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rebuilding dampers (shock absorbers)

Posted by nomis3613 
July 31, 2009 11:33PM
Hi suspension gurus,

If the spring rate did not change, would the dampers still be suitable if the ride height was lowered (say 30mm)? (I guess I am asking if the operating range affects damper performance)

If so, can old dampers (in particular, the Bilstein option that BMW offered) be rebuilt for a different ride height?

Also, could the dampers be rebuilt to match a different spring rate?

Here's the situation: My car has the BMW badged Bilstein dampers (probably 20 years old, too!), but the springs are some cheap'n'nasty lowered job. I would like to end up with the H&R Sport springs/ Bilstein dampers combo, but if I can save some cash by getting my Bilsteins rebuilt instead of buying a new set, this would be great!

But my Bilsteins were built for standard ride height and spring rate, so they're not designed to suit the H&R sport springs (yes, I realise that they're an even worse match for the really really low sucky springs I bought the car with!). Therefore, to have a properly matched setup for my rebuilt Bilsteins would I have to go for OE spec springs (hmmm...a bit too high for my liking)? Or can I get them rebuilt to suit the H&R springs?

Hope my questions make sense!

I doubt the stock dampers can be rebuilt, and it would probably cost more to rebuild them than simply buy new ones.

Changing ride height alone shouldn't affect damper performance. But changing spring stiffness obviously will.

There is a danger in using the long stock dampers with shorter springs though. It is the dampers that limit how far the suspension can move at full droop. If you jack up the rear of the car until the wheels are hanging free at full droop, the suspension will be hanging from the shocks extended to full stroke. A shorter lowering spring could potentially fall out of the spring perches at this point, which would be a nasty surprise while driving.

You should really buy the springs and shocks as a matched set, like the H&R springs with shorter Bilstein Sport Shocks.
rebuilding your Bilsteins is not necessarily a DIY job. Factory will rebuild them, but I am not sure of the cost (rebuild vs. buying new). Call Bilstein and ask about the price. As Ferdinand mentioned, springs and dampers should have "matching" rates...
Hi guys,
Thanks for the tips. Yeah, I'll be sending them to the Bilstein distributor for rebuilding, not gonna try it myself!

Due to stuff being more expensive here in general, it'll still be like 40% cheaper to get them rebuilt if possible rather than buy new ones.
I have some Koni shocks (dampers) and have wondered how one rebuilds what appears to be a welded assembly.

Bob in Everett
There was a show on cable and they showed shock manufacture. Bob is correct, they assemble the innards, weld it and then using a special machine, fill and weld thru a port. Perhaps they cut them apart, rebuild the innards and then reweld and refill with oil/gas?

I suppose a "disassembly" could be done with some machining of the welds but from what my experience with manufacturing that kind of stuff is that it would be less expensive to just take the old ones in need of repair and "exchange" them for new because the cost of disassembly and inspection would exceed the cost of the parts in a new one.

One place I used to work wound up doing that. The exhange rebuild process cost more than the direct labor and materials of the new parts. We kept the pricing and started throwing away the old parts instead of reprocessing them. Customers did not know that they got new parts for the rebuild price. There was not quite as much profit as selling new but the customer good will was maintained.

Bob in Everett
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