Wobble Problems

Greetings all and hope everyone had a enjoyable and safe Memorial Day weekend. Yesterday I was coming back from the ranch and decided to ride the old 1973 850 Norton Roadster like I used to when I was 18. Well when I hit around 75 mph the bike started to wobble really bad--- not up and down but side to side. Actually had to put some muscle into controlling it. Long story short does anyone have any ideal on what could cause this action. Isolastics?? It rides smooth as silk from 0-70 mph but then goes really radical. Just throwing this out to see if anyone else has experienced this. I would think that if there were tire issues, bent rims etc it would be noticed at lower speeds as well?? The only alterations or modifications I have made to the bike is put a solo tractor seat on it, different handlebars and removed the exaust crossover pipe. Any info or input would be appreciated. Semper fi devildog

Isos, swing arm shaft/bushes, head steady, tires, mud flap, spokes, head bearings, fork oil missing on one leg.....shake and check everything....the reason is in there somewhere. My wobble turned out to be tires and the mud flap...mostly. Keep speed down till you find the reason.... :wink:

i felt the wobble too... how does a mudflap play into this?

My 750 has always done this at 75-80 +. It's a late 850 frame with the 850 yokes (triple trees) and unbraced 750 swingarm. I'm told it's usually a tyre thing or not having two mirrors to balance things up. Have always run 110-90-18 and 90-90-19 AM20/21 combo and tried different pressures, two mirrors, no mirrors, tight ISO's, new SA bushes etc. but made no difference. Take one hand off the bars and it shakes side to side, like a minor slapper? Both hands on and it sort of snakes down the road?
Well i finally replaced the worn out Avons a few weeks ago and put on BT45's in 100 & 110 sizes. Could not get a 90 for the front so that increased the trail and rake and guess what? no weaving. It's gone! It might come in at higher speeds now but I'm running-in new rings and an expensive head job. We'll see.

Had a mudflap on the front fender...no more. Old hard tires are a no no.

Thanks

Pretty much what I figured. The tires on the bike are old and weather cracked but have good tread still-- they do need replaced badly. One thing I do have to check howver is the fork oil as the front end shocks do seem a bit squishy?? Its not a high priority at present however did scare the hell out of me when it first happened. Maybe a bit to much firewater in my system!!!! Thanks for input. semper fi devildog

Re: Thanks

devildog said:

shocks do seem a bit squishy??

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I have heard that worn shocks can cause Commandos to wobble.