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Author Topic: suspension settings  (Read 5664 times)
Lennart Sorth
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« on: September 27, 2008, 10:40:00 pm »

Unfortunately I don't think anybody have the technical specs of the suspension,- spring "k" values, shock absorber parameters etc. If I'm wrong, PLEASE let me know.

My new springs and shockabsorbers have resulted in the rear being too soft, and the car can bottom out quite easily. A bloody nuissence as I had requested to get a *replacement* setup, as I had no intention of fiddling about with suspension settings - all I wanted was lower springs so the rear came down where it belongs, and then modern shosckabsorbers. period.

(Unfortunately you cannot get modern absorbers unless you get them "adjustable", which I requested to have adjusted once-and-for-all to "Murena standard" values.)

Initially I thought the problem was that the springs were too soft, but I have come to the conclusion that it only is the shockabsorbers that are different.

My left one is either set way too soft, or has failed already(!) - the right one feels right.
The left actually bounces when I let it go, - the right just comes back up and stops, - so the left absorber is either set to *very* low absorbtion, or has failed already (?!)


Now for some measurements:
--------------------------------------

The rideheight, as measured at the top of the rear wheel-arc on my car is slightly different right/left with nobody sitting in the car.

        Left: 602mm   right: 610mm 

This may however be caused by the body having been fitted by a French worker on a monday morning, so it is more interesting to look at the compression:

When I put my weight (84kg) on each corner, they compress to:

        Left: 584mm   right: 594mm

ie compression is :   Left: 18mm   Right: 16mm


However, I only have one Murena, so I would urge all owners weighing approx 84kg (however many stones and pebbles that amounts to)  to measure the compression when you sit on the rear corner of the car.

Please also say if its 1.6/2.2 and the year.

If you don't match the 84kg then find somebody who does :-)
Alternatively we could establish a concensus on a Murena driver weight, and I could re-do my measurement.

/Lennart
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Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
suffolkpete
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« Reply #1 on: September 28, 2008, 10:53:00 am »

For our English readers, that's 13 stone 3 pounds.  I think your left shock absorber is defective though.  It should never bounce, whatever its rating, only go up and stop.
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Anders Dinsen
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« Reply #2 on: September 28, 2008, 04:20:13 pm »

For our English readers, that's 13 stone 3 pounds.  I think your left shock absorber is defective though.  It should never bounce, whatever its rating, only go up and stop.

I agree. It shouldn't bounce, at least not very much, and if they are set identically (which I assume they were when they were fitted according to your instrucitons), then they most certainly should NOT behave differently. Your 2 mm difference between left and right indicate that your springs are okay. I would have thought it was more. The stabiliser helps of course.

I haven't got my car on a level surface, but I'll try to take measurements as soon as possible.

- Anders
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Waldo
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« Reply #3 on: September 28, 2008, 04:36:36 pm »

I agree with the other guys... sounds like you have a defective shock absorber!
I have heard that the spax units quite often fails, especially if they have been stored/shipped wrongly (not topside up!)
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suffolkpete
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« Reply #4 on: September 28, 2008, 05:06:57 pm »

Waldo raises a good point.  I read somewhere that shocks that have failed in this way can be restored by mounting in a vice in their correct operating position and manually forcing them through several full strokes.  I've measured my car and found that the ride height is 660mm left and 655 right.  That's a 1981 1.6 with steel wheels and 185/70 tyres.  When I sit on the corner my 72 kg weight compresses both sides down to 643.  If you're currently resident in the UK, come to the Wobbly Wheel next Sunday.  There should be a good selection of cars for a comparative test  Wink
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Lennart Sorth
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« Reply #5 on: September 29, 2008, 09:55:22 am »

I too came to the conclusion that the left shock is bad.

Suffolkpete: good idea with Wobbly, except next Sunday I will be at the Autumn Airshow in Duxford - among other things I want to see the Vulcan fly again (one of my friends is active member of the restoration group).

Interesting that your springs compress differently. There has always been talked about the Murena having different springs right/left, but according to the spares catalog they are the same. (?)

It still would be good to have more measurements done, so go sit on your Murena's please :-)

/Lennart
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Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
Lennart Sorth
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« Reply #6 on: September 30, 2008, 09:43:00 am »

I have adjusted the height at the rear to bring the car up to an aesthetically pleasing level - it had been set half an inch too low, which in combination with the failed shock absorber had the car bottoming out on normal English B-roads. (read: rather uneven surfaces). It still feels fantastic at the front though.

I still would like to check the look when I'm sitting in the car, but I think this is close to optimal. It is visually slightly too low at the front, but as we know, the car likes to be a little lower at the front, so I don't plan to do anything about that yet.

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Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
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« Reply #7 on: October 01, 2008, 01:01:13 pm »

Quote
My new springs and shockabsorbers have resulted in the rear being too soft

I had felt that exactly the same happened when I fitted my "GAZ" suspension.
I have tried to adjust the dampers, but I have the feeling that its the springs that are a bit too soft. 
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Anders Dinsen
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« Reply #8 on: October 01, 2008, 01:58:28 pm »

Quote
My new springs and shockabsorbers have resulted in the rear being too soft

I had felt that exactly the same happened when I fitted my "GAZ" suspension.
I have tried to adjust the dampers, but I have the feeling that its the springs that are a bit too soft. 

THe problem can of course be both the springs and the dampers, but it's possible to eliminate one or the other by some simple checks. The key is to remember that the springs handle mostly static loads, the dampers only dynamic loads. With fixed spring positions like what we have on the standard rear shocks or KONI's, you will notice that the car sits too low if the spring is damaged. I had this problem, and it was due to surface corrosion on the spring. With adjustable springs like those you have on the rear GAZ shocks, you will have to do a "load test" like the one proposed by Lennart: Put X kg in the car and measure how much it compresses - then compare with a known good car.

When Lennarts car "bottoms out" over bumpy roads, but it okay on the load test, the problem is definitely not the spring, but the damper: This is the kind of dynamic loads that the shock absorber should handle by adding some "stiffness" to the suspension.

Is this common on the GAZ shocks? Michal runs these too AFAIR, and he's a very happy owner.

- Anders
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« Reply #9 on: October 01, 2008, 02:20:33 pm »

My main issue is excessive "body roll"..
Stiffening the dampers doesn't help
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Anders Dinsen
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« Reply #10 on: October 01, 2008, 04:35:00 pm »

My main issue is excessive "body roll"..
Stiffening the dampers doesn't help

If we have a deadly virus among GAZ shocks, and by excessive, you mean that it is 'undamped' (i.e. you got sick from it), then the shock may have failed. Adjusting a defective component normally doesn't help, but I don't know how they have constructed the adjustment mechanism. On standard shocks, shock rates are tuned by changing the viscosity of the oil and/or changing the number and diameter of the holes in the piston. Piston diameter is also a tuning variable.
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
Lennart Sorth
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« Reply #11 on: October 02, 2008, 10:22:39 am »

My main issue is excessive "body roll"..
We have to remember the car is a 1980 design (I'm sure you do).

Modern sporty cars have beefy antiroll bars to keep them horizontal through bends, but I don't think that per default give you better handling, as it sort of defies the purpose of independent suspension.

Did you know that the Ariel Atom actually doesn't have any antiroll bars at all ? - for that car, its all about having a low center of gravity, which makes it corner completely flat.

So maybe you should cut the roof off your car (just kidding)

However, having felt the weight of the rear hatch when I replaced the gasstruts, we could easily save a lot of high-placed weight by replacing it with perspex or similar.

/Lennart

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Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
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« Reply #12 on: October 02, 2008, 10:28:32 am »

I remember that Mr.Diensens car had a more firm poise even on standard springs/dampers
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Anders Dinsen
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« Reply #13 on: October 02, 2008, 12:27:48 pm »

Did you know that the Ariel Atom actually doesn't have any antiroll bars at all ?

Ultima doesn't have antiroll bars either Cool

Anti roll bars are primarily for tuning grip during cornering between front and rear, not to prevent the car from rolling. They do it by transferring load diagnoally through the chassis on the car.

I remember that Mr.Dinsens car had a more firm poise even on standard springs/dampers

And that was even with my old front shocks, which came off Roy's silver car - i.e. they were 25 years old and had coveret a lot of kilometers. Lennart had a ride with those as well.

I have since replaced them with new ones, and the grip on the front has improved by a little, especially (of course) on uneven surfaces. I have a bit better feeling of confidence with the car.

Tery 'direct' steering pattern of the Murena makes it noticable on the steering wheel: Slippery contact on the front wheels is felt by the steering getting lighter. Heavier steering during cornering is an indication that I'm safe to go faster Cheesy
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
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