dougisaacs

I have heard many people describe dampers as tired or worn. Except for the obvious leaking seals that show as oil weeping out, what actually wears on dampers? My limited understanding of a damper is a piston that pushes and pulls oil through small holes, so what wears out? I know fancy dampers can have numerous valves and shims to control the damping rates at different speeds and compression and rebound etc but if the seals are all OK what else goes?

NUTTYNICK

Mainly the seal that goes around the piston within the damper. This seal prevents oil 'blow by' making all the damper oil flow through the valves.

Wear in the damper tube itself (effectively the same as the seal wearing above)
and finally the mounting bushes.

If you take a damper off, and try to compress it, is should have a similar feel all the way down. If you get sudden 'easy' spots where the compression speeds up, then this portion of the damper is worn. More than likely, it will be over the portion of damper used all the time when driving.

Sometimes, lowering a car on old dampers means that a new portion of the damper tube is used, which can in some cases cause more damage than good.

In other cases, the gas used to keep the oil under pressure leaks and mixes with the oil. This will cause cavitation and poor damper performance when the oil gets hot (it going to the shops on a bumpy road).

lookout

On twin tube dampers, the footvalve spring/shim is normally rivetted and wears, reducing low speed bump damping.

On both twin tube and mono tube dampers, main piston seals wear, some makes of shims/springs lose tension, both reducing the force needed to move the damper rod.
The top guides/bearings sometimes wear allowing sideways movement of the rod.
Damper oil degrades with use as a lot of the heat is absorbed by the oil. I have seen dampers where the oil had turned black, with the shims coated with black sh*t. No wonder the damping curve had changed beyond recognition...........

So in short, a vehicle's dampers are hydraulic valves that turn energy into heat therefore start reducing in efficiency the moment you start using them.

The quality of a damper can not really be assessed from the outside. Internal fluid management design and quality of internal parts make the difference between a good damper and a not so good one.

There really is a difference between cheap Taiwanese dampers and premium European and American dampers, although they might look similar from the outside.

dougisaacs

Thanks for the reply, interesting. However, I don't understand your quote:

'lowering a car on old dampers means that a new portion of the damper tube is used, which can in some cases cause more damage than good'

Why would this cause more damage than good?

NUTTYNICK

The piston seal has bedded into the part of the tube most used I guess. I lowered a car 50mm on the original dampers in a moment of madness to make it look good. 20 miles later, the damper had completely lost it's damping/rebound ability. I hack sawed the end off, got rid of the oil and found the seal and gone around the main piston.

It seems to have happened a couple of times when I enquired about it on the 205gti drivers forum.

Not saying it will happen all the time and it will depend largely on the condition of the damper in the first place, but it does make mechanical sense to me.

dougisaacs

Thanks again, is it easy to tell if my dampers are 'gone' when they're on the car? How would I do this?

I've got a classic 2000MY with 120K on the clock, which I've just lowered a bit with prodrive springs. I knew the bloke who had owned it from new and most of these were motorway miles. Will the dampers definitely we on their way out?

Anyone a got a view on the dogs danglys in terms of dampers / coilovers to replace them with? Cusco and tein seem to be very popular.

lookout

After 120K miles the dampers won't be anywhere near their original specification. Fitting fresh ones will make a big difference and stop a lot of unnecessary body movement and will keep the wheels on the ground a lot better.


Dogs danglys: Reiger, Bos, Penske, Ohlins, Proflex, Moton, some Exe-tc etc.

Mid: AST, some Teins, Bilstein, Koni, Cusco, some Exe-tc, etc.

Lower end: XYZ, D2, BC, Tein etc.

dougisaacs

Brilliant, that's next year's christmas list sorted! I assume fitting heavier (bigger) wheels will also increase the work the dampers have to do (I have some to go on)?

Also, when I fitted my new springs I noticed that the dampers are not central in the springs, i.e. they don't run down the centre of the springs. Any idea why this is? why are the factory springs also so much bigger diameter than all the coilovers seem to be? Would you recommend buying coilovers or are there good replacment dampers in the standard strut size that could use my current springs? Presumably coilovers have the spring 'matched' to the dampers.

Thanks in advance

lookout

Yes, all extra unsprung weight needs damping.

There are a couple of reasons why the OE springs are slightly angled and off-set. Probably a bit much to go into here, but suffice to say that with OE type springs you will have optimal spring travel, without much noise or coil bound issues. The serious rally suspension also runs larger springs.

For road use on a classic I do like the P1 set up, with the addition of some Whiteline bits. For a track car, I prefer the Reiger set-up. It is personal preference though. Each to their own............