Can you rebuild MZ shock absorbers?

[stuart-glos]

I have a few MZ shock absorbers for my MZ301 projet but have found that some damp on compression, some damp on rebound and some damp neither way!

I've read you can take MZ shockers apart but you can't rebuild them - is that correct?

And if you CAN rebuild them, does anyone know how please?

thanks

stuart

[therealche]

I'm sure Fred Rogers used to rebuild shocks. There is a simple guide to dismantling shocks at http://www.sweller.co.uk/mz/workshop/wrk_shock.html.
If you have some shocks that have reached the end of their useful life its probably worth a go taking them apart. Just cleaning the innards and replacing the oil should make a noticeable difference. If the seal at the top has gone you might find something to suit at http://www.simplybearings.co.uk/shop. ( from the sweller link it looks if it might be a 10x19x7). The top eye unscrews from the rod, though how you hold the rod without damaging it I'm not sure.
The seal removing tool looks like this

shockspanner.gif (10.6 KiB) Viewed 6086 times

Although a small pin wrench might work.
Anyway if you have a go come back and tell us how it's gone!

[Norman Wade]

I rebuilt a number of shocks about 15 - 20 years ago, so I'm relying on memory here!

(I've copied the picture from the link in the last post to save jumping between the two)

I had a tool made based on the drawing, and used that to unscrew the 'threaded seal ring' (part 4). The ring usually comes out OK, but if it is seized in place, the body of the shock can distort first. Soak it well with penetrating oil, or use a little heat.
Once you get the ring out the shock comes apart. The seal is fitted into a cup that is made of very thin metal and easy to distort, so take care. The seal used was unobtainable as an MZ part, but was a standard seal available (very cheaply, I seem to remember) from engineering suppliers.
I never had a problem taking the eye off as they never were that tight. I used to hold the rod in a vice with soft faces and unscrew it, usually by hand.
Clean everything, fit the new seal, refill with oil, and reassemble. If you've got this far, then it will probably work.
Just bear in mind that the shocks are really cheaply made, and if they're suffering from corrosion, don't be surprised if you wreck them trying to take them apart! But a pair of shocks with no damping are worthless anyway, so it's worth giving it a try.
Good luck!

Norman

[Trogolodyte]

Thanks for that information, just what i needed...

[stuart-glos]

Thanks very much for the advice - I'll give it a go and let you know how I get on....

cheers
stuart

[mr_luke]

Hi Stuart, did you have a go at this? If so, how did you get on, and did the oil seal turn out to be 10x19x7? I need to have a go at this myself, and if possible was hoping to order the seals before I start!

[stuart-glos]

Hello

I made some soft jaws for my vice and clamped the rod. It took a sharp whack from a hammer to loose the top nut and locking nut.

I made up a tool to unscrew the top of the shocks. The pins need to be fairly accurately mounted else they won't stay in the slots, but once made the tops unscrewed quite easily.

But then nothing else would move. I ended up hack-sawing the shock body to see how it was made. I should say the pair of shocks I worked on squirted water when compressed, so perhaps they were so rusted inside they were well beyond repair.

I must admit it was difficult to see which bit was the seal. The bit that unscrews had what could have been a seal in it, but then the bit stuck inside the body of the shock also seemed to have an O ring and a seal.

What I did find was hanging the shocks vertiacally (for 2 weeks) and pumping then a few times has brought them back into life (as in, the dampig has re-appeared).

stuart

[mr_luke]

Since I posted, I've had a bit of a go at my spare pair. The first one came apart really easily. The top eye unscrewed from the rod with no problems, and I was able to unscrew the cap with a pair of 6 inch nails held in an adjustable spanner! Once the cap was removed it all just pulled apart. The seal (which is 10x19x7) is held in a small and fragile looking aluminium ring, and there's a felt seal above it. Apart from the seal, everything looked to be in good condition, and there was even a bit of oil left in there!

The second one put up a bit more of a fight when it came to removing the threaded cap, so I started to make a tool to unscrew it from an old socket. I ran out of time before I had a chance to have another go, so I'll see how I get on later.

I'll try and remember to take some photos of it all.

[mr_luke]

Well, I failed on the photo front, but I spent a few hours in the shed last night, and have met with success!

I filed 4 slots in an old socket of a suitable size, and used it to unscrew the top ring. I had originally intended to use a breaker bar to turn it, but it turned out to be much easier to clamp the socket facing upwards in the vice, turn the shock absorber upside down, and use a bar through the bottom eye to bear downward and unscrew the ring.

Once that's undone, the innards should just pull up out of the body of the shock. Galvanic corrosion had done its thing on one of mine though, and it was fairly well stuck. I refitted the top eye to the rod, and used it to hang the shock from the vice. A few gentle taps on a bar placed through the bottom eye got things moving easily enough.

At this point, it becomes clear that the diagram above is rather simplistic in places. The component '4. Threaded seal ring' is actually made up of no less than eight individual parts!

Theres an aluminium ring which carries the actual seal. A pressed steel cup sits over the seal carrier, and carries a large diameter rubber washer and a steel one. On top of all this sits the threaded aluminium ring you can actually see from outside (and which also turns out to contain a fibre washer and a felt one)! Galvanic corrosion had, of course, stuck the whole lot together, so all the bits had to be carefully prised apart and cleaned up. I think the general idea is that the rubber washer is supposed to be squashed when it's all tightened up, and seal against the shock absorber body.

I knocked the old seal out from behind with a small screwdriver, and pressed the new one in with the vice. The rest of the unit didn't seem to need any more attention other than cleaning. The surface of the rod was a little worn at one point, but it was the best I had, so I thought I'd stick it all back together and see what happened!

It all seems to work OK, with no leaks. I only had 20w fork oil to hand, so I hope that won't turn out to be too heavy.

These two were my spares, so I'm planning to fit the springs and adjusters from the pair on the bike tomorrow, and get them fitted - I'll keep you posted on how they are!

P.S. The shocks currently fitted to the bike have pumped all their oil out onto the swinging arm, so I might have a go at rebuilding them in the near future, so I've actually got a pair of useable spares! Perhaps I'll get around to taking some pictures of the seal assembly then!