The Morgan Roadster Limited Slip Differential

 The Morgan Roadster Limited Slip Differential.

It was this comment from Terry Seymour that prompted me to compile this topic.

"I started to move back and heard a clonking sound from behind me, checking my mirrors again, saw nothing, started maneuvering again only to hear the awful noise. 

While I was on the shoot, MMC engineers had Frog Mog up on a ramp and ascertained the noise was coming from the rear axle Limited Slip Differential. 

Having explained it was quite normal and not unusual ”they all do that sir”, and not dangerous to drive."

Noisy Limited Slip Differentials During Cornering.

Limited Slip Differentials lock the two rear wheels together when traveling in a straight line but allow one wheel to slip when turning.

 They provide better traction on slippery surfaces. During a turn the wheel on the outside ~ 10% faster than the inside wheel. 

By overcoming Clutch Tension the two wheels can rotate a different speeds during turns. 

The Roadster 100 Differential contains friction plates when other types may contain Cones.

A multiple disc clutch differential consists of two sets of multiple disc clutch packs located on each of the two side gears. 

These clutch packs have friction plates splined to the side gear, interlaced with steel plates that have tabs locking them to the differential case.

The Spider and Side Gears are bevelled. The turning pinion gears force the side gears outwards towards the case. 

The mechanical force of the bevelled gears and spring tension apply the clutch. For a set of friction plates to slip they must overcome the preset spring tension.

Service the differential fluid at recommended intervals. Special Limited-Differential Fluid compliments the engagement and release of the limited slip components. 

Adding standard differential fluid to a limited slip differential can result in noise and vibration while turning.

A vehicle with a Limited Slip Differential 'Chatters' while only taking turns. Using the wrong differential fluid causes chatter. 
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A Morgan Plus 4 Exploded Diagram Showing both Normal & Limited Slip Differential Options.

  
A Morgan Dana Spicer Rear Axle Diagram with a Cone Type Limited Slip Differential. 

A Newly Fitted Roadster Axle as seen in The Morgan Factory.

The Dana MRA 0061 - 001403 Rear Axle with Limited Slip Differential. 

The Large Hexagon Differential Filler Plug can be seen just above the lower right yellow blob.

These axles were supplied by the Spicer Axle Australia PTY Ltd. The 0061 LSD model is used on all Roadster 100's has a gearing Ratio of 3.73 : 1 

Interesting that the Series 1 Roadster used a 0060 model with a Ratio of 3.08 : 1.

The Axle Label on my car Series No 015

The Offside End of the Axle Casing and Air Vent.

The small protrusion to the right of the label is an Air Vent presumably to equalise any pressure build up within the axle.

No 015's Differential Casing seen from above. 

The Oil Drain Plug is at the lowest pint of the rear cover adjacent to the Fuel Tank. 

The Filler Plug is on the same cover mid way down and towards the offside featuring a Large Hexagonal Head..

(The polished area seen here is where the factory fitted Tool Rack 'Jack Recess' bounced and rubbed on the Diff. Housing during rear suspension bottoming. )

The Nearside end of the Axle Casing.

The Complete Axle Unit.

Changing The Limited Differential Oil.

Changing the differential fluid is not that easy on a Roadster due to the location of both Drain Plug and Filler Caps to the Fuel Tank.

Terry's Rear Axle and the Proximity to the Fuel Tank.

The Drain Plug at the Lowest Point.

The Hexagonal Filler Cap with Specification Tag.

Dave Wellings - Draining the Fluid.

Dave - Refilling using a Funnel & Rubber Tube.

The Recommended Oil is: 80W/140 Full or Semi Synthetic. such as Morris LODEXOL XFS Semi Synthetic or Penrite Pro Gear 80W-140 GL5 GL6 Fully Synthetic.

A Friction Modifier is also recommended such as: Red Line Limited Slip Friction Modifier from Demon-Tweeks

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Comments found on Talk Morgan and Piston Heads Forum.

Before we all get euphoric about LSDs there are few points to consider:

1. The Morgan Motor Company  "standard" in the 'Dana' Axle from Spicer Axle Australia PTY Ltd. which is the Friction Clutch Type, and is quite susceptible to begin set up wrong from the start. Some versions need a special additive in the oil.

The Component Diagram for a Dana Clutch Plate Limited Slip Differential.

2. The Quaife torque biasing diff recommended by Tim (which I fully endorse, by the way) is a much better option for most applications and Morgans in particular.

The Quaife ATB BMW Limited Slip Differential

3. The LSD will promote understeer at most times when used with a gentle throttle, this might detract from your enthusiastic driving but it is the "safe" option

4. When you reach the point at which you do break traction , now both rear wheels will be spinning, and you had better be used to this , and good at catching it. If you are, and can, then there is no doubt that an LSD is a great addition to your car and will enhance your Morgan driving experience.

I summary, think about what you want from your Morgan and how you drive it. If you regularly go off road then an LSD provides much needed traction, if you compete with the car then it gives far superior traction out of corners, but if you just want to tour around (at legal speeds?) and are a fair weather driver, you might not get as much from it.

Andy G at Talk Morgan.

Noticed a similar knocking with my Chimaera, I thought it might be the CV's so I asked Dave Batty to take a look when it went to him to be serviced last week. 

He couldn't find anything wrong and he reckoned it was the Limited Slip Diff causing the knocking, nothing unusual and nothing to worry about. - 

Furry Dice at PistonHeads

Noticed it on mine too, full lock in reverse or pulling out of side turning, glad it's a case of 'they all do that sir'

Raceboy at PistonHeads

I think we're talking about how the rear wheels judder and slip slightly as you turn on full lock at slow speeds. With a Limited slip diff a certain amount of drive is always supplied to both wheels, unlike a normal diff where you can hold one of the drive wheels still and all the drive will go to the other wheel.

I think the cause of the juddering on a LSD is that one of the wheels doesn't 'freewheel' and ends up been dragged along at the speed of the (slower moving) inner wheel.
Dannyboyo at PistonHeads

You are right to say a certain amount of drive is always supplied to both wheels, that is why a LSD exists. The juddering, if it is coming from the rear is more likely to be due to the LSD "working" than anything to do with tyres scrubbing. If that is how a LSD worked tyres would be scrubbing all the time - I think not.
Ivan at PistonHeads