Original AC cobra differential

[grybrd123]

Does anyone know what differential was used originally in the 260 and 289 cobras? Did the Ace/Bristol diff have to be changed to a stronger unit because of the V8?

[Mark IV]

It is a Salisbury 4HU and is the same as the later Aces.

[grybrd123]

Sorry to be so dense, but do you mean that all the 260/289 Cobras and the later Aces used the same diff, the 4HU? Or did the earliest Cobras and Aces use something different than the later ones?

[Mark IV]

The 4HU was used on the later build Aces, 260/289/427 Cobras and AC "Frua" 428 cars as well as the "Paramount" chassis and the electric AC chassis. It handled from 150 HP to godafful torque on the 427 S/C cars!

[Dan Case]

Originally Posted by Mark IV

The 4HU was used on the later build Aces, 260/289/427 Cobras and AC "Frua" 428 cars as well as the "Paramount" chassis and the electric AC chassis. It handled from 150 HP to godafful torque on the 427 S/C cars!

Early Cobra upper differential hangers, bolted onto sides of the differential that contained a steel and rubber vibration isolation core, originally had cast iron bodies. That first version tended to break in any kind of competition. They were replaced with similar looking assemblies with high strength steel bodies pretty early in Cobra production. Apparently, late in the 427 Cobra era another design revision was made available as an upgrade for competition use.

Salisbury O.E. differential output shafts were somewhat soft. 289 powered cars that were drag raced or 427 powered cars with wide rear tires tended to twist them or in extreme cases break them after sufficient twisting. Custom replacement output shafts were a common solution for race cars. I bought a custom American made pair for a friend’s 427 Cobra circa 1985 to replace the deformed originals. Legend says that Ted Halibrand's company made extreme duty replacement for racing output shafts for differentials and custom rear hubs (axles in rear uprights) for Shelby American.

[Cobra #3170]

Originally Posted by Dan Case

Early Cobra upper differential hangers, bolted onto sides of the differential that contained a steel and rubber vibration isolation core, originally had cast iron bodies. That first version tended to break in any kind of competition. They were replaced with similar looking assemblies with high strength steel bodies pretty early in Cobra production. Apparently, late in the 427 Cobra era another design revision was made available as an upgrade for competition use.

Salisbury O.E. differential output shafts were somewhat soft. 289 powered cars that were drag raced or 427 powered cars with wide rear tires tended to twist them or in extreme cases break them after sufficient twisting. Custom replacement output shafts were a common solution for race cars. I bought a custom American made pair for a friend’s 427 Cobra circa 1985 to replace the deformed originals. Legend says that Ted Halibrand's company made extreme duty replacement for racing output shafts for differentials and custom rear hubs (axles in rear uprights) for Shelby American.

Those original diffs. had 10 spline stub shafts that were quite soft as you stated. I broke 2 before switching to 19 spline Jag units which also broke occasionally. I have the 30 spline Kirkham stubs now and they are holding up perfectly. I still have my original 10 spline diff but have not used it since
1981.