Converting diff back to M800 from a VS1400 unit.

I am returning my M800 back to standard gearing to suit the kind of riding I'm doing these days and thought I'd put any useful info I on here.
I have had to buy a used  M800 drive shaft from America as the robbing bas...er I mean breakers here are charging about a fiver less than a new one ( which are on back order from Suzuki ). I was reading how in the USA they cut, lengthen and weld the original VS1400 shaft to fit our bikes and I will try to find out if anywhere here can do this as the VL/M drive shafts are a bit thin on the ground here.
I bought a VX800 diff spacer which going by the dimensions is the same as the M800 one.
I'll update if I find anything else of interest .

I forgot to add, I'll be keeping the VS1400 unit built up ready to fit if required ,if I have to do a long motorway journey etc as I reckon it can be changed over in approx half an hour ..

I forgot all about this thread while I was looking into this , I did change the drive back to standard but after two days realised it was so annoying to feel like I was over revving in every gear (vs1400 conv has spoiled us) that I changed it all back to the vs1400 diff again.
One thing I did notice was a fair bit of wear on the splines , so I was going to get the vs1400 shaft lengthened and a new UJ, asked around but only found a couple of places willing to do it , cheapest wanted £278 plus VAT so that was a no go ...thought about doing it myself . The cutting, sheathing and welding would be easy enough but the balancing needs to be very precise if you don't want to wreck gearbox output bearings.
That leaves me with my spare 800 shaft and new UJ ,I have looked closely, measured up etc and I reckon it only needs the shoulder milled back 4.5mm and the end of shaft milled back 1mm ,also I don't see the need for the shaft to milled at the shoulder end of splines as the UJ has a 5.5mm unsplined recess at that end .
So I will get this done and see how it all fits/works before I try on bike. I would prefer to leave the splines untouched if possible as with the tuning work and fact I travel two up a lot I feel there is too much stress on the current shortened splines ...

rossmofo wrote:

I have looked closely, measured up etc and I reckon it only needs the shoulder milled back 4.5mm and the end of shaft milled back 1mm ,also I don't see the need for the shaft to milled at the shoulder end of splines as the UJ has a 5.5mm unsplined recess at that end .

The shoulder needs milling back (shortening in theory) to allow for the suspension movement Ross, same with the end as it will snag on the U/V joint once the shoulder has been milled, if you use a stock length shaft it'll put pressure on the bearings once the bike is under any weight.

ps. I've never ever heard of any reported failures of splines after having this modification done.

I know why the shoulder needs milled back and that will happen but the overall length will still not foul any other part of the UJ , my current splines are within service limits but defo have worn , but I have done 10k ,mostly two up and I'm heavy on the throttle ... I will get the shoulder milled back and then try it to make sure my calculations are correct ...

Note the recess which will accommodate the milled area after the shoulder has been altered

Keep us informed of your findings 

ps. I've always liked the idea of taking 3/16th's (4.76mm) off the UV joint end and the same off the shaft end without touching the shoulder, difficult operation on a lathe apparently?

url=https://servimg.com/view/18130989/20][/urI think I will mill the end of the shaft back to the start of the splines just to be sure but even with out that it doesn't look possible for end to make contact with UJ.... I'll post some pics up when the work is done in a week or so ..

Well my local gunsmith and biking friend helped me out with a lathe , we looked at several options including taking half of the 3/16ths off the entry of the UJ and diamond grinding the taper on back end of splines but in the end went for everything coming off shaft and just under cutting the rear of splines. We only took the end of the shaft back to the start of the splines by cutting back the chamfer and making a smaller one. By not taking much off the end this shaft could be reused in the 800 diff with just the addition of a 3/16 spacer butted up and fixed to the shoulder, but I will probably buy a spare shaft .
I'm still going to pursue having the VS1400 shaft cut and extended when I find a suitable method of balancing it afterwards ..
Will take some pictures of both modified shafts for comparison once I remove the diff .

rossmofo wrote:

Well my local gunsmith and biking friend helped me out with a lathe , we looked at several options including taking half of the 3/16ths off the entry of the UJ and diamond grinding the taper on back end of splines but in the end went for everything coming off shaft and just under cutting the rear of splines. We only took the end of the shaft back to the start of the splines by cutting back the chamfer and making a smaller one. By not taking much off the end this shaft could be reused in the 800 diff with just the addition of a 3/16 spacer butted up and fixed to the shoulder, but I will probably buy a spare shaft .
I'm still going to pursue having the VS1400 shaft cut and extended when I find a suitable method of balancing it afterwards ..
Will take some pictures of both modified shafts for comparison once I remove the diff .

I'll look forward to seeing the pics 

So that's the job done and I'm glad I did it ,got to grease the swing arm bearings etc. The UJ on the bike was in perfectly serviceable condition with no noticeable wear. The shaft was a different story , quite noticeable wear ,even though the splines were within Suzuki service limit along 75% of their length. A few of the splines were hooked too as you can see in photo below.

They only seem to be 'hooked' at the end?

Don't know why they are hooked on the end ,but the drive face of the splines have some wear too . We did consider taking the 3/16ths off the  UJ  by using a 4jaw chuck  and the vs1400 shaft held in a spinning centre but I saw it as more work if in the future if I had to change the diff over again. Saying that it would mean not having to under cut the spline ramps and you would only need to shave a mm off the shaft end for peace of mind ...
Might get Jim to give it a try on the old UJ and pick up another 800 shaft ..

I'm sure the old shaft would have lasted another 10k but I had mistakenly assumed the UJ would have been marginally softer and would have shown more wear than the shaft but it was near perfect.
So anyone else that finds a little wear on the shaft , check it against the service limits then refit and forget,