My Differential Pinion Has Almost No Preload (Replacing Seal)
 

I'm getting ready to replace pinion oil seals in two differentials. The first is from a 1960 Ford F-100. The pinion gear housing actually unbolts from the axle with no other gears attached, so the preload can be easily set off of the vehicle. I went to measure the rotating friction of the pinion using an lb-in beam torque wrench, but there is no measurable friction. I can spin it easily with my hand and the shop manual says it's supposed to have 8-12 lb-in of friction for used bearings. So, I guess this means that the bearings are just worn to the point that there was no longer any friction left and I should install a new crush sleeve and then tighten the pinion nut until I get 8-12 lb-in of friction.

The second one is from my 1980 W116 300SD (the same 3.07 type that's in a W123 300D or W126 300SD). I have the differential removed from the vehicle, axle shafts off, and drained of oil. I measured the friction and got 25ncm/0.25nm/2.2 lb-in (which is almost nothing). The factory service manual states that used bearings should have 50-100ncm of friction WITHOUT the gear set installed. So, apparently the friction of the pinion of my differential is only half (or less) than what it should be, and that's with the added friction of the gear set that's not supposed to be installed.
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I guess this means that wear of the bearings has caused there to not be enough preload on the bearings and I can't use that as a point of reference when I reset the preload. I'd be happy to remove the gear set so I can set the preload to factory specs, but it appears I'd have to spread the case with a spreader which I don't have and then it might cause even bigger problems.

I'm thinking I should probably set the friction to the high end of the specs indicated without the gear set installed (which is 100ncm), since I don't have any point of reference for what it should be with the gear set installed since mine was too low. At least the setting will be better than it was before, and even if it potentially might not have as much preload as it should, I'll at least know it's not too tight, yet tighter than it WAS.

Also, I wish I could replace the crush spacer, but it appears the nose bearing won't come out with the pinion still in place, and once again I don't want to pull out the gear set if it requires a special spreader tool and a bunch of other difficulties.

Why would you need a new crush sleeve? Generally, a new sleeve is needed only when rotational torque needs to be reduced.

Preload can be increased by tightening the nut, no need to replace the crush sleeve. Be aware that when tightening the nut, preload will increase very rapidly. It will go from loose to too tight with less of a turn than you would expect. Loose is better than too tight.

Your torque measurement will be affected by the gold adapter making the reading low by a slight amount.

I agree with the others on reusing the old crush sleeve.

For others beware of aftermarket crush sleeves. The pics are parts from my Chevy Astro Van.
Notice the difference as the formation of the used sleeve and the new sleeve. I installed the new one and tried to crush it and it did not want to crush and I got scared I was going to shear the end off of my pinion gear.

I reused the old sleeve.

From the pics I think it is clear which sleeve would be easier to crush.

An unrelated issue is if the pinion bearing is just worn or is it worn enough that it needs to be replaced? I think to decide that you would need to actually inspect the inside of the bearing race and the bearing rollers.

Thanks for the advice, everyone! From what I've been reading about crush sleeves (from both Ford and Mercedes books and sites) is that it's highly possible that the sleeve may already be crushed too far, so once the maximum tightening torque on the nut is reached, there may not be enough rotational friction, which would indicate a new crush sleeve being needed.

I put a new crush sleeve on the Ford pinion because it came with the seal kit, but I haven't tightened down the nut yet because a new yoke needed to be ordered due to excessive seal surface wear. I suppose if it turns out the old crush sleeve is compressed too much, I can remove it and install the new one without having to pull out the new oil seal. For some reason I was thinking I'd have to pull the new seal out and then buy another new seal if the old crush sleeve was compressed too much.

I wanted to install a new crush sleeve for my Mercedes pinion, but don't think it's feasible for me since I don't have a spreader tool and don't want to make one and risk messing things up. So, then I'll just reuse the old crush sleeve and hope I can get the prescribed preload without going past the maximum nut tightening torque.

I replaced the rear wheel bearings on my car, and it was basically the same procedure with a crush sleeve, but the torque needed to crush the sleeve down was insane and I broke a socket in the process. I was able to observe how small tightening increments made an effect on the dial indicator.

I figured the yoke holder may make a slight difference in the torque reading due to leverage. I actually moved the torque wrench to the center where the nut is and took a reading again, and there wasn't any difference that could be seen with the eye, but good observation. It should be close enough in this instance.

I got an aftermarket crush sleeve for the Ford pinion and it seems like it would be more difficult to crush than the original (the bead is smaller). I got a genuine one for the Mercedes, but I'll likely not use it and hope I won't have to.

The race of the pinion bearings of the Ford are visibly worn down and have a few little rust pits. The roller bearings are smooth but have a rust pit or two, and likely wear. I'd like to replace them, but then it will likely need to have the backlash adjusted and I don't want to get that far into it. Realistically, it will probably be fine for a long time and the condition of the other bearings in the differential are probably the same.

I have no way of inspecting the bearings of the Mercedes differential without taking it apart, so I'll just have to hope they are good. My intention was to replace the oil seals while the axle shafts are out for replacement.

Funny story--the previous owner told me he spent $6,000 having a new driveshaft, differential, axle shafts, and flex discs installed at the Mercedes dealership. It turns out all he did was have some small shop install a used differential and axle shafts with old, cracked boots. The new brakes were not new; the master cylinder was leaking brake fluid all over, the "good" tires were mismatched and threadbare, the "excellent paint" was peeling off in sheets--in short, almost every claim he made about the car was a lie, but it was the only Walnut Brown W116 300SD with a sunroof I could find in my price range (even though it had been repainted black), so I bought it anyway and have sorted out most of the issues.

8-12 inch lbs. is 1 ft/lb on the high end, almost not detectable. If the diff's we're sounding ok and it was just a leaking seal, I definitely would not change the pre-load at all, especially on used bearings.
IMO, new seal, clean it up inside a little, fresh high quality gear lube and ride on!!!
Good luck!!!

Maximum nut torque? In the W126 FSM there is a minimum torque of 185Nm. That's pretty hefty.

Yep, this is why when anyone posts a high price for repairs, I ask to have the invoice posted. Most of the time they just run and hide.


Yep, I buy cars / items on what they are not what the seller tells me.

On a lb-in torque wrench that starts at 0, 8-12 lb-in (what it's supposed to be on the Ford truck) is up there a ways on the scale. But, the preload I measured didn't even read past 0 lb-in, so the bearings had no detectable preload, or were possibly loose, which is not good. I wouldn't want to put them back at that setting. Also, the preload will change once the yoke comes off, which it has to for the seal to be replaced. So, to the factory specs of 8-12 lb-in (for used bearings) it will go.

I was reading in some forums that (at least for the Ford) there is a torque limit that should not be exceeded when tightening the nut. In other words, if you are at that final torque limit for that nut, and there is not yet enough preload on the bearings because the crush sleeve is collapsed too much, then they say to stop and replace the crush sleeve before you strip out the threads.

I'm of the same mind, but the seller had me in a bad spot because I wanted a specific make/year/model/color/option of car and after years of searching his was the only one I found in my price range. So, I dealt with the consequences. I had to ride the train for six hours to meet him and then he had the nerve to tell me to be timely and not waste his time.

The car had an empty fuel tank, no coolant, and wouldn't drive above 10MPH until I rigged the vacuum system. The transmission turned out to be bad, and the nice interior was sun-baked and trashed. The rear seat was a blue one out of a W123. The great stereo system he said was working was an early 1990s unit that wouldn't power on and he had ripped out the speakers. Rust and dent-free it was not. He also didn't have the title, but I eventually got one after a few months.

If I wasn't so picky about the car I wanted and specific with my vision, there is no way I would have purchased it. But, with the car being so old, it's not unreasonable to expect everything to need replacing, and pretty soon almost every single mechanical component will have been rebuilt or replaced, so it will be like a new car. I also have the peace of mind of knowing that the repairs I've done were carried out correctly.

PO on my 84SD fixed 1/2 of a system. Compressor for the AC but the push button didn't work and the compressor locked up. Brake master but pads were on metal etc, etc, etc.

I'm hoping to sell 1 SD which will leave 1 more, the Dodge Cummins, a 78 280Z that should be a DD in a week or so, a 15 Volvo with 50,000 left on the warranty & an 08 Prius. That's 5 licensed vehicles for 3 drivers. Should be enough and I'm getting tired of working on them.

There's a thread on rebuilding steering boxes here which shows how to make a tool (apparatus) to measure the smallest rotational frictions factors. It involves a wooden board with a hole that attaches to the shaft you're moving, a couple weights and some high school physics including the math.

In your case the math won't matter. You mount the board (level) on a horizontal oriented shaft and move the weight along the board starting near the shaft center until the shaft rotates. That will be the reference point for your goal of resetting the bearing friction.

I looked a bit for the thread yesterday but couldn't find it. I believe the simplicity of what it would take to manage your issue is much less than setting the friction on the output shaft bearing on a steering gear.

The correct tooling to measure such low torque is a torque screwdriver - it has a dial on its top and not everyone has a use of it.

The other correct way is the way our member "army" showed us with a scales setup from wood, thread and some weight. - Infact some old mazda repair manuals show a similar trick too when setting wheel bearing preload.

The FSM shows a similar tool but much smaller with predetermined weights which I presume come with the tool.

It's just a flat blade with a hole in the balance point and a set of hanging masses.

Yeah, the factory service manual shows what's essentially a torque screwdriver. The lb-in beam type torque wrench I have is suitable for the job, and is common practice. My area of concern was that the pinion bearings of the Ford truck differential had no preload (and may have been loose), and also that the pinion bearing friction in my 300SD's differential was almost not measurable due to having almost no preload like it was supposed to. I'm sure in both cases it's due to wear.

So, since the preload on my 300SD's bearings was too low, it led me to wonder what the correct preload would be since I can't use the previous setting as a reference (and I wouldn't have liked that method anyway, since there is no guarantee the setting is correct). And then the specifications in the factory service manual is with the gear set removed from the housing, not with it installed as mine is. Having the gear set in place no doubt adds friction, but how much I do not know.

So I think the most logical thing to do is set the preload so I am at the high end of the settings indicated for used bearings in the factory service manual, because 1. the bearings will not be as loose as they were before 2. they won't be too tight, and 3. they are likely to be in the correct range.

It would be nice to know if someone who has done these before has taken note of the friction on several different differentials which have the axle shafts removed but the gear set in place so they could give me a definite proper setting. But, I think going with my plan will suffice.

In reading through some threads on pinion seal replacement from W123 owners with the same type of differential, they are reporting 5 lb-in, 8 lb-in, and 10 lb-in for differentials removed from the vehicle and no axle shafts installed, but with the gear set in place. This is right within the factory service manual specifications for used bearings without the gear set installed, so the gear set either has a negligible effect on the friction, or the normal bearing wear has caused them to get to that value.

Either way, they are higher than at what mine were, which was about 2 lb-in. So, I feel better about my plan to set them in the 8-9 lb-in range.

Yours is on the bench without axles, and axle bearings in the wheel area. I didn't see directions for this project on the bench.

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Exactly. This is the issue I am having, but it seems that setting my pinion bearings to the high end of the settings should be close enough to compensate for any drag from the side bearings. It will at least be a more correct setting than what they were at before.

There may be two issues with your evaluation.

The length of a torque wrench handle is altered because your socket isn't centered with the pinion shaft. That alters the moment arm. Imagine using two pry bars. One is 1 ft in length the other significantly longer. Which will generate the most leverage. Imagine sitting half way to the pivot point, center, of a seesaw with your seesaw buddy being the same weight sitting all the way back to his end of the board. The distance from the middle is significant

The second factor is that there's a significant load generated by wheel bearings, friction on axles when leveled resulting in them sitting on jacks. Imagine how much force is needed to rotate a tractor trailer wheel as opposed to the force required to move a 12in wheel on a lawnmower.

What you have here, I believe to be a situation that the FSM does not address. I have certainly exaggerated the previous examples but only to share my concerns of the concepts involved.

These factors may be is significant when the measurements are so delicate as a Ncm. That's the rotational friction unit which a dentist uses as instructions when he screws a tooth implant into your jaw.

Best of luck.

The socket not being centered on the axis of the pinion shaft will not be a problem as the torque wrench will be attached to a socket over the pinion nut when I check the friction. I also checked it with the wrench over the center before to see if there was any noticeable difference, and there was not. But, it's a valid point.

The factory service manual covers checking the friction with the differential installed in the vehicle and the axle shafts in place. This same situation would apply for a differential that's out of the vehicle and on a bench. Where I am having a problem is the friction I was reading was less than what it should have been even with the gear set out. The reading with the gear set in place should be the same or higher than with it out, not less. So, this indicates the friction in my differential was far too low, and therefore could not have been used as a point of reference.

Had I had the differential installed in the vehicle and used this method, I would have gotten a higher friction reading due to the axle shafts being attached and turning wheel bearings and possibly wheels, however it would have been false security as when I went to set the friction to that same amount, I would have also been setting it too low (without knowing it).

Setting the friction to the previous value essentially allows for replacing of the pinion seal without changing the friction value, however, if the previous friction value was too low due to wear, it will be too low also when going back together. So, the method of setting friction back to the previous setting is only a good method if the previous setting was correct, which is just an assumption or hope. Now, if the differential has lasted a long time at the "too low" setting, it may well last a long time further at the same setting, and removing the differential may not be practical in all situations, but I'm glad I decided to remove it so I can get it more correct than it was.

The factory service manual also covers setting the friction with the differential out of the vehicle, but with the gear set removed, so that is a different situation than what I have before me, however, I can safely say that I do not want the friction set any lower than what it specifies without the gear set in place, as it is on mine. I can't know how much friction the gear set and side bearings add, but if I set the friction to the high end of the range I should be close, and I've read from others that have removed their differentials and axle shafts, but have left their gear sets in place and have checked the friction before removing the nut, that their friction was typically in the middle to high end of what the manual states it should be for used bearings without the gear set in place. So, this means that either the gear set and bearings make a negligible difference in friction, or after normal bearing wear it puts them into that range. So, I should be safe to set mine into the high end of the range.

I definitely don't want the friction with the gearset installed to be lower than what it's supposed to be without the gearset in place. Now I'll be able to get it closer to the correct setting and hopefully that will help it to last a little longer than it would have had I put it back to the previous setting.

I put the nut on the pinion, without the yoke in place, to see how much friction there is with no preload on the pinion bearings. It was exactly the same value as when the nut was on, so there was no measurable preload on the bearings before, or the bearings may have actually had slop.

So, 25ncm is how much friction there is due to the side bearings, gears, and unloaded front bearings. I think I could add 25ncm to the recommended bearing settings and come out spot-on, but I might still refrain from exceeding the 100ncm limit just to be safe. Even if 25ncm is the correct value for the friction of the gears and side bearings and setting the friction at 100ncm actually puts the pinion bearing friction at 75ncm, that's still in the middle of the range, which is fine with me.

Also, were KOYO bearings used from the factory in Mercedes differentials in 1981? That's what are in mine, and I wonder if they are original.

I would not take the carrier and pinion out. I have not done so in a MB, but have replaced carrier bearings and pinion bearings in a jeep. Setting up gears is not for the faint of heart, and learning by trial and error means lots of checking, adjusting, rechecking, more adjusting, swearing...

Put the seal in, slap some locktite on the threads, tighten the pinion nut to get you back in spec and install it. I would assume the pinion preload is measured with the carrier installed but without the axles unless specified otherwise.

Without preload on those bearings, the gears will be noisy at best and broken at worst.

I'm trying to avoid removing the gears. The pinion nut gets staked in place, so no thread locker is needed. The factory service manual says to measure the preload with the pinion gear in place, but not with the carrier gear, so therein is the confusion because I sure don't want to remove the carrier gear so I can do it the way the book says to do it.

The book also says it can be done on the vehicle, in which case you are measuring the amount of force it takes to turn the pinion before you remove the nut, and then tighten up the nut so the friction is once again the same. The flaw with this method is if the setting was wrong before, it will be wrong again. In my case, my pinion bearings did not have any preload, so if I had followed this method they would have once again ended up with no preload.

In my situation, there was no amount of preload for me to use as a reference, because my bearings didn't have any preload, and I couldn't set the bearings according to the book's specifications because the carrier gear has to be removed in order for that to happen.

Ultimately, the carrier gear and side bearings don't create much more than 25ncm of drag, so even though the book says to remove them in order to set the preload on the pinion bearings, leaving them in place isn't likely to make any real difference, so if a person wants to play it safe, they can still set them at 100ncm which would put the amount of friction at just the pinion bearings at around 75ncm, which is right in the center of the 50-100ncm range.