Length of damper link

[don58van]

A friend is replacing worn links for the rear dampers on his '56 Traveller. When comparing the new links with the ones he removed, he found that the old ones are significantly shorter than the replacement parts (which he is confident are the correct parts for a Minor).
The old links are about 160mm centre to centre of the mounting bolts compared with 180mm for the replacements.
One of the old links has the (part?) number 3541/A. This number differs from the two part numbers listed in the BMC Parts List for the Minor.
Has anyone else found a difference in the length of these links?
Can anyone identify the old links from the 3541/A number stamped on one? I know they aren't Spriget or MGB links as I have checked their link part numbers in their respective Parts Lists.
Eagerly hoping for your reply...
Don

[olonas]

I don't know how to post a picture, but I have just measured an old link from my '62 saloon. I would say it's 175mm-180mm centre to centre. The new replacdement links are the same length/measurement.

[geoberni]

I don't know how to post a picture, but I have just measured an old link from my '62 saloon. I would say it's 175mm-180mm centre to centre. The new replacdement links are the same length/measurement.

Posting a picture is either drag and drop if your screen/device is big enough, or use the TAB that says Attachments, just below where the SUBMIT button is....

[geoberni]

As I was curious and it's only a 2 minute thing to check my car in the garage, I just did so.
Basil is a '55 SII and as far as I know, the Axle and it's attaching parts are original.
I just did a rough measurement.....
About 160mm Centre to Centre, or 140mm length of the connecting bar.
I didn't go as far as cleaning them to look at numbers.

Perhaps they changed with the introduction of the S3 and another 20mm or so is the default size now??
.

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20221003_182050.jpg (1.06 MiB) Viewed 1413 times

[geoberni]

Interestingly, MOSS Motors site gives 2 different numbers for the Link

To (c) 217204 Pt No: AAA173 (Unavailable)
From (c) 217205 Pt No: BMH2289
https://www.moss-europe.co.uk/rear-susp ... 51-71.html

Now I'm assuming that Chassis/Body Number is mid range on Series II. Basil is 32****, so I'm even more confused.......

[don58van]

Thank you very much for your replies.
Its a bit of a mystery.
From your helpful replies, it looks like the old/shorter ones are correct original fitments. However, the part number stamped one does not agree with the factory parts list or the Moss data.
I guess we will go ahead an fit the new, longer ones.
Don

[olonas]

"Posting a picture is either drag and drop if your screen/device is big enough, or use the TAB that says Attachments, just below where the SUBMIT button is...."
Sorry to go off topic, but thanks, I'll give that a try.

[philthehill]

Duplicated post (as below) deleted.

[philthehill]

Whatever length of link is fitted it must be ensured that the damper does not bottom out before the bump rubbers hit the rebound pad or bottom out the other way when the axle drops away from its normal operating ride height. If the damper does bottom out either way up or down serious internal damage to the damper can occur.
I suspect that when the style of damper (i.e., valve location) was changed at car No: 24067 (see wksp man section L5) the operating arc of the internals were modified/varied leading to a change in damper link length. The new later damper link being BMC Pt No: AJA5012 (MOSS Pt No: BMH2289).
The difference in lengths of 160mm and 180mm (20mm) can have a serious effect on the operating arc of the damper internals.

[geoberni]

I suspect that when the style of damper (i.e., valve location) was changed at car No: 24067 (see wksp man section L5) the operating arc of the internals were modified/varied leading to a change in damper link length. The new later damper link being BMC Pt No: AJA5012 (MOSS Pt No: BMH2289).
The difference in lengths of 160mm and 180mm (20mm) can have a serious effect on the operating arc of the damper internals.

Phil
Your logic is very sound regarding arc of operation etc, and quite reasonable, but there is one flaw which I hinted at in my last post.

As I understand the Chassis/Body numbering, 24067 would be fairly early in MM production since the MM went up to 179839. So perhaps 1950 ish?

Basil is a post update 1955 Series II car 32**** but I as I reported, the links are the 160mm/6.25" length.

Nothing adds up; the damper change would seem to be many years before the arm length changed.....

[philthehill]

Perhaps BMC did not realise about the length of the arm till much later!
Again, Perhaps BMC had a large stock of the earlier arms to use up!
But who know what the reasoning behind the change is really about?
In my opinion BMC made some strange decisions over the years.

[geoberni]

Perhaps BMC did not realise about the length of the arm till much later!
Again, Perhaps BMC had a large stock of the earlier arms to use up!
But who know what the reasoning behind the change is really about?
In my opinion BMC made some strange decisions over the years.

I can't disagree with that statement , but with more thought, I think it's another reason.
A very rough look at the situation, with just a little thought, and assuming:
a) the diagram in the Workshop manual is of the median/null point when the car is typically loaded
b) the diagram is of the original shorter connecting rod
c) the range of travel of the Damper is between the Red Lines (as best as I can remember when I took them off)

Damper.JPG (157.05 KiB) Viewed 1287 times

The original line (Yellow) sits quite high, so when the vehicle rises, or more accurately the axle drops away, there is only about 1/4 of the dampers range of movement before it reaches the end of it's travel.
With a longer connecting rod (Blue line), it's nearer the mid point of the range of travel, perhaps 1/3...
Giving the Damper a more effective use in both directions?

I've never seen the MM/Series II equivalent of the AKD 3541 Service Parts List, despite frequently looking around Autojumbles etc, ....but perhaps that included a note that the early one was no longer available and to use the AJA5012 (fitted in pairs of course).

Just a thought....