Rear Axle Play?

[yukonsc]

I have a 2000 yukon with 138,000 miles on it and I am in the process of trying the diagnose the clunking and varies other noises in the suspension of the vehicle. I am trying to systematicly approach the issue/issues.

 

I jack up the truck and was 'shaking' down the rear of the truck and notice the rear axle has play in in (I would say lateral - back and forth motion). Both sides seem to have the same amount It doesn't seem to be a lot - but enough that I am asking the question. Should there be play in rear axle?

 

Also - I had the rear rebuilt 50,000 miles ago an had an eaton posi installed.

 

Also any other input as to what to check under the truck suspension wise - it feels as though the entire suspension is shot - maybe it is who knows.

 

Thanks...

[pm26]

There is play between the teeth of each meshing gear. That play is known as backlash. It is not possible to assemble gears with zero backlash. It is important however, that the backlash be within specification for each gear size. This is why differential gears are carefully shimmed when assembled to ensure that the collective backlash is not excessive.

[yukonsc]

There is play between the teeth of each meshing gear.  That play is known as backlash.  It is not possible to assemble gears with zero backlash.  It is important however, that the backlash be within specification for each gear size.  This is why differential gears are carefully shimmed when assembled to ensure that the collective backlash is not excessive.

 

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How much should the wheel move? Is there a way to measure backlash or do I really need to drop the cover and measure there. I would say (without measuring) 1/8" play

[pm26]

Yes, there is a way to measure backlash. It is done by inserting a feeler gauge between the gear teeth. The backlash specs are dependent on the gear size and there are general backlash tables found in mechanical engineering handbooks. Also, the GM specification book for your truck should have that information.

 

Excessive backlash will often produce whining noise coming from the rear axle, for example during coasting. I you do not have any noise or excessive clunk, you should not be concerned.

 

What you are perceiving as 1/8 inch total play is the cumulative backlash.

 

When assembling differentials, two basic criteria are of importance:

1. proper gear backlash

2. proper gear tooth contact pattern

[fossil]

Actually to measure backlash you need a dial indicator and not a feeler gauge. Up to the year 2000 model you wanted somewhere between .008 and .010 backlash. I believe from year 2000 on up GM changed the gearset to a different cut and the required backlash is around .003 to .005 inch, hence the need for 75W90 synthetic gear oil. Backlash doesn't really make the gear noisy as much as the depth of the pinion gear does.

[yukonsc]

Actually to measure backlash you need a dial indicator and not a feeler gauge.  Up to the year 2000 model you wanted somewhere between .008 and .010 backlash. I believe from year 2000 on up GM changed the gearset to a different cut and the required backlash is around .003 to .005 inch, hence the need for 75W90 synthetic gear oil. Backlash doesn't really make the gear noisy as much as the depth of the pinion gear does.

 

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There is clunking in the rear - I thought something was loose in the suspension, however after reading this I am thinking maybe it is the backlash. I'll have to pull the cover and measure.