Differential Pinion Pre-Load Adjustment

[Peter]

I want to (re)-adjust the Pinion Pre-Load because the differential is whining after a change from 4.08 to 3.27.

I use the following procedure:
• Both rear tires / rims must be removed for the measurement.
• When checking, the support tubes must be horizontal and the brake drums must be removed.
• With disc brakes on the rear wheel, the brake pads must be pushed back and the handbrake released max.
• The current friction is +/_ 1 Nm. This will be gradually increased by tightening the groove nut  to 20 - 25 cmkp = 1.96 - 2.45 Nm.

The questions:
1. How much Nm is needed to tighten the groove nut? I used around 10Nm and the groove nut was not moving an inch!
2.If I would make a mistake and over-tight resulting in a crushing too much the “crush sleeve”, can the crush sleeve be changed by taking out only the flange, seal ring, bearing and then the crush sleeve, without disassemble the whole differential?

Thanks, Peter

[Benz Dr.]

We had this problem last winter and we made up a fixture to hold the pin socket tightly to the nut. Any other method would make it pop off although we did find that a high-quality impact gun would make it turn enough to affect adjustments. We also found that the crush sleeve doesn't '' crush '' very easily at all and that we had to let everything relax overnight a couple of times until everything settled into place before we achieved success. Then, after a couple of hundred miles of test driving, it loosened up enough that we had to go back in and tighten it some more.  We did that with the axle installed in the car by using a high-quality impact gun. It's not easy to get right, not even close to easy.

I believe you could remove the crush sleeve with the axle in place. I would try to tighten it first.

[Shvegel]

It takes a ton of force to get the crush sleeve to crush. I usually stand on a breaker bar with a clamp keeping the socket in place. You can change the crush sleeve in place as you described.  My fear is the pinion bearing races are not driven all the way home.  Hopefully they are now.  They are sneaky buggers.  I use a screw press to make sure they are all the way home. 

[Benz Dr.]

It takes a ton of force to get the crush sleeve to crush. I usually stand on a breaker bar with a clamp keeping the socket in place. You can change the crush sleeve in place as you described.  My fear is the pinion-bearing races are not driven all the way home.  Hopefully, they are now.  They are sneaky buggers.  I use a screw press to make sure they are all the way home.

Your assessment is accurate.  That crush sleeve is anything but.

[Peter]

Thanks Gents, very helpful information.

Peter

[450sl]

I used a long scaffolding pipe as breaker bar to get it crushed............

[Nicolas Aristodemou]

Peter where did you source the 3.27 diff from?

[Peter]

Hi Nicolas,

From Van Dijk in NL, some years ago.
At that moment they had stock.

Frank or Leon van Dijk.
They are specialized in MD 1950- 1980.
Very good, professional and service minded!

See website: https://www.classicsl.com/

Peter

[Cees Klumper]

I think Peter is saying he obtained the 3.27 gears from Van Dijk, to install in his existing differential - rather than purchasing an entirely different 3.27 differential. Years ago there were obtainable from aftermarket suppliers, now probably no more. But perhaps Mercedes still sells gear sets, I don't know.

[Peter]

Correct Cees,

Thanks for clarifying, it’s only the 3.27 gear.

Peter

[Nicolas Aristodemou]

Thanks Peter and Cees for the clarification. I think Niemoeller has a gear set but it’s 3.69:1..... I am afraid to go through the exercise of opening my diff to replace the crown wheel and pinion because I don’t think that anyone can do this properly for me in Cyprus. So my only option is finding a 3.27 or. 3.45 or even 3.69 complete diff from a compatible car (108 or 109?) but chances of finding a good one are very slim.....

[GM]

Nicolas,
If you haven't seen it, our very own Pagoda genius, Joe Alexander made a YouTube video about it:
https://www.youtube.com/watch?v=18nY1u0GUYM

[Shvegel]

Because of the design of our rear axles it is very hard to swap new gears into them successfully.  The critical pinion depth measurement is nearly impossible to do without factory tools that are almost non-existent.  It is a little less difficult if you swap used gears from one complete axle to another but you have to have both complete axles available in order to measure the installed depth of the pinion in the donor axle so you can install it at the same height in the new axle.

[mercakungen]

Hello,

My plan was also swap from 4,08 to 3,27 gears. So, I placed an order to SLS for 3,27 gears. I was quite surprised when they contacted and told me that they didn´t want to sell the gears to me. They told me that the gears they have are noisy even properly installed. I ended to buy genuine Mercedes parts. At that time only 3,46 was available. That ratio works very well on 280 SL.

Pinion pre load is just a one thing. The ring bearings has to be also pre loaded. New oil seal causes also friction so it is very difficult to measure pinion pre load on complete rear axle. Pinion depth and back lash have to be correct too =>correct contact pattern.

As Shvegel wrote it is not a easy task to swap gears into these rear axles. Done that.

BR,
Matti

[Peter]

I have today adjusted the Differential Pinion Pre-Load using the following procedure:

• Both rear tires / rims must be removed for the measurement.
• When checking, the support tubes must be horizontal and the brake drums must be removed.
• With disc brakes on the rear wheel, the brake pads must be pushed back and the handbrake released max.
• The current friction is +/_ 1 Nm. This will be gradually increased by tightening the groove nut  to 20 - 25 cmkp = 1.96 - 2.45 Nm. Average 2,2 Nm.

Some special and/or self-made tools are needed:
1.   Special  tool to fit the grooved nut
2.   Torque wrench to measures the 2,2 Nm
3.   Self-made tool to keep the grooved nut in place
4.   Self-made tool to prevent the pinion to turn

I went very well, the whining problem is solved.

Peter

[Shvegel]

Nice job!  Well done!