The future of Hydrolastic suspension
Page 1 of 16

Author:  mab01uk [ Sun Jan 10, 2016 8:30 pm ]
Post subject:  The future of Hydrolastic suspension

Found this interesting write up below on the 'Landcrab' forum, originally published in the ADO16 club magazine and thought it worth posting here:-

The future of Hydrolastic suspension

All owners of Hydrolastic-sprung cars certainly know the big advantages these suspensions give to the ride and handling of the cars. But many will by now also know the downside. Due to the age of the systems, failures of spring units start to get more often. Bear in mind, that nearly all Hydrolastic units are now older then 40 years! Quite impressive for a highly loaded piece of rubber, which forms the spring in these cars.

Keep it or replace it?

It cannot be denied that modern standard steel spring and damper suspension have come a long way since the 60s and do work very well. And computations can help to adjust the rates close to getting perfect even before the first test drive. With this in mind, the question should be allowed, if a replacement made of standard springs and dampers cannot be made. Of course this is possible and has already been done to my knowledge to at least one 1300 and one Austin Allegro. And there are – of course – kits available to replace the rubber springs in Minis and Hydragas on the MGF. But this requires quite a bit of effort and specifically made parts, so it will be quite expensive.

So why not try to keep Hydrolastic? There will be a day, one day, when no original unit will be in working condition anymore. It is already getting more and more difficult to get hold of good working ones. New ones out of the box are a rarity since a couple of years. Due to the great resilience of the units in the first place, the amount of spares produced was quite small. On the other hand, there are good reasons to think about ways to keep Hydrolastic working. For one it was one of the defining features of the ADO16, so an important part of keeping one of these in original condition to preserve as a classic. On the other hand the ride experienced with Hydrolastic cannot be replicated with a conventional setup. The reason is, that both spring rates and damping rates are highly progressive, both increasing with the load of the car in a way that the car 'feels' roughly the same, independant of the load. And this is before getting the interconnection of the units on each side into play. Today similar effects are achieved using very sophisticated computerised adaptive damping and anti-roll systems.

The late Dr. Alex Moulton was well aware of the problems owners of cars with 'his' suspension system may have in the future, as well as some shortcomings particular in the ADO16. During a couple of meetings over the past 10 years he has shown me a possible solution.

There are generally 3 problems arising with Hydrolastic units:

1) The lower diaphragm, which houses the push-rod with the cone may split. In many cases a damage of this membranes can occur if there is dirt or corrosion trapped between the cone and the rubber. If a unit is out of the car, it is adviseable to clean this area.

2) The rubber hose attached to the units may split. This problem has already been dealt with. A new hose can be attached by using a strong clip, as is done by the Landcarb (1800) club for some time now. This is close to the way the original fitting was attached and the preferred solution for durability.

3) The rubber spring ages and may eventually burst. This is a slow process and usually shows itself in the spring 'bulging' out of the unit together with a slight degradation in ride quality over ridges or small bumps.

There is not yet a possibility to deal with problem 1), as this would not only mean to open the unit, but also to have the diaphragm remade. So trying to keep this in good shape seems necessary. As stated, failure 2 can be rectified by adding a new hose. This leads to dealing with fatigue of the rubber spring itself.

Dr. Alex Moulton has put some thought into this issue and came up with two possible solutions. The first idea was to add a flat steel-spring on the top of the Hydrolastic units, taking on the load as long as the rubber spring itself has no leaks. In some cars this idea would have lead to installation problems due to space requirements. Discussing this with contacts in the car supplying industry the conclusion is that it will actually be possible and not very expensive to remould the rubber springs, even in small series, if the metal parts were supplied. This is the key problem: Due to the needed strength re-manufacture of the steel parts seems to be prohibitive due to the cost involved. So the steel pressings would need to be re-used. The units will need to be opened and re-sealed for this kind of repair.

There are three major steel parts forming a Hydrolastic unit: One almost tube shaped piece containing the rubber spring (or rubber cheese, as Moulton called them), a 'hat' shaped part containing the damper and separating spring and displacer in the middle and last the cut-off cone containing the displacer diaphragm with the actuating rod and cone. During fabrication all three parts with all internals were put into a press and then the overlapping edge was rolled to form the rim in the centre holding all three parts firmly together. The first step, opening them, is relatively straight forward: The rolled part of the edge needs to be carefully removed. The three parts can be separated afterwards from each other for inspection and replacement of rubber parts.

Dr. Moulton came up with a solution how to close the units again. Three rings where manufactured, practically creating a kind of compression fitting held together with a large captive nut in the place where the original joint was. The ring around the spring unit needs to be split in halves to be able to be fitted, whilst the other ring and the captive nut can be slid over the unit from the displacer end. Tightening these should be done in a hydraulic press similar to the original process. Dr. Moulton actually has had a prototype made and put it into a test bed to check the unit after refitting successfully.

So right now the plan is laid how Hydrolastic units can be partially refurbished. The rubber internals and the connection hose can be renewed using the method described above. Also the possibility of combining intact parts of units to a working one is given. As the damper valves are also accessible when the unit is dismantled, these can also be renewed or even modified to address the weakness of the installation in the ADO16.

Right now it would be worth considering that the club, or individual members, collect all Hydrolastic units, even those with defects. Dr. Moulton advised us not to throw any of them away to secure the future use. They might - apart from directly keeping cars on the road with intact units - be a valuable source of spares for the reconditioning process of Hydrolastic units.
Read more: ... z3wr5kxKyF

Section through a Mini Hydrolatic Unit - (Sectioning & Photo: Tim of Minimail)

The one millionth Hydrolastic unit was gold plated and presented to Dr Moulton who invented the system.

Author:  mab01uk [ Sun Jan 10, 2016 8:43 pm ]
Post subject:  Re: The future of Hydrolastic suspension

Also a trial repair to the top rubber area of an Austin 3 Litre displacer unit below....... :o
(At least Hydrolastic Mini owners have rubber cones available if all else fails but of course most other BMC/BL Hydrolastic cars have no long term alternatives).

"Just to recap on what I think is achievable with regard to repairing these units, the three failures are; hoses split, top rubbers burst open, lower rubbers burst open. From a repair point of view, hoses are easy to replace, a burst lower end is beyond hope of repair currently, a burst top end I felt could be repaired and I have managed to do just that. Some of the problem with the top end is the rubber thickness is quite thin, once this thin film perishes and splits open water gets in and attacks the top of the valve area, this of course causes more deterioration. I thought if I could get a liquid rubber that would bond to metal and existing rubber, and cope with some flexing and contain the 250 psi of fluid pressure within the unit it may be possible to repair one. I have two spare units which are both split and leaking from the top so I decided to use these as the basis for my trials......
(see PDF link below for further details and photos) ... 202014.pdf

Author:  Spider [ Sun Jan 10, 2016 9:26 pm ]
Post subject:  Re: The future of Hydrolastic suspension

It's an age old problem that's only getting worse as the years go by and it's also a real testimate as to how well these were designed and made that there are still so many about today, but, in time, these too will diminish in numbers.

While I tip my hat to the late Dr. Moulton for looking in to how owners may get some more life from the units they have, I really think the longer term solution is new units. Very easy to say, though, there were well in excess of 1 million Units made for production, but how many cars are about today?

Does anyone know what happened to the original tooling? We made them here for a while, but the tooling was supposedly scrapped or lost in a fire that they had at the Dunlop factory where they were made. Did they manufacture them in South Africa?

Apart from obvious production costs to re-manufacture them, there was also a wide variety of them not only across the Mini, but also different sizes as used in the ADO16 and the 1800, so a further put off I guess. Another headache is the supply of the right rubber. Or is it?

In general, I like the way the system rides and handles, but the damping could receive some attention to give it some better longevity, that seemed to fade out very early in the life of them.

It dose make me chuckle that only in recent years have other manufacturers been able to 'replicate' the system, however it needs shock absorbers that cost as much as a house and more computer power than it took to land Man on the Moon,,,, bahahaha,,,,,

Interesting article mab01uk, many thanks for post here.

Author:  mikep [ Mon Jan 11, 2016 7:00 pm ]
Post subject:  Re: The future of Hydrolastic suspension

"It dose make me chuckle that only in recent years have other manufacturers been able to 'replicate' the system, however it needs shock absorbers that cost as much as a house and more computer power than it took to land Man on the Moon,,,, bahahaha,,,,,"

Sorry but Citoen got there first, gas not rubber and slightly more complicated but it added variable height and ride levelling all without shockers and the computing power of a jubilee clip. It also removed the need to carry a jack to change a wheel!
Hydrolastic was great but those 1100s didn't half point skywards if there was too much weight in the back.

Author:  geroch [ Wed Jan 13, 2016 1:05 am ]
Post subject:  Re: The future of Hydrolastic suspension

This is the future:





:( :(

Author:  gr4h4m [ Wed Jan 13, 2016 3:51 pm ]
Post subject:  Re: The future of Hydrolastic suspension

Maybe some limited run of new replacement

Author:  mab01uk [ Mon Sep 12, 2016 11:50 pm ]
Post subject:  Re: The future of Hydrolastic suspension

First 10 pages of this PDF (link below) is an in depth detailed technical article on the ADO16 Hydrolastic suspension (Sep 1962) and the last 9 pages are devoted to the Austin 3-Litre Hydrolastic suspension (March 1968) both are from the 'Automobile Engineer' magazine.

Hydrolastic Springing - Automobile Engineer - Sep 1962
The Design & Development Story for the Morris 1100 suspension as told by Alex Moulton ... lastic.pdf





Author:  nileseh [ Sat Aug 05, 2017 7:10 pm ]
Post subject:  Re: The future of Hydrolastic suspension

I’ve got a 67 Cooper S that was dismantled maybe 30 years ago. All the bits were pretty much preserved, or at least retained and I have been working slowly on rebuilding. It’s a wet car and my intent is to retain the hydrolastic suspension. However, the individual who dismantled the car simply covered the hydrolastic unit hose end with foil rather than drain and seal. So after 30 years of sitting with a water based solution the interior of the bags was pretty much rusted out. I tried to clean thru the hose but the exiting solution never cleared. So I found a scrap unit and cut it open. I designed and built a clamping ring assembly by which the unit can be reassembled and I have tested at pressure (300psi) for extended periods without pressure loss. That is the background and this is where I am on the project.
1. I opened the unit by chucking the unit in a lathe and cutting the crimp on its circumference at the largest diameter. This technique preserves a ring on the lower housing that can be used to grip with the clamp ring assembly.
2. The corrosion on the interior can be slight or can completely destroy the interior structure; the appearance of the outside is not an indicator of the condition of the interior
3. The only way to get to the inner fluid chamber is thru the metering valve assembly, so the inner chamber cannot be cleaned without further lathe cutting the top of the interior housing. But once this is done, you have full access to the inside of the flexible membrane and the metering (damper) valve. I designed a new metering valve that will be metallic or perhaps printed ABS plastic.
4. Metering of the fluid flow is accomplished by two one-way valves comprised of solid rubber blocks with sloped ends that are retained by a winged “hat” that restrains the movement of the block ends. The inside valve is a mirror image of the outside valve. The metering adjustment for the different part numbers appears to be the position of the wings relative to the base plate. It’s the same part in all the units I have disassembled, but the wings are bent to a different position restricting the flexure of the rubber block and fluid flow permitted.
5. The inner and outer valves (inflow and outflow) are set to different heights, therefore different flow rates.
6. The only other difference I can determine in the components is a bypass opening in the side of the inner chamber wall. It is typically .145” diameter, but on the Cooper S units (21A2012 and 21A2014) it is .070” diameter.
7. The key to part number differentiation seems to be the valving (the position to which the valve retainer is bent) and the diameter of the bypass hole. All other components are the same, including the rubber “doughnut” spring thru which the hose passes (this bit has a part number molded in to its face: MOWOG 21A1477; it is the same on all unit I have seen).
8. The conclusion is that the units can be usually rebuilt (only a couple were totally destroyed by corrosion on the inside) and they can be rebuilt to whatever part number is required. That is the rub.
9. I have dissembled 9 of these units, but the only units I can identify by part number are the units that came with my car. The rear units are in good condition, minor corrosion, interior components intact and measurable. However, the interior of the front units is completely destroyed and I am unable to measure any the interior components. I can make as many of the 21A2014 parts as I have cores for; I’m stuck on the 21A2012 or any of the other part numbers.
10. It occurs to me that to go much farther I need units identified by part number so I can collect the dimensional data to enable remanufacture to a specific part number.
11. I have no realistic estimate of the cost to rebuild these things, but I will develop one. I own a manufacturing facility so it has been easy to do the prototype work on this project. I’m going to build 4 sets of the clamp ring assembly and metering valve plate so I can finish my car. I will soon have a better idea of the production cost of these parts. It doesn’t take much machine time to open the units however cleaning the interior is a bit of an unknown depending on the condition. The machined parts bits will not be cost prohibitive even at low volumes. The hose is not much of a problem if the original fittings are available; I found a stock Gates hydraulic hose that works well. I can also make new fittings if they are not available. If there is interest in rebuilding, I should be able to offer a kit of components and instructions, or even provide a rebuild service.
12. But I will need data to build to a part number.
So that’s where I am. To finish my car, I need a 21A2012 unit that I can disassemble and measure. That applies to any other part number: a unit that can be identified with an interior that can be measured. If enough such units can be obtained, I should be able to tabulate the data to enable remanufacture of any part number.

Does anyone have a store of these things that can be identified so I can go forward to build the part number data?

Author:  timell [ Sat Aug 05, 2017 8:16 pm ]
Post subject:  Re: The future of Hydrolastic suspension

Great work! I may have a spare S displacer I would be prepared to donate....need to dig it out to confirm it's a 2012 which may take a day or two.
Another difference between S displacers and standard is the distance from the steel 'crown' to the top of the rubber doughnut spring (21A1477) S's it is about 30mm and on standards appears to be about 40mm. Have your dissections shown a specific reason for this?
Additionally, earlier Mk1 S's used 21A1872's front and 21A1874's rear.....I have had to mix and match in the past using 21A2012's and 2014's, with no discernible difference in handling and suspect they may be identical internally but would be good to know.
The other most common displacer is the standard 21A2008 used both front and rear on all Cooper's and other mini's, Elf's and Hornets.

Author:  Spider [ Sat Aug 05, 2017 9:34 pm ]
Post subject:  Re: The future of Hydrolastic suspension

Sensational research, effort & work nileseh

timell wrote:
Another difference between S displacers and standard is the distance from the steel 'crown' to the top of the rubber doughnut spring (21A1477) S's it is about 30mm and on standards appears to be about 40mm. Have your dissections shown a specific reason for this?

Wonderful of you Tim to donate a Hydro Bag to the cause.

In regards to the difference in height, when I went through a number of Hydro Bags here a few years back, I found that height difference related to whether it was an early or late type of Bag, not if it was Cooper S.

Page 1 of 16 All times are UTC [ DST ]
Powered by phpBB® Forum Software © phpBB Group