Thread: What are acceptable wear parameters ?

Originally Posted by Jason F

Hello, There has been lots of discussions re investigating backlash in drive train components, but have not found any pass fail criteria advice.
I have the same clunk some people complain about when the auto transmission catches up sometimes especially when braking down past 40km/hr.
I took it to auto box specialist and a differential specialist and a few mechanics, none were prepared to advise what is causing the problem without stripping everything down. The auto expert said its still moving up and down the gears very nicely, and did not recommend refurbishing the box.
The diff specialist said he does not think I will see any real value in re-building the diffs.
I did put heavy duty splined drive nuts on the front just in case its in the stub axles splines, but found no wear there.
So I decided to measure the angles myself this morning, as follows:
REAR: With hand brake on, 3.2 degrees movement.
FRONT: With hand brake on and auto in park, 8 degrees through CV and diff.
FRONT: With hand brake on and auto in park, 9.6 degrees through transfer case.
Total for FRONT is 17.6 degrees.
Is this a lot? I have no idea?

I now know I have a LT230T (tapered bearings). Anyone know how to adjust the bearing re-load when the PTO plate if off ?
Anyone know if there are any adjustments behind the rectangular cover plates that I can do myself from under the vehicle ?

Jason F
Just a thought, my V8 Disco has also had issues in the past with the clunk when decelerating.It was related to the idle speed dropping to 700rpm or so before the car become stationary. Its a while ago now but as I recall the road speed sensor via ECU holds to rpm slightly higher around 1000rpm?? until the vehicle comes to a standstill then drops back to the normal idle speed. I think this masks any backlash and subsequent clunking by maintaining a loading on the drivetrain.
In my case I checked the speed sensor but ultimately it was the eventually overcome when I sorted the dreaded uneven idle speed out.
I don't have any clunks now other than the usual when moving between D and R.
Hope this helps

There was a problem with some models, (not sure what years), where the output shaft spline out of the 5 speed manual gearbox flogged out inside the gear that drives into the transfer case, (the one behind that PTO end cover that Jason F has mentioned), this gave a lot of lash in the drivetrain but I suspect it is not where 98discovery's problem is, but from what I have seen on mine and others there can be lots of lash.
Not too sure if the same scenario applies to auto box models, but I saw in my mates manual '85 County with LT77 gearbox, the splines in the gear and on the output shaft of the LT77 had worn to about half thickness, lots 'o slop.
I know there was a factory mod that overcame the problem and my '97 Tdi has had it done, or it is factory original, whatever, I have the transfer case out right at the moment addressing the famous and classic "intermediate shaft oil leak".
By the way Jason F, I think that there would not be much gained by doing pre-load on that set of bearings at the PTO, my Disco has done 300,000 plus and the bearings were perfect and in perfect adjustment. Gaz

Your backlash measurements seem low. Clunks while driving that may seem like backlash can instead be suspension bushes or the a-frame ball joint.

X2 for the Aframe ball joint. I thought my transmission was knackered my backlash was that bad. I got the mechanic to replace it anyway as I didnt know when ut had been replaced last...

Bang drives like a dream! I couldnt believe how much difference that thing made!

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