Yamaha RD350LC caliper & new bleed nipple

1980 Yamaha RD350 LC 4L0 Restoration – Part 6 – Reassemble is a Reversal of Removal!

Project Elsie Episode 6 – Let’s get together again.

It seems weird but at last something is actually going back together rather than being taken apart. The brake parts that were ordered from our good friends at www.wemoto.com arrived less than 24 hours after the order went in – all present and correct. This enabled me to do a bit of work while waiting on the engine parts. Talking of which, there is some very good news on that front as Ian at classic-motorbikes.net has sourced an unmolested pair of exhausts so that’s another big item off the “to find” list, well done bloke!

First job was the master cylinder, yeah, I know I said it was putting stuff together but I took it off the bike first. The piston was very well jammed full in the bore so a bit of careful persuasion was needed to get it back out. The hardest part was getting the circlip that retains the piston assembly out. There is a dust cover that goes over it that wanted to fall to pieces rather than be removed from it’s home of 40 years. I had to dig it out with a dental pick and then get the rusty old circlip out, which is rather deep so my usual circlip pliers wouldn’t reach it. A pair of dental picks did the trick – not easy but it didn’t take long.

When comparing old with new it quickly became apparent that it’s a good job we decided to do it as the old parts looked very sad and sorry for themselves.

Yamaha RD350LC caliper re-buildThe wemoto supplied kit came with a small pot of RR red rubber grease – no other grease should be used on or around rubber components. The red stuff is vegetable oil based, it mixes ok with DOT3 and DOT4 brake fluids and will not cause any harm to the rubber – the same can not be said for mineral oil based greases. The new parts all fitted perfectly and for the first time in I don’t know how long the master cylinder is now working as it should. I have put it back on the bike, when the calipers are finished it will all get joined up and the whole system can be tested.

The parts for the calipers also arrived so I thought I would get on with them too. They were already stripped apart from the slide pins and the sliding blocks that allow equal pressure to be exerted by both pistons when it comes to braking time. They came out easily enough – each pin has a split pin that has to be removed first. It’s best to so one caliper at a time as they have shims that allow the calipers to slide without juddering, it’s too easy to get them mixed up if you have multiple parts on the bench. Also take care as the shims have very small springs behind them that keep them in contact with the caliper body – you don’t want to lose them.

The calipers on this bike had a large amount of grease between the shims and the caliper body, all the references I can find make no mention of grease in this area and I’m pretty sure it shouldn’t be there. If that were to get hot it could easily drip on to the disc or pads and while that might be highly entertaining for onlookers it wouldn’t be at all good for the rider. They have been carefully cleaned and put back together with new dust seals on the sliding pins. A little smear of the red rubber grease helps the pins to go through, they can be a bit fiddly. New split pins have been fitted to retain the sliding pins. I noticed that there were no retaining clips holding the pins in when I got the bike, which was a bit of a worry. Some will be sourced to make sure the pins can’t work their way out and render the brakes useless.

So it”s all looking much better now, next job is to install the new seals, dust boots and the pistons.

The parts were another gift from the Gods, or in this case Wemoto. The seals and pistons all slid in to place perfectly, just as one would expect. I can’t stress how important it is to make sure that the grooves that the seals go in to are absolutely clean and devoid of corrosion or any other nastiness. If the seals don’t slot in easily, fully remove them again and investigate why. The pistons should slide in with moderate finger pressure and should be smooth all the way.

So now it’s on to the next little hiccup – bloody nipples again!! The one that I retapped is fine, the other one isn’t. I am guessing when it came out the thread picked up as when I went to bleed the system the threaded hole stripped!! I had hardly any pressure on it so it must have been damaged, maybe it was before I started and it was only corrosion holding it in there. Anyways the chances of getting another caliper are pretty small so my only option is to retap and go up a size. There may be other fixes but as we are talking brakes this is the only solution I feel comfortable with.

The next size up is 10mm, there are re three different tpi’s available for 10mm 1mm, 1.25 and 1.5. I had a set of 1.5 taps on hand so that was what I ordered. I got a couple of different types as I wasn’t sure which sort was going to seat best on the hole that was designed for the original smaller diameter nipple. I had to use a bottoming tap with the end slightly ground down to get my chosen nipple to seat securely – no big deal I can always grind it back if the next job demands it.

Bleeding the system proved to be a bit of a challenge – I think what sometimes happens is the seals in the master cylinder don’t seal at all until they have slight hydraulic pressure, therefore when the system is empty it’s quite hard to get things started. What I did was to use a syringe full of clean DOT4 brake fluid and to crack open the nipple on the left hand caliper to force fluid back up the pipes. There was much gurgling going on as the air was expelled through the master cylinder reservoir. Once air stopped coming out I reversed the process and bled the system in the usual way. For the first time in many years Elsie now has brakes that work and feel pretty good. I think they would benefit from braided hoses, I think they would have better feel but they certainly work as is

Yamaha RD350LC caliper & new bleed nippleThe appearance of the left caliper is slightly changed due to the oversize nipple but it would take a keen eyed person to spot it, unless of course I went and told everybody. Doooohhh!

So that’s it for this time, thanks to anybody still reading, I hope you are enjoying it. Next time I will be taking the forks off and rebuilding them with all new seals and stanchions, the ones on there are not pretty. It’s another one of those things that appears to be cosmetic but it essential to the safe operation of the bike, you don’t want forks leaking on to your brake discs and you don’t want the bike to handle like a dog so they have to be done. Seeya next time.

Article sponsored by Wemoto.

Article provided by David Powell of Boston Bike Bits.

Boston Bike Bits