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My Diplomat 430 has been getting harder to drive recently, slowing down and suddenly taking off again, even pushing it without the motor running is the same, pushes easily then the left drum seizes up, it is not clutch related.
I took the drum assembly apart, cleaned everything and reassembled and everything was smooth until I put the aluminium drum housing back on.
I cleaned the inside of the drum with a wire brush and even used a stone to get rid of any burrs, but the problem remained.
Closer inspection revealed the rubber 0 ring around the housing was swollen and distorted, and I think is the cause of the problem.
Question is, if I remove the rubber O ring will that be a problem? (I'm assuming a replacement is not possible)
As I see it, it is a seal to keep dirt out of the drum gear and will just mean an extra maintenance task every spring.
Anyone else had trouble with a distorted drum housing rubber 0 ring?

How are the bearings? I have noticed my diplomat 430 has new bearings. Has your ring gear bean replaced with alloy gears? Wouldnt be hard to strip them if there plastic. I will inspect mine and see if I can shead some light on your problem. It's pulled down anyway the reel& bed knife are getting sharpened. Sounds like your clutch is slipping or belt. Bearings could be tight, dry.. If it has plastic ring& it's slipping then it wouldnt go at all.

I like how basic the diplomats are. They seem smoother than model 45's I used..

Bearings were all replaced months ago when I replaced the plastic ring gear with a metal one.(And I use a lot less petrol now because the 2 bearings on the cutter and drive shaft were well gone)
When I reassembled the rollers I did it when it was sitting vertically, the 2 rollers on and the M12 nut on the end tightened and everything was sweet.
As soon as the drum bearing housing was put on the roller locked up.
If you look inside the roller you will see a groove that the 0 ring should fit into, my 0 ring is swollen and wont fit into the groove any more, hence it jams the roller from turning, thats why I'm thinking of removing it altogether and just adding it on as an extra task come service time and remove any crap that has got in

If the O ring has failed it should be replaced. Have you tried ordinary industrial O ring suppliers? It isn't very likely SB would have used a non-standard size. Just take the old one, and the part it fits on, to a supplier. Sometimes it's surpising how much help they are if the project is a bit interesting.

Hi Kempe,
Please give Keith a ring mate, he may be able to help with a genuine replacement...Click HERE

Yeah i had a look at mine it sounds like your o ring is locking up the drum. A bearing place should have one for you.
Have you had it long? I cant wait to get mine going again. Great little mower!

Have fired an email off to Keith in the first instance to see if he can supply the O ring, and if not it will have to wait till the weekend till I have time to look around.
Will post back the results for other people who might need to know

Hi Kempe and thanks for keeping us in the loop....Keith should be able to help you out.

An update....I didn't need a new O ring.
I carefully removed it and soaked it in an All Purpose Cleaner to get the gunge off it.
I then noticed the groove it sat into on the drum bearing housing was all gunged up causing the rubber O ring to look stretched because it wasn't seating properly.
The groove took quite a bit of cleaning/scraping with a flat bladed screwdriver to remove everything.
I then wire brushed it and replaced the now clean O ring.
Works beautifully, the drum spins easily without any hint of binding
If anyone else does this don't forget to also wire brush the groove inside the drum itself

Kempe, O rings seldom swell significantly unless some obnoxious chemical has been put on them, so I'm not surprised it turned out to be all right under the crud. I'm not sure the wire brush was the best tool for cleaning out O ring grooves, and I'm sure it isn't the right tool when one of the parts is aluminium (as I think the drum drive reduction gear housing is). However it sounds like you have overcome the problem and all should now be well.

Hi Kempe, and thanks for updating us on your progress, I'm glad everything worked out OK and your machine is now working as it should.
As this thread is now complete, I will now close it.