4/4 rear axle questions (racing)
Posted: Sat Jul 16, 2016 5:22 pm
I'm hoping the knowledge to answer the following three questions will be found on this forum:
A) Will I miss having a limited slip diff when racing a Series V 4/4? I will not be racing on slicks. Final drive ratio is 4.56:1 and engine power will be around 120-135 hp. Weight would be around 1450 lbs.
B) Is there any history of breaking rear axle half shafts on a Morgan? I am aware that TR3s and TR4s have suffered breakage with a very similar Salisbury axle (and this 4/4 currently has a TR3 axle in it). I know that the TRs outweigh the 4/4 by 550-600 lbs and am wondering if that's why I've never heard of a similar failure in a 4/4.
C) Does anyone know whether Salisbury axles in TR3s and Morgans have the same taper at the outer ends?
A bit of background: My Series V 4/4 has a Detroit Locker (a.k.a. "Detroit Unlocker") limited slip, which is reportedly great for drag racing but seems not to be the ideal setup for road racing although there are those that swear by them. 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 Triumph, at any rate), causing loss of a rear wheel.
I have before me several options -- 1) find a stock 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. 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 from a Plus 8, with Salisbury lsd but needing gear replacement to get the proper final drive ratio (this particular axle can be purchased with two 4-lug Morgan hubs that are not installed), 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 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?
A) Will I miss having a limited slip diff when racing a Series V 4/4? I will not be racing on slicks. Final drive ratio is 4.56:1 and engine power will be around 120-135 hp. Weight would be around 1450 lbs.
B) Is there any history of breaking rear axle half shafts on a Morgan? I am aware that TR3s and TR4s have suffered breakage with a very similar Salisbury axle (and this 4/4 currently has a TR3 axle in it). I know that the TRs outweigh the 4/4 by 550-600 lbs and am wondering if that's why I've never heard of a similar failure in a 4/4.
C) Does anyone know whether Salisbury axles in TR3s and Morgans have the same taper at the outer ends?
A bit of background: My Series V 4/4 has a Detroit Locker (a.k.a. "Detroit Unlocker") limited slip, which is reportedly great for drag racing but seems not to be the ideal setup for road racing although there are those that swear by them. 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 Triumph, at any rate), causing loss of a rear wheel.
I have before me several options -- 1) find a stock 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. 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 from a Plus 8, with Salisbury lsd but needing gear replacement to get the proper final drive ratio (this particular axle can be purchased with two 4-lug Morgan hubs that are not installed), 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 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?