DIY Diff Ratio?

[lemusa]

Hey finally got around to getting some 3.7 gears. Getting a complete R31 diff with low k's.

Thinking about changing them over into the vn myself. Ive had every part out of or off the car except the diff. There much work involved in that? And also changing the gears? Like could someone with half a brain sus it all out in a weekend and be driving to work on monday?

Any help would be nice, I know sfa about diffs and not sure how much of what I've found on the net is relevant

Cheers

[wraith]

Make sure the backlash is correct or it will cause dramas. It's really something better left to a diff shop because it's better to get the bearings etc done while it's all apart knowing how old R31's are.

[lemusa]

The fact i don't have a clue what you mean by backlash tells me I shouldn't do it lol How much labour and parts would you expect in a ratio change with me supplying the 2 diffs?

Also is there any way of tightening an open diff? Cant really be bothered with LSD's etc but wouldnt mind a little less open in my open diff haha

[lemusa]

The fact i don't have a clue what you mean by backlash tells me I shouldn't do it lol How much labour and parts would you expect in a ratio change with me supplying the 2 diffs?

Also is there any way of tightening an open diff? Cant really be bothered with LSD's etc but wouldnt mind a little less open in my open diff haha

[delcowizzid]

finding the 3.7 diff is the hard part we got too many jap assembled skylines seems the 3.7 is aussie assembled versions only.as for setting the gears up get it done by a diff pro you need shims etc to get it set right ring steelie gears in auckland he will have someone in CHCH who he sends local jobs too we use his recommended guy here in town

[lemusa]

The guy is spliting it and counting the teeth for me so fingers crossed. Didnt realise that imports where different

[delcowizzid]

you probably have 3.89 should have a tag with ratio on it on the cover bolts or its stamped on the gears LOL

[lemusa]

havent got it yet. Guy is gonna check before sending it to me. I dont really mind either way if its 3.7 or 3.9. would prefer 3.7 though. He seemed sure but we will see

[Calaber]

As said earlier, there is a lot more to setting up a diff than just bolting the parts together.

You will need a press to press the pinion shaft out of each housing - they are pressed in and tensioned when the pinion flange is tightened - you won't be able to just hammer them out of the housings.

The rear pinion bearings also require a press to remove and replace them.

Once the pinion is assembled into the housing, it needs to be pre-tensioned by tightening the pinion nut to a specified torque. You will need a tension wrench for this and a jig to hold the pinion from turning whilst you tighten the nut.

The crownwheel (large ring gear) should fit on the diff centre without too much hassle. You then need that tension wrench again to torque the bolts on the crownwheel to the correct tension.
When assembling the pinion, there is a spacer between the front and rear bearing and adjusting shims. Those shims are intendedto ensure that the pinion is tightened to the correct depth in the diff housing, which is vital for the correct operation and durability of the diff assembly.

The crownwheel assembly has to be centred in the housing to ensure the correct backlash. Backlash is the freeplay between the crownwheel and pinion gears. This should be within a specified range and the adjustment is effected by inserting the correct thickness shims on either side of the centre.

Have I managed to convince you that assembling a diff is not an amateur's job? Get it done properly by a diff specialist. Too many special tools required and too much to go wrong if you don't know what you are doing.

[lemusa]

You have well and truely convinced me! And thanks for the useful info. I will try talk to my mechanic tomorrow and see what sorta rate he gets from the guys he sends his stuff to.

I will remove it myself though just to save labour and itl teach me something

[1_johnboy]

very useful info there Calaber, Couldnt agree more that leave it to a pro to do.