Banjo Differential

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Original submission by T Apr 5th 2007:

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3.08 Banjo Diff Centre. Note the long boss at the highest point in the photo. There is also a bulge at the top right of the diff for the larger pinion. Click to Enlargen. Photo by WBUtebloke.

Banjo Differential:

A Banjo Differential has the gearset built into a removable centre in the rear axle housing. Note that the diff centre is held in the axle housing by a series of studs that look like the drum tuning keys on a banjo.


2.78 - 3.08 Banjo Differential Centre, identifies by the Pinion Gear boss and the long stud. Click to Enlargen. Photo by Stock-EJ.

 

3.36 - 3.89 Banjo Diff Centre. Note there is no boss and no long stud. Click to Enlargen. Photo by WBUtebloke.

 

Banjo Rear Axle. Note there is no rear Cover. Photo by Ben Campbell. Click to Enlargen.
HR Banjo Rear Axle. Note there is no bolt-on rear cover. Click to enlargen. Photo by HQ SS.
Limited Slip Banjo Diff Centre. Photo by Ramo_Legends. Click to Enlargen.

 

Banjo Differential Rear Axle. Note the similarity in appearance to the drumhead on a Banjo and its tuning keys. Click to Enlargen. Photo by Ben Campbell.
   


Thread1
9 Inch Banjo Thread A Banjo diff does not have a removeable tinplate cover on the rear of the axle.  

Ratios:

if the car is original and you can guarantee it has the original diff you could go off the body ID plate under the bonnet.
However if someones replaced the diff at some stage it may have a different ratio. Look for the plate under the bonnet on the cowl with ENG TRANS RRAXLE down the bottom. compare the code next to RRAXLE to these:
GU4 = 3.08:1
GU7 = 2.78:1
GU8 = 3.90:1
GV2 = 3.36:1 (V8 HQ's Only)
GV4 = 3.36:1
GV7 = 3.55:1
G70 = 2.60:1
GM9 = 4.44:1


LSD:

Limited Slip Differentials have been made in either Banjo or Salisbury form.   LSD

Banjo Advantages:

Their advantage is that they are easy to replace.

Banjo Disadvantages:

Their disadvantage is that they rotate and break axles under high torque.  

Banjo Diff Housing. Click to Enlargen. Photo by Nobody123.

 
Banjo Diff centre. Click to enlargen. Photo by Nobody123.
 
Banjo Diff centre. Click to enlargen. Photo by Nobody123.

 
Banjo Rear Axle Housing. Click to enlargen. Photo by Nobody123.
 
 
Exploded Banjo Diff. Click to enlargen. Photo by LMH.
 
  
Exploded Banjo Diff. The Side Gears are for Coarse Spline Axles because they have 10 teeth in the Spline. Click to enlargen. Photo by LMH.
 
 
Exploded (literally) view of Banjo Diff Centre. This came apart without the need for a spanner. Note the side gears are for use with Coarse Spline Axles. Click to enlargen. Photo by LMH.
 
 
Exploded (literally) view of Banjo Diff Centre. The Hemisphere has cracked completely in half. Click to enlargen. Photo by LMH.
 
Salisbury Doff. The Pinion Nut in a Differential is not tightened to any torque setting. It has been tightened to set a specific Pre-Load (drag) in the Pinion Bearings. Before undoing the Nut is must be marked so that it can be re-tightened to exactly the same position to preserve the Pre-Load. Photo by March17th . Click to Enlargen.
  
The Image shows what the Axle Housing studs look like. Note the seration on the stud that makes it locate in the Axle housing. Click to Enlargen. Photo by HQ_SS.
 
Housing Studs  hammer in to install them and hammer out to remove them. Click to Enlargen. Photo by HQ_SS.
   
   

   

Ratios:

Banjo Differential Centres. The lower diff is from a grey motor Holden; identified by the yoke. See Thread 1. Click to Enlargen. Photo by Stock-EJ.

The ratio can sometimes be found stamped on the tinplate disc behind the pinion and scribed into the
crownwheel.
2.78 and 3.08 share a common centre. Their centre requires 2 long studs on the driver's side. The other diffs use only short studs and nuts.

Note that Banjo Carrier bearings are bolted to the removable centre. When enough tailshaft torque
is presented to them the whole banjo centre can rotate and cause an axle breakage as in the famous Bob Morris 1976 L34 Bathurst 1000 win.
Only that the car had a Limited Slip Differential was power still provided to the unbroken axle which allowed him to cross the finish line.

Salisbury:

A Salisbury Rear Axle solves the rotating centre that Banjos have by placing the carrier bearings
in the axle housing rather than in the removable centre.
The diff is built into the axle rather than into a removable section.

Rear Axles:

 Note that there are coarse and fine spline axles.

Coarse Spline Axles:

 The coarse spline axles have the fewest teeth and are the early type. These were prone to breaking.

Exploded Banjo Diff. The Side Gears are for Coarse Spline Axles because they have 10 teeth in the Spline. Click to enlargen. Photo by LMH.
 

Fine Spline Axles:

The fine spline axles have the most teeth and are the later type. These solved the axle breaking problem.

Coarse and Fine Spline Spider Gears. Click to Enlargen. Photo by HQ_SS.

Diff Change:

Note that when changing the differential the axle type must be observed. Changing the side gears inside the differential is a quick job for a diff ace and can make it easy to match axle type to the side gears.

Rear Axles  

9 Inch:

A 9 inch is a type of Banjo diff that has been toughened considerably. V-Eight's Shed  

9 Inch (left) and a Banjo Differential (right). Click to Enlargen. Photo by V-Eight.
9 Inch (right) and a Banjo Differential (left). Click to Enlargen. Photo by V-Eight.
9 Inch (left) and a Banjo Differential (right). Click to Enlargen. Photo by V-Eight.
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.
 
9 Inch Banjo Differential and Rear Axle. The axle in the back ground is a Salisbury because it does not have a removable centre with studs and nuts that look like the skin tuning keys on a Banjo. See the 9 Inch Thread. Click to Enlargen. Photo by HQDreamer.
Banjo Rear Axle and Diff Centre. Click to Enlargen. Photo by HRPanelvan.
 
LH Sals yoke. RH banjo 6cyl yoke. Click to Enlargen. Photo by HQ SS.
 

 

Historical:

This is axle portrayed is not a traditional "Banjo" rear end. This is more like a "8"" type floating axle "modern" rear end. Typically, a banjo rear end is a 29-41 Ford (Merc) with two identical "bells" (look like trumpet bells) which bolt on each side. The axles are retained by the differential and axles drive unique brake drums through a tapered end of shaft square key which fits in slot on both hub and drive shaft. They are easy to identify by the center section/bell symmetric shape. The classic hot rod look uses the Halibrand, Winter or other center sections modified for quick change gears (used originally for racing) and can be (when fully modified to floating axles) be quite robust.  Regards; Gregg (31 Coupe/PontiacV8/banjo in process) Schluntz T adds - The diffs portrayed in this page are what GMH refers to as Banjos.

Links:

Ben Campbell's Shed

Grey Motor Diffs

Terms:

Terms

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