! Tough choices I know! 4:88's are great gears but your pushing a lot of power through just a few pinion teeth! I have run 4:56's in Wild Rice(my 40) for years driving 36" grooved swampers by a perky F! Except on the highway up long grades I have no power issues! On those long grades it will still pull 40-45! The place you want to address is your tranny/t-case gearing! you already have a 700R4 which has a great 1st gear (3.06:1!) plus the almighty trail handling torque converter. Focus some thought on more than a 2-1 t-case and you will create the best of both worlds.....great highway gears that are strong and great crawling ability that lets you save the body by the use of finesse instead of speed!

....that is just about :twocents: worth.... ;)

Mendocino 08-27-2008 04:26 PM

Quote:

Originally Posted by Uncle Ben (Post 84433)
Jeff, Keep in mind there is more to final gearing than just math! Physics is a huge chunk of the pie! If you are running a 2F or some anemic 4 popper in a rig then low gears are your only choice. When you double or even triple your hp and torque you have to take into factor the strength. You don't need as low a gear with more power so you can get by with a higher pinion tooth count (stronger) and still pull hills that would kill a tractor engine! Tough choices I know! 4:88's are great gears but your pushing a lot of power through just a few pinion teeth! I have run 4:56's in Wild Rice(my 40) for years driving 36" grooved swampers by a perky F! Except on the highway up long grades I have no power issues! On those long grades it will still pull 40-45! The place you want to address is your tranny/t-case gearing! you already have a 700R4 which has a great 1st gear (3.06:1!) plus the almighty trail handling torque converter. Focus some thought on more than a 2-1 t-case and you will create the best of both worlds.....great highway gears that are strong and great crawling ability that lets you save the body by the use of finesse instead of speed!

....that is just about :twocents: worth.... ;)

Hmmm...:confused: Well I had been strongly considering a Marlin Toy Box between the 700r4 and the Toyota LC and was thinking of doing that as a winter project. To adapt the 700R4 to the Toyota TC you need an adapter (mine is from AA) which is the same length as the Toy Box. I was thinking I could remove the AA adapter, install the Toy Box with the 4.7 to 1 reduction and have some serious gears. Years ago I had a Ford F-250 with a six cylinder 4 speed w/granny low (6:1 I think) and 4.56s. The thing was awsome. I really enjoy the ability to use near idle rpm with tons of control.:blah:

To add the Toy Box, or put the 40 back together correctly I think I will need to extend the wheel base by moving the rear leafs back. The rear drive shaft has no play in the slip yoke and I think this may have caused some problems on the pinion shim preload (it was crushed according to Squishy). Alas, yet another project:(

However, UB, you bring up some very good points. The last time I had the thing dyno'd it had 310 ft lbs of torque at 3300 rpm, and 215 HP at 4400 RPM at the rear wheels. [Parenthetically, I was surprised that this 355 HP, 405 ft lb engine lost so much at the rear wheels but was told that was not surprising by the tuner]. I really don't want to eat R&Ps so maybe the 4.56s and Toybox are not such a bad idea. Can I re-gear my 75 LC TC to lower than 2:1? I looked at Mark's gears but they appear to be only for later model year TCs.

Cheers,

Jeff:cheers:


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