Accidentally Dismantling a Differential....Ooops

Why?

Ok, I didn't start out meaning to dismantle it, I only wanted to clean it. After the diff came back from shot blasting I couldn't turn the drive plate. On closer inspection it seemed as though the bearings had seized because they were full of grit. This was not in the plan. I couldn't leave it like that as corrision would set in. After a quick call to Road and Race transmissions and a few local companies the cheapest rebuild quote I got was £250. Ouch. This was not in the plan either. I was always planning to run the open diff until funds allowed me to change it to a Quaife ATB differential. In one of my early posts I had become diinclined to run a limited slip differential, having done a lot more research and experienced a Quaife ATB first hand my mind was made up. The articles I researched previously related to the viscous coupling differential used in the XR4x4. This uses a different principle and didn't yield the results expected, anyway I digress. More on LSD's later in the build.

Method

• Undo the drain plug and drain out the oil


• Remove the back plate to inspect the crown wheel and planet gears. You can do a normal clean of the diff internals without going any further, unfortunately I couldn't as the grit was well and truly in the bearings.


• Unscrew the two crowned bearing races caps from each side of the drive shaft. These hold the gears in place and are used to set the 'backlash'. The pressure and position of the crownwheel against the pinion.


• The crown wheel and planet gears should just fall out in one big lump.


• Remove the nut holding the drive plate onto the front of the diff.


• Remove the drive plate


• STOP!

The reason I say stop is, the nut underneath the drive plate holds the pinion and bearings in place. Changing the setting of this nut means you need special equipment to reset it again afterwards, firstly to centre the pinion and secondly to get the right amount of torque on the bearings (to collapse the washer). Too loose and it will shake itself apart, two tight and it will wear prematurely, get hot and you will lose power though the diff.

So my next job was cleaning. I took it down to a friend at the local garage we used a combination of a long soak in the parts washer combined with using a compressed air line to blast through whilst the parts washer was dripping fluid through the bearings. After an hour or so everything seemed clean to me. I dried it off and tested the bearings with a little lubricant. Phew.... they were all clear.

Reassembly would be a little more tricky and required some research. I needed some new oil seals for the two drive shaft bearings and a seal for the pinion. I got these from http://www.bearingkits.co.uk/ for about £12. The tricky part is getting the crown wheel gears to mesh correctly with the pinion. For this its required to smear the teeth with engineers blue (available from Frosts for £3). This helps you see how well the teeth are meshing with each other, the wider the smear mark the better the contact. Fortunately as you may remember I have the second diff, which I can't use as it has the bolt on shafts, I can however, use it as a guide to getting the backlash correctly set. I found this technique on the mycaterham site.