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I've never looked really closely at different hydro units before but is there a quick way to tell an S unit from a non S other than part numbers (which have usually fizzled away) or coloured bands (also often not evident) because the part numbers quoted for normal hydro units on both Coopers and S's here are the same ?

http://mk1-performance-conversions.co.u ... _units.pdf

Also, I recently bought some 21A2008 green band units (off here) that I can't seem to find evidence of them being S at all. Am I right to say they were normal units only fitted to non S's?

The other thing I noticed when looking at a few different units I've got is that the ones I knew definitely came off an original low mileage Mk3 S look different from both the green band 21A2008 units and the 21A1477 (marked on the steel housing) units (not to be confused with said number found on ALL the rubber springs across the board) in that on the S ones the depth from the top of the steel housing (hose end) to the top of the rubber spring is about 7mm less than the other two. You can see the difference here , with the late S one on the right...



The other thing I noticed on the S one is that the rubber has a constant smooth radius compared to the other two where the rubber dips down toward the hose union. You can see the indent on these two..

The thickness of the top rubber is what makes them stiffer isn't it, that and the valving.

I wonder where all the tech information is on them now, I guess Moulton kept it all as he seamed a bit of a horder

rich@minispares.com wrote:The thickness of the top rubber is what makes them stiffer isn't it, that and the valving.

I think that's right so could we say that to identify an S displacer quickly all you have to do is look at the top? Or is it more complicated than that? IE, did some S units look identical to non S? Like I say some of the part numbers for S and non S are the same (except 21A2008 funnily enough which are not listed as S anywhere to my knowledge...)

There was some speculation that those with the rubber closer to the top were S units, but I have found that not to be the case, as I have come across many with the rubbers close to the top that were Non-S types.

The difference here appears to between early and late displaces, that's all.

Every S Displacer I've come across has always had the part no. stamped in to the metal body, most of the others do also, but not exclusively.

Spider wrote:There was some speculation that those with the rubber closer to the top were S units, but I have found that not to be the case, as I have come across many with the rubbers close to the top that were Non-S types.

The difference here appears to between early and late displaces, that's all.

Every S Displacer I've come across has always had the part no. stamped in to the metal body, most of the others do also, but not exclusively.

I wondered whether this could be an early/late difference, anyone else confirm that? The 1477 pictured above with deeper top is dated '66.

Yes they usually do have the part numbers on the body but it's usually very hard to see on used UK units (with our climate! )

I would be very keen to read more on this subject if anyone has anything to add.

M

Hello mk1,
If you want to read more, there are occasional items on the ausmini website about hydrolastic systems, like this one that includes some technical drawings and specifications from the Australian factory:
http://www.ausmini.com/forums/viewtopic ... astic+bags

and others that cover all the various part numbers and what was fitted to what.
Bill

Thanks for that heads up Bill, an excellent thread.

I have most of the factory reference stuff on the main MK1 forum already though. It was mainly the practical application of the data that I was particularly interested in, I therefore found the thread above very interesting. As this is generally speaking a black hole of disinformation, gossip & lies.

M

As has been mentioned earlier,best identify by the p/n stamped on the side of the unit. If it's so crusty you can't determine it, the thing will probably be toast anyhow.(the top end of the can starts delaminating).
All the Cooper S bags I've discovered have been p/n 21A1872/21A1874 and they have been shallower compared to a 21A2008 unit.
Can't read the Auzmini link .....

So ST units aside are we saying that S and non S displacers were all the same as they all have the same generic part number? (Apart from 21A2008 which seem to be the only displacers that weren't fitted to an S??) OR is the depth of the top the identifying factor?

Anyone else anything to add to this discussion?

At least it's reassuring to know that me and Mark are as much in the dark as everyone else when it comes to S displacers!

Writing from "in period" memory, with no more recent years experience at all, it is news to me that S displacers might be in any way different from non S. Are the differences discussed above only relevant to later cars? There is a reference to ST units above but I know of none. The uprated units were never sold through ST in my time and had to be obtained from a normal dealer source as export spec items with a non-competition part number. I am aware they appeared on some ST lists (later?) with non comp part numbers - but if you actually tried to order those from ST itself, would you not have been referred to a dealer? (ST dealer or non ST dealer).
I recall reading other threads here and could not fully follow the colour coding data. From "hands on" experience "in period", I changed the yellow standard units on my 1965 998 Cooper in early January 69 for what I thought were going to be uprated blue units, but had just been changed from blue to silver when I collected them.
The corresponding uprated unit when yellow was standard was red. My understanding was that red units were the "export" spec used on the 66 Monte, under slightly dubious homologation. The standard unit soon became orange in 66 and the uprated unit became blue at the same time. When a newish 66 998 Cooper I knew well had the standard units replaced (by Abingdon) (this was Comps, prior to the creation of ST for private work) prior to the 66 RAC, blue units were fitted. I personally replaced one of these very same units on that car when it retired from the July 68 Gulf with a burst unit. One of the original standard units was re-fitted and the car was sold before it could be replaced by another proper uprated unit (so I am not sure whether a blue or silver unit would have appeared across the counter if bought then). At the end of 68, I ordered uprated units for my own car and (as covered above) these were ordered as blue and turned up as silver.
Of course it was normal to replace any earlier helper springs/rear struts with (by then standard production) orange items when fitting uprated displacers around then. Later in 69, I personally fitted new uprated (silver) units to a brand new 998 Cooper prior to the 69 RAC. It was green units that came off it.
At no time when talking with anyone (including dealers and Abingdon) do I recall any suggestion that units for an S were not the same as others.

Am I right in saying the all units had the same part no moulded into the top of the rubber pictured.

Austin Costin wrote:Am I right in saying the all units had the same part no moulded into the top of the rubber pictured.

I am going to check my stash of hydro bags latter, but yes, I am fairly sure this is the case. The only variation to this maybe that the Aust made ones may have had an AY* prefix.

Austin Costin wrote:Am I right in saying the all units had the same part no moulded into the top of the rubber pictured.

That's right Paul though just to confuse matters some of the units also had that part number, which was stamped into the casing.

What we need to nail now is the question as to whether all the specific hydro units listed in the parts books as being fitted to non Coopers, Coopers and Ss were essentially all exactly the same (as suggested), with only the later cars fitted with a dedicated uprated unit?

I'm fairly certain that the main differences between S displacers & their lowlier brethren were the fact that there were different restrictor valves fitted to the S ones to make them stiffer. What I don't know is how to identify these once the colour coded band has rusted away.

M

The bleedhole must have bin the thing, had a works displacer (came from the stash of a former Works driver) that had 1/16 as a bleedhole size painted on the outside and a yellow band. Sadly there was only one...

In that case, surely if you put a 1/16" restrictor anywhere in line in the system you will have hydro units that behave line S ones.

M

If all the part no's are the same for the rubber one would guess they are all the same, I was also under in impression that the valve in the unit was the difference with restricting the flow.

I wonder also if Australian cars were sent the package of up rated units as standard as the landscape was harsher, maybe a standard unit was in fact the same as a UK cooper S?

Of course the old trick was to cut down rather like a dry car and then pump in more pressure to make the car stiffer.