mk1-forum.net

To save me ploughing through 610 index pages relating to anything to do with 'arms', can any one in forum-land tell me the difference between Mk2 Cooper and S steering arms (BTA 894 and 5) and the standard car steering arms, (896 and 7)? The steering rack is identical as are the standard and Cooper wheels, as are the retaining bolts and locating bushes.

I'm aware of the angular differences between the Mk1 and Mk2 arms and racks (to cater for tighter turning circle) but it's never even crossed my mind that there's a difference between the Mk2 basic car range and the Coopers. To be honest, even the castings look identical

Just starting a tutorial to convert a 998 Cooper from ball to taper rollers so thought that I'd include a breakdown of the parts too.

Nope....., I don't understand it either

added at 2100; To make this even more mysterious...... Just looked under my '69-S and cast into the left hand steering arm is 897! A standard saloon steering arm. That's made me look at the right side and it looks like that is a standard arm too. The plot thickens! Maybe there is no difference

I always thought s arms were thicker. Not compared them myself though,
I fitted taper rollers on my 998 Cooper front and back and they are working fine, I did use genuine timkens though.
I did fit new hubs though and I found the nose on new hubs needed turning down to clear inside of my genuine 998 discs, not sure if same problem with current repro discs.

Peter Laidler wrote: ↑Thu Jan 28, 2021 6:06 pm ,,,,, the difference between Mk2 Cooper and S steering arms (BTA 894 and 5) and the standard car steering arms, (896 and 7)?

Geometrically, they are the same and for all intents, interchangeable, the (so called) S types as Daz mentioned, are thicker. They did fit the BTA894's and 895's on cars other then the S's, though they started with them.

Daz and Spider have pretty much answered all the Q's PLUS why my S seemingly has 'standard' arms. As for the supposedly different thicknesses.... Not that I can see. The differences using external calipers are marginal. Hey ho.

Peter Laidler wrote: ↑Fri Jan 29, 2021 9:26 am Daz and Spider have pretty much answered all the Q's PLUS why my S seemingly has 'standard' arms. As for the supposedly different thicknesses.... Not that I can see. The differences using external calipers are marginal. Hey ho.

Glad it was of help mate.

Don't go off the numbers on the Arms, they'll be a Forging No. of which seldom align with part numbers !

Here we are, S vs standard

Mmmmmmmm, I think that you're showing a Mk1 against a more angled Mk2 type.

Both definitely mk2

Minisprinter wrote: ↑Fri Jan 29, 2021 10:51 pm I must admit, I didn't think the mk1 arms had the ears.

MS

I used to think the same, until I came across this;-



MKI on top, MKII under

I've come across many of these now.

One definitely looks fatter to me, although it may have had a bit of clearance ground from it for that vented disk

Spider wrote: ↑Fri Jan 29, 2021 11:50 pm

Minisprinter wrote: ↑Fri Jan 29, 2021 10:51 pm I must admit, I didn't think the mk1 arms had the ears.

MS

I used to think the same, until I came across this;-



MKI on top, MKII under

I've come across many of these now.

Are you sure they're mk1 and mk2 arms Spider?
I used to have a set of genuine mk1 S arms (came with a complete mk1 S disc setup I bought from Tim Harbour in the mid 80's) and they were very obviously different length and different angles (and thickness) to the mk2 drum braked arms I had (the thin arm in my photo). Unfortunately I don't have the mk1 arms anymore for comparison.
Only info I can find is a picture you've previously posted that shows the mk1 arm should be the shorter arm with more angle to it.

In regards to the 'strength' discussion, the old engineers (and that's my era sadly.....) used to have a phrase banged into their heads during their long apprenticeships and during the metallurgy phase at Uni, something to the effect that '....you measure dimensions, you can SEE strength...' Or something like that. If something really IS stronger, then you should be able to SEE it. (But I don't think that strictly applies today)

The fact is, and aft stated on the forum, that the Mk1 arms = Mk1 steering rack. Mk2 arms= Mk2 steering rack and NEVER the two should mix for reasons to do with thread engagement.

But the real question is, so far as I can tell from a couple of parts lists, why ONE set of arms across the Mk1 range and TWO sets of arms across the Mk2 range

Peter, there are, or were, two sets across the mk 1 range too.

Mk 1 standard: 21A73/4. Mk1 Cooper S : 21A1464/5.

Mk 2 standard : BTA 896/7. Mk 2 Cooper S : BTA894/5

The 894/5 was also used on the1275 GT until 74. Curiously it seems the 12" wheel GT then went onto 896/7.
But I've also seen the fatter 894/5 on a drum braked 1982 car.

Yet another case of what was in the parts bin? It seems the Mk 2 arms can be interchanged , not with standing any strength differences. But for road use not really an issue I guess.

Ah yes, my 69 1275gt had the fat S steering arms.

imack wrote: ↑Sat Jan 30, 2021 8:48 am Are you sure they're mk1 and mk2 arms Spider?

When I first came across this, I was like " WTH " and so thoroughly checked them.

Peter, there are, or were, two sets across the Mk 1 range too.

Mk 1 standard: 21A73/4. Mk1 Cooper S : 21A1464/5.

I know the thread was originally about Mk 2 arms but as Mk 1 have been mentioned the early Mk 1 Cooper and S arms have so far been missed.

For the sake of completeness, the original Cooper and S arms are BTA188/189; these are noticeably thinner when compared to 21A1464/5.

Virtually all 1071 S should have BTA188/189 - change points are in AKD 3509.

Thanks for clarifying that Simon.