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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

 
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post #1 of (permalink) Old 03-23-2000, 08:18 AM Thread Starter
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Match tires or PAY $$$

[img]/wwwthreads_images/icons/frown.gif[/img] I was in a shop recently and saw a delivery van up on the rack with the rear end opened up. The spider gears in the differential and the axle gears were COMPLETELY shot, as was the cross shaft. I mean these things were TOAST. The shaft was worn about half way through, and there were only little shreds left of the thrust washers. The van finally ceased forward motion when the spider gears were simply too far apart to touch each other anymore and what was left of them just shredded from slippage. I looked around for the rear tires and wheels and without being too obvious about it I rolled them side by side. There was over an inch difference in the height of the tires. NO BIG MYSTERY THERE!!! I always pester the owners of full-time 4WD rigs to match the tires, but in truth, ALL tires need to be matched if you don't want to wear out the differential needlessly. I have a regular fixture that our moonguy[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img] crew uses on the Quadra-Trac CJ and on our Select-Trac ZJ to match the tires perfectly and make it easy on the drivetrains.[img]/wwwthreads_images/icons/smile.gif[/img]

CJDave
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post #2 of (permalink) Old 03-23-2000, 09:22 AM
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Re: Match tires or PAY $$$

<font color=purple>Good point Dave. I very recently got on my Dad about this very subject. He has a limited slip rear in his '94 Dodge Ram (BTW, he ordered it with the 235HP 360 w/o driving a 360 truck. For the past 6 years, he's been wishing he'd gotten another 210HP 350 Chevy, but that's another story altogether). Anyhow, he upgraded from 245/75's to 265/75's. So, the other day he has a flat on the rear & puts his spare on there - you guessed it, 245/75. D'OHH! Drove just a short distance & no damage this time, but............ there's always next time. It just never occurred to him that it would be a problem. He kept the stock size on his last truck with a limited slip & at 5' 7" he's hardly one to go UP in tire sizes anyway. But, I told him he needed to either get a 265 spare or swap a front to the back & put the spare up front next time that happened. When I get my next truck a year from now, I plan to immediately upgrade the tires. So, I'm going to order it with a spare rim, but no spare tire. Then, I'll buy 5 identical tires & trade in the 4 stockers. I won't drive this truck much, so it'll take a long time for the spare to become "too big" as the others wear down.</font color=purple>

TEX

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post #3 of (permalink) Old 03-23-2000, 07:38 PM
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Re: Match tires or PAY $$$

Not exactly on the topic of mismatched tires(per differential) , but I had a box van(ton chevy dana 60-I had to peek[img]/wwwthreads_images/icons/smile.gif[/img]) that had 8.75's-16.5's on the front and MT 39/16.5-16.5's on the rear!!!!!!!!!!! MUD TIRES! It was a P.O.S. but the big block even sounded healthy with the turbos on it.
I guess our Jeep things aren't wierd after all![img]/wwwthreads_images/icons/wink.gif[/img]

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post #4 of (permalink) Old 03-23-2000, 07:57 PM
 
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Re: Match tires or PAY $$$

I often see cars driving down the highway at speeds (around 55MPH) with one of those "Donut " spares on the front (driving) axle..... I wonder why they don't wreck or ruin their trans-axle. [img]/wwwthreads_images/icons/crazy.gif[/img]...They are really a danger to themselves and other vehicles on the highway.[img]/wwwthreads_images/icons/frown.gif[/img]

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post #5 of (permalink) Old 03-23-2000, 08:00 PM Thread Starter
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Re: Match tires or PAY $$$

[img]/wwwthreads_images/icons/smile.gif[/img] A local couple took their all-wheel drive Whatchamacalit (Not a Subaru, but a....?) to get some tires. They replaced the worn out front tires with new ones, and drove to the homo capital. When they got there the gearboxes were smoking.[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #6 of (permalink) Old 03-23-2000, 10:19 PM
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Re: Match tires or PAY $$$

Tex
if i read your post correctly, you are plannin on ordering a new truck and you plan on getting it with the four stock tires and rims, and only getting a spare rim and tire??? you can do that what are your savings?? almost 100 bucks?? i have no idea i have NOT yeat looked into a brand new vehicle!
Also what truck do u use for competion?? is it the Toyata p\u if so what is in it for a motor?
later
Andy

post #7 of (permalink) Old 03-23-2000, 10:41 PM
 
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Re: Match tires or PAY $$$

Dave, the failure of the differential and axle gears would be the result of constant differential action caused by the mismatched height of the rear tires even when the truck was driving in a straight line and it would be even worse when the truck was turning. Do I have that right?

Wouldn't this be a much worse problem if the axle had a limited slip or a locker? What about the effect of a locked center differential in a transfer case or a part time system with a permanent 50%-50% split? It seems to me that driveline bind would be much worse if the tires were "forcing" the locked components to spin at different speeds. What do you think?[img]/wwwthreads_images/icons/smile.gif[/img]

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post #8 of (permalink) Old 03-24-2000, 05:18 AM Thread Starter
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Re: Match tires or PAY $$$

[img]/wwwthreads_images/icons/tongue.gif[/img] If you look closely at most differentials, you'll notice that there is really no provision for a great deal of spinning on the part of the spider gears. They only have hardness as their durability key, and no real bearings, only thrust washers. USUALLY, limited-slip differentials require a given amount of power to begin to lock up. That's so they don't have to crab around corners in a shopping Mall. If the tires are mismatched and you DO have lots of power on, the destruction is well,.....predictable. Vehicles like our CJ with Quadra-Trac drive have spring-loaded clutches which "wring into" the differential housing to cause limited-slip. Mismatch is DEATH to those units....absolute death. The cone clutches get hot and wear away the tapered surfaces till one of two things happens....the clutches quit holding, or the splines in the side gear blow out. In that case, you can still "go" in "Emergency Drive" with the rear axle pulling you home. [img]/wwwthreads_images/icons/smile.gif[/img] Quadra-Tracs are actually pretty good in that respect.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
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post #9 of (permalink) Old 03-24-2000, 05:56 AM
 
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Re: Match tires or PAY $$$

Thanks, Dave. As usual, your common sense, easy to understand answers are very much appreciated!![img]/wwwthreads_images/icons/smile.gif[/img]

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post #10 of (permalink) Old 03-24-2000, 10:18 AM
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Re: Match tires or PAY $$$

<font color=purple>Andy, what I'm planning on doing is getting the stock rubber, plus a spare "rim", but no spare tire. That is an option. And yes, it's not much of a savings, but it will save a bit. Then, I'll drive the truck straight to my tire dealer & trade in the 4 stock tires against 5 of my liking - what I want is not a factory option. See, if I traded 5 for 5, that'd leave my tire dealer with an extra tire & he wouldn't give me as much for it. If I trade 4 for 5, he'll be left with a complete set of four that he can sell to someone who WANTS stock tires. See, he doesn't carry Goodyears (which is the stock brand on the new GM's), so once he sells the four off my new truck, he'd be stuck with one oddball unused tire if I sell him my spare. And I actually plan to get the upgraded rims to go with my stock tires. The alloy's are only a $90 option. I may or may not keep them. If I decide on aftermarket rims, I have plenty of pals that would like a nice cheap set of 8-lug alloy rims for their Q78's, R85's, or 38.5X11 Boggers.

And yes, the Toyota pickup is my current racer. I run a 408" Chevy small-block, TH350, 2.28 T-case, open 4.37 gears, & Q78 Super Swamper TSL's.

Prior to this, I had a '78 CJ5 with a balanced 375HP 360, 3.54 full-width Scout 44 front, narrow-track 3.73 44 rear, 38X12.50 TSL's on 15X10's up front & 38.5X16 TSL's on 15X15's in the rear. The long-wheelbase Toy does a much better job of going in the direction you point it[img]/wwwthreads_images/icons/laugh.gif[/img].

</font color=purple>

TEX

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