[Fot] Salisbury rear axle questions

[Duncan Charlton]

I hope there is someone on this forum who might be able to answer the following three questions:

A) Would I be likely to miss having a limited slip diff when racing a 1450-lb car (not on slicks) with engine power of around 120 hp and final drive ratio of 4.56:1?

B) Does anyone know whether Salisbury axles would have used the same taper at the outer ends?  I have a set of Morgan rear hubs from a Salisbury axle and am wondering if I can fit them to a TR3 axle that’s mounted in my Morgan 4/4.

A bit of background: My Morgan Series V 4/4 has a Detroit Locker (a.k.a. "Detroit Unlocker") limited slip, which is great for drag racing but not ideal for road racing because it unlocks the outer wheel when cornering, allowing all of the torque to go to the inside wheel. It would seem to offer no advantage over an open diff except when going in a straight line should there be enough power available to cause one wheel to spin. I'm aware of other drawbacks to my current setup as well -- front and rear wheel stud patterns are different, and it is not unheard of for these axles to break under racing conditions (when mounted in a 2000+ lb. Triumph, at any rate), causing loss of a rear wheel.

I have before me several options -- 1) find a stock Morgan 4/4 rear axle with a 4.56:1 final drive and either a) use it without limited slip or b) purchase a Salisbury or Quaife limited slip for it. 2) Use the Triumph TR3 axle currently in the car but adapt Morgan 4-lug hubs to gain interchangeability of wheels fore and aft and either a) remove the limited slip apparatus entirely or b) replace the lsd with a Quaife lsd, 3) use a 7Ha Salisbury with lsd from another Morgan but in need of different ring and pinion, or 4) use an MGA "banjo" type axle with a Quaife lsd unit.

Choice #1a sounds straightforward -- but I only have one (albeit highly experienced) racer's opinion that lsd is not necessary on a 4/4 race car. Option #1b would add at least $900 to the cost of the conversion. This does not address the question of potential axle breakage.

Choice #2 might be possible but #2b requires replacing the lsd with a different type and the question of likelihood of axle breakage remains.

Choice #3 likely would not be the least expensive way to go once I've purchased a new ring and pinion set and perhaps new axle half-shafts but if the axle tubes are of the proper length (this axle came out of a Plus 8 so the axle may be wider) there would be few modifications needed. This option doesn't address the question of likelihood of axle breakage.

Choice #4 offers full-floating axles, removing the risk of losing a wheel when an axle snaps, and one of the available final drive ratios is probably close enough to 4.56:1. Quaife makes an lsd for this unit and the larger rear brakes (10" diameter, I understand) reportedly will not present a problem but altering the outer axle flange to fit the Morgan wheel stud pattern doesn't look likely (from photos it appears that the flange is not large enough), so adaptor plates would be required, introducing one more potential failure point. This option would also require redoing the spring mounting bracketry. Besides answering any concerns about losing a wheel, should an axle break, unsprung weight would be reduced since these axles weigh less than the Salisbury units.

Opinions?
Duncan Charlton
Elgin, Texas USA



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