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Old 11-13-2002, 04:44 PM
rayford rayford is offline
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drive train damage from unevenly worn tires

I was told that it is very critical that all the tires on the all wheel drive SVX have even tread wear and nearly exact tire air pressure or there would be damage to he drive train. I had my transmission done a few months ago and now the front differential is apparently going out... the shop said they would fix my problem but first I have to have all four tires new,, I am not objecting to that as it is cheaper to buy the tires than to have to pay for the repairs,, I was just wondering if anyone has ever run into this kind of thing causing damage to the drivetrain. I am not saying they aren't correct but I just never heard of that before. Just a note.. I think it is very nice of the shop to warrentee the differential when actually to me that seems like a seperate unit from the transmission on this type of car.... Thanks. Vernon
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Old 11-13-2002, 05:29 PM
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immortal_suby immortal_suby is offline
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Different rolling circumference on tires in an AWD system will eventually destroy something. The car will read the different speeds of the tire rotation as slippage. Results will be bad. The same goes for different tire sizes on the same axle with a locking differential.
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Old 11-13-2002, 08:38 PM
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Yeah, but how much tolerance is there?

This sounds as potentially bad as a timing belt issue on an interference motor! How much "off" can tire pressure be on an AWD system?
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Old 11-14-2002, 06:24 AM
mattski mattski is offline
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I believe someone mentioned 1/4" difference between circumferences is the allowable limit. I do not know what that translates in PSIs. There is a specified difference between the front and rear tires so I believe that you can adjust the pressure upward a few pounds while maintaining the difference without any ill effects.

Matt
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Old 11-14-2002, 03:53 PM
oab_au oab_au is offline
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Wheel difference.

I don't think that this is as critical as they say. There is allways a difference in the rolling dia of the wheels, Due to wear, weight change when cornering, air pressure, front to rear 60/30 weight bias, etc.

From memory the TCU considers anything below a 20% difference as cornering. So only applies a small additional pressure to the clutch.

I mean don't run different tyres side to side or front to back. Also use 2psi. more pressure in the front than the rear. There should not be a problem.

Harvey.
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Old 11-14-2002, 05:08 PM
rayford rayford is offline
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oab_au,,, what you are saying makes sence to me.. I wouldn't think if tread wear , unless maybe an extreme amount would damage the drive train very quickly,, obviously , all the tires should be the same size and have reasonably the proper pressure. I am not familiar with the SVX awd system but in general, if you run different size tires ,that makes the spider gears be in motion all the time and of course they are mainly supposed to only turn when cornering or if one wheel is not getting good traction. As I said ,, SVX might be different, I am used to the old Ford and Chevy four wheel drive pickups and they will work even if the bearings are about worn out .. but the shop seems to be very convinced that it is a serious problem.. Maybe it is ,, that is why I wanted other people's opinions that know, because I really don't ,,, Thanks.
Vernon.
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Old 11-14-2002, 06:24 PM
oab_au oab_au is offline
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Quote:
Originally posted by rayford
oab_au,,, what you are saying makes sence to me.. I wouldn't think if tread wear , unless maybe an extreme amount would damage the drive train very quickly,, obviously , all the tires should be the same size and have reasonably the proper pressure. I am not familiar with the SVX awd system but in general, if you run different size tires ,that makes the spider gears be in motion all the time and of course they are mainly supposed to only turn when cornering or if one wheel is not getting good traction. As I said ,, SVX might be different, I am used to the old Ford and Chevy four wheel drive pickups and they will work even if the bearings are about worn out .. but the shop seems to be very convinced that it is a serious problem.. Maybe it is ,, that is why I wanted other people's opinions that know, because I really don't ,,, Thanks.
Vernon.
The US car uses a transfer clutch only, in the center, No diff.
The rear wheels, or front to rear wheels, won't make any difference to the front diff. Only a difference in the front wheels, as these wheels have the most difference in rotation when turning at full lock. Thats why they don't have a LSD in the front.

I reckon they made a balls up when they refitted the front diff thats in the transmission housing, and yes, they had to pull the front diff down to do the transmission.

Harvey.
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  #8  
Old 11-15-2002, 05:37 PM
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Some really nice vandals slashed one tire and since there was 50-60% tread left I bought 1 new tire ( wanted to keep them all the same ) and found a tire shop that would sand the new tire down to match the circumfrence of the others. It took a lot of searching to find someone that could do it, but it's fairly common for racers to do this type of thing so search for a racer's tire shop if possible. And it only cost $10 and about 5 minutes time.
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