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Replacing 80 rear transfer case seal

Chris

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I am by no means the first person to tackle this job, but as there will be others to come, it’s always worth having as many references and help guides as you can get your paws on.

I would grade this as well within the capability of most home DIY mechanics. Probably a rating of ‘6 out of 10 spanners’. Very few tools needed, only special tool would be snap ring pliers. No measuring or technical stages. However, as I shall explain, there are some stages that require you to be experienced in auto problem solving. If you have won the Crystal Maze or been on Scrapheap Challenge, you’ll be fine. Either that or seek the help of an adult.

I did this with the car on the drive, not raised at all. I have listed some part numbers in the narrative. Please do not use these blindly to order parts without checking. They are just there to type into an EPC so that you distinguish between stages. Some of them have more than one part number for different sizes. I have picked these arbitrarily.

Drop the rear prop shaft. 14mm spanners. It’s worth servicing the prop whilst it’s off. I gave the yokes a good scrape out and pumped them with grease until it came out of all 4 bearings and split the sliding joint too and gave that a real clean, greasing the splines before reassembly.

Drop the oil and leave to drip for a while (do the prop in the meantime)

There are 9 x 14mm bolts holding the extension onto the transfer case. Some are long and some short. They cannot be confused. All the long ones run down the right side under the bottom and the short ones up the left side and over the top. All are easily accessible with a spanner or socket.

Disconnect the speedo plug and the two lock sensor plugs on the top of the box. The smaller of the two (angled into the box) is the one you should disconnect to enable the better low range gear changes and full control over the centre diff lock button.

The extension is on two studs so it can’t fall off. It’s not that heavy but put two long bottom bolts back in to hold it as you prise it off the transfer case. Watch out for the oil pump drive key falling out and some thin large round shim washers that might come out too. If they do, you can put them back onto the TC using the oil film to ‘stick’ them in place. What is left on the truck should look like this:

IMGP4416.jpg



The brown is 17 years of residue.
OK this took me around 40 mins to get to this stage.
So it’s onto the bench from here.

This is what’s facing you. The small clock dial is the oil pump. Nothing to mess with there but there is a small drive key that sits in there that MUST be lined up again with its opposite slot when you come to put the two halves back together. It just turns by hand. Best just leave it be.

IMGP4423.jpg


Now we are into the real workings. The first challenge is getting the snap ring 90520 39022 off the splined shaft. I had some long SR pliers, which were no help at all. The gap is too narrow to get the pliers in! I thought about grinding them down. The FSM says use two screwdrivers. So I did. Having grown another arm and holding a 4th screwdriver between my teeth and a 5th gaffa taped to my head, I managed to get the end of the ring lifted onto the shaft. From there it took me seconds to work it round and off. But probably 45 mins at least to get to that point. I ground down a long wood screw that was useful to get under the snap ring to stop it reseating.

IMGP4425.jpg


This exposed coupling assembly 41330 60010 that could simply be lifted up and out. It’s several kilos. Don’t quite understand it, but it seem to be a mass damper of some sort.

IMGP4427.jpg


Next comes a metal shield held in with 2 x 12mm head bolts. The bolt pattern is unique and can only be fitted one way. There is a third bolt to come out which does not go though the shield.

IMGP4428.jpg


Underneath there is a thick alloy plate. The plate is a snug fit and I used 3 bolts screwed into the boltholes to lift it out. This exposes the speedo drive gear. Another snap ring; this time easy to take out with the SR pliers. Lift out the main speedo drive gear 33481 60090. It goes in splined edge upwards - just in case you forget.

IMGP4430.jpg


IMGP4433.jpg


Underneath, one more stupidly tricky snap ring 90521 84002 against the main bearing 90363 50005 to go and that’s it. A little tricky to get up the shaft around the secondary speedo drive gear - so don’t bother, leave it there and when you pull the shaft out it will drop off the end into the casing. When you put it back, you can get the gap in the ring around the speedo gear.

IMGP4434.jpg


I supported the casing in the vice so that the companion flange was clear, put a long socket over the end of the shaft and whacked it once. It moved easily.

IMGP4435.jpg

IMGP4437.jpg


The seal, 90311 58008 came out easily. It was as hard as nails, completely inflexible and worn. Well it is the best part of 20 years old. I tapped the new one in using a roll of brown vinyl parcel tape. Perfect size.

IMGP4439.jpg


After giving everything a real good clean and inspect, including the main bearing which seemed perfect, I put it all back together. This took me around 40 mins including seating the new seal. No mysteries at all. I have to confess that the final snap ring which took so much getting out, was placed over the splines and got pretty much rammed home using a couple of large flat screwdrivers.

Here it is all clean and reassembled. I used Wynns black RTV sealant after cleaning up both gasket faces with a steel rule. Again I used two of the long bolts to seat the casing back onto the TC. It slid together with ease. I left it whilst I put the prop back on before filling it with lovely new oil.

IMGP4440.jpg


Went for a road test where I got 10p off a litre at Tesco. Bargain. £1.26. Eee,it were like the olden days. I'm happy, the car's happy.

Job done.

Chris
 
The heavy lump is the viscous coupling :) if it's playing up you can just leave it off when you put it all back together.
 
I would just like to add that if you remove the speedo sensor with the speedo pinion gear you will have better access through the hole in the casing to the last circlip which holds the shaft in place.
 
But what is that exactly Jon. It's clearly not a solid machined lump, it is made of several parts. It sits on the main shaft, on splines. So it can't turn independently. it didn't seem to engage with anything on the TC and neither could it slide up and down. It's just a solid lump spinning. How come you can leave it out?

Genuinely intrigued.


Chris

Rob, I could not get the speedo drive out for love not money. Absolutely jammed solid in there. Took the little keeper plate off and everything. TBH the last clip isn't the hardest. But a good tip IF you can get the drive out of your casing.
 
The viscous coupling looks like this inside:
viscous-coupler.gif


It is connected to the centre diff ring gear and rear output. It is filled with some sort of oil which is has shear thickening properties, basically the greater the difference in angular speeds of the ring gear and rear output caused by loss of traction in at least one wheel the more friction the coupling applies. As it does not transmit drive you can leave it out and the centre diff will be fully open, simples.
 
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Rob, I sincerely wish I could say "right, cheers for that' but I can't I'm afraid. I still don't quite get it. I do understand oil and plates and holes etc plus shear properties - makes perfect sense. But I don't understand how this unit operates. My problem is that I can see the shaft - which locates into the splines in the CD. I can see that the larger outer splines in the CD engage with the viscous coupling unit too. But to me it seemed that ALL of that was locked together, there are no other moving parts, are there? The inside and the outside of the VC didn't move separately for example. If the VC had been effectively a joint between two halves of a shaft, I might have understood that. But effectively it's just a big mass locked onto a shaft that is turned at one end. I can't see what it 'couples'.

What am I missing old chap?

Chris
 
Chris,
There is an excellent PDF doc on this subject that I found here. Suggest having a read on page 10 for the explanation of how the drive works through the VC and why the centre diff still functions without it, just as a pure open diff.

Cheers,
 
you might not have tried hard enough to rotate the VC or yours may be starting to lock up.
 
Chris I was just as confused as you were when I first took it apart, I know it does not look it but the viscous coupling is not a solid lump that just sits there, it is split into 2 different parts which can rotate independently given enough force. One part is connected to the centre diff ring gear and the other is connected to the rear output shaft. If there is any difference in angular velocities between the 2, caused by a wheel slipping somewhere in the drive train, the viscous coupling applies a torsional load ensuring some torque is transmitted to the other wheels. If the rear wheels loose grip the rear output shaft rotates faster than the ring gear and if the front wheels loose grip the ring gear rotates faster than the rear output shaft. Think of the VC as 2 fiction plates, one attached to the diff ring gear and the other attached to the rear output shaft, and difference in angular speeds causes the plates to slip and as a results transmits some drive to the axle with most grip.
 
Ahh hah!!! That's the magic I was looking for. It DOES move in separate parts then. Thanks Rob. Andrew, I shall have a read mate thanks. Jon, didn't try hard enough? I didn't try at all. I looked at it and said 'Hmm, solid lump, moving on....'

Now I genuinely AM with you.

Thanks lads.

Chris

PS I have a spare! :thumbup:
 
Fantastic read up and pictures to go by for myself and others in the years to come. thanks chris. :thumbup:
 
You're welcome. Feel free to add to the thread as we go along. We could do with a write up on the front extension housing too. Mine isn't leaking so it must be someone else's turn. :hand:

Although after this weekend who knows what will be leaking next.

Chris
 
Front extension you say...

Well mine is leaking. So just maybe I could assist in that department. When is a good time for me to drop my truck off Chris... :lol:

Oh and I see your name has turned green. What, are you the hulk or summing... :obscene-birdiedoublegreen:
 
Ryan, I have said before, I'm always happy to help out. If you're sure you can afford my hourly rate!

I would think it's very similar to the back one.

Chris
 
Jon Wildsmith said:
The heavy lump is the viscous coupling :) if it's playing up you can just leave it off when you put it all back together.
How does one know if it is playing up please Jon? I'm sure it has been covered before somewhere but as Muxley seems to be weeping a bit from the rear of the TC, it could become pertinent for me to find out at some stage...
 
Gav Peter said:
How does one know if it is playing up please Jon?
Truck feels 'tight' going round tight bends like a roundabout and might even be chirping the tyres when you're not going fast enough that it should do that.
 
I'm currently trying to tackle this job but i cant get the rear extension off. The seal is broken, the speedo sensor is removed along with the 2 bolts on the top. The out put shafts seams to be stuck in the transfer. Its in neutral too if that helps. Any help is apreciated! Thanks!
 
There are a couple of dowels in the mating face that mey be holding it on. It needs to come off straight. Twisting it by levering will probably make it bind. There is nothing else holding there. 9 bolts, disconnect speedo cable. That's it. The rest is simply dark magic I'm afraid.
 
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