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MGB Modifying an MGB Differential

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Man, the things one can learn on a BBS! WOW!
 
I'm familiar with the reasons for the modification. However, you've also answered my question excellently. We can think of the carrier-side axle spline as being akin to the ball-ended hex wrenches, that can turn a hex head cap screw while not being co-linear. I'm sure there's additional wear involved in that solution as well, but it's probably better than the solution relying on clearances between the splines.

Since splines are difficult and expensive to cut at best, it would appear that there is not a whole lot of option in gaining the necessary clearance. One possibility is to use worn components. Another is to shorten the length over which the two splines mesh. None of these solutions is terribly appealing.
 
The angle change on the axle tubes is created by heating up an area on the top of the axle tube red hot and quenching it with a wet rag shrinking the metal. Yes parts wear out faster. Run it till it fails or until you get caught, depending on the local rules. :smile:
 
That method seems somewhat inconsistent to me, as the shrinking will probably be hard to equalize between the two. Does it work to within very small errors?
 
It is a trial and check method. If one performs this operation on several differentials a rule of thumb can be developed, but you need to shrink and check the angle. If you go too far, the bottom of the tube can be shrunk to reduce the angle.
 
yeah, I can understand that. I'd also imagine that the clearance axially is adequate to deal with any difference in length resulting from a 1-1.5 degree change.
 
Some of the misalignment is also taken up by bending the axle. This is also not a good idea for long term use as the axle repeatedly bends for every revolution of the axle. To a short track racer replacing the axle several times a season is an inexpensive and reliable speed improvement. You have to finish to win.
 
Yes, cyclical fatigue loading in this case will probably enhance the rate of failure, as bending is not a typical load the axle has to endure.
 
The whole idea of applying these mod's to an LBC repulses me on more than one level... but the technical considerations are fascinating. 'specially th': "...or until you get caught" comment. niiice, startech. Conjured up "Stroker Ace" with that /ubbthreads/images/graemlins/devilgrin.gif

But then, longevity of the system has been a higher priority here. Life is full of compromises. /ubbthreads/images/graemlins/wink.gif
 
After having slept on this. Please note that these modifications only work for fully floating solid rear axles. By this I mean the wheel bearings are mounted to the axle housing and the axle flange is trapped between the hub mounted to the bearings and the brake drum or wheel. If you have a live axle set up (early American passenger cars), the bearing is pressed onto the axle and this assembly is slid into the housing, you will get no negative chamber and only wear on the bearing. On stock cars this technique is more effective as the hub is mounted to two tapered bearings that are spaced about 3" apart. This technique would be less effective on LBC cars if they are equipped with the single bearing set up.
 
If it is not prohibited by the rules it is legal. Many racers read too much into the rule book. Our late model class did not allow parts of the engine to be coated. Everyone in the grand stock class would not use the coatings. The grand stock class cars are the same as late model except 8" wide tires vs. 10" 6 cylinder vs. V8 and the use of quick change rear ends. The coating rule did not apply to this class. For $500.00 we ceramic coated the tops of the pistons and polymer coated the piston side walls and bearing inserts. My driver complained that we wasted the money as he did not see substantial power gains. The second week out our engine man set up the two cars we ran the same. They were set way too lean. His engine, without the coatings, was destroyed including holes burned through multiple pistons and destroyed cylinder walls. We ran the coated engine for the rest of the season. The driver owner/owner now realized the purpose of the coatings, reliability. When we had the engine re-built at the end of the season we had to force the engine builder to replace the bearing inserts. He didn't feel they were worn enough to be replaced. Our team followed the rules strictly. It took Gary 20 years to win the championship legally. That was a proud moment winning over those that bent the rules. If you are making a radical legal change that you do not want other racers to notice. Make an obvious change at the other end of the car that will be noticed and the rules changed to eliminate that modification that you really did not want.
 
I did send a PM to Tony regarding the modification of the axle housing mating the tubes to the center section of the banjo VIA machined flanges that would eliminate any guessing as to angle accuracy. If he cares to display my thoughts it might offer another alternative to the bending issue. I realize that there would be some binding at the splined end of the shaft but I suspect that use of slightly worn yet serviceable parts coupled with the very slight angle in question would not present a problem, especially over the course of a few short solo races. Just yank the bits after two or three weekends and check for wear. The theory of binding and breakage is undeniable, but the reality of the standard outer shaft/flange joint surviving tens of thousands of miles of everyday side loading and torsional torture could be an indication that the solid and well splined opposite end might be up to the calling. Loosely set up carrier bearing packing washers and differential gear shims might also help. I too would have some second thoughts on doing such mods to a street car, both from a purest point of view and because of the expense, but racing is racing guys and what ever it takes, if you don't do it the other guy will and if he does and you don't win you can only blame yourself. BTW: Has anyone told Hap that he out to be following this thread? :smile: Jack
 
I'm not sure that I follow Startech's reasoning here. I do see that a full floating shaft might lend a little more slack in the train of stresses but I don't yet see why the fact that a unified flange at the end of the shaft would materially affect things. I'll study on this for a while and try to visualize it better. Jack
 
Dear Startech, I don't partake of the racing realm any more so I am out of the loop on most everything therein, but the idea of coating the pistons and bearings with these high tech materials is very interesting. Could you please forward some links so that I might be able to begin some research on that sort of thing? Thanks, Jack
 
2 things:

1. A complete Salsbury (tube) rear end with brakes weighs 159.2 pounds

2. I also slept on the 'bending the tube to achieve negative camber' posts....can't do it with the late MGB axles as the bearing is pressed onto them & then fits tightly in a race with a seal over it to preclude fluid loss...if the tube was heated & shrunk on top edge thus 'bending' it, the bearing wouldn't fit properly in the race & you couldn't tighten the seal down properly, IMDHO (In My Dumb Humble Opnion)...were I to try to gain negative camber, I'd have to go the entire tube replacement route that Jack talked about - & that would negate a lot of my weight savings opportunity.

I'm new to this sorta modification & find everything that's been posted fascinating - just don't know how to achieve it all while doing what I really wanted to do: lose about 50-70 pounds of unsprung weight from the rear end of the car.
 
I'm with you on getting things lighter. I shed 20 pound off of my rear end (looked more like a banjo than a Salisbury steak) and looked for 20 more but it all came back. It must have been all that lubricant I poured back in. ;-) Jack
BTW: Got to run to a Christmas party but I have more stuff to throw into the camber/axle stew. Probably post tomorrow AM.
 
Try www.swaintech.com/coatings.html for ceramic coatings and www.polydyn.com for polymer coatings as a starting point. Apparently the late model B's went to what I discribed as a live axle set up. I'm only familiar with the early LBCs. By full floating the two tapered bearings are pressed into the bearing hub and the bearing hub fits on the axle housing retained by a lock nut. The axle inserts into the axle housing and the brake drum and wheel are mounted to the outside of the axle. This is like early LBC, but with two bearings spaced apart. The bearings need to be spaced apart to generate the forces to bend the axle. These modifications would not be suitable for a road car. Re-fitting with IRS is the proper solution when rules do not apply. When you heat the housing and shrink it you change the angular relationship between the differential part of the axle housing and the out board end. As you tighten the wheel and compress the hub, axle, brake drum, wheel stack this bends the axle shaft. Stock cars also run larger diameter tires on the right side of the car, stagger, to induce a turn to the left. The spider gears are normally locked or welded. The cars also run cross weight to induce left turns as well. Thats what the pit crews are adjusting with a ratchet through the rear window when the cars pit.
 
Every once in a while, well a lot of the time for me, a fellow just has to trust his friends and take that leap of faith that he won't look too stupid when he opens his mouth. So... Here goes...I am confused about this whole thing. I think that I have or am missing something. What I envisioned in it's simplest form was a "rigid swing arm" axle. That is, from the point of leaving the differential carrier bearing the axle, shaft and its housing would be at the slight 1.0 to 1.5 degree angle "up" in order to attain the negative camber. I did not envision any sort of change out at the the wheel end of the assembly. In essence the outer wheel hub and it's bearing would not be aware that it was not running in a plane horizontal to the center line of the differential. The only angle that I was thinking of was that which would be produced by cutting/bending/etc. the housing as near as possible to the side-gear/carrier bearing. Setting aside the several possible methods of producing that angle change in the housing for the moment it was (is) my belief that there would be enough slop across the carrier bearing and into the differential gear as to accommodate the induced angle. As I understood it Tony went out to an axle assembly and stuck a shaft into it and surmised that there wasn't enough to accommodate due to the fitting of the outer bearing into the boss at the end of the axle. The way that I see it the correct test would be to remove the bearing from the shaft and THEN stick it into the axle housing sufficiently to fully engage the female splines within the differential gear. Then one could lift the outer end of that shaft and measure the change from true horizontal. If the upward movement of the shaft turned out to be, say a quarter inch at the outer end of the shaft, one could take the next step of actually measuring that movement and calculating the arc from horizontal and thereby identify the camber change range that it might accommodate. If the arc was on the order of 1.0 to 1.5 degrees I don't see why someone who is handy with milling machines and torches couldn't produce the desired change in the axle housing and then stuff the axle shaft back into it. The shaft and outer bearing boss wouldn't know the difference. If I am completely wrong in my reasoning please show me where. I can take it. I have had a lot of practice being married to Kathleen for 30 plus years. If I am not all wet perhaps Tony could mess with one of his axles without benefit of outer bearing and give us a report as to the real world application of this theory. If he reports that said slop is sufficient as noted above to allow for the angle change I will take the next step in offering my humble suggestion concerning modification of the housing itself. Love to all! :smile: Jack
 
For small changes of chamber this is a splendid modification method. The stock cars we were running needed a greater amount of chamber change and the drop of the pumpkin and angle changes would be noticed by the tech officials. We acually needed negative chamber change on the passanger side and positive chamber change on the drivers side. On a road race car you need negative chamber on both ends and allows the modification at the in board location.
 
I'm starting to think Jack's on to something. Ascertain the "fudge" tolerance (full unforced upward distance of the axle without the bearing in place), then it would be prudent/possible to set up two spacers in lieu of bearings (I envision a half-moon "pillow block"* with a bit smaller O.D. than the bearing, and an off centre I.D. or "V" notch-out). This to enable engagement of the axles, determine a 1°~1.5° NEG. camber with shim stock or a bit deeper "V" in the "pillow block", measure the necessary difference in angle and have the ability turn the input (pinion) through several rotations to check for binding, etc... I can't see the hub assembly "knowing" the difference either. Faster deterioration of the bearing and friction surfaces like splines and cup washers, yes. But the deflection would be shallow enough over the length of the unit at +1° it wouldn't seem to be an immediate "Vroom...*BANG*" situation.

But I've been ~horribly~ mistaken before /ubbthreads/images/graemlins/wink.gif

*the blocks could be cut from hard wood. Just so they're both the same.
 
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