Hydro displacer struts

[whistler]

20190303_160602.jpg

After reading a 2017 post regarding displacer strut lengths I though I'd check what mine were, as I've just stripped the rear subframe.

According to the BMC parts book mine is 21A1497 but it is only a couple of hundred numbers short of the chassis number change.
The length is 9 3/8" (abiout 23.8cm), 0.5" internal and 0.75" external diameters.
Both struts have the spring behind the dowels.

Would I be advised to replace these with the slightly longer 21A1805 struts or leave well alone?
My car is a 1966 mk1.

[Dr S]

Calling Pete Laidler!

I’d say no at this point, I’m about to shorten mine to this spec ( and a touch more ) to offset the middle age sag.

[whistler]

Calling Pete Laidler!

I’d say no at this point, I’m about to shorten mine to this spec ( and a touch more ) to offset the middle age sag.

I'm hoping Pete picks this one up; he's been very helpful to me with hydro.

[Peter Laidler]

Well..........., looks like Pete is about to come unstuck here!!!!! While I was researching the subject of the struts, dowels and springs I searched and searched the old parts lists and the only reference to another strut was one that catered for the dowel but NOT the spring - which caused a problem on rebound. The ST booklet mentioned fitting the later 9.75" strut but was pretty ambiguous as to exactly what the original length was. So to be really honest, when Dr S said his struts were shorter that the spec length of 9.75" or so, I thought that they'd been got at in the past as a modification by 'someone'! But now there's another, shorter strut, well...., I'm buggered if I can get my hydro head around it. But there it is, in black and white. But looking back, I still can't see a reference to a shorted strut in any of my Mk1, AKD 3509 issue 2 parts lists.

But if I had to set my car up again and it was sagging at the rear, with shorter struts (and serviceable helpers) I'd be using the current 9.75" struts. They'll lift the rear by the average 5:1 or so ratio.

Interesting that while I could find differences in the helpers, no such luck with the struts except for the springless variety mentioned. Incidentally, I did discuss the struts at some length in another hydro article where I described making a new set from 18mm(?) stainless steel bar for my needy car. Worked a treat and looks good too. Keep me up to date!

[Dr S]

I reckon it happened with the spring changeover. Either way mine will be lopped sooner rather than later

[Peter Laidler]

I couldn't find the spring changeover date either Doc! Enlighten me and I'll correct the article - or at least get Mark to do it for me!!!!!

Do any of the much earlier parts lists mention the change point(s). Maybe I should have read Parnell again!!!!!

[Dr S]

I think it’s referenced in vizards htmym. I’ll have a look tomorrow

[bwaminispeed]

Strut Change over

Austin: A-2S7-830893 RHD, 832054 LHD

Morris: M-A2S4-370194

And, you are correct, springs and struts were both changed at the same ser. numbers.....

[Peter Laidler]

Where on earth did you get that good info from? It's nowhere I could ever find. Mind you, my tech library is a bit thin. It's not mentioned in the Parnell book either.

While we're here, maybe someone can tell us an approx month/year when hydro car chassis numbers Austin 830893 and 832054 and Morris 370194 were made

Thanks BWA

[mk1]

"Where on earth did you get that good info from?"

Probably from here;

http://mk1-performance-conversions.co.uk/AKD3502.pdf

Page MH10

[whistler]

Strut Change over

Austin: A-2S7-830893 RHD, 832054 LHD

Morris: M-A2S4-370194

And, you are correct, springs and struts were both changed at the same ser. numbers.....

My chasiss number is 368... so just before changeover. AKD3502 parts list, which covers ordinary saloons, not cooper variants.

[Peter Laidler]

I'm totally confused comparing the earlier and later parts lists now because my '66 AKD 3509 parts list STILL only mentions the early obsolete 21A 1497 strut - but the later 1704 dowel!!!!! A sort-of hybrid set-up!
And while there are two known* part numbers (p/n's) for the strut there's no indication that they are different lengths - except for two solitary examples.
There's two p/n's for the dowels too but we know that the later 1704 dowel was configured for the loading spring.......
............which the next strut 1805 was machined to accept the spring 4G7809 (so that it couldn't bottom out)

Time for a coffee to unwind my brain. But in short, to my way of thinking mech engineering, if the car is sitting perfectly at the front (with drive shafts exactly horizontal) and low at the rear then investigate the cause first. If all OK then increase the length of the struts. It's a really simple fix but DON'T add spacers!. If it's high at the back then shorten the struts by the recognised (is it 5:1) ratio

I hope this thread runs for a bit because there's a lot to learn as the hydro physics bit is pretty simple the mechanical parts aren't so!

*there is another strut mentioned for the Mk3 hydro part in AKM 0031 - October 69 on - 21A2276, presumably for the early Mk3 hydro S's but the spring and dowel remain the same as before

[whistler]

CHeck out the different recommended tide height ranges pre 65 and post 65.
http://www.hydragas.co.uk/technical.html

[bwaminispeed]

Yes, I have a complete AKD 3502...….

It appears the displacers were changed then as well.....

[whistler]

There might be some regrets that I was allowed to join this group. It seems I ask the questions that few others have thought of! Lol

[bwaminispeed]

As requested, here's the change points for the Coopers and Ss

previous strut: 21A1497
From these numbers on: 21A1805

Standard Austin Cooper

C-A2S7-830061 RHD
C-A2S7-829417 LHD
Cooper S C-A2S7-820487 RHD
Cooper S C-A2S7-820514 LHD


Standard Morris Cooper

K-A2S4-830127 RHD
K-A2S4-829490 LHD
Cooper S K-A2S4-820705 RHD
Cooper S K-A2S4-820706 LHD

[Andrew1967]

Reopening this thread ...

We have ascertained previously that earlier Hydro cars have different struts and displacer 'cones' than the later (presumably late 65 onwards).

I'm getting the hydro bits together for HOY and have found that it has the cones with the longer noses and shorter struts .

What I have found today is that there is only about 3mm difference (280 early and 283 later) between the overall length of the nose + strut length on the later set up than the earlier one ... see the pics ..

So, what was the point in it ?