Rear shock absorbers

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Re: Rear shock absorbers

Postby max midas » Fri Sep 02, 2016 9:16 am

I'd be interested to hear the reply as my back end sits too high as well!
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Re: Rear shock absorbers

Postby Stuart » Fri Sep 02, 2016 9:44 am

My MK3 coupe had some 4 lb/in run flat springs on standard Spax dampers to lower the car, it ran 150 lb/in springs, at the time I thought the ride was perfect at the rear.
I wouldn't like to say what length and rate will suit you though, but the run flat will allow you to achieve a lower ride height on standard dampers.

http://www.dfaulknersprings.com/acatalo ... pring.html

Q23 back.jpg
Q23 back.jpg (97.81 KiB) Viewed 13447 times


and one with a bit more fluid in the front displacers

yyyu.jpg
yyyu.jpg (56.65 KiB) Viewed 13446 times
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Re: Rear shock absorbers

Postby Geoff Butcher » Fri Sep 02, 2016 8:27 pm

If you lower the ride height too much you stand a chance of bottoming out the dampers, from which no good will result. What rear ride height do we have? Mine is 13" from wheel centre to under the wheel arch.
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Re: Rear shock absorbers

Postby Hans Efde » Sat Sep 03, 2016 9:10 am

Mine is 13 inch at the back as well (33cm). But at the front the distance is 32,5cm (12,8 inch) and I want them to be equal. At the front my Watson spring is at its maximum height, so no more room there. I don't think bottoming out is an issue of Spax dampers. I had Avo's previously, these made a clanking noise so quite sure these did bottom out. Also I have rubber up and down stops and my Spax have also a sort of donut rubbers around the stem to prevent a mechanical bottom out. In fact the rear feels solid and well composed. The springs are around 100lbs, but (as recorded earlier in this thread) Alistair pointed out the Spax put the highest pretension on the springs. I believe this is the reason why this combination feels so positive. I am not sure if half a cm shorter shock/damper combination will cause suspension travel problems, but I will check.
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Re: Rear shock absorbers

Postby Hans Efde » Fri Sep 09, 2016 4:00 pm

Today I removed the shock absorbers, springs, did a few measurements and then destroyed one of my shock absorbers.
First the measurements. I measured the distance from (the hole in) the wheel arch to the mounting bolt of the shock absorber. I measured from the top of the bolt, not the heart.
Suspension without shock absorber, so maximum deflection only stopped by the upper and lower bump stop.
Suspension full down: 40,5cm
Suspension full up: 29 cm
With the suspension full up the distance between the wheel hub and arch is 28cm.
Image
(suspension full up, hitting the bump stop but many owners don't have this bump stop fitted)

The wheel inclusing tire measures 27cm. That seems safe but if you put weight on the suspension, the rubber bump stop compresses enough to make the tire touch the wheel arch. Ofcourse this is without shock absorber and spring so only hypothetical.

Now the Spax shock absorber without spring. My spax have a bump stop on the stem:
Image
I again measured from the top of the hole to the large washer that supports the half mounting rubber (maybe I should have included the rubber):
Full extended: 36,5cm
Full in: 29cm.

BTW my spring measures 32 cm uncompressed. Space on the spax damper for the spring is max 29cm (so a pre-compression of 3cm, quite high) and minimum 21,5cm.

Conclusions:
Fully extended the shock absorber bottoms out since it has 4cm less throw than the suspension itself.
Fully compressed also the shock absorber bottoms out, but it is close.
But fully compressed the bump stop on the car and on the absorber take the load. I have never heard clunking noises on my present rear suspension. I have on my Avo dampers.

So it seemed safe to shorten the Spax dampers by 5mm. There is a collar on the stem of about 15mm high, seemed like a good idea to cut it back to 8mm high. It sits between the spring mounting plate and the rubber support washer.
Here's a pic of that top collar:
Image

While cutting back the collar, the stem broke in 2:
Image
I had expected it to be 1 long part, but in fact it consists of 2 parts welded together. Yes I could weld it together again, but then the rear suspension would still be too high and it would be unsafe. So 1 Spax absorber scrap?

I took it to a local machine shop and they think it can be fixed. I made a sketch of the top part how I want it:
Image
The shop will clean up the shock absorber side, but leave a small 3mm stud extended for alignment.
Then a professional TIG welder wil weld the new mounting pin on (I could MIG weld it, but my skills are very rudimental) and hopefully I then have a safe and lowered suspension.
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Re: Rear shock absorbers

Postby Stuart » Wed Aug 02, 2017 11:08 am

Old thread resurrection. I have long wondered if it was the characteristics of the Gaz dampers that were the issue. Having never driven with Gaz dampers I wasn't sure.

Stuart wrote: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?


I saw this on the 16 valve mini forum yesterday, it would suggest my suspicions are correct in that the damping of the Gaz is too stiff.

http://www.16vminiclub.com/forums/showt ... post372673

As a simple test i have chucked on a pair of old (very old!) koni's to see if anything changes, wound to just over half way up their adjustment and to my surprise they seem to have solved the wheel hop (of at least significantly reduced it) as well as that the ride is much smoother than the gaz even when the gaz was adjusted right down and body roll feels reduced, in fact the car felt much more planted with the koni's yet much less harsh.
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Re: Rear shock absorbers

Postby fozzza » Wed Aug 02, 2017 11:55 pm

Stuart wrote:Old thread resurrection. I have long wondered if it was the characteristics of the Gaz dampers that were the issue. Having never driven with Gaz dampers I wasn't sure.

Stuart wrote: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?


I saw this on the 16 valve mini forum yesterday, it would suggest my suspicions are correct in that the damping of the Gaz is too stiff.

http://www.16vminiclub.com/forums/showt ... post372673

As a simple test i have chucked on a pair of old (very old!) koni's to see if anything changes, wound to just over half way up their adjustment and to my surprise they seem to have solved the wheel hop (of at least significantly reduced it) as well as that the ride is much smoother than the gaz even when the gaz was adjusted right down and body roll feels reduced, in fact the car felt much more planted with the koni's yet much less harsh.


I'm inclined to agree.
I have Gaz dampers with 90lb springs on my MK2, and the back end still feels hard and only improved when I had a full fuel tank and a boot full of luggage.
I chose the Gaz dampers as I wasn't too happy with the original spax coilovers and unsure what else to use, and thought 90lb springs would do the trick (obviously not)
I don't think I will be using Gaz dampers on my MK3, but unsure what dampers to go for, or what spring length and rate to use for that mater, but I definitely want my Mk3 sitting better on the road than what my Mk2 is at the moment.
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Re: Rear shock absorbers

Postby Stuart » Thu Aug 03, 2017 10:39 am

I read an article on Lee Noble's new car where he mentioned using cheap production dampers (forget the make, Koni's perhaps) and he said they were better than any of the other fancy expensive dampers he'd ever used previously.
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Re: Rear shock absorbers

Postby DavidL » Thu Aug 03, 2017 1:04 pm

Stuart wrote:I read an article on Lee Noble's new car where he mentioned using cheap production dampers (forget the make, Koni's perhaps) and he said they were better than any of the other fancy expensive dampers he'd ever used previously.

I'm all for cheap and effective, Stuart, have you got a link to the article?
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Re: Rear shock absorbers

Postby Stuart » Thu Aug 03, 2017 1:13 pm

DavidL wrote:I'm all for cheap and effective, Stuart, have you got a link to the article?


I've been looking, but so far drawn a blank, and I'm not sure if it was in relation to the new beach buggy thing or his new supercar.
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