Ford 9 inch components in an MGB axle?

[302GT]

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...

[mgb260]

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.

[Scott Costanzo]

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

[mgb260]

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.

http://www.v8forum.co.uk/forum/viewtopic.php?t=12520&postdays=0&postorder=asc&start=0

[MGBV8]

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.

[BlownMGB-V8]

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

[Moderator]

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

No, different carrier and gears.

[mgb260]

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.

[roverman]

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.

[mgb260]

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.

[BlownMGB-V8]

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

[mgb260]

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.

[roverman]

With perhaps less machining ?

[302GT]

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...

[mgb260]

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.

[Scott Costanzo]

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.

[BlownMGB-V8]

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

[mgb260]

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.

[Scott Costanzo]

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.

[mgb260]

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.

[mgb260]

Hey, Perry got his 31 spline axles in!  Check the V8 forum link above.

[BlownMGB-V8]

I'd say the 300-350 range is going to be a little iffy myself but it's a judgement call. If the helix angle matches the 7.5 it is just possible those and the carrier could be used in the MGB housing, eliminating the machine work and making the swap to new gears, a cheaper posi, and stronger axles a distinct advantage. It's worth looking into.

Jim

[perrymgbv8]

Hi Folks!

There seems to be a little confusion on this thread but its mostly on the right lines.

I'll try to be brief: But anyone that knows me already knows that this wont be brief

The crown wheel is 7.5" O/D.  This is the same for the V8 diff and the 1800cc diff. Both crown wheels have 43 teeth. But the angle of the teeth on the V8 version is steeper to accomodate the angle on the bigger V8 pinion which has 14 teeth as opposed to 11 teeth on the 1800cc pinion.

My first thought was to fit 31 spline side gears into the original diff cage. As I use a welded diff this was going to be done by cutting some metal off the sides to make two flats so the gear would slide into the cage. This was not a bad idea, but the messing around involved in boring out the side bores of the cage were going to mean making some tools for the lathe. While I was playing with a spare axle in the garage I remebered that a friend had given me a 9" spool last year as something to play with. That was easy to fit. The axle tubes are more than big enough to take the thicker shafts. My man at the shop has reduced the raised section of the spool so the MGB crown wheel / ring gear will fit. In order to get the mesh right he is skimming 5mm off the face of the spool. And grinding 3mm off the mating face of the crown wheel. He said the spool was very hard material. And the crown wheel is harder, hence the surface grinding required.

The Shaft bearings for the Ford 9" shafts are a stock item where I work so they are free. The bearing size is what Moser call "Big Ford" ?  The O/D of the ford bearings is 1mm bigger that the stock MGB shaft bearings. So my friend at the machine shop has made up a mount so the bearings can go on his paralell grinder / tube grinder to trim them down.

The bearings on the 9" spool are smaller in O/D than the MGB bearings. The bore on the MGB diff bearings is just a few thou smaller than the Ford. So I cleaned up the ends of the spool after cutting off the Ford bearings and heated the MGB bearings in the oven to 220C. They dropped on easily with just a light tap from a hammer with a block of wood.

I dropped the spool in and only needed to trim 25thou off one of the side shims (which were 132thou) to make it sit nice and snug.

The shafts I have are multi drilled. I'm going to use the 5x4.5" holes.

I need to trim the O/D of the wheel flanges down to fit into the recess on the brake drums so I can get them fitted flush.

The shafts are 30" with 8" of splines cut into them so I can trim them to length as required.

I'm going to re drill the brake drums to 5x4.5" and then find some 5 stud steel rims that I can get banded to the backspace and width I want to fit the slicks.

This weekend I'm going to clean up the casing and weld the tubes onto the diff housing.

The brake assemblies will be re fitted as the wheel flanges will sit in just like the originals.

So its just wheels I need to look for now.

Regarding the MGB axle and its strength!!

This is the original MGB V8 axle from 1975. It had 90,000 miles on it when I bought the car back in 1999 and used it as a show car.
The car has been drag raced since 2004 when it was a 3500 with stock tranny and nitrous. In 2006 I fitted the TH350 gearbox and a 4.6 engine with nitrous. We ran like this for 5 years until I started snapping the stock shafts. I then had the MGB shafts copied by Moser and they were very strong. However, they were machined down to 1" at the drive end to fit the stock diff. They lasted really well I think. Up to the point before I fitted the blower I was running the engine with a 600DP carb and a 250 shot of gas which made 390hp on the dyno with 602 ft/lbs of torque.  To be honest, the stock MGB shafts would have held this on the dyno as the power build is quite gentle to stop the slicks overheating. But they would have broken on the launch in the strip.

So I now had the 4/71 fitted and the Moser copy shafts. And I kept adding boost and nitrous until I got down to 10.1's on the drag strip. No problems with the shafts or the diff. But con rods were now an issue.

So I scrapped the 4.6 and found a 3.9 to work with. I wont go into too much detail about the engine. But suiffice to say it has a lot more grunt than the old 4.6 did.

When we took the new engine for shakedowns it ran 9.8's on the strip. Then I did a few tweaks and got it on the rollers. With 12psi and  a 175 shot she made 525hp with 545 ft/lbs on the dyno with AFR rich and timing knocked back around 10 degree's from where I think it will end up. This again was with a gentle power build on the dyno.  The Moser copies were holding up fine with months of 9.6's on the strip while I was testing and data logging.

The car was so predictable that almost anyone could jump in and run a 9.6 second pass with ease.

The car was put away last November and was then hauled out for some use on 19th Jan this year. First pass was a 9.6 as usual.  Then I decided to add 2.5 degree's of timing and try again. This time the engine came to life and broke a shaft and twisted the other within 2 feet of leaving the line. So the Moser copies had now been tested to their limit.  

After some talks with folk in the USA it seems that the difference in thickness between my old Mosers and the Ford 31 spline (at the drive end) would yield around 89% more strength on paper.

So the obvious thought was to buy a Ford 9" axle and have it shortened to suit my car and have all the brackets welded on etc so it would drop in. And I would want a gear set as close to 3:1 as I could get. This would run out to at least $5000.00 over here.

But  $250  for shafts with $290 for shipping I have what I need to work with for a lot less than a full axle.

Which is why I'm doing what I'm doing now.


I'm under no illusions regarding the diff. I know that improving the shafts will now just go backwards through the drive train to find the next weak link. That may be the diff gears, the prop shaft or the gearbox which has now been dragged for 8 years ??

If I add on the $400 that I will pay my friend at the machine shop for doing all the work I'm still under $1000 for the whole job.

Track info to date is:
60 foot = 1.37 seconds

The rest you can see here:

https://www.youtube.com/watch?v=N_yCCMlQ7ME&list=FLqIlXfSAoiZ--GyG4tfRrjw&index=16


And the first test run this year with the new exhaust sytem fitted:

https://www.youtube.com/watch?v=119ozwyIVbU&list=FLqIlXfSAoiZ--GyG4tfRrjw&index=9


And what happened when i added 2.5 degee's of timing

If you look closely you will see that the new Hoosiers dead hooked and the front left wheel was off the ground immediately. As you can see I backed off the pedal within a few feet.  I coasted over the 60 foot beam in 1.40 seconds I normally only run high 1.3's with full power in the 60 foot. So hopefully the new shafts will help me go sub 9.5 this year ?

https://www.youtube.com/watch?v=dSKYSH6vmRg&list=UUqIlXfSAoiZ--GyG4tfRrjw

[mgb260]

Hey Perry, Thanks for keeping us posted! I just signed on the V8 board and I find you over here!

[perrymgbv8]

No problem Jim

I've been quite busy and not had much time to come on here to update


Perry