Rear shock absorbers

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Further thoughts on Midas Mk1 (From Alan D)

Postby manifold » Sun Oct 17, 2010 6:33 pm

Further thoughts on Midas Mk1, 2 and 3 rear coil-over suspension.

History

I purchased my Mk 3 convertible in 2005, this car was GTM built car, with Hydro-gas front and rear suspension. The car did not handle and my previous article on the changeover to coilover suspension is detailed on Hans’s excellent forum magazine. Follow this link to the article.

http://midas.orba-design.com/?dir=&down ... gazine.pdf

Since it is now two years since I did the conversion, I thought I would update you on my progress.

I did not put the car on the road in 2009; in fact it has been in the garage untouched until the spring of 2010. I decided to put it on the road, to go to Stoneleigh Kit Car Show. The car was pushed out of the garage, the key placed in the ignition, cranked over a few times and it started. I never even had to charge the battery!

The car was MOT’ed, washed and we set off for Stoneleigh, three Midas cars in convoy. Alberto in his Mk 2 Decathlon, George in his Mk 3 coupe and my convertible. We had a good weekend, but I was unhappy with my car, there was a noisy wheel bearing and you couldn’t hear yourself think. Johnny Fixit was my passenger and I think we shouted ourselves hoarse, during the journey!
The rear suspension was still too hard, but much improved on the Hydro-gas setup! So when I got back home I was determined to sort out the car once and for all! I just wanted a comfortable touring car; the engine in this car is just a standard (but very sweet 998cc engine). So no need for a racing suspension set up!

I’d changed the rear wheel bearings in 2008, so it must be the front wheel bearings making the noise. So I duly changed both sets of front wheel bearings, along with new discs, pads and for good measure, new ball joints as well. I’m a bit deaf now, in my old age, and yes I’d got the wrong bearing, it was the rear offside making all the noise. This bearing can have only done about 3000 miles (5000Kms), so this has not been a very good component! I also changed the rear springs for some lighter ones, but I will go into more detail about this later in this article.

The car was transformed, the handling was much improved, the scuttle shake has disappeared, and I’m bragging now, I can actually hear the radio!

Rear coil-overs

I’m now getting to the nitty-gritty of why I’m writing this article. I’ve noticed that some of our new forum members have not quite got to grips as to how the rear coil-over set up works.

On the my Mk 3 the coil-over set up consist of a standard 13 inch Gaz adjustable coil-over, a 40 pound per inch helper spring and a standard spring (spring rate to be discussed). These two springs are joined together with a special spring seat platform. Yes that’s right I have two different rate springs on the one coil-over, which is a suggestion from Stuart which I would take up and explore further.

See picture 1 to view the unassembled component

Image


The blue spring is the helper spring, the black ring is the spring platform and the black spring is the main spring. The C shaped item on the right of the picture is the locking ring, which holds the whole assembly together.

I purchase my springs from Faulkner Springs:

http://www.dfaulknersprings.com/index.htm

See the above website for the differing variations.

Purpose of the helper or run flat spring. (HS)

The idea of this spring is that it gives you a progressive spring rate or alternately it has no rate, but just takes up the slack in the main spring when it is on full droop! This stops the main spring from dislodging from its seats. I use 2 inch (50mm) (length) helper springs which come in 4, 40 and 60 pounds per inch rates. I used 40 pound helper springs. When the car is sat on the ground these 40 pound springs, serve no purpose whatsoever as they are compressed completely flat, but when the car wheel drops into a pothole and the suspension goes onto full droop ( fully extended) the helper spring (HS) extends and keeps the main spring in its seats. Those of you with Mk1 & 2’s, will notice a load bang when your rear wheel drops into a pothole, this is because your main spring is too strong, forcing the suspension down at the full spring rate and the bang is when the spring bottoms out. The HS takes this shock load out of the system!

HS can also be used in stronger rates to give an initial softer setting. I.E. 60 pound HP and 100 pound main spring (MS). In this situation you would be driving about normally with a soft and comfortable spring rate, but if you were to give the car some throttle into corner then the 60 pound spring would compress and the 100 pound spring would come into play, giving you a much stiffer suspension setting. So that it the idea Two springs doing different jobs! From speaking to Faulkner’s the Subaru type of cars use HS at a third of the MS rate, but this won’t work on a Midas as our spring rate is so low!

Main Springs (MS)

I use 9 inch 2.25 inch ID MS. There is a smaller 1.9 inch ID (internal diameter), but Stuart tells me that they have a tendency to rub on the shock absorber (coil-over) body. So on his advice I used 2.25 inch ID MS.

I initially started off with 140 pound springs, but these were too hard, so I changed to 120 MS, better but still too hard. So I’ve changed them again to 90 pound springs. The car was transformed. I immediately noticed an improvement in handling and the scuttle shake has stopped, because the spring is starting to do its job, giving some compliance to the car.
At 90 MS the suspension is still a little too firm, but vastly improved. The trouble is the springs are £58 a set (2010 price), so it is quite an expense to experiment with springs! I’ve purchased three sets up to now! I think for a Midas I would go for an 80 pound MS and a 60 HS. 80 pound is the lightest rate they do in a 2.25 ID, 9 inch spring, so a 60 pound HS might just do to take the initial load and make for a very plush ride (for my old bones). I know that my 90pound spring rate is too high as I have the softest setting on my shock absorbers, so the spring is still in charge. This cannot be correct; I feel I must be able to have some damper settings to get the best handling car!

I may in the future try a different HS to soften my suspension slightly, I’ve noticed that Faulkner’s do a 75 pound 4 inch HS in 2.25 ID; this may be the way to go in order to maintain my 90 pound MS.

Show picture 2: fully assembled coilover

Image


Gaz Coil-Overs

I’m slightly disappointed in the Gaz products, they work correctly, but the main tubes are steel with nickel plating. There are spots of rust appearing on the main body, even on my cosseted car, which spends its life in a garage! Also the stem at the top of coil-over which fastens through the top of the wing is too short, as it is designed for a steel bodied car. A Midas specific coil-over was ordered from Gaz, but I’m sure that this is just the standard coil-over and no adjustments have been made, even after 30 years of supplies to Midas car owners. Because the stem (which attaches through the inner wing in the boot) is too short you can only use one rubber cut in half and not two as it should be! I think other suppliers need to be investigated.

Midas Mk 1 & 2’s

All of the above applies to Mk 1 & 2’s, excepting that you may need a shorter than standard coil-over may be needed. Every Mk 1 & 2 that I’ve seen is too high on the rear suspension, in my opinion. The only acceptable car for rear ride height (to my taste) that I’ve seen is Bronze nuts! The White Mk 2, now owned by Eddie the Mini. The above modification in my opinion would transform the handling of these cars!

Further developments

It’s been some months since I wrote the above explanation and I have changed my approach to the problem again! I have left the above explanation, so you can follow my thought process! I’ve changed the springs again!

I’ve been in conversation with Dave at Dampertech and a gentleman at Faulkner Springs. They both advised me to ditch the two spring idea as the car is too light at the rear, for such a complex arrangement of two springs.
The both urge me to go to a very light one piece spring. This I did. I fitted a 12 inch (300mm) 75 pound per inch spring.
They did suggest that I go lighter again; the gentlemen at Faulkner’s suggested I go for 50 pound springs! Dave at Dampertech agreed with this and was telling me about his experiences whilst helping Lotus set up some of their cars. He explained that their springs were so soft that they ended up with all sorts of banana shapes.

I should have listened to them because a 75 pound spring is still too hard for the rear of a Midas car! The reason I say this is because; I still cannot turn up the damper setting and am running the dampers at the minimum setting.

I decided to go for the 75 pound spring as I’m a bit of a lard arse and I thought because of my great personal weight, I needed a high spring rate.( wrong again). I think that both gentlemen are correct I should have gone for maybe 50 or 60 pound springs!
The idea behind soft spring is that springs are progressive in operation. On a 50 pound spring, the first inch of compression needs 50 pounds of weight, to compress it, to compress the spring 2 inches you need 100 pounds of weight and so on and so forth.
The thinking behind this is that with a coil-over having an adjustable seat, you just wind up the adjuster in order to set your ride height! So you have soft compliant springing and you use the damper settings to adjust your ride comfort! So on a track day you wind your dampers up and stiffen your suspension and get greater cornering ability, and then on the way home you wind your damper setting down again to give you a comfortable ride home!


Conclusion

Colin Chapman of Lotus once said soft suspension with the correct geometry is the way to go! I was once in conversation with another Midas owner about designing a rear beam with an antiroll bar built in for the Mk 3, to replace our rusting rear sub frames. Midas’s don’t roll was the comment; too right they don’t roll, as they are all over sprung! The next task is to get rid of the Hydro gas in the front subframe. I’ve been working on a new front springing idea with Johnny Fixit. We have two alternative front springing methods, both different to the Watsons Rally idea, which is employed effectively by both David and Rich! So I’m not going to do any more work on the rear subframe, until I get the front suspension on coilovers and see how they balance up together! But that’s a future story.




Disclaimer

I don’t know what I’m talking about with regards suspension all of these mods are based on my seat of the pants engineering and trial and error methods. I’m very happy if someone with more knowledge and experience can put me right!

Alan
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Re: Further thoughts on Midas Mk1 (from Alan - pics to follow)

Postby Stuart » Sun Oct 17, 2010 7:34 pm

This Black mini has 150lb rear springs in this photo

Image

and 450lb rear springs in this one, note I've also found a Midas in each photo :)

Image
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Re: Further thoughts on Midas Mk1 (from Alan - pics to follow)

Postby Geoff Butcher » Sun Oct 17, 2010 8:15 pm

I've still got the original dual rate rear springs. Does anyone know what rate(s) they're supposed to be?
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Re: Further thoughts on Midas Mk1 (from Alan - pics to follow)

Postby Stuart » Mon Oct 18, 2010 10:27 am

Alan you mention the damping being a bit high, have you considered that the damping of the Gaz damper may be completely wrong for a Midas?

Perhaps this could explain why I found 160lb rear springs on my mk3 coupe perfect for me with a small 1" run flat on none height adjustable Spax dampers. and also why I find 110lb springs on shortened AVO dampers perfectly fine on the mk2

As you're probably aware only the rebound damping on all cheaper adjustable dampers is adjustable, having excess damping can give the impression that the car is too highly sprung. Haven't you got any old Spax dampers that you can put a set of your new springs on just to do a quick comparison with?
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Re: Further thoughts on Midas Mk1 (From Alan D)

Postby manifold » Fri Nov 05, 2010 12:52 am

Pics now added (top)
Midas Cars Forum & Facebook Page Founder

Midas Gold Convertible: 1380 steel 16v KAD & 5 sp dog box, Titanium mania, KAD fr/rear callipers, CF Steering

Midas Gold Coupe: 1380 7 port xflow, SC/CR gearbox, Titanium mania, CF Steering & seats.
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Re: Further thoughts on Midas Mk1 (From Alan D)

Postby Hans Efde » Fri Nov 05, 2010 9:06 am

I have Spax dampers at the back, a second hand buy (new old stock) from Ebay.
Via a former Dutch Midas enthusiast I bought locally made springs. I believe these were a copy of the original Corby springs on the Spax dampers. I have driven with Avo dampers and soft springs and these Spax dampers with the Corby springs, original and copied.
The car feels fantastic with the Spax dampers and Corby springs. The car feels stable yet properly damped and sprung, no dancing around, bottoming out or too harsh. I have a graph of the locally made springs added to this message. It says load 320 (325 measured). I am not sure what it means, 325 N/mm?
Perhaps Alan can take a look at it and test them out. I am quite sure they will solve Alans problems although his sprung weight is a bit higher than mine :D

rearspringgold.jpg
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Re: Further thoughts on Midas Mk1 (From Alan D)

Postby Geoff Butcher » Fri Nov 05, 2010 9:02 pm

I reckon that's about 100 pounds per inch, without resorting to a calculator
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Re: Further thoughts on Midas Mk1 (From Alan D)

Postby Geoff Butcher » Fri Nov 05, 2010 9:05 pm

Or 110 with a calculator
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Rear shock absorbers

Postby DavidL » Thu Aug 29, 2013 12:33 pm

I've just bought a pair of new front shock absorbers which cost me, in total, less than £20. Definitely nothing fancy, but the main aim is to get back on the road.

I want to replace the pair of GAZ shock absorbers at the back since I'll need to adjust them and they're a mass of rust around the adjusters, and have found that a pair of AVOs will cost me about £228 from AVO direct. I don't mind paying the money if that's what the going rate is, but does anyone know of any cheaper worthwhile equivalents? Having experienced the GAZ "always rust" product (my front GAZes were just as rusty, and seemed to be too short), I wouldn't willingly use those again.

More importantly, how well do AVO shocks perform against other manufacturers' shocks? My old Bronze had SPAX on the rear, but I never tried anything else since that was the make that Harold recommended...
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Re: Rear shock absorbers

Postby Stuart » Thu Aug 29, 2013 12:56 pm

I've had AVO's and in all honesty they were comparable with Spax and GAZ. I imagine the production techniques and paints used have also changed over the years too.
GAZ do a shiny zinc finish, but that still rusts. Pro-tech are well rated these days, with an alloy body, but I'm not certain if they're anodised.

Here's some of my shortened AVO's next to a standard length GAZ. I've not actually driven on the GAZ dampers so can't really comment. I know Alan hasn't had much success with getting a nice ride with his GAZ set-up and they've gone rusty despite the zinc finish.

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