Grinding/knocking noise when reversing at an angle

[jchunter]

My 2001 AWD Mountaineer just recently began making a grinding/knocking noise from the front passenger side, but only when reversing and only with the wheels turned at an angle. It may or may not be a coincidence but the problem started shortly after I had both front tires replaced. The week before I got the new tires the car shuddered while driving above 30 mph (due to uneven tire wear I assume) but the problem went away as soon as the new tires were fitted.

Any suggestions as to what might be causing the noise and will driving the truck in its current state exacerbate the problem?

Thanks.

Colin

 

[my pos mounty]

When you replaced the tires on the front, what about the rear? As of right now, do you have a difference in the outer circumferance of the two different sets of tires? As little as 1/4 inch difference can be a huge problem, or should I say, can cause HUGE problems.
Unless you are absolutely sure they are the same, go measure the differences with a cloth tape.

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Not trying to sound condescending or anything, but 1/4 inch difference is a big deal. Doesnt sound like much, but lets do some quick math. 1/4 inch times how many rotations the tire turns in one mile, times how many miles you expect to drive the truck before replacing the tires so they match. The difference of the circumferances have to be made up (from front to rear) by the viscous coupling in the transfercase. Thats actually why it is in there, to do just that. However it is not designed to be constantly doing that. It will create alot of heat and literally cook your transfercase from the inside out.
Having different tires front and rear can also stress your hub/bearings, eat your CV/axles, chew up your front and rear differentials, render your front driveshaft useless, and eat the U-joints on the rear driveshaft.
Don't ask how I know this. $$$$$

 

[jchunter]

All four tires are now BF Goodrich Long Trail T/A Tour. I had the rear two replaced late last year and they only have about 2,000 miles on them so they're still practically new. I didn't get the chance to measure the tire size last night but they should all be essentially the same size.

Your warning about driving with different sized tires makes me wonder if I was doing damage before I replaced the front two tires and made them all the same. The old tires are long gone now, but could the damage you describe only show up when reversing at an angle? Is there anything I can do now or is it already too late?

 

[my pos mounty]

A noise only present when backing up, and turning at an angle? I may be wrong but I would say that that points to only a few things. First would be the CV/axles. By reversing and turning you are putting forces on it that don't occur when driving it normally. Perhaps one of them is on its way out. It would be a semi-loud "snap" or "click". If thats the noise, its a CV. Have you looked at the rubber boots?
Next could be transfercase issues with the viscous coupling. Typically get sounds that are broadcast thru the drivetrain, I have a weird kinda groan/scrape coming from mine right now. I know its junk.
Theres also a chance it could be the hub bearing, but the noise should present itself when turning, whether or not in reverse.
Worst case scenario is transfercase issues, the others are not any where near as costly. If the CV boot is ripped, the axle should be replaced as soon as possible, and if the bearing has created "wheel play" it must be replaced now before it fails. Continuing to drive like this should not create any additional problems, "can't break what is already broken" kinda thing, but the issue will get worse as time goes by.
Hope this helps you

 

[jchunter]

That information was very helpful.

From your description of the different noise types I'd say it sounds like it is coming from the drive train and is therefore most likely a transfer case issue. It's also more of a grinding noise than a clicking - I've heard worn CV joint noise and this is very different.

So to summarize, we're probably looking at an expensive repair, but it will not get any more expensive if I continue driving before having it fixed?

Many thanks.