Front diff pinion bearing oiling.

[Rob-o]

Evening everyone,

Today whilst the good lady was visiting family I finally got around to removing my front prop to test whether it was my front diff that was droning under load, turns out it was! There is an almost imperceptible amount of up/down movement in the drive flange so presume it’s time for a rebuild, is there an allowable amount? I presume there isn’t. I assume it’s not possible to add a little preload to the pinion bearings without a rebuild?

So after discovering this I moved on to fitting the castor correction plates that I’ve been meaning to fit for about 6 months. All fitted now, I am amazed at how the pinion angle has changed. I was also able to add about 300ml of oil with the diff in its new position. I wonder if the high pinion angle caused by lack of castor correction has caused the outermost pinion bearing to run dry(er) than normal and accelerate wear?

I’ll be a little annoyed if I have damaged the front diff by taking my time with the castor correction. I will of course refit the front prop to rule out unequal UJ angles as the source of the drone, but as the drone is fairly recent I think unfortunately that the diff is the source.

Any thoughts, especially regarding pinion bearing preload, greatfully recieved!

Rob

 

[Jon Wildsmith]

There shouldn't be any detectable up/down pinion movement. If you can feel it then there will be quite a lot when under load. You can often get away with tightening the nut slightly to eliminate the play. You have to be very careful because if you tighten it too much you will have the opposite problem of the bearings being too tight and backing the nut off even a fraction returns you to having play with no in between. Sometimes the nut turns really easily and sometimes you'll need a breaker bar. Depending how bad it is you'll get a bit of drone from loose pinion bearings that may go away but if it's loud then it's a less likely fix.

As long as you had oil level up to the fill plug then I don't think lack of caster correction will be the cause of a diff wear.

 

[Chris]

The only problem here is that whilst you may be able to take up that bit of play in the bearing, it's no guarantee that it's the cause of the noise just as JW says. I had this on a member's diff just recently and in the end we pulled the diff completely to replace all the bearings inside. I set it all up correctly with the preloads etc and when it went back in, whilst marginally better it was still noisy. I'd inspected the teeth on the crown and pinion and they looked fine. I even got a pattern to show when I rebuilt it. I suspect it had been overheated at some point. Maybe even run dry. It smelled absolutely awful inside and there seemed to be signs of heat / burning.

In the end, we put a new gear set on it from Milner (I had a spare diff on the shelf which we used) and now it's beautifully silent again. I said then that I'd probably not rebuild anymore diffs without doing the ring and pinion. For the extra £180 or so, there's just no point. It's so much work to pull it that not doing the gears is really a false economy. Give it a nip as per JWs instructions and see if it's quieter. If not, I'd suggest going for a full strip and rebuild. That way you get everything right including the preloads and backlash.

 

[Rob-o]

Thankyou for your thoughts gentlemen. I’ll try a little nip up then. Sounds like a reasonable first step. Failing that it’s a bag of oats and if that doesn’t work (could it fail!?) a rebuild.

Chris were the Milner ring and pinion a good buy quality wise in your opinion? I’d probably try and get hold of a diff carrier to build the new bits into as my 80 is my only vehicle and daily driver.

Thanks!

 

[Chris]

It's really hard to say. They were nicely packaged and looked well machined. It's not really something that is easy to define. I have rebuilt two diffs recently for members and they're both running silent. They set up very well indeed with good patterns on the teeth. I have a spare carrier which I use as a swap out. It does mean that you can do a fast change but in fairness that last one I built took me 2 hours and three minutes start to finish. The worst part was trying to get the damn locker motor off. The two long studs from the diff had welded themselves into the motor body and the pinion shroud was stuck in the steel diff case. It all came off in bits in the end. If you can get your locker off then swapping out a rebuilt diff doesn't take long. Of course if the rest of your axle is in a state then you might as well do all of that too. Remember that you can very easily run around with no front diff, prop and driveshafts in an 80 if you have the centre lock button on the dash. So it's not critical having to get the diff back in the same day. What is important is building the diff properly. Aside from the gears and bearings, you need the shims, oil ring, crush tube a dial gauge and micro torque meter plus some bit pin spanners.
Roughtrax now sell the bearings kit with the oil ring in but they don't sell the gears. Milner sell the rebuild kit, but not sure if they've included the oil ring in theirs yet. Both kits have exactly the same bearings in.

 

[frank rabbets]

Nothing to lose by creeping up the nut until the play has gone. But has the nut come undone or have the bearings worn? Back in the day the rule was if the diff moaned or whined under load it was the crown wheel and pinion teeth having a rough surface. I ruined one once by driving off after having washed the diff out with paraffin, putting it back in the axle and not putting oil in. Drove gently back home and felt sick when paraffin steam came out of the filler hole. Anyway a dose of 10% molyslip and EP 90 made the noise gradually less as I drove the car. 1500 hours rebuilding a car and then making such a stupid mistake.

 

[Chris]

Just to emphasise what Jon and Frank have said here - the nipping up on the pinion nut at this point is VERY small. Don't be swinging on it putting a 1/4 turn on. When you set up the diff on the bench, the difference between not quite there and oh bugger is 3/5ths of a gnats chuff. One tiny bit at a time.

 

[Rob-o]

Thanks folks. I haven’t had a chance today but tomorrow I will nip up the pinion nut and refit the prop. I have a bottle of molyslip in the shed and fresh oil so I’ll change that and see how I get on.

 

[frank rabbets]

Molyslip helped me but I only tried it out of desperation. It is'nt a cure. I had a vision that it might polish up the crown wheel and pinion teeth. The noise slowly got better but it was still very audible a few hundred miles later. Then the car went to Switzerland and the new owner did 130,ooo k miles in it.

 

[Jon Wildsmith]

No need to un-stake the nut btw it will sort itself out when you turn it.

 

[Rob-o]

Thought it was time for a little update. Nipped up the pinion bearing, added some molyslip and have covered about 800 miles since.

It’s getting quieter! The pinion play hasn’t returned, and the diff oil looks good.

The rumble hasn’t gone altogether although it’s barely noticeable over the mud terrains now. I’ll give it another 800 miles and see how it sounds.

Rob.