Strange vibrations after rear subframe replaced

[FatBob]

I recently had the rear subframe replaced under warranty because of corrosion on the original one. Since getting the bike back, there seems to be some strange vibrations sometimes that I don't think were there before. Its hard to describe, its an irregular sort of knock like you have just ridden over something in the road, but it happens too much to actually be something in the road, quite often several knocks one after the other. I have only ridden once or twice with a pillion since getting the bike back, and the pillion seemed to make the knocking more frequent. Also I haven't managed to get the MPG above 47.8 since the work was done; previously the standard was 48.7 and above that sometimes.

Replacement of the rear subframe is a big job and must involve prretty much disassembling the whole bike. I don't know if I am just being paranoid, looking out for problems. Maybe the knock was there before and I just didn't notice it. Or maybe there is something not quite right. Other than that the bike seems fine.

Any diagnosis? Should I be concerned? I suppose the answer may be to take the bike back to the garage to have it checked, but its a real hassle to get it there and vague/intermittent problems, if there is one, can be a bugger to find.

 

[Wapping]

Have a look that you do not have a stone or large bolt embedded in your tyre.

Chances are you are imagining it. If you told your pillion: "I am sure there is a knock, hop on the back....." then their view is probably biased.

As it is difficult (impossible?) to describe you are probably in a land of your own vis-a-vis remote diagnosis. take it back to whoever fitted the new sub-frame, is probably your best course of action .

 

[John Armstrong]

With such a big job the alignment of bolts / exhausts / drive shafts etc etc is bound to be different, and this will cause changes on how the bikes feels / rides / the noises it makes. Is there another similar spec bike with simialr mods and miles that you can ride to see if it's a "they all do that sir" type problem?

One thought, is the noise when you go over the bump or after, that is, suspension compressing or extending?

Re the loss of 0.9 mpg, you'll see bigger changes doing a ride into / down wind IME.

 

[RickG]

The slightly lower mpg may just be because it's colder now.

The obvious thing is to check all the fastners are tight in case they have missed one. Insufficiently tight frame bolts can cause more vibration too.

Given the swinging arm has had to come off I'd give that a good heave-ho to check they have re-set the adjustment on the bearings properly and not left a load of free play.

I had a big clunk on my bike when these bearings were on their way out. If you ride in a low gear at tick-over and then roll the throttle on and off a tad it will provoke a lot of movement down there if there is any to be had, but as I say, you should easily be able to feel any play in the swing arm with the bike on the main stand

 

[Wapping]

Lose weight, perhaps, Fat Bob?

That may cure it.

The fuel issue?.... Ride it faster, that MPG is disgraceful!

 

[FatBob]

Thanks for the suggestions. I will see if there is any excessive play in the swingarm and just keep an eye on it I guess. I check the tyres weekly so I don't think there is anything in the tread, and my pillion didn't notice any difference. I can't quite work out where I am feeling the knock, i think its coming through the footpegs mainly.

Re MPG displayed by the computer, up to the first service at 6000 miles it was pretty much always 48.7. After that service it seemed to go up a bit, 49 or sometimes up to 51 but usually back down nearer 48.7 by the next fillup. Since the last (12000) service I think, which was a few weeks before the frame was replaced, I don't think it has ever got over 47.8, even temporarily, and I am riding the same routes in the same way. Maybe even slower now because its dark in the evening on the way home! I think they switched the oil over to fully synthetic at the last service, don't know if that would make any difference.

And why is it the MPG always displays particular values...47.8, 48.7 etc but never say 48.1? Are they just making it up?

 

[Wapping]

.... and my pillion didn't notice any difference. I can't quite work out where I am feeling the knock, i think its coming through the footpegs mainly.

.... Looks like you may well have to do a lot more work.

.....I think they switched the oil over to fully synthetic at the last service, don't know if that would make any difference.

.....Take care, you are now drifting into oily waters.... This thread will be 300 pages long by teatime.

And why is it the MPG always displays particular values...47.8, 48.7 etc but never say 48.1? Are they just making it up?

No idea and probably.

 

[Shep]

As for the knocking sound i'd check the rubber stops on the stands, also the exhaust will have been moved so make sure the stands arn't touching it somewhere.

I agree with Wapping about the fuel consumption you should be ashamed, next week you'll be posting about how you get 12000 miles from a rear tyre

Shep

 

[Prattapillar]

Re: MPG

Have you changed your tires? I went from Battlewings to to Trail Attacks and saw the MPG drop from 48.7 to 46.9. This observation made me realise what a sad old tw@ I've become!