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MG Midget and Sprite Technical - Steering arms and stub axle

I'm rebuilding the king pins from my Mk1 midget project and have noticed they seem to be mis matched somehow. They are in very good condition and were fitted to the car when I got it but on closer inspection the RH steering arm looks either bent or the wrong type. I thought at first it might be off a drum brake car (this is a GAN2 disc brake) but looking at the Moss catalogue the steering arms are the same right up to the rack change in the early 70's. I've also noticed that the part number on the RH stub axle assy is different

What I've got is:

LH
Stub assy. BTA 747
Steering arm. BTA 649 S

RH
Stub assy. BTA 602
Steering arm. ATA 4130

All parts have MOWOG on them.

Can anyone shed any light on what I've got?!
I'm fairly happy that the stub axle assy will be ok (it looks pretty much identical) but I'd like to fit a matching pair of steering arms. If anyone has a pair they would be willing to sell please get in touch!

Thanks!
John Payne

Stub Axles
BTA 744 RH
BTA 745 LH


Steering arms:
BTA 648 RH
BTA 649 LH

or assumedly for the later rack:

AHA 9957 RH
AHA 9958 LH

From the parts book. Note that the number cast into a part may be the casting number rather than the part number.

However, yours looks to be a mixture of early and very early parts?
Daniel

Google helped (Spritespot) ATA 4130 is the drum brake steering arm.
Daniel

Thanks Daniel, looks like I at least need to replace one of the arms then. If anyone has a pair (or a RH one) please let me know. There are some on eBay but they seem a bit pricey for what look like fairly rough examples.
John Payne

The first generation of disc brake cars used BTA 602/603. At some point they were changed to BTA 746/747. The part number on the part is one off of the part number listed in the book.My personal theory of broken stub axles is the first generation was made of a lesser steel and was uprated with the second generation. In over 40 years of ownership of multiple cars including two autocross cars, I have never seen a broken stub axle. The drum brake steering arms are different (angle of bend, I think) then disc brake cars. The later arms differed in the size of the hole for the tie rod end. Later ones were smaller.
Not that it matters for performance, but the early disc brake cars used a different hose bracket and mounting bolt.
J Bubela

That sounds like decent theory John, the BTA 747 stub axle I have has EN16T on it whereas the 602 one hasn't.

I've seen a stub axle break on a friends car a few years ago. It just snapped clean off at the inner bearing and made the car roll. He was ok but the car needed a new roll cage and a bit of straightening out. It was a fairly well campaigned car with slick tyres so obviously under a lot of stress. I've got a picture of the broken axle somewhere.

I've seen new stub axle/king pin assemblies advertised but whether or not that is a mistake and they are reconditioned I'm not sure.

You are right about the early arm, it has more of a twist to it which is what drew my attention to it being different.
John Payne

I have several steering arms worth only the price of postage - I'll look for them later this evening, hopefully.
Daniel

I am pretty sure that all steering arms are handed L or R, as the hole for the TRE is tapered, so you need
ATA 4130 Right side
ATA 4131 Left side
Dominic Clancy

Cheers Daniel, that would be great. I'll look out that photo of the broken stub axle in case anyone wants to use it in a book for example!
John Payne

I have a BTA 648S which I think is what you need.

I also have an AHA 9957 and an AHA 9958

I can post this Wednesday or tomorrow if you are desperate - e-mail me your postal address and let me know if you want 1st or 2nd signed for.
Daniel

ISTR that John Sprinzel, in "Spritely Years", mentions breaking a stub axle forcing retirement from a european rally he was leading at the time. On investigation it became clear that the stub axle mounts had a casting hole in them, an unnecessary left-over from the prototype molds. This was subsequently eliminated from later stub axles.

Its several years since I read that so I cannot immediately give page reference etc. but it may explain why many know of the supposed axle weakness, but few have actually experienced it!
GuyW

Daniel, email sent!
John Payne

Even though I have never broke one, and really stressed the auto cross cars, my track car in progress has the welded stub axles just to be safe. The AHA 9957 and an AHA 9958 would work if you could find a TRE with the smaller taper and the larger female thread. I never bothered to research it.
J Bubela

This thread was discussed between 05/08/2018 and 07/08/2018

MG Midget and Sprite Technical index

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