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Need some rear end education

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bugedd

bugedd

Jedi Knight
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I have found a limited slip rear end that I'd like to purchase at the end of the month, but I really know very little about them. Here is the link....
https://www.mgexperience.net/phorum/read.php?41,2268867,page=1
Now, he mentions in the ad that he thinks gearing from 4.22 and higher will work. How can someone find out what gears will go on this lsd? Will stock gears work on it, which is 4.11, right? And how does one change that?
And from what people have told me, this is a direct bolt it. Just bolt it up, slide the axles in, and go?
He says its made by Competition Department, which I can't find anything about.....anyone know of this company?
And the stamping 8/39....what does that mean?
Thanks for the education :smile:
 
8/39 divide and equal's the 4.88 to 1 ratio that the seller mentions. Great for racing on a short track with a high revving engine but awful low for the street. Probably could swap ring and pinion but that is sort of a tricky job. Get a good manual and read up on it.

Kurt
 
Forgot to mention that the 8/39 would be the number of gear teeth on the ring and pinion gears.

Kurt.
 
So I assume the ring gear could be changed, but how would I know what would be interchangeable?
 
If you use his diff as-is it will be plug and play as described. If you change the ring and pinion you will either need a shim kit, crush sleave and appropriate tools to set up the gears OR take it too a pro to get that done.

Just out of curiosity, does your car have enough power that you would even notice the switch to limited slip? My car has a 948, wheel-spin is NEVER an issue :smile:
 
When I throw it into a corner, very spirited, the inner wheel spins like ****. Honestly, I drive like an ass, like I stole it most of the time, and I want it to hook up. The car is my rebellion for being 40 this year, so I like to drive it like I stole it. And I remember the wonderful feeling of a LSD, and I want to feel it again. So call it a mid life crisis :smile:
 
Rings and pinions need to be changed as a set. They are custom ground to each other when manufactured. Mixing them will result in howling, early wear and destruction.
Bob
 
So would that mean I can use the ring and pinion that are stock in my rear end and use with that limited slip?
 
I'm no expert in Spridgets, but I would say yes ^^^^^ It will be to be installed by someone who knows what they are doing.
 
If you look at this pic from mossmotors.com, it shows 2 diff housings that were used:

  • The "C" type was used in MK1 and MKII sprites. All the "C"s were 4.22
  • The "D" type was used in later models. "D"s were 4.22, 3.9, 3.7

The visual differentiator between the 2 is the extra drain/fill plug on the "C" type - Shown as item 5 below. Both versions had a lot of the same parts, but the ring and pinion were different.

The one on Ebay is the "C" type. So if your current diff has the plug you should be good to go. Again, if you want to swap in your ring and pinion, it can be done, but is more work than just swapping parts.

SPM-027.gif
 
So .... why can't the LSD just be installed in his existing rear end?
 
The pictured "limited slip" looks more like a Detroit Locker to me. A true "Salisbury" limited slip has more of an open assembly and one can see the cross pieces for the axle drives. Color is typically a rustoleum primer red. Parts are rather difficult to come by. Detroit Lockers are much more susceptable to throttle induced "lock/un-lock" in the middle of the turn. Preference should be towards the Salisbury which is a clutch-pack type carrier. Modern equivalent is the TranX. The break away torques are set by the shims in the clutch pack itself. Any of the differential carrier types (Open/Stock, welded, Salisbury, TranX, Detroit-Locker, Phantom-Grip and ZF-Cam&Pawl) can be setup with any of the casings whether C or D from the exploded view of the parts catalog. Rings and pinions can be moved from casing to casing if the right bearings are used.

The inside wheel spin is caused by load transfer and the open differential. Same as getting stuck in mud or snow. The wheel with the least traction will spin. Can be resolved with a "limited-slip" differential or welding up the spiders. The inside wheel will still have to slip/spin when cornering. Now, it just breaks loose from the pavement or inside the diff and then regains traction rather quickly. The inside wheel will always turn slower than the outer due to the shorter effective radius.

The "Competition Department" that Tom speaks of is the BMC/BLMC Competition Department (US equivalent of the UK Special Tuning). Probably the east coast location that was in Leonia, NJ until the mid-80's. Based on the 4.88 ratio, it was likely sold in the 60's or early 70's when there were quite a few "short" road courses on the east coast. Not much call for a 4.88 rear diff unless autocrossing or hill climbing any more.

HTH,
Mike Miller
 
I was hoping you would give your two cents Mike :smile:
So, if it is a detroit locker style, I assume I should pass on it?
And what is the deal with the Phantom Grip? Do they really work? They sure are much more cost effective.
 
I would go back to Tom and ask him to double check what kind of a diff it really is. The BLMC Competition Department did sell a Salisbury limited slip differential under part number C-BTA1226. I've got one and it looks as I've described. I've got a couple of Detroit Lockers as well and they look more like what is pictured. If it is indeed a Salisbury, and the price is reasonable, I would buy it immediately.

Phantom Grips do work. They are simply a spring loading of the drive gears. The center piece has 4 springs inside that push the center plates against the drive gears. The increased "friction" between the gear and the plate is what holds it locked until that friction is overcome by cornering and the inside wheel slips as one turns the car. Ingenious idea. Simple, but requires some modification to the drive gears themselves to locate into the plates.

The Salisbury has Belleville washers, clutch plates and more than likely some shims that have been added to adjust the clutch slip. I usually set my Salisbury up for about 65 lb-ft of break away torque. One downside of the Salisbury, at least mine, is when hot and turning in the paddock, the diff pops and growls and people turn to look at what is making the noise. When cold, no noise at all. Vizard has some picture or drawings of the Salisbury in his paper back book "How to Modify your Mini". Also a discussion of the merits/cons of various types of differentials.

Tom and I will likely be at VIR racing in April. I can ask him about the diff there and what type it is. He might come down to Atlanta in March.

HTH some more,
Mike Miller
 
The diff on the left is a Detroit Locker. The diff on the right is a BLMC C-BTA1226 Salisbury.
The one on the right
is a clutch pack limited slip. HTH some more. 4.55 Detroit Locker vs 3.90 Salisbury.jpg
 
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