R51/3 Throttle Cable Conundrum

[Darryl.Richman]

For these throttle cables, definitely follow Vech's advice. If you're making a cable and the cable end has a through hole -- like the ball shank end that fits into a barrel on a brake or clutch cable -- pull the cable through and then unwind and spread the strands. Once you solder it, it will never come apart, because a lot of the load is being held by the strands against the cable end.

[Seek]

Spreading the strands is more important then the type of solder. Cables have been soldered with tin/lead mixtures since the dawn of motorcycles. But when you don't spread the wires coming out of the nipple thoroughly, you have a very weak connection.
95/5 certainly is stronger, but needs a higher temperature and flows less greedily into all the little crevasses.
You also need a proper flux. With stainless wires you need a special flux. Wash off the residue well.

[Tinkertimejeff]

I used one of those quick action throttles on my Rennesprt Replica project and ran into the same issue with the cables. I simply worked the little metal cup off the end of the cable outer sheath, measured out how much of the outer sheath needed to go and carefully unwrapped the outer metal sheath and then cut it away. I gently and carefully filed down the sharp edges and stuck the metal cup back over the end of the outer cable sheath on both cables. Works great and no need to solder or buy custom cables.

[niall4473]

I have made many cables, including Norton clutch cables, which get a very hard life, always using 60/40 solder, and have never had a nipple come off, but as I said, I was told by a training instructor on a gas fitting course never to use 95/5 solder on anything brass as they were not compatible, I will see if I can remember why.

[johnlacko]

Yes, as member R68 points out, you do in fact have a Magura race throttle on there. They were a faster acting unit, as the stock BMW throttle required two fist-fulls to open up wide. The benefit to the stock setup is a much more precise throttle control, which most BMW owners enjoyed - but it’s not what you want for racing. The later versions of the Magura throttles like the one in the alloy tank photo allowed for the cables to be replaced without any tools (as in a pit stop for a race, or after a crash on an off-road bike). The earlier type like you have had to be disassembled. Magura offered these throttles in both 22mm and 25mm handlebar versions, and with single or double-cable pulls. They still pop up new in the box a few times a year on eBay. I’ve had a few over the years, but I don’t recall whether they used a stock BMW throttle cable or not - which you seem to have discovered! Here is my own 1970s Magura ‘trap door’ throttle from my 1973 BMW F750 Imola racer, one of two made that year, and currently under restoration. The third photo is of the other one, which is in Germany in the BMW collection.

[Vegtamr]

I used one of those quick action throttles on my Rennesprt Replica project and ran into the same issue with the cables. I simply worked the little metal cup off the end of the cable outer sheath, measured out how much of the outer sheath needed to go and carefully unwrapped the outer metal sheath and then cut it away. I gently and carefully filed down the sharp edges and stuck the metal cup back over the end of the outer cable sheath on both cables. Works great and no need to solder or buy custom cables.

That's the conclusion I came to as well. I actually had a pair of fairly new cables that had come off of a much later bike (think it was my R100R), and I decided it was worth a try. I peeled back and trimmed the sheath, slid the ferrule back into place, and applied a short length of heat-shrink tubing around the joint for good measure. I had to grind down the fitting at the carb end to fit into the slides, but it worked just fine in the end.