MGA MGA vs MGB rear axles and differentials

[tdskip]

OK - take me to school here guys if you would on how to tell them apart.

Any pro/cons between the different set ups?

 

[bob67bgt]

Early banjo diffs from As and Bs...You can tell what its from weather it has 7/16"(A) or 1/2"(B) bolts for the axles to bolt on with. The gear ratio is stamped on the top of the aluminium pumpkin. The hubs ,backing plates,and case are different. The only difference in the case is(??? from memory)the bracket that the ebrake cable bolts to is a little different. The later B diff (68 and newer or all GTs) does not have a removable aluminium pumpkin and normally will only be found in 3.9 ratio. MGA's also had 3 different spline axles at the spider gears. My thoughts are the later MGB units are stronger and quieter but heavy. Also later ones may need a thrust washer kit installed to keep them from clunking. The only real prefrence i have is a quiet diff! Bob

 

[200mph]

Among racers, and for high horsepower street cars, the hot ticket is a "hybrid" rear end. This combines the durability of the Salisbury rear end with the ratio-swap capability of the Banjo rear. Racing forums have more details and sources.

 

[tony barnhill]

From top to bottom:

Salisbury Rear End
Banjo Rear End
"Hybrid" Rear End

Banjo rear is lighter and real easy to change 3rd member.
Salisbury rear is heavier but the the axles, as 200mph stated, are stronger & axles get more lubircation.

My "hybrid' is a wire wheel banjo (about 2" narrower than a steel banjo) with Salisbury differential/axle bearing ends welded on..& negative camber built in when we did that welding...now, I have the lightness of the banjo, the ease of changing gears of a banjo & the axle strength/lubrication improvements of the Salisbury.

Dave Headley is an expert in hybrid differential casings. He'll build you one if you want...https://www.fast-mg.com

 

[Hap Waldrop]

I've built a couple of Hybrid rear ends myself, this is more for the racing crowd though.

Skip if we're tlaking the difference in the rear end end set uyp, I'm guesing we're just tlaking banjo set up, then you have different diff ratio, and you have switch out spider gears in some sets to amke the different ratio to work.

here's a picture of one of my hybrid rear ends

 

[tony barnhill]

Hap - your picture didn't show up...I knew you did them for racers but didn't know if you did them for the general public.

&, you're right....if all he wants is better gears in his MGA - MGB banjo gears fit.

 

[gblawson]

As an aside... TD/TF owners are always looking for MGA 4.3 gears to swap with their original 5.123 gears...some also use MGB 3.9 or 4.1 .... Don't throw away those rusty old diffs.....!!!!

 

[tdskip]

Blast from the past. Can you believe that it "only" took me 3+/- months to walk into the garage and take these pictures?

Are these enough to help me make the determination as to which one this is?

Thanks!

 

[Steve_S]

That's a salisbury "tube" axle.

 

[tdskip]

Hi Steve!

Check me to see if I got this right, as a Salisburg axle it would have been used on later cars, starting with the BGT right? Did the ratios vary in Salisburg axle or where they constant through the production run (can't imagine they were constant)?

 

[tony barnhill]

Looks to me like a Salisbury MGB/MGB GT rear end.....just compare it to my photo a few posts ago.

 

[tdskip]

Hi Tony - hope you are doing well. Yep, got that it is a Salisbury. Thanks again for the pictures.

Do know of a way to tell what the ratio is short of pulling the rear cover?

Thanks!

 

[DrEntropy]

Mark a spot with chalk on drum and backplate, set it where you can lock the other side and spin the input yoke. Turn the yoke until the drum makes exactly one revolution and count the number of turns of the input as you do. You'll have your answer.

:wink:

 

[tdskip]

No flux capacitor needed Doc?

 

[DrEntropy]

Nope! Just a piece a chalk. :wink:

 

[tdskip]

Left hand, or right hand threaded chalk?

 

[DrEntropy]

'k Tom... let's go thru it s l o w l y, once more, shall we?

 

[tdskip]

'k Tom... let's go thru it s l o w l y, once more, shall we?

LOL Doc. Thanks for playing along.

 

[tdskip]

OK - back from the garage. I got two turns of the yoke for one revolution of the drum.

 

[tdskip]

Found this as a resource;

"Here’s how to check out your diff ratio easily if you need to:

Jack up one of the rear wheels (doesn't matter which)

Block the other wheels (both directions), put the gearbox into neutral and let the handbrake off

Mark the diff pinion flange with a bit of chalk or whatever, with another mark on the diff housing nose next to it.

Put similar reference marks on the wheel which is in the air and the adjacent bodywork.

Rotate the wheel two turns, counting the drive shaft revolutions as it goes. There will be about 4 turns of the driveshaft* - note which direction the driveshaft is rotating, so you can determine whether it does more or less than 4 turns.

The fraction of a turn is what we want - make your best estimate of it, to the nearest "O'clock" is close enough (take 12 O'clock as being when the marks on the diff line up, even if it isn't straight up)

* MGA, B, Midget. V8, MGC are closer to 3 turns

Now for the calculations:

Because we have only one wheel in the air and the other not turning, the crown wheel will be turning only half as far as the wheel, so in the two turn of the wheel the crown wheel will do one full turn.

Because any given model of diff had a number of set ratio options rather than continuous range, it is now only a matter of matching the measurement up to whichever is closest:

A series diffs came in the following ratios

3.55, 3.727, 3.9, 4.22, 4.55, 4.875 (and others even lower but not much use to MG's)

B series diffs came in

3.07, 3.31, 3.7, 3.9, 4.1, 4.3, 4.55, 4.875 and other unmentionable options past 5:1

The difference between even the closest of these readily shows up, corresponding to the following positions of the driveshaft (remember, 12 O'clock is where the two marks on the diff line up, and I'll assume the wheel was rotated forwards, making the driveshaft go clockwise viewed from the front):

3.07 = 3 turns then round to 1 O’clock

3.31 = 3 turns then round to 4 O’clock

3.55 = 3 turns then round to between 6 & 7 O'clock

3.7 = 3 turns then round to betwen 8 & 9 O’clock

3.727 = 3 turns, then round to 9 O'clock

3.9 = 3 turns, then round to 11 O'clock

4.1 = 4 turns then round to 1 O’clock

(taken from https://www.mgparts.co.nz/diff_ratios.html )

<span style="font-weight: bold">I counted 3 turns then 10 O'clock</span>, so I'm guessing 3.9?