New Shocks, Different Spring Rates. Advice Please!

[SkyQuake 70 1 Cars]

Dear All,

 

Having recently gotten around to putting my car back on her wheels (more on this in my project thread, soon), I have noticed a potential problem with my front suspension. I seem to have differing spring rates on either side of the vehicle.

 

Just some background. The vehicle is partially stripped, so currently consists of suspension and glass only; no engine or anything too heavy. It has been fitted with a brand new pair of Sachs shock absorbers purchased from Euro Car Parts. I stripped the struts and painted up everything, before re-assembling it all, and re-fitting it to the car.

 

Having now dropped the vehicle back onto it's wheels, I decided to test the shock absorber response by pushing down sharply on the front corners. There is a dramatic difference between the responses of the two sides. The passenger side shock gives what I believe to be a fairly normal response, depressing and returning to position in a damped fashion. The drivers side however is very much stiffer. I can barely depress it with my bodyweight, and it returns much more swiftly.

 

Now I realise that the engine is heavier on the drivers side, so the shock could be differentially pressured to compensate, but the difference is more than I would have expected. Therefore, do I have a problem here, or is it simply because I am testing the response with the engine out and the car incorrectly weighted?

 

I have checked the struts, and can't see any assembly error on my part (although I certainly wouldn't rule it out!) I have checked that the spring support plates are correctly positioned, so the springs aren't loaded differently. Obviously I don't want to go stripping down the struts and sending the shocks back to euro car parts unless I really have to, as this is a massive job!

 

Any advice is greatly appreciated.

 

Kind regards,

 

Mike

[EdCherry 34 1 Cars]

Mike,

 

The 'test' you are performing is not repeatable enough for a start, how do you know what velocity you are inputing into the damper to get the same forces in response.

 

Secondly, the dampers should be exactly the same on internal build. Although you say they are exactly the same, the tolerances in mass manufactured dampers is often pretty poor, the difference you will be 'seeing' is most likely a difference in bleed/friction/stiction. This can be from other things than just the damper, any part of the suspension the moves can effect it.

 

Thirdly, if the spring rates are different, you need to fix that before you start blaming dampers.

[SkyQuake 70 1 Cars]

Ed,

 

Many thanks for your response on this. I'll try and come up with some more scientific methods of testing the response.

 

In the first instance, I'll simply put a known mass on each side of the vehicle in turn, and measure the displacement. This should give me an indication of the rates.

 

Then, I'll have to come up with a way of instantly unloading the previously mentioned mass, and timing the return to top.

 

But in summary, it would be safe to say that both shocks are supposed to be equal, but you wouldn't get excited about a small amount of difference between the two?

 

Mike

[SkyQuake 70 1 Cars]

Ok, so I've tried to do something slightly more scientific (lol!) to get a better idea of what's going on here.

 

Firstly, I've checked the setup again, and cannot find any differences between the two. It all appears to be assembled correctly. Both wishbones are free moving, and there is no noticeable difference in the movement of the ARB (although again, this is difficult to quantify). Drive shafts are currently not fitted, so don't come into the equation.

 

I double checked the struts, and there is a difference between the part numbers, which I hadn't previously noticed.

 

 

Now this could be because they are totally different parts (because I have to trust what eurocarparts supply me with), or it could simply be the denotation of differing hands. I have no way of knowing, as I haven't been able to find a way of looking this up on the Sachs website.

 

Therefore, on to the 'precise' experiment..

 

In order to compare the two sides, I decided to measure the resting height of the vehicle, and then load a heavy mass (in this case, the girlfriend), and repeat the measurement. This gave me the following:

 

Test 1 - Driver's Side

 

Test 1 - Passenger's Side

 

And then repeating the test with a slightly heavier mass:

 

Test 2 - Driver's Side

 

Test 2 - Passenger's Side

 

So, in both cases, there is a greater displacement on the passenger's side of the vehicle, with a common 3mm difference, between the two masses. Now obviously this is a pretty ropey test, and this isn't the best data to draw useful conclusions from, but it does support my initial gut feeling that the driver's side is stiffer than the passenger's.

 

What I don't know is where I go from here. I can double check the part numbers with eurocarparts, but there's nothing to say that they won't cock it up twice (if they've already cocked it up once!) Or am I worrying too much, and this is something that will sort itself out once the shocks have been used a bit?

 

Any advice is greatly appreciated.

 

Kind regards,

 

Mike

 

[welshpug 1,657]

That's more a difference in the spring than the damper.

 

the part numbers will be different, as the dampers are handed.

[EdCherry 34 1 Cars]

Mike,

 

These dampers do not effect ride height in any which way. Even if one side was stiffer than the other one it would only delay the time taken for the damper to compress compared to a softer one.

 

This is a difference in spring rate, spring pre load or spring length. If you have a press and some scales you can roughly measure how big the difference is.

 

Anything more in depth you know how to get hold of me.

 

Ed.

[Batfink 201]

Where are the springs from?

[Cameron 16]

It can be one of two things - the damper or the spring.

 

If you want to find out whether your spring rates are different, you can do the following slightly-less-shonky test.

 

1 - Jack the car up and measure from the lowest point of the wheel rim to the highest point of the wheel arch trim. This is your most repeatable measurement; measuring to the ground brings tyres into the equation.

 

2 - Place bathroom scales under the tyre and lower the car on the jack until the scales read 50kg or so, then check your wheel rim to arch distance. Write down the weight and the distance moved.

 

3 - Lower the car until the scales read 100kg or so and check / note down everything again.

 

4 - Grab a calculator and divide Force 1 (measured in step 2) by Distance 1 to get your wheel rate in Kg/mm, then multiply by 9.81 to get N/mm. Do the same for the measurements in step 3 just to check that everything's ok.

 

5 - Repeat for the other side of the car.

 

This is by far the most accurate way of doing things, as you can compare the exact Force / Displacement of each side and stop all this internet guess-work.

Edited June 25, 2013 by Cameron

[EdCherry 34 1 Cars]

How can it be the damper?

[Cameron 16]

Could be an out of tolerance / mis-built part. It won't affect ride height, but it will affect how stiff the suspension feels on the "bounce test".

[Anthony 1,003]

Are the springs new, or did you reuse the existing ones? Could be mis-matched springs causing the issue, say a GTi one on one side and a diesel on the other for example.

 

Is the rear beam sat level and built to the same dummy shock measurement side to side? If it isn't for whatever reason, that will have an effect on the front ride height (and vice-versa)

 

Also, were the ARB droplinks the same length so as not to pre-load the ARB? Disconnecting one of the droplinks should quickly prove it's nothing ARB related.

How can it be the damper?

Unlikely, but if the spring pan hasn't been welded in the same position each side, that would certainly do it.

 

Oh, and Cameron - measuring distances based on the arch trims if you're wanting a reliable comparison side to side is asking for trouble, as they're often a fair way out side to side owing to shoddy French tolerances, previous accident damage/repair, etc. I've seen them measure 10-15mm different between sides before now to give you an idea. Fine for doing comparisons on the same side though, of course.

[Cameron 16]

 

.. Fine for doing comparisons on the same side though, of course.

That was the idea; you're measuring displacement, not setting the ride height.

[Mattr5uk 20 5 Cars]

May be worth asking whether you "primed" the shocks before fitting. When I had someone a while ago try to sell me some shock absorber equipment he went through correct fitment of pulling the shaft to its full extent and back to the bottom again a few times to work the air to top of shock. Something I'm sure you may have done it anyway but I was told this can affect them and I have experience them knocking initially if its not been done. Once again I may be teaching you to suck eggs but I like adding my 2pennies worth

[Mattr5uk 20 5 Cars]

Oh and the shocks certainly won't affect ride height there's only one car I've come across that does though an that's the Alfa Romeo sport wagon and they're about £400 a shock!

[SkyQuake 70 1 Cars]

Dear All,

 

Ok, firstly. Many thanks to everyone who responded with advice, it is greatly appreciated. I'll go through some of the points/questions one by one:

 

It can be one of two things - the damper or the spring.

 

If you want to find out whether your spring rates are different, you can do the following slightly-less-shonky test.

 

1 - Jack the car up and measure from the lowest point of the wheel rim to the highest point of the wheel arch trim. This is your most repeatable measurement; measuring to the ground brings tyres into the equation.

 

2 - Place bathroom scales under the tyre and lower the car on the jack until the scales read 50kg or so, then check your wheel rim to arch distance. Write down the weight and the distance moved.

 

3 - Lower the car until the scales read 100kg or so and check / note down everything again.

 

4 - Grab a calculator and divide Force 1 (measured in step 2) by Distance 1 to get your wheel rate in Kg/mm, then multiply by 9.81 to get N/mm. Do the same for the measurements in step 3 just to check that everything's ok.

 

5 - Repeat for the other side of the car.

 

This is by far the most accurate way of doing things, as you can compare the exact Force / Displacement of each side and stop all this internet guess-work.

 

This is a much better test, thanks Cameron. I'll do exactly this, hopefully tomorrow evening. I'll mark the measurement points on the arch and on the rim, and then conduct the test as described.

 

Are the springs new, or did you reuse the existing ones? Could be mis-matched springs causing the issue, say a GTi one on one side and a diesel on the other for example.

Is the rear beam sat level and built to the same dummy shock measurement side to side? If it isn't for whatever reason, that will have an effect on the front ride height (and vice-versa)

Also, were the ARB droplinks the same length so as not to pre-load the ARB? Disconnecting one of the droplinks should quickly prove it's nothing ARB related.Unlikely, but if the spring pan hasn't been welded in the same position each side, that would certainly do it.

Oh, and Cameron - measuring distances based on the arch trims if you're wanting a reliable comparison side to side is asking for trouble, as they're often a fair way out side to side owing to shoddy French tolerances, previous accident damage/repair, etc. I've seen them measure 10-15mm different between sides before now to give you an idea. Fine for doing comparisons on the same side though, of course.

 

Anthony. The springs are old, and came with the vehicle. I have no history relating to them, so indeed, they could be anything! All I did was remove, de-rust and plastidip them.

 

The rear beam appears to be level. I did not fully disassemble the beam, all I did was unbolt the easy bits, clean it, paint it, replace the bushes and put it back together. I deliberately did not fully strip, as I'd read up on here about ride heights etc, and got scared. The only measurement I used was the prescribed 288mm (from the Haynes guide) between shock absorber hole centres. This I did by raising the radius arm with the jack until the measurement was achieved, and then tightening the shock absorbed bolts.

 

In order to eliminate the rear beam from the equation when I undertake Cameron's method above, I'll put the axle stands under the rear jacking points.

 

Unlike the springs, the ARB droplinks were brand new, and exactly the same length. The ones that came off were completely different types (in appearance), and may have been different lengths. I've looked back at some old photos and there does visually appear to be a marginal difference between them. This wouldn't cause the ARB to twist and set over time would it? In either case, I'll disconnect them and remove them from the equation.

 

I'll also measure the distance from the wheel hub to the spring pan on both shocks, to see if there is a difference.

 

May be worth asking whether you "primed" the shocks before fitting. When I had someone a while ago try to sell me some shock absorber equipment he went through correct fitment of pulling the shaft to its full extent and back to the bottom again a few times to work the air to top of shock. Something I'm sure you may have done it anyway but I was told this can affect them and I have experience them knocking initially if its not been done. Once again I may be teaching you to suck eggs but I like adding my 2pennies worth

 

Matt. Good question. No, I wasn't aware there was a procedure to follow here. Nothing is mentioned in the Haynes guide, and I don't remember it featuring in the instructions which came with the shocks. That said, I'm not a total prat, and I did actuate each shock before fitting it, to check that it was working. I didn't however go through any of the procedures which I've now found (after some googling), which mandate several full actuations with time delays in between.

 

In order to get around stripping the whole lot back down again, if I were to compress the spring as fully as possible on the vehicle (using my spring compressors) and then travel them several times as much as possible, would this do the job do you think, or do I need to take them off again?

 

Again, many thanks to all for your help.

 

I'll keep you informed on progress.

 

Mike

[Rippthrough 98]

It's only to get air out of the valving, it wouldn't alter the ride heights.

[SkyQuake 70 1 Cars]

Sorry for the delay on this; I've been meaning to tell the end of this story for a while!

 

After spending some time fannying around trying to compress the springs on the vehicle (don't waste your life!), I gave up and did what I'd been told to do. I removed both shock absorber assemblies, and stripped the shocks back out of them. In order to gauge the difference in damping rates, I clamped both of them side by side in the workmate, and used a piece of wood to compress them fully before releasing them. The difference was massive; one returned to top more than twice as fast as the other.

 

I did this several times with no change. I then decided to go and get the video camera and a stopwatch, and see if I could get some figures to go back to ECP and Sachs with. While trying to work out a good way of doing this, I actuated the shocks a couple more times. One of these times, one of the shocks gave off a farting bubbling 'blarp' noise and suddenly started moving differently. At the next stroke, the shocks were both much more similar in movement, and 20 strokes later, pretty identical.

 

I proceeded to give them another 10 minutes vigorous pumping (you should never miss the opportunity, should you?) and then reassembled and put them back on the car. Of course, like magic everything was fixed!

 

So the moral of the story is make sure you've done a good job of priming the shocks before hand. I obviously did a lousy job! One more factor may be that I primed the shocks (badly) before leaving them lying horizontally in my shed for a week. This may have allowed some air in or messed up the oil/gas balance or something.

 

So for anyone else changing their shocks for the first time:

• Always change shocks in pairs.
• Always fully prime shock absorbers immediately prior to fitting
• Compare the shocks and make sure they have the same response.
• Don't leave primed shocks lying on their side, keep them upright before fitting.

Many thanks to all those who commented, your help was much appreciated.