Diff Ratio

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Page created by T May 31st 2010:

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The Yoke Plate on a Banjo Differential Centre. Click to Enlargen. Photo by Stock-EJ.

Diff Ratio:

These are the ways you can determine the Diff ratio.
LH Sals yoke. RH banjo 6cyl yoke. Click to Enlargen. Photo by HQ SS.
 

LSD:

If the Rear Axle is a Limited Slip Diff you will need to jack up both Rear Wheels and place the Car in Neutral.You will need to chock both Front Wheels to prevent the Car from rolling forwards or backwards.
3.08 Diff Ratio stamped on the Yoke Plate. Photo by Davequey. Click to Enlargen.
An LSD Diff forces both Rear Wheels to act as if they are locked together even when they are both Jacked Up.
10 Bolt LSD Salisbury Differential Gearset. A 10 Bolt is an Heavy Duty type of Salisbury DIff. Click to Enlargen. Photo by HG383PREM.
With the Handbrake released, rotate both the Rear Wheels and count the number of turns the Tailshaft makes.The Diff Ratio will be the number of turns the Tailshaft makes to one turn of the Road Wheels.

Non-LSD:

If the Rear Axle is a Non-Limited Slip Diff you will need to jack up one Rear Wheel and place the Car in Neutral.You will need to chock both Front Wheels to prevent the Car from rolling forwards or backwards.A non-LSD Diff allows both Rear Wheels to rotate seperately once the Rear Axle has been Jacked Up.
Spider Gears in a Banjo Diff. Click to Enlargen. Photo by WBUtebloke.
With the Handbrake released, rotate  the raised Rear Wheel and count the number of turns the Tailshaft makes.The Diff Ratio will be the *double* the number of turns the Tailshaft makes to one turn of the raised Road Wheel.The Ratio will be double because the Diff Spider Gears are activated when either Road Wheel is stopped.The Spider Gears cause the free spinning Road Wheel to rotate twice as fast as when both Rear Wheels are turning equally.

Markings:

The Diff Ratio is often etched into the Crown Wheel.Removing the Rear Cover Plate on a Salisbury Diff will expose the Crown Wheel. The Crown Wheel will have to be rotated until the etching becomes visible.

Yoke Plate:

The Yoke Plate is at the front of the Diff near the Universal Joint. When the Diff left the Factory the Ratio was stamped on this plate. After all this time the Factory Yoke Plate could have been used with another Diff. The Yoke Plate is attached to the Yoke and is Spot Welded into place.
The Diff Ratio is stamped on the Crown Wheel. In this case 2.6 LSD Salisbury from a V8 VK Commodore. Click to Enlargen. Photo by Benzit116.

Tacho:

If you know your Tyre size and which Gear will give you 1:1 coupling, the Diff Ratio can be calculated.
9 Inch (left) and a Banjo Differential (right). You can see where the ratio has been engraved into the Crown Wheel on the Banjo. Click to Enlargen. Photo by V-Eight.
  This is a more tedious method than the others.

Crownwheel and Pinion:

By HQJeff 06/06/10@01:05 Banjo crownwheel and pinion will fit UC diff. UC carrier and side bearings are different.
3.9,3.55,3.36 carriers differ from 3.08,2.78 carriers in both banjo and UC sals.Jeff.

The Diff Ratio is stamped on the Yoke Plate. Photo by Pugsly. Click to Enlargen.

Links:

Banjo Diff

Salisbury Diff

LSDDavequey's Shed

Terms:

Terms

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