MGB Modifying an MGB Differential

[tony barnhill]

Okay, I’m starting my rear end “switcheroo”…I’m mating the ends of a Salisbury (tube) differential housing to a banjo differential housing….that way, I can use the stronger late axles with their superior bearing & hub…..plus, I can change out the rear gears easier & quicker…..& I have the lightness gain by switching from the heavier Salisbury tube differential housing to the lighter banjo housing.

So, today I disassembled both rear ends & marked where I think I need to make my cuts for welding…I’m planning on cutting the ends off the tube axle leaving about 1” of the tube on the bearing ends…then, I’m going to turn down that tube so I can slide a steel blank (with the same I.D. as the O.D. of the banjo differential tube) over it for welding…..then, I’ll slide that tube over the outside of the banjo rear end (after cutting it off just behind the hub end (I‘m using a banjo wire wheel differential housing that will be widened to steel wheel dimensions)…..I should then be able to insert the Salisbury tube axles into the banjo differential, ensuring that they seat properly in the gears…..then its just a matter of welding that steel blank to the banjo differential housing tube & the Salisbury differential axle end.

I hope that makes sense so you guys can confirm it’ll work.

In the ‘chunk’ itself (actually, I‘m going to build 3 chunks as explained in a moment), I’m going to remove the pinion gear & pin and weld the differential (spyder) gears solid….I‘ve several sets of those differential (spyder) gears that match the splines on the Salisbury MGB axles so that, in addition to the standard 3.9 MGB gear chunk that mates to the Salisbury axle, using my extra MGB banjo differential (Spyder) gears & the 4.3 MGA gear, & 4.875 Magnette gear chunks that I have, I should be able to modify the extra MGA & Magnette ’chunks’ to fit into the banjo differential and align with the Salisbury axles by using early MGB differential (spyder) gears (welded solid) that match the late Salisbury axle splines.

Does that make sense?

By now, you’ve probably guessed that I’m looking to be able to change the gears in my SCCA car to whatever fit’s the course……….thoughts?

 

[DrEntropy]

Sounds both practical and clever to me, Tony. Pinion preload and lash all preset! How long will it take to swap out chunks this way? I'm thinkin' more about dirt 'n FOD than any need to do it quickly for racing reasons, y'see. And mebbe have a couple extra case studs along... they'll always get thread damaged or bent/broken if ya DON'T have spares: "Edsel Murphy's Probability Corollary" has bit me more'n once.

 

[tony barnhill]

Doc...I'm thinking switch to the lower gears for motorcross (i.e. around the cones), higher for road, mid for hill climb....I'm guessing to change out might be half hour to 45 minutes (jack rear, pull wheels, loosen & pull axles part way out, move driveshaft, undo chunk & replace, replace driveshaft, push axles back in, install wheels, drop to ground....VAROOM!

 

[DrEntropy]

Slicker'n owl p00p. Good HEAVY jackstands and two 24" square pieces of 3/4" plywood... "In Case of Dirt."

 

[tony barnhill]

Good idea with the plywood!

 

[DrEntropy]

Been there, done that... could change out the gearset on a ZedF Hewland in less than ten minutes /ubbthreads/images/graemlins/wink.gif

 

[Steve_S]

Take photos along the way!

 

[Guinn]

What do you do about the speedo - or does it matter?

Guinn

 

[DrEntropy]

Guinn... on a "race car"???? Tach, yes... speedo, wellllll too distractin' /ubbthreads/images/graemlins/wink.gif

 

[twigworker]

Good morning Tony! As I understand it you plan to chop the ends of the banjo axle way out at the ends and glue on the tube type ends and use their axle shafts. If I am correct I suggest that you look into the work needed to chop the banjo way in toward the chunk, as closely as possible, and sticking as much of the tube axle as possible on to the chunk. This way, when you do the gluing you can figure in a 1 to 1.5 degree of negative camber. There should be enough slop in the chunk to accommodate the angle and it should make a noticeable difference in your cornering sticky. It is old hat to the domestic car racers around here so I don't see why it wouldn't work on a B. Something to think about. Jack

 

[tony barnhill]

Jack - not a bad idea so long as I don't end up around the samw weight as the Salisbury axle...one reason I'm doing this is lightness

Am weighing an empty banjo & Salisbury differential in a few minutes to see weight difference in cases.

 

[tony barnhill]

Weight of stripped differential cases:

Banjo - 24.6 pounds
Salisbury (tube) - 55.4 pounds

 

[DrEntropy]

WHOA!!! That's significant! I never gave it much thought... but that kinda unsprung weight difference puts it into a "must do" kinda light. what about a Watts link type arrangement while you're engineering the axle, too? Stiffen up the suspension and ~still~ gain a bit of weight savings at the same time. Can't ever have that roll centre too low, y'know /ubbthreads/images/graemlins/wink.gif

Edit: ..and I *HOPE* you're photo-documenting this!! I'm sure more peeps than just me would be interested.

 

[twigworker]

Just back from the dentist. Oh joy, oh joy, oh rapture unbearable! I am really surprised at how light the banjo unit is, but what does this weight differential mean? Mmmmmm...I suspect that most of the weight in the tube axle is in that massive center section and that the weight in the banjo unit is probably spread out across it's length. If I had to guess I'd say that 75 percent of the tube type weight is in the center and 50 percent of the weight is in the banjo center. 11.5 pounds for the banjo center and 14 pounds for the tubes from the Salisbury unit equals 25.5 pounds for the glued up lump, very near to the OE banjo unit with the added features you were looking for plus the possibility of getting a little negative camber thrown in as frosting. Another thought...I have never looked too closely at this but does it look like you might be able to heat and separate, perhaps even cut away the weld, and pull the tubes out their bosses in the center of the Salisbury axle? If you could and it didn't make too much of a mess it might be nice to have them sitting there in sort of a pristine condition as you plot your next move. Ice all over everything up here, but that's what bubba trucks are made for! Pray for GM's well being Tony. You are always going to need to have a Chevy or GMC around to pull that Dodge out of the ditch. LOL Jack

 

[tony barnhill]

Jack - LOL...we drive our little Sonoma most every day & the big Dodge on weekends & towing trips....I'm looking closely at what you said about inducing camber.....the weight of those Salisbury axle tubes has got to be heavier that the banjo tubes (though they are part & parcel of the center) just because they are thicker.

 

[startech47]

Speaking from short track stock car experience. The gain from having the negative chamber will probably out weigh the gain from lightness. This is not saying the gain from decreasing the unsprung weight is not important.

 

[Matthew E. Herd]

I don't really understand how you're achieving the negative camber. Please excuse me, as I'm more familiar with A series rears, like the one on my 1500. I'm not really familiar (at all) with the Salisbury type rear. However, the thing that I can think of, when dealing with a banjo-type rear, is that the splines fit into the carrier. If the axle tubes are inlined upward (inducing negative camber), there should be tremendously greater friction (or possible binding) between the shaft splines and the carrier splines. How is this reconciled?

 

[tony barnhill]

Matthew - good question from my persepective also...I was out in the garage a bit ago & shoved an axle up in the banjo rear end...I think it might even bind a bit.

 

[Matthew E. Herd]

I guess the next question is how to the circle track guys compensate for this problem? (or do they simply run it till it fails or wears out?)

 

[startech47]

In the high buck version for stockcars both ends of the axle are splined, with the outer end being shaped like the outside of a barrel. This properly alows for the angle change. The angle of the hub to the axle tube is also located near the outboard end of the axle tube. The inside of the axle flange is splined in this application. The low buck version depends on the play in the splines. More rapid wear will occur, but this is a race car. The reason for the negative chamber is to have the most tire contact on the outside wheel during cornering and the attendant body roll. The reduction in unsprung weight is to keep the tires in contact with the road overbumps and dips.