MGExp

MG Motorsports Forum

3.9 Salisbury Limited Slip Differential

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

Rick Starkweather Avatar
Raleigh, NC, USA   USA
Looking to buy a 3.9 Salisbury LSD. Other ratios OK, as we can swap out the R&P, but would prefer one all set up and ready to go. Let me know.

Rick

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Rick, why Salisbury?

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Rick Starkweather Avatar
Raleigh, NC, USA   USA
Dick:

That is what the team requested. I know there have been a number of discussions about clutch-type, Quaife, Salisbury, etc. I'd welcome your thoughts.

Rick

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Rick,

For competition nearly everybody I know uses a banjo differential rather than the later Salisbury. The banjo allows for fast and easy changes of the diff for alternate ratios, and the banjo rear axle assembly is much lighter than the later Salisbury. There are also more gear ratio options for the banjo.

For serious competition, some folks opt to upgrade to a hybrid rear axle, which starts out life as a banjo axle, the housing is cut, and Salisbury outer halves are welded on. This allows for easy change of gear ratios while providing the strength of the outer wheel bearings, hubs, and axles of the Salisbury. Dave Headley or Hap Waldrop can build such a hybrid axle. It also allows the fabricator to build in some camber and toe as may be desired.

As for the type of limited slip unit, a Quaife is not a good choice for serious racing because it is a "torque-biasing" unit. The flaw in this design is that, while it progressively sends torque to the wheel with less grip, when a wheel lifts and has no grip, the Quaife sends all of the torque to the spinning wheel, which is just the opposite of what you want. When one wheel loses traction, you want all the torque to go to the other wheel, and the Quaife does not do that.

There is an inexpensive "limited slip" unit called Phantom Grip. It is junk. Don't even consider it for street use.

A Detroit Locker is generally not considered a good choice for road racing because its engagement and disengagement are very abrupt and can upset the balance of the car.

IMO the best choice of limited slip unit is a clutch-type limited slip unit, like that offered by Tran-X. Such units offer progressive torque transfer with all torque ultimately going to the wheel with the most grip.

Many racers, including many/most who are way faster than me.. grinning smiley prefer a welded rear, in which the spider gears of the differential are welded solidly together. This forces both rear wheels to turn at exactly the same speed. Such a setup allows the driver to use a "dirt-tracking" method of hanging the rear end out in turns, since in turns the outside rear wheel will have to turn faster than the inside rear wheel because it has farther to go. But since the gears are welded together, in a turn one wheel must necessarily break traction. Really fast drivers like Dave and Hap like this effect. It's likely a faster setup than using a clutch-type limited slip unit, but it is uncomfortable for me because the rear wheels break traction rather abruptly. This is good for dirt-tracking, but disconcerting to some, including me.

Of course an advantage of the welded setup is that it is cheap or free, depending on your resources. However another consideration is when it is necessary to push the car around in the pits or elsewhere. Since both rear wheels are locked together, as soon as you try to turn the car the rear wheels are fighting each other for traction, and the car becomes very difficult to push other than in a straight line.

So it pretty much comes down to driver preference and budgetary considerations...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
I think the OP is looking for a Salisbury Diff, which is a torque biasing clutch type for a banjo axle. The tube type axle is also referred to as a Salisbury axle. Unless planning on racing in the rain, the welded diff with added camber and a touch of toe-IN is faster in the dry. With a proper rear suspension setup, there would be no need to "dirt track" with the welded diff.

I see lots of mis-used terminology in these kinds of discussions. The rear of the car is supported by and rolls on an axle assembly. This contains two drive axle shafts. Longitudinal motion is converted to transverse motion via the crown wheel and pinion(ring and pinion). On a banjo axle assembly, the ring gear is bolted to the diff carrier which rotates on side bearings mounted within the 3rd member(pumpkin, hogs head etc). The differential which allows the two axles to spin at different speeds is mounted inside the diff carrier and contains spider/pinion gears mounted on a cross shaft and side gears which engage the spiders and are in the diff carrier in a manner which transmits motion and torque from the ring gear to the shafts. The drive pinion is mounted in bearings in the 3rd member and drives the ring gear. A tube type often referred to as a Salisbury axle contains all the same features but the diff carrier as well as the drive pinion mounts into bearings inside the integral axle housing, no separate 3rd member.smoking smiley

OK, I feel, better now. Back to regular programming.grinning smiley


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
I ran a welded diff for years, but as Dave pointed out, they suck big time in the rain. When it rained I had to tippy toe around very, very carefully. I even won one race doing that because all the rest of the guys in the class fell off the track!



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

Rick Starkweather Avatar
Raleigh, NC, USA   USA
Thanks for all of the feedback. Apologies for the confusion about the use of a Salisbury LSD versus a Salisbury axle. As Dave said, the application is for a hybrid rear axle with a banjo diff. But we are looking for a clutch type LSD, like a Tran-x (which is also sometimes referred to a Salisbury unit).

Also to Dave's points, I run a locked diff in my SCCA car, with a hybrid axle set up by Dave for camber and toe-in. The Tran-x unit is for the B Stingers vintage MGB.

Rick

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Rick, I think Craig Chima may be a source for importing the Tran-x diff.


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
atosler Alan tosler
USA   USA
yes he is

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
twentyover Avatar
twentyover Greg Fast
Lives in SoCal, Resides in the Burbs of Detroit MI, USA   USA
I believe Norm Murdock @ Team Blitz also peddles them on ebay

britcardoc Dan Dougherty
Marietta, GA, USA   USA
Looking for a used clutch type for my Bugeye Vintage racecar, too.

Can handle a vintage Mini one too...slightly different but takes very little mod to go in a Spridget.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions

Members Sign In   or   Create an Account

Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster