The future of Hydrolastic suspension

[geroch]

Yesterday I recovered 4 units, it's mk3 cooper s, 21a2012, dated 1970.
The 2 rear units are badly reduced, I should try to clean them inside.

[Peter Laidler]

Lucky you! I would flush them out thoroughly until clean water runs out freely then dry them out until you need them or fill them with a silicon based fluid. I'd use silicon brake fluid as it's got all the non this that and the other properties you need to protect the rubber and the steel internal components. Plug the open hose ends with wood bungs or BSP blank-end fittings and store upright. Others might disagree of course but that's what the chemists suggest. As for the hose attachments then if they ain't broke - or leaking - why fix them? The hydraulic loadings they're subject too are nothing in the real world of industrial hydraulics. But if you do want to rep[ace it's an easy fix so long as it's not absolute authenticity you want

[nileseh]

geroch:

Are all 4 displacers out of the same car, and are they all marked 21A2012? The literature I've seen shows 21A2012 front and 21A2014 rear. but I've only seen documentation up to the Mk2. Is it possible that Mk3 went to the same front and rear? If they are not marked with the number, 21A2012 has one silver band on the hose and 21A2014 has 2 silver bands.

[timell]

geroch:

Are all 4 displacers out of the same car, and are they all marked 21A2012? The literature I've seen shows 21A2012 front and 21A2014 rear. but I've only seen documentation up to the Mk2. Is it possible that Mk3 went to the same front and rear? If they are not marked with the number, 21A2012 has one silver band on the hose and 21A2014 has 2 silver bands.

Niles, my displacer is on it's way...hope it works. I believe all Mk3 S's and early wet 1275GT's were all 2012 front 2014 rear. Early Mk2's were 1872/1874 and later Mk2's 2012/2014 but internally they are no different. I'm not yet convinced that front and rears differ in anything other than part no. but your work should decide this.
Tim

[Peter Laidler]

I'm pretty sure that in the next couple of years the remanufacture of, or attempts to fix the knackered internals of hydro displacers will flounder. It's not that I am a total defeatist but rather, a pragmatist and realist. Because it's not beyond the wit of man to design and develop a rubber cone suspension rubber bonded onto a x4-way bayonet fitting as per the current hydro units. Got me so far......? Then inbed or bond into the opposite end of the rubber cone a fitting the extends forwards (or downwards for the front susp.....) so you could use your current rods still sat into their cups while the rear (or top) of the new rubber cone is locked into the sub frame..

I wish I'd taken more notice during the production engineering phase at Uni!

[Dearg1275]

I believe all Mk3 S's and early wet 1275GT's were all 2012 front 2014 rear. Early Mk2's were 1872/1874 and later Mk2's 2012/2014 but internally they are no different. I'm not yet convinced that front and rears differ in anything other than part no. but your work should decide this.
Tim

21A2010 was the part number for the front displacers on hydro 1275GTs. Also listed for uk police vehicles. The rear was the same as the mk3S. Whether harder or softer who knows?

[nileseh]

Hmmm.

The internals are the same for all the displacers I've opened. The differentiation seems to be the damping valve restriction. The dampening valve serves as the shock absorber in the unit. The spring rate is the same for all displacers (the rubber donut has the same part number on all) so the difference would appear to be a stiff shock or a softer shock. It makes sense to me, much like tuning shock absorber stiffness to the weight distribution of the car. I've not studied suspension systems, but I would expect a stiffer shock up front where all the weight is. Is that correct? 21A2010 is an interesting notion. We never saw the 1275GT here; was it a performance iteration? As used in a police vehicle I would expect a stiffer dampening.

I got the tracking number from timell; we'll see what that has to offer. If I can't get the original dampening data, perhaps I can just make up some dimensions to restrict the valve for a stiffer rate.

I thought we established a while ago that part number difference from early to later was a tooling issue, rather than a performance change. On the displacers I've opened there is a slight difference in the configuration of the stamped components. I think probably a tooling upgrade for manufacturing efficiency.

I'm not sure where Peter is going. I agree that any notion of a solution for the ages is probably not realistic. But I think we can get a few more years out of the inventory of 50 year old components. The rubber does not seem to have deteriorated as much as I would have expected, even in the displacers that have completely rotted interiors. The metal falls apart but the rubber bits clean up nicely and are quite supple for their age; considerably more supple than I at my age. I think Peter is suggesting that a solution is a unit with the form factor of the displacer with a rubber spring unit to be a drop in replacement. That would work, but that would be the "..lastic' portion losing the "hydro.." bit. We could also simply change to any of the many coil spring conversions available but what is the fun in that? I think this clamping ring will work, it has worked on the bench, I'll build it and find out if it stands up to the rigors of motoring. I'll work it as hard as I can short of "Italian Job" jumps. But it will be a while because I have to put the rest of the car together first.

[Peter Laidler]

Nileseh, I thought that the hydro splitting and clamping idea was absolutely fantastic and a mechanical work of art. But, alas, financially beyond the scope of the average bloke with a knackered unit - or even someone like me with a reasonably sized engineering shop and facilities at his disposal. You're absolutely right about the direction I was thinking and you put it well....... A 'lastic unit....' without the 'hydra' part! A rubberised unit that would fit and lock into the space of the old HYDRAlastic unit AND use the existing sub frame, rods, cups etc etc.

You're right about the variations of hydro units. The rubber content mix was the same*. It was the valving/damping that differed between the units that made them different. And I often wonder whether the average road user or restorer would/could really tell the difference between them. Nope....., me neither!

*That's an easy test using simple lab facilities to undertake

[geroch]

This cooper s mk3 has all 4 factory-fitted 21A2012 units. I have the certainty of the 2 former owners. Even those I found on my cooper s mk2, 2 certainly are 21A2012, but I do not know if they are of the same car.

[Spider]

Don't take this as gospel, however, I seem to recall that the difference between the front & rear Hydro units (in sets) was only the internal damping between.

I think I have some info on this.

[nileseh]

Interesting. My mk2 has 21A2012 front and 21A2014 rear and that is correct according to the literature I have seen. If my reasoning is correct, the 21A2012 displacers will be have increased damping over the 21A2014. So it may have been determined at some point that a stiffer dampener would provide better handling without compromising the ride characteristics.

When you get to the numbers, the difference in the opening of the valve isn't much. The Cooper S rear is only about .015" more restricted than what I believe to be a MG1100 displacer. (the .015" is, however, over a opening perimeter a bit less than 2.00", so it the small number is deceptive). The by-pass opening is .070" dia. (.0038 sqin) on the Cooper; the by-pass on the MG1100 is .140" dia (.0152 sqin). I suppose I could calculate the combined difference in flow cross-section, but for the moment it seems that there is quite a bit more area available on the MG1100, so a rather soft ride compared to the restrictive Cooper S dampening. My expectation is that the Cooper S front (21A2012) will be further restricted. I think the by-pass is the same diameter, if timell's displacer that is in transit is different (should be more restrictive) then we will know the data for the mk2 front and apparently the mk3 (and police iterations) all-around.

It's a bunch of empirical data that may help in rebuilding these things to something close to the original specifications from what ever donor car to what ever transplant recipient car in need of a wet suspension.

Then I keep going back to the notion of removing the internal dampening all together and adding an external adjustable telescoping shock absorber to enable adjustment to personal preference. It should work the same way: your'e just slowing the motion down by restricting the flow of fluid. Internal fluid thru a restrictor or external thru a restrictor acting on the suspension arm should provide the same result: impeding the motion of the suspension.

[winabbey]

Don't take this as gospel, however, I seem to recall that the difference between the front & rear Hydro units (in sets) was only the internal damping between.

I think I have some info on this.

You may have seen it on the BMC Australia engineering drawing I posted in another thread.

Here's the section in that drawing that compares spring unit specs and damping characteristics. YDO5 is the base model Mini and YDO6 the Cooper S.

AYA4090 Spring Unit Specs.jpg

AYA4090 Damping Characteristics.jpg

[Spider]

Doug, cheers.

I have seen that drawing somewhere a while back, but I couldn't recall what thread nor what was on it.

It does indeed to to indicate that the valves are different between basic units, but in the case of the Cooper S, the same front & rear, only with 'hard' and 'extra hard' rubber springs being the difference.

Next time you speak to John, ask him about this, his answer may surprise you.

[timell]

Doug, cheers.

I have seen that drawing somewhere a while back, but I couldn't recall what thread nor what was on it.

It does indeed to to indicate that the valves are different between basic units, but in the case of the Cooper S, the same front & rear, only with 'hard' and 'extra hard' rubber springs being the difference.

Next time you speak to John, ask him about this, his answer may surprise you.

Great stuff guys, thanks. Guess it makes sense that the damping rates would be the same front to rear as the units' talk' to each other and only the spring rates could be changed...I still think it's a genius system!

[geroch]

Very interesting! thanks for the informations.

This cooper s mk3 has all 4 factory-fitted 21A2012 units. I have the certainty of the 2 former owners. Even those I found on my cooper s mk2, 2 certainly are 21A2012, but I do not know if they are of the same car.

errata-corrige

I looked at the rear units well, and after a nice wash, the 2 silver rows appeared. The printed mark is not very readable, I must have read it badly.

20170818_183756
20170818_183822

Is a 4? Certainly does not look like 2.

20170818_183834


There are also 2 silver dots over the unit.

20170818_183747

[Peter Laidler]

Personally I think that the colours painted around the hose, coloured dots on the diaphragm, amount of dots. shape of the dots, colour of the hose lettering are all a red herring. The units are the 21A xxxx number that's marked on the input end of the displacer. I know it's been said here before but I'll just add my two pence worth. Having two different damping valve characteristics at the opposite ends of a liquid transfer system - like different value hydro units in the hydro cars - is really a waste of time especially in these instances. There ARE instances where it is beneficial but I can only think of one instance where it is. And that ain't in cars!

[smithyrc30]

I thought the valve was one way?

So in one direction (fluid going in) it restricts, then in the other direction it opens fully. So having different damping rates at opposite ends will not be an issue.

I think this would stack up with the different wheel to damper movement ratios and the differing weights at either end of the car, it makes sense to have differing damping rates.

If the rates were not different the car would pump up at one end and down at the other on a continuously bumpy road.

[nileseh]

I've seen documented in a number of locations that the bands painted on the hose are indicative of the part number of the displacer. For Cooper S, one silver band is 21A2012, 2 silver bands is 21A2014. I found this somewhere:

EARLY CARS LATE CARS
TYPE MARKING PART NUMBER TYPE MARKING PART NUMBER
Normal - Front None 21A1477 Normal - Front 1 Orange or Green Band 21A 1804 or 2008
Normal - Rear None 21A1477 Normal - Rear 1 Orange or Green Band 21A 1804 or 2008
Stiff - Front and Rear 1 Yellow Band C - 21A 1705 Stiff - Front and Rear 2 Orange Bands 21A 1811
Hard - Front 1 Red Band C - 21A 1819 Hard - Front 1 Blue or Silver 21A 1872 or 2012
Hard - Rear 2 Red Bands C - 21A 1821 Hard - Rear 2 Blue or Silver 21A 1874 or 2014

(I can't get this table to tabulate correctly on the posted version. my typed version is in nice columns, but when posted it removes all the tabs. there are two tables, early and late, with the column titles: type, marking, part number. )

I think the part number printed into the rubber on the hose end of the displacer is the part number of the rubber donut "spring" similar to the dry minis. I have only ever seen on number here: 21A1477. It's a Dunlop part, also also marked with "Moulton" the outfit i believe holds intellectual property rights to the hydrolastic system of front-rear interconnection. (apparently has also been applied to bicycles in the UK, quite a following). Interesting note in the table is that the "early-normal" part number with no other marking is listed as part number 21A1477. That part number is on all of them as noted above. Perhaps that was the original part number, then the need to change dampening for different applications was seen and the other part numbers and markings were developed to differentiate these applications.

The valve is 2-way, comprised of 4 oval ports in the top of a shell that separates the diaphragm cavity from the spring cavity. Two of the openings are for bump dampening, two for rebound dampening. The dampening is provided by two rubber bars that close the aperatures, one bar on the diaphragm side, one on the spring side. A bump in the suspension deflects the diaphragm and moves fluid into the spring cavity. The spring donut flexes and then returns on rebound moving fluid back into the diaphragm cavity. The fluid is restricted (damped) by a bridge that restricts the flex of the rubber bar. The position of the bridge determines the degree of dampening: a low bridge provides increased dampening (stiffness) by restricting the flex of the rubber bar and reducing the area available for fluid flow. The flex permitted by the bridges is different for bump and rebound fluid flows. A portion of the fluid is vented thru the hose to the connected displacer providing a similar but opposite action there (it would be rebound first then bump motion). I think probably also a reduced movement because only so much fluid can move thru the interconnecting tube.

I think they spend a lot of time working out the "tuning" of the system to get an acceptable result. I think this describes the mechanics but it is tough to quantify the reactions.

[Peter Laidler]

Yes Niles and others. a wrong choice of words on my part by my saying '.........The units are the 21A xxxx number that's marked on the input end of the displacer' above. I mean stamped or otherwise marked on the end of the diplacer as we can sort of see in Geroch's and others. To be honest, marking the hose or something with a dob of paint marker is a recipe for a cock-up especially when some greasy hands get hold of the displacer - and it's gone! Mind you, it's gone pretty soon when it's painted or stamped onto the displacer.

Quite how you save a perfect set of displacers with badly corroded shells is another matter. If it were me I'd wrap them in a layer of special tape that's known as DENSO tape here in England. It's a sort of hessian tape impregnated with the stickiest grease you ever saw and sticks like xxxt to a blanket. It's so good that we used it to waterproof certain parts of our Centurion tanks for deep wading. Anyway, one layer of this stuff will still mean they'll fit into the sub frame and no amount of water will ever get to the shell/casing again, believe me!

[nileseh]

I see. If only all of the things had the part number stamped into the body. None of the parts I have seen are marked such. I could barely make of the silver bands on the ones I removed from my car, and some have the part number stenciled on the barrel. The displacer timell is sending has a replacement hose and a repainted body as I recall so there is no identification available. He just knows it was a Cooper S unit.

I've not seen a displacer that is rusted thru the body. Interior deterioration is the problem I've seen the exterior appearance has nothing to do with the interior in my experience. In fact my displacers that are cleanest on the outside are entirely destroyed on the inside. If the outside is rusted thru, I'm not sure I would spend much time on it unless it is the only one available. I think I know the material mentioned to wrap a leaker. Do you think it would work under pressure? I think the service instruction say to take it to 400psi to seat everything then relax to 280psi or so.