Crown Wheel Question

[MatthewMyerscough]

Hi Everyone,

I'm just in the process of rebuilding the D-Type rear axle for my Nippy. I have checked the runout on the crown wheel this morning and I am getting a reading of between 3-4 thou.

I was just wondering if this was within the expected tolerance?

Thanks

Matthew

[Howard Wright]

Matthew

3-4 thou sounds OK to me, Woodrow suggests less than 4.

Howard

[MatthewMyerscough]

Hi Howard

Thank you for clarifying that, its much appreciated.

Thanks

Matthew

[MatthewMyerscough]

Hi Everyone

To follow on from my question above,  I have now re-assembled the diff and torque tube in order to check the mesh pattern. 

As part of the rebuild I have replaced the pinion thrust bearings, diff carrier bearings and the original pinion shim thickness (15 thou in my case) and I've set the backlash to within spec (1.6mm just over 1/16" at the tightest spot). I have also pre-loaded the adjusters as per Woodrow.

The pictures below show the results on the drive side of the teeth (the overrun pattern is more central and oval in shape). I have read in the service journal that the mesh needs to be towards the bottom of the teeth. I believe this is to allow for the pinion to travel up the teeth slightly during normal operation.

My question is does this mesh pattern look ok/useable taking into account 90 years of wear, or is it likely to destroy itself as soon as I go down the road   ?


Thanks

Matthew

[Ian Williams]

It looks a little nose heavy for my liking, did you try to load up the Crownwheel at all when taking the markings? Was there any wear on the pinion bearing spacer? This is common and can affect meshing

[MatthewMyerscough]

Hi Ian

Thanks for your reply. I must admit that was my first impression. 

I did load the crown wheel as best as I could and from memory the bearing spacer wasn't badly worn, having said that I don't have a comparison to look at.

I think I might tweak the adjusters slightly to try and bring it more into mesh and then see what that effect that produces. 

I'll keep the thread updated.

Thanks

Matthew

[Ian Williams]

You may need to adjust the shims as well

[MatthewMyerscough]

Hi Ian

Yes, that is the next thing I am going to look at. I was hoping to avoid increasing/decreasing the shim size because the one bearing I haven't replaced is the pinion roller bearing. I'm conscious that this will have worn into a particular area on the internal surface of the outer race so moving the pinion in this plain might create a separate issue. I'll try it and let you know the results.

Thanks

Matthew

[Ian Williams]

Hi Mathew,
if the roller bearing is worn enough to be affected by shimming the pinion it should be replaced. The pinion bearings are very important to A7 axle survival.

[Terry McGrath]

I'm sure that there is a living to be made for a new Cherished Supplier who deals exclusively in rebuilding A7 back axles. It's a dark art, frightening to many owners, and keeps many cars languishing unused in garages.