Scot's Rear End -- The IRS

Ahh yes. I’ve heard of that. Never used it tho. Now is the time!

And here is something nice. These came back from Mara Plating today. This pic is distorting the colors, and I only opened one so far. But this is an amazing renovation of 60-year-old knockoffs. They were beat up and loosing their chrome. Gorgeous


!
I’ll take a good pic of all 4 and post it tomorrow.

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@Confused1, another data point we were talking about.

I just call it “engineer’s blue”. I’ve had the tube forever.

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Here’s a pic of all 4 spinners. I took them outside to make a good picture and the blue sky and tree reflections are a nuisance. Trust me, the lettering is terrific and the plating is first class.


I am very pleased with Mara’s work and their friendliness.

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It has been a very long time since I’ve been into a differential for serious work. Like 1965 when we stuffed a 1962 Dodge 426 Wedge’s running gear into a '56 Chevy Belair. I forget what the differential was, but a Dana 44, or 60 IIRC. Long time ago.

So, seeing as you all have convinced me I need to go through this thing to make sure it is put together correctly, I’ll start with the very basics.


Here are two pics showing the bearing caps are actually in the right location and orientation. Note on the right that the stamping of 11 in vertically oriented just like the 11 on the flange for the cover. That is correct.
On the left bearing cap is the 11 horizontal and that matches the 11 on the cover flange. So, Step 1 is good to go.
Next I’ll run a pattern with this Prussian Blue. Can’t say as I’m impressed with it though. It is very dark and I think it’d be better to be light colored. Nonetheless, moving forward…

Here are some measurements and patterns:
The scribing on the edge of the ring gears indicates the backlash is 0.007". I measure 0.0095". I don’t think that is too far off. The ring gear run out measures 0.0035" and it is allowed to be 0.005"; so that is good. I haven’t measured the axle or pinion run out yet. I did try to measure the pinion pre-load. It is 0.00 lb-in; as in no pre-load. However, I’m told the pre-load spec applies to new installation and there is no spec for a used differential. And that 0 lb-in or close to it is common.
the gears all look good, no undue wear is noticeable.
On the patterns, the drive side is almost to the edge of the toe. Back in my early years that was called a competition setup as the pattern moves towards the heel under pressure. (So the pattern shifts towards the heel and, in this case, presumably becomes more centered.) The drive side is fairly centered from crown to root. On the coast side, the pattern is more centered but it looks to be rather deep (down in the root) to me.
Backlash 0.0095"


Run Out 0.0035"

Just showing another run out view.

Drive Side Pattern

Coast Side Pattern

Assuming these gears have not been disturbed since initial install, you likely have a typical wear pattern. If you try to change it, it will likely get noisy or have problems. If the bearings look good, I would leave well enough alone. But I will bow to other more experienced folks on here as I have only done 4 diff setups. They all are still working…

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Hi Scot,
Common because bearings wear over time.

That shift in the pattern on the drive side is usually caused by insufficient preload of the pinion bearings. The preload actually diminishes under hard acceleration and if it was marginal to begin with, a shift in tooth contact results. I suspect this was realized and is the reason the preload applied to the pinion bearings has increased from circa 10lb/in for the S1 cars to circa 26lb/in in Salisbury diffs used in the late 70s.

Brent

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Thanks Bill for your comment. I know the differential has been opened up, but I cannot tell if anything was changed. Probably the pinion seal and probably the output shaft seals. We know two of the output flange bolts were replaced and I’ll be replacing them with correct ones. I can see that there are shims between the carrier and the outside bearing housing, but I doubt I can get an accurate measurement on them. I’ll give it a try though. My guess is the factory setup is what I’m still looking at.
I note in the manual that it is recommended that the pattern for the drive gear be biased towards the toe. These are certainly that.
Brent. What you say on the preload makes sense to me. I know a current DANA 44 pinion pre-load is just 15 lb-in. Not so high as the later Salisbury specs.
My question is: should I leave it be?
What is the consensus on the oil I should use?

I am impressed by what a good job you are doing, and can see you have been around mechanical stuff for a long time

from just an amateur guy here, you are doing a great job off fixing up what some so-called pro did ?

I’ve been though the same BS, and I think they charge at least $A4500 locally for a full IRS job these days, maybe @BrentKeats can say if I am way off, I think he is a pro (and I dont want to disparage most pros, its great that they are on a forum, and a half-decent one can save your backside in the real world)

Once, (about 20yrs ago) bought a “rebuilt by a pro for $3500” V12 IRS to replace the one I blew up (one of the weirdest parts pickups I ever done, the sellers Mrs was screaming at everyone about him selling it too cheap, and the seller got involved in a near-scuffle with my mate)

When I had to dismantle it (due to a subsequent snapped outer drive shaft axle!), I found all sorts of poor workmanship quite similar to yours

That diff is marginal, like mine was, but mine had a better gear marking pattern, some pinion preload, the same backlash, but less runout.

I allowed mine to remain unmolested, as I dont do many miles (and its a big & risky job)

Yes you probably got to change those output seals, it is an exacting job

You can get special Yellow diff paint, but I found the Prussian blue to be just as good, more readily obtainable, and cheaper.

Wow that IRS has been worn and abused more substantially than mine,

It would be interesting to know how much a quality shop would charge to fix that up as good or better than you, probably more than what I said if it was done better

It cost me about $A1500 in parts, (that was 8 years ago)…that would be about US1000, but includes brake re-sleeving and painting

Parts are more expensive here because we usually have to freight items from the UK or USA, as even after freight, they usually cost a handy amount less than locally sourced product (local suppliers got to try and make a profit as well). Labor is (now), mostly well over $A100 for a specialised pro

took me quite a few weeks

Hi Scot,
The preload is a measurement of the torque required to rotate the pinion alone, without it driving anything. This is much easier to do when the diff centre is removed from the housing, but it can be done in a pinch, by measuring in the area of the backlash.

Your differential will use shims to set the pinion bearing preload and the outer bearing should be a close running fit on the shaft. Accordingly, you could adjust the preload without striping the diff housing if your intention is to not do any other work relating to the diff centre. Some will say that used bearings shouldn’t be preloaded to the extent of new bearings. I don’t go along with that thinking, nor does a retired production engineer/manager of Timken Bearing who is a friend of Bill’s and with whom we discuss such matters. If you didn’t feel comfortable going the full monty of the current specified preload, using the original specification for the S1 diff would be a compromise.

Brent

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Bill, I tend to agree with you and have others not in the J-L conversation also agreeing. That is, leave well enough alone. My only real experience with re-setting existing gear sets (I had specialty shops do the work) was not satisfactory and resulted in gear whine on the coast. Very irritating. :slight_smile: On the other hand, at my current age I cannot hear squat…so what’s to worry!
Brent. I like your comments (and thoroughly enjoyed you thread on planetary gears a few months ago!). So, yes, I believe this differential has seen use. But I also believe this car has spent far more time in the shop than on the road since new. For instance the odometer reads under 12,000 miles. The numbers all line up, but who knows if it has gone around at least once. For giggles here’s a pic.


I am under the impression that the contact pattern shifts towards the heel when under acceleration. Is that incorrect? Anyway I’ll have to think about trying to adjust that pinion.
Tony, thank you. Such kind words, but I am not a real mechanic, just an anal tinkerer and I’ve been doing that for as long as I can remember…I took my tricycle apart for cryin’ out loud!
The interesting thing about the Jag’s differential is that it is essentially a DANA 44 and folks who work on Jeep differentials should be able to do a great job with this Salisbury. We have a great shop within driving distance of my home in Coventry West. But they are so backed up it would be months before they’d work on my differential and actually, they don’t want any more in the queue. Still, there are 4X4 shops around. I don’t know what the going price is for a rebuild; I’ll check that out locally.

Some more numbers: The Pinion runout was 0.005" measured on the shaft’s end. This is not a good place to take a measurement as I doubt that shaft end is machined flat…and it has spotty paint on it. The runout spec. is 0.003". I can not induce any end-float by pulling on the input flange. Likewise with both output flanges: I cannot measure any end-float, but the runout is: Left - 0.007" and Right = 0.002". Again the output flange is not a good surface to get an accurate reading. I Note the manual gives an output end float of 0.001" to 0.003, but nothing for runout. Maybe if I pulled harder, I’d find 0.001" of end float.
Actually Tony, I think the gears are not in too bad of shape. The teeth all look healthy, I feel no bearing roughness. It is too hard to get a photo of the pinion gear, but I’ve inspected in while rotating it and it looks very good. The pattern is close to what the manual says is ideal but a bit low and a bit more towards the toe.


Thanks for your last comment Brent. I finally figured out I shouldn’t be turning the ring while measuring the pre-load. I’ll go back and do it again in the backlash area as you say. Still, it’s going to be zero I’ll bet. I’m afraid I don’t see how to adjust the pinion pre-load without removing the center section. All the shims for the pinion are installed on the inside of the carrier. Did you have something in mind?

Hi Scot,
The output shaft bearing setup is another area where evolution has occurred. Where end-float was once specified, its now pre-load for the systems that use opposing taper roller bearings. The Type 3 differential that used double row, angular contact bearings had pre-load built into the split centre race of the bearing (no longer available)

When I read your earlier Post that you had a Zero reading for pre-load, I thought, “that can’t be right, otherwise, theoretically, the pinion would be rotating as if on air bearings”. You should have some resistance from the oil seal at least.

The shims for adjusting pre-load are just inboard of the outer bearings. The Pinion seal has to be removed and replaced and may not be a bad thing to do, given that you have the diff out of the car. The only other shims associated with the Pinion Shaft are under the Cup of the inner Taper Roller Bearing and these are to adjust the axial position of the pinion gear relative to the Crown Wheel. You add or subtract shims under the inner Tapper Roller Bearing Cup to adjust the height contact pattern on the gear tooth.

Brent

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Hey…you know this stuff! Thanks for the edification. On the pre-load of the pinion, I went back to measure it again and I discovered that my lb-in torque wrench is not able to get a measurement that low; it is just a bending beam wrench but just too large for measurements under 25 lb-in. I was disappointed it that. That said, I can feel there is some resistance to turn the pinion flange by hand. 15 lb-in? I don’t know; it doesn’t feel like much and feels more like stiction than pre-load. I’ll see if I can’t borrow a more sensitive wrench.
Brent are you saying that pinion pre-load shims, the small diameter ones, can be removed or added to by removing the pinion seal, lifting out the tapered bearings and then the shims? The shop drawing shows these as a stack-up to be inserted from the pumpkin (carrier) side. In my case I would want to remove one shim and see what that does to pre-load (without the seal).

Here’s more pics. I focused on the condition of the pinion and the ring. They look very good to me. And I note the pinon has the same number on it as does the ring gear. 2464. So they are indeed a matched set and were run-in at the gear factory. That’s good, eh? At this point I am reluctant to mess with the pinion/ring set, but I’d take a shot at the pre-load in an attempt to control the pattern under load. What do you say?

Hi Scot,
The shims inserted from the diff centre end are for setting the position, axially, of the pinion shaft. There will be a value etched or engraved on the gear end of the pinion shaft, that indicates the distance above or below the standard Cone Setting value of 66.67mm. The Cone Setting is the distance from the centre line of the Crown Wheel to the ground face of the gear end of the Pinion Shaft. Varying this distance will vary the contact of the Pinion and Crown Wheel from the Crest to the Root of the Gear Tooth Form.

Pre-load of the Pinion Bearings is accomplished by varying the shim stack between a shoulder on the Pinion Shaft and the inner face of the outer Taper Roller Bearing. These shims can be accessed by removing the Seal at the Companion Flange end of the Pinion Shaft and the bearing closest to the Companion Flange. This bearing should be a close running fit on the shaft.

With regards to measuring the Pinion Bearing Pre-load, simply turning the shaft and driving the Crown Wheel at the same time will be inaccurate. As I mentioned earlier, setting the Pinion Bearing pre-load is normally done with the diff centre removed and before the Pinion Shaft seal is installed. That way, you are only measuring the pre-load on the bearings and not the drag of the seal and Crown Wheel. That’s why I said that, at a pinch, you can measure the pre-load in the Backlash area of rotation of the Pinion Shaft, if you’re not going to remove the diff centre.

If you don’t have an lb/in torque wrench that can register low enough, a spring balance can be used arranged so that its pulling on a line tangent to the circumference of the circle the radius of which is where you have the spring balance attached. Torque = Force x Length from Pivot.

You know the Torque you want (25 lb/in) and you can measure the Length of the Lever from the centre of the Pinion Shaft (the distance from Pinion Centre to where the Spring Balance is attached). Therefore, to calculate the Force to apply, divide the Torque by the Length of Lever.

Brent

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a very inexpensive digital (or analog) luggage/fish scale will work for this situation, used as you describe, as a “spring balance”

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I have exactly that Tony - a couple of old analog fish scales I use to set trigger pull on my rifles. I went looking for them as soon as I recognized the dilemma with my torque wrench. They’re here somewhere…!

And thanks Brent your comments are most helpful.

When I pulled the seal out of the right side’s output shaft, I noted it was quite soft and flexible…even after 30 years of sitting. It certainly was very clean and showed no wear. As the differential had a bit of oil in it all these years and there’s no evidence of leakage, I think I’ll replace the one I pulled out and leave the others alone.

from my memory, the side shaft seals are the time consuming job to do, and far more expensive and exacting

The pinion seal on a Jag or Dana 44, I consider to be a relatively quick and moderately easy job, can be done in situ with only a few tools, maybe 2 hours if you work hard, not really supposed to if you have a “crush sleeve” model, but I avoid them, but would do the same anyway, mark the pinion nut, measure pre-load before I took the Pinion Nut off, and just do it back up to the same mark & pre-load, I get the seal out with a self-tapper slide hammer, pops it right out

Hi Tony. The side shaft seals are just a bugger to get as you have to pull the IRS apart. But mine is apart and I suppose it would be wise to replace the pinion shaft seal ($11) as well as the output shaft seals ($14). I have a seal extractor around here but can’t find it. I just used a longish screwdriver to remove the one that’s out. Not a hard thing to do at all…a few minutes. So, I guess I’ll do them all as every thing is 30+ years old.

Did you notice the bearing shot I made on the output shaft? It shows a Bower made in USA bearing. That was before NTN bought Bower. It tells me this rear end has been apart.