3.8 E diff input seal

[david muir]

Hi,
If I replace the input seal on my 3.8 diff. does the pre-load need checked/rest on the crownwheel? Is there a crush tube on a 3.8-parts book doesn't show one , did the crush tube come in with the 4.2?

Thanks, D

[44DHR]

Hi David,
Yes earlier 3.8 diffs had shims to set the Pinion bearing preload and later diffs use the collapsible spacer.
It is quite common just to mark the Pinion nut before undoing it and once the new seal is refitted - preferably the modern lip seal type rather than the old leather type - the Pinion nut is retightened to the initial mark to maintain the preload. If the diff has a collapsible spacer it is vital this is not over tightened.

A previous discussion :-
viewtopic.php?f=3&t=12186

Regards,
Dave

[angelw]

David Wrote:

If I replace the input seal on my 3.8 diff. does the pre-load need checked/rest on the crownwheel? Is there a crush tube on a 3.8-parts book doesn't show one , did the crush tube come in with the 4.2?

Hello David,
I suspect that your meant Pinion, rather than Crown-wheel. Unless the Crown-wheel and Pinion have been replaced in your 3.8 car's differential, Pre-load of the Pinion Bearings is adjusted using shims. Accordingly, replacing the Pinion Shaft Seal with have no effect on the current Pre-load setting. However, that's not to say that the Pre-load is correct if the differential has been in service for a long period of time.

The Pre-load is normally checked during the overhaul of the differential, with the Crown-wheel and Pinion Seal omitted from the assembly and is determined by noting the torque required to rotate the Pinion Shaft; it's specified in the Work Shop Manual for early cars to be in the range of 8lb/in to 12lb/in torque. This test is carried out with the Crown-wheel and Pinion Seal omitted, so that the torque being measured is only for the Pinion Shaft.

It is possible, however, to be able to check the Pre-load with the Crown-wheel in place, but with the Pinion Seal removed. You will be able to detect an amount of backlash (clearance between the teeth of the Crown-wheel and Pinion gears). With the Companion Flange in place and the nut done up tight, first take up the clearance between the gears by rotating the Pinion Shaft Counter Clockwise (looking at the front face of the Companion Flange) until you can feel resistance. Using a lb/in Torque wrench, or Spring Balance, set at the appropriate distance out from the centre of the Pinion Shaft, measure the amount of torque required to rotate the Pinion Shaft in a Clockwise direction. You won't be able to rotate it far before the clearance is taken up between the gears and resistance from the Crown-wheel is felt, but it will be sufficient to get a result.

The torque specification has evolved and is now specified for much later cars (using a similar differential) at circa 26lb/in torque. If the torque is less than the low end specification, too much deflection of the Pinion can result under load. This results in a shifted contact between the teeth of the Crown-wheel and Pinion gears and presents as noise. If the Pre-load is less than the 8lb/in low range, I would be rectifying the issue.

Regards,

Bill

[david muir]

Thanks folks for the info. So , if I decide to replace the input seal I should get away with marking the nut and shaft!
D