Engine and Transmission Tech

This seems hard to believe, but the British web site, V8 owners forum, has an interesting thread in the drivetrain section. Someone has found that Ford 9 inch spider gears will fit in an MGB differential cage once 10 mm is machined off the backs of the gears. This allows the use of Ford 9 inch axle shafts (though with a custom length) in the MGB axle housing. Further experimentation with a Ford 9 inch spool showed that the spool fits perfectly in the MGB housing using stock MGB bearings. Machining a little off the crown wheel mounting faces on both the crown wheel and the spool gives a perfect mesh of the MGB gears once the usual shimming procedures are followed (new crown wheel bolt holes have to be drilled as well). The next step is to see if an actual Ford 9 inch differential cage assembly will fit...

Larry, Probably the small 9"/8" 28 spline. It would be much easier to use a 4X4 locker in the MGB case with no machining (may need a custom cross pin)and do away with the spider gears entirely. You can get cut to fit long spline axles and make it any width you like. With the Moser 8.8 small 9" bearing ends, Mustang disc brakes bolt up too.

Interesting. I wonder if it would be possible to fit a 9 inch lunch box locker with the same modification?

Scott, that is what I suggest. I looked at the article on V8 owners forum that Larry refered to. It's our friend Perry Stephenson's drag car and he machined the spool to fit and is using the larger 31 spline axles. My idea is to use the Powertrax No-spin, more streetable than the clunkier 4x4 ones but, about $100 more.

[www.v8forum.co.uk]



Edited 2 time(s). Last edit at 03/09/2014 06:59PM by mgb260.

I have lurked on the V8 Owners Forum for many years, It's a great resource.

Jim's Powertrax suggestion would make much more sense in an MG than a regular locker. The on/off nature of a locker is not very sports car friendly.

WOW, who would ever have thought that?
This is phenomenal news because the axle housing can be retained and still have an axle as strong as any available with that diameter of ring gear. No more weak spiders or axles!

So I have to ask. How about the banjo axle? It uses the same carrier and gears right? So you can do the internal stiffening mods and have a very stout but super light axle, right?

I expect that's the way I'd go if I didn't already have IRS.

However... I must say one thing here. I *have* destroyed an MGB Salisbury ring gear by putting too much torque through it. (But I also have broken spiders, and have broken a transmission case. Have never twisted an axle shaft though, surprisingly. I imagine the 28 spline Ford axles are plenty strong enough. YMMV)

Jim

Quote:

How about the banjo axle? It uses the same carrier and gears right?

No, different carrier and gears.

Also on the Salisbury I think another weak link is the pinion crush sleeve. When the crush sleeve gets hammered with drag race starts you increase clearance and slop. A solid spacer with shims such as Ratech makes for the American axles would fix that.

FWIW, I would like to meet the very skilled machinist, who can actually machine the backsides of spyder and ring gears,AND drill/ tap new mounting holes, at 62rc. hardness ? Soo, the late MGB has very close, to a 9" ring gear dia ? roverman.

No Art, The inner axle bearings are close between the two. Perrry cut the spool way down to fit the MGB ring gear. I've never measured the MGB ring gear but heard it was 7 7/8". I think he is going to redrill the spool or case not the ring gear. The spider gears and ring gear can be milled, but is damn hard on the tool bits and slow going.Or they can be ground down. You would need to reheat treat though I would think.



Edited 1 time(s). Last edit at 03/10/2014 05:30PM by mgb260.

Just the spider gears, the back side is flat and you should be able to cut those with a carbide bit. May or may not be through hardened but it probably doesn't matter there. The pinion flange could be pinned and re-drilled as well as faced down thinner. May not have to touch the ring gear, it depends on how much meat is there but from Perry's photos it looked like there was plenty. Also it makes a difference which carrier you use. Normally there will be 3 or 4 with different flange offsets for different ranges of gear sizes. If he's using a carrier for a 3.31 it might be possible to switch to the 4.10 or even 5.13 carrier and not even have to machine the flange at all.

I measured the MGB ring gear and got 7-7/8" at the mounting flange but ring gears typically are larger at the teeth so where you measure it determines the spec. At the teeth I believe it would be 8" or possibly a bit larger. But it's been awhile since I measured it. Dana44's are often referred to as a 8-1/2" gear but at the flange they are 8.4" I'm sure Basil could answer that question though. Is the 8" Ford 8" at the flange or at the teeth? I don't know. The MGB gear could be the exact same size as the 8".

Jim



Edited 1 time(s). Last edit at 03/11/2014 12:03PM by BlownMGB-V8.

I know the 7.5 ring gear is actually bigger than the 8" because of the angle of the ring gear so I assume it's flange measurement. here is a picture , big hunk of steel.




Edited 3 time(s). Last edit at 03/17/2014 04:15PM by mgb260.

With perhaps less machining ?

As I understand it the intent was to build a stronger axle for drag racing but keep a stock appearing axle. The first approach was to try to put Ford 9 inch spider gears in an MGB differential carrier to allow the use of Ford 31 spline axles. Measurements showed this would work if about 10 mm were taken off the backs of the spider gears. But then a Ford 9 inch spool was acquired and it was found to fit with no modifications except to the crown wheel mounting surface. This is apparently where the original project is going to stop. The unanswered question is if a Ford 9 inch carrier complete with spider gears will fit in the MGB axle housing. If it will, probably the only machining needed would be to the crown wheel mounting area. However this needs to be checked by someone in this forum...

The 9" has 2 different carriers, one large one with 4 pinion and 31 spline side gears. A smaller one with 1 pinion and 28 spline side gears that is practically the same as the 8" except ring gear bolt pattern. I think the smaller one would fit better in the MGB housing. Like Jim B said there is a carrier break for lower or higher gears also that would affect the width same as MGB/MGC. I still think the Powertrax Locker would be easier. It already has the side gears for the Ford axles and would fit in the MGB carrier with modification to the pin and maybe shimming or machining depending on width. I agree with Larry one of us would have to lay out the parts and compare.

I wonder how the 7.5 or 8.8 spider gears would fit into the MGB carrier? It would be great to find a locker that would fit into the stock axle with minimal machine work. One of these days I'll try to get some spider gears out of a junk 7.5 axle at the local pick n pull.....when I can find the time. :)

That might work Scott. I didn't realize the ring gear was bigger than 7.5" on those axles. Wouldn't hurt to get an accurate measurement. Pinions tend to fall within a fairly narrow range of diameters but the spread from large (like 3.08) to small (like 4.10) is much more than you might expect, and this is the determining factor in whether the gears will mesh properly. So the mesh interface for a 7.5 (or 8" - different helix angle though) should fall very close to the mesh interface for the OEM axle with the same gearset, but the mesh interface for a 9" 4.10 might be about where a 3,54 or a 3.08 is for the stock gears, meaning that is some cases you might have to put 3.31 gears on a 200 series carrier for instance. But it's worth looking into, and if the journals don't match up there are a LOT of Timken bearings in different sizes. You also may have to play with spacing the pinion in or out some. In is easy. Out, not so much. Obviously the helix angle, or offset from centerline has to match exactly.

Jim

I think the 8.8 carrier is too big also.The Ford 7.5 spider gears are usually what break under high horsepower, second most failures are the thin main caps(Girdle type cover helps). I would just try to adapt the carrier to fit for the 28 spline Ford axle in the MGB housing. Track-Loc with spider gears for lower than 300HP any more either go Tru-Trac(like Quaife) or Powertrax No-Spin for higher HP. Or just use the Powertrax No-spin for the 7.5 in the MGB carrier with Ford 28 spline axles.



Edited 1 time(s). Last edit at 03/12/2014 06:03PM by mgb260.

Quote:

The Ford 7.5 spider gears are usually what break under high horsepower, second most failures are the thin main caps(Girdle type cover helps).Or just use the Powertrax No-spin for the 7.5 in the MGB carrier with Ford 28 spline axles.

Jim,

Not sure your last post was in response to mine or not but I wasn't suggesting that I would use the 7.5 spider gears in the MGB carrier. I'd be using them to test fitment for a lunch box locker like the Powertrax.

It still isn't clear, in my mind at least, if it there is an advantage to modifying the stock rear end over just swapping in a narrowed axle. I'm guessing it will cost a bit more to modify the stock axle. Maybe this will be one of those things that some of us will do just to see if it can be done.

Scott, Yes, I did think you wanted to fit the spider gears to fit Ford axles. The main advantage is you already have the axle and there are better ratios now. The MGB axle is pretty tough if you eliminate the spider gears and use a solid pinion spacer instead of the crush sleeve. The one piece cut to fit Ford axles are much better than the 2 piece also. So everything you would do to beef up the 7.5 can be done to the MGB axle. Cost difference for 3.31 gears in MGB axle vs paying someone to narrow the Ford axle. Doing it yourself the Ford would be a little cheaper. For your HP I'd go with the 8.8 instead of the 7.5. I only recommend that for under about 350HP.



Edited 1 time(s). Last edit at 03/13/2014 06:15PM by mgb260.