Hydrolastic Colour Coding

[mab01uk]

Some NOS Hydrolastic Displacers with original colour coding on ebay a few years back...

[mab01uk]

Note: Minispares sell reconditioned 21A 2008 displacers on an exchange basis or can recondition your own S units.
https://www.minispares.com/catalogues/c ... 8/page/77/

[Peter Laidler]

Interesting. But as I and many others have said in the past, the only thing that hydro unit reconditioners can do is just that! They can bead blast, prime and paint the steel casing and replace the hose. You cannot get inside the unit to recondition the actual hydraulic or elastic (the hydro-elastic) components of the unit.

If you are of a delicate nature regarding the wonderous properties of Hydrolastic, look away now.

It seems as though Dunlop, BMC and BMC publications here at Cowley didn't understand the inner workings of the units either. Take the sectioned drawings illustrated in the previous page, taken from the workshop manual and kindly put up by Martin. Have a look at the part called the 'damper valve'. It should be called 'the MAGICAL damper valve'.
Why is it shaped differently in drawing 1 from drawings 2 and 3. And then...
In drawings 2 and 3, the same damper valve has suddenly, magically by dint of some of its mysterious properties, has been pulled through the metal seating (that it is operating against....., see it?), turned through 180 degrees vertically and re-appeared BELOW the support plate........, upside down!

Not even Paul Daniels (an English TV magician...) could do that!

If you ever chance to remove your units and flush them out, not difficult, have a look at the bits of rusty metal and chunks of rubber that come out with the foul smelling rusty sewage. Those bits that you have shaken out while flushing through are the remains of the rusted out damper valve

[Aussie Bill B]

....

If you are of a delicate nature regarding the wonderous properties of Hydrolastic, look away now.

It seems as though Dunlop, BMC and BMC publications here at Cowley didn't understand the inner workings of the units either. Take the sectioned drawings illustrated in the previous page, taken from the workshop manual and kindly put up by Martin. Have a look at the part called the 'damper valve'. It should be called 'the MAGICAL damper valve'.
Why is it shaped differently in drawing 1 from drawings 2 and 3. And then...
In drawings 2 and 3, the same damper valve has suddenly, magically by dint of some of its mysterious properties, has been pulled through the metal seating (that it is operating against....., see it?), turned through 180 degrees vertically and re-appeared BELOW the support plate........, upside down!


If you ever chance to remove your units and flush them out, not difficult, have a look at the bits of rusty metal and chunks of rubber that come out with the foul smelling rusty sewage. Those bits that you have shaken out while flushing through are the remains of the rusted out damper valve

The reason the damper valve appears to change position is because there are 4 of them: 2 above, and 2 below the "port plate" to control rebound and bump fluid flow. Their shape varies in the diagrams because they are not symmetrically round and have a different profile depending on viewing angle. See Mini Spares technical article on Hydrolastic units, which contains this photo of the valve (port) plate:

[winabbey]

If you ever chance to remove your units and flush them out, not difficult, have a look at the bits of rusty metal and chunks of rubber that come out with the foul smelling rusty sewage. Those bits that you have shaken out while flushing through are the remains of the rusted out damper valve.

Regardless of the state of the damper valves there must be thousands upon thousands of hydro sprung cars (Mini, 1100, 1800) worldwide that are happily cruising the highways today with owners very happy with the ride quality. Anecdotal statements of support for hydro versus rubber cone continue.

One conclusion from this is that the state of the damper valves is not a major factor in the workings of the hydro suspension.

[Spider]

If you ever chance to remove your units and flush them out, not difficult, have a look at the bits of rusty metal and chunks of rubber that come out with the foul smelling rusty sewage. Those bits that you have shaken out while flushing through are the remains of the rusted out damper valve.

Regardless of the state of the damper valves there must be thousands upon thousands of hydro sprung cars (Mini, 1100, 1800) worldwide that are happily cruising the highways today with owners very happy with the ride quality. Anecdotal statements of support for hydro versus rubber cone continue.

One conclusion from this is that the state of the damper valves is not a major factor in the workings of the hydro suspension.

The late John Smidt of the Mini Kingdom fame often would say to me (and no doubt others) that he found within short time, the internal damping would fade and there after, all cars felt like they rode and handled the same. I'm very much inclined to agree with John's remarks.

[Peter Laidler]

Yes, Spider and John Smidt are right...... Regardless of the state of play INSIDE the rusted out, sewage filled, neglected hydro units, there will always be a damping effect. It's because of the not uncontrolled (?) fluid movement. But like gas (not absolutely correct but descriptive enough...), you can only pass a certain amount through a given diameter. So far as I can see, there is another valve in the system too. The 5mm (or is it 7mm?) restrictor in the bulkhead hydro pipe adaptor.

Mind you, in my experience, this will have become so rusty internally that the bore will have almost closed up. Make sure that you clear out the clag and shxx before you assemble the system up. Or better still, get the stainless versions from Gordon at Catmint.

Like thousands of others, as Win says, my car is still on hydrolastic and I know that the guts of the units have rusted out. But there is stil a semblance of damping for that reason

[mab01uk]

Hydrolastic unit Part Numbers & Colour Code Identification:-
https://www.minispares.com/blog/2022/07 ... t-numbers/

21A1477 Front only, 1 orange or green band, standard use pre December 1965 for Cooper and S, Hornet and Elf.
21A1703 Rear only, 1 orange or green band, standard use pre December 1965 for Cooper and S, Hornet and Elf.
21A1804 Front and Rear, one orange band, standard use December 1965 on for Cooper and S, Hornet and Elf.
21A2008 Front and Rear, one green band, standard use December 1965 on Cooper and all Mini models except S. Most common & most made.
C-21A1705 Front and Rear, one yellow band, Stiff, Rally use, pre December 1965 for Cooper S.
C-21A1819 Front only, one red band, Hard setting, Race use, pre December 1965 for Cooper S. Rally for 998/1275 0ctober 1969 on
C-21A1821 Rear only, two red bands, Hard setting, Race use, pre December 1965 for cooper S.
21A1811 Front and Rear, two orange bands, Stiff, Rally use December 1965 on for Cooper S.
21A1872 Front only, one blue band, Hard setting, Std and Race use December 1965 on for Cooper S.
21A1874 Rear only, two blue bands, Hard setting, Std and Race use December 1965 on for Cooper S.
21A2012 Front only, one silver band, standard harder unit, December 1965 on for Cooper S.
21A2014 Rear only, two silver bands, standard harder unit, December 1965 on for Cooper S .
21A2010 Front and Rear for 1275GT and UK Police, standard use, 1969 on.

[winabbey]

As for the different stifnesses, all I would ask is this. Has anyone ever seen any reference to ascertain exactly how the stiffness was quantiified by, say, fluid flow or a measure of resistance? Nope, me neither.

Hi Peter - these tables are on the BMC Australia displacer engineering drawing AYA4090. Is that the sort of data you are referring to?

YDO5 is the model code for the Mini Saloon, YDO6 for Cooper S.

The Spring Element Spec initials probably stand for Normal Rubber, Hard Rubber and Extra Hard Rubber - just a guess. There is more rubber in Cooper S displacers, the level being closer to the top of the displacer body where the hose exits when compared to a "standard" displacer. Maybe the rubber formula was the same in all displacers and the increased springing is due to the greater volume of rubber to be compressed in the S part.

I understand they were made here by Dunlop.

AYA4090 Spring Unit Specs wm.jpg

AYA4090 Damping Characteristics.jpg

AYA4090 Hydrolastic Spring Unit Assembly subset.jpg