My Differential Pinion Has Almost No Preload (Replacing Seal) - PeachParts Mercedes-Benz Forum

Squiggle Dog · #1 03-25-2019, 11:23 PM

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.

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.

tangofox007 · #2 03-26-2019, 08:56 AM

Quote:

Originally Posted by Squiggle Dog

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.

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

97 SL320 · #3 03-26-2019, 10:40 AM

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.

Diesel911 · #4 03-26-2019, 11:25 AM

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.

Squiggle Dog · #5 03-26-2019, 02:43 PM

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.

97 SL320 · #6 03-26-2019, 06:01 PM

Quote:

Originally Posted by Squiggle Dog

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.

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.

Quote:

Originally Posted by Squiggle Dog

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.

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

Sugar Bear · #7 03-26-2019, 02:47 PM

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!!!

Squiggle Dog · #8 03-26-2019, 07:01 PM

Quote:

Originally Posted by Sugar Bear

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!!!

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.

Quote:

Originally Posted by SD Blue

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

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.

Quote:

Originally Posted by 97 SL320

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.

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.

SD Blue · #9 03-26-2019, 05:46 PM

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

Junkman · #10 03-27-2019, 12:20 AM

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.

Clemson88 · #11 03-28-2019, 09:27 AM

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.

Zulfiqar · #12 03-28-2019, 11:32 AM

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.

Clemson88 · #13 03-28-2019, 12:16 PM

Quote:

Originally Posted by Zulfiqar

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.

Squiggle Dog · #14 03-28-2019, 01:08 PM

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.

Squiggle Dog · #15 03-28-2019, 01:30 PM

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.