Hi team.

I have been searching for days but can't find what I need to do to change my 3.07 power lok gears to 4.1/4.09.

I have both rear ends - an '81 XJS 3.07 power lok, and an open 4.1 from a 2.8 XJ6 (?). I want to combine the two to make one 6 speed happy 4.1:1 ratio power lok rear end.

I know this topic has been discussed, but can I find the relevant threads? No. Am I right that would need a spacer ring or something?

Cheers!

 

I don't believe the 4.1 gears will go into the 3.07 banjo.

 

It should be as simple as swapping the ring and pinion gears, and then appropriate shimming to set clearances. The carrier breakpoint is 2.88 and numerically smaller, so 3.07 and 4.1 should be the same carrier.

You can measure the offset of the ring gear mounting face on the carrier from the centerline of the pinion gear and see if they are the same. Going from memory, the difference between a 2.88 carrier and 3.54 is about 1/4", so it's a noticeable difference.

 

Thanks for that. I want to be armed with the correct info when I take the diff heads to the workshop.

 

To a certain extent the shop can compensate with the shims under the carrier bearings, those get moved from side to side to align the ring gear with the pinion. 3.07 will have a relatively large pinion head and thin ring gear compared to a 4.09, so the carrier will need to be shuffled over. All part of the setup process.

I am assuming the bearings are coming off to be replaced, so you'll have access to the shims under the bearings anyway. The shop will need the proper bearing puller, as getting the clearances correct is an iterative process and the bearings will need to come on and off a few times to adjust the shims underneath. It's critical to use a proper puller that can remove the bearings without damaging them. They are pressed on, and it's a very tight fit. A usual gear type puller will not work (the voice of experience!!)

 

Yep the 2.88 pinion is very large, I do not have 3.07 but I do have 3.58, 4.09 and 2.88 gear sets. and the 2.88 is pretty unique in the diameter of the pinion. It's possibly more than 1.4". I did machine a spacer for the hemisphere until I found a cheap ($50) LSD 3.58 hemisphere.

The crown wheel may also be thicker so the measurement should be from the center of the pinion to the mounting surface of the crown wheel.

 

Hey thanks for that. I guess I need to get both of them on the bench and have a look. Cheers

 

All you need to do it take off the back cover. If there is a difference, it should be apparent. Although sometimes it can be difficult to tell the exact spacing without removing the bearing caps.

My general approach (assuming the carriers are suitable) is to remove the powr lok carrier and change over the ring/crown gear from the open carrier to it. Then place it in the 4.09 case to mate with the 4.09 pinion. Setting up the pinion is a lengthy process, so if the bearings are good I would leave it untouched and the just set up the carrier and ring/crown gear to match the pinion.

Often the condition of the oil can tell you a lot about the condition of the internal components. Do you know any history of these differentials?

 

Seems like sound advice, thanks, I will pass that on to the workshop.

I have no history on the 4.09 but I do have about 30 years service history on the 3.07 - the car has done about 90,000 miles and the diff oil has been changed a few times.

The 3.07 is still in the car, so I have a bit of a job yet to get that out.

Cheers.