My MK 2 has had it’s brakes de - linked by the previous owner and although the front brakes are really good, the back brake is useless. It won’t even stop me from a crawl.
The Spada is still linked, and I like it, so I am looking to re - link the Le Mans. However I am missing the proportioning valve thingy and can’t seem to find one as a spare on the usual web sites.
I have seen one for a Ducati that looks exactly the same but it’s a new part and I’m unsure if it will work.
Ideas anyone?
The Mk2 would have had a simple manifold rather than a proportioning valve. The manifold should be easy to find. You also need to check that the rear master cylinder is a PS15 and the front one a PS12.
Is the manifold the part that sits behind the grab handle. Left side under the seat and just behind the side panel. It links the rear m/c to the front and back calipers?
Yes, that’s the one. There’s plenty about secondhand and also proportioning/limiting valves if you want one. You might not find the exact one but not critical in my opinion. You might get more out of your back brake if you change the master cylinder. If you have Guzziology there’s some stuff in there.
Also worth checking that the fluid flows from Master Cyl to caliper to check the pipework is clear, i had one that was blocked.
Sounds like you might have some air in the system, de linked my 1000s, used a H*nda vfr front master cylinder, rock solid front brake, the back brake can still lock the wheel (when asked nicely), standard rear master cylinder, took a while to purge the air, try cracking the banjo on the back of the master cylinder under pedal pressure, that’s where the bubble was 
I have bled the rear so no blockage evident, but I will try again. Thanks all. 
My Mk3 was de-linked when I got it and suffered from the same issue.
Very good and progressive front braking from the original handlebar master cylinder, even though it it technically too small a diameter fro twin callipers.
(it’s fine with bedded in pads and stainless brakelines)
The read however was diabolical, the master cylinder being designed for operating two disks.
My solution was to find a 12mm Ducati Brembo master off ebay and fit that ( http://www.ebay.co.uk/itm/360446989620?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT ) It did need some lathe work as it was originally intended to go on the other side of a bike, so the mounting holes need reversing.
I now have well matched brakes with a rear I can apply on it’s own, should it be necessary in the winter on wet leaves for example.
Also with 4 bikes in the stable, it provides some similarity of braking setups between them.