RD350LC calipers

1980 Yamaha RD350 LC 4L0 Restoration – Part 5 – Brakes

Project Elsie Episode 5 – give me a brake!

Yamaha RD350LC caliperIt was decided by the powers that be i.e. Scott and Ian at www.classic-motorbikes.net that while the engine gubbins were off at the machine shop I should turn my attention to the brakes, which at the moment won’t do a lot of braking because they are broken. In fact it’s true to say that one of the calipers is even more broken now than it was before because I had a spot of trouble with my nipples. Now before you start tittering like Finbarr Saunders with his double entendres I shall remind you this is a serious build started from the bottom up, we don’t want somebody falling off and scratching their helmet on a thistle due to dodgy brakes – it needs taking seriously.

The calipers look horrible but will clean up ok, it’s what is inside that counts and we won’t know that until they are in pieces.

So – back to my nipples. Both were extremely tight – one gave way after a moderate application of heat, I wasn’t worried about harming the seals as they will be replaced anyway. Turns out my other nipple was still very hard. I started trying to treat it gently while warming it up slightly but it wouldn’t budge. In the end the inevitable happened and it snapped clean in two with the end below the body of the caliper so my only option is to drill it out and re-tap it.

These are a bit weird as even though they are Japanese the nipple threads are 5/16 of an inch and 20tpi. Fortunately one of my other hobbies is making steam engines and I have a tap of the correct size and form – it’s a fairly common size on miniature steam fittings. I just have to drill out the old bit, an operation I hate as it has to be 100% accurate or the new nipple – with which I am now obsessed – won’t seat properly. Before I hear you cry “use an easy out!!” I hate those things. The holes in bleed nipples are pretty small so any easy out or similar will be thin and pretty brittle – if one snaps off it’s game over and we will be looking at a replacement caliper – if I did that I could expect Mr and Mrs Nike to pay a short sharp visit to Scrotum Land so I won’t risk it.

RD350LC bleed nippleGreat care will be taken to make sure all traces of swarf are removed before the whole caboodle gets re assembled.

So now it’s on to the next part of the brake job – getting the old pistons out of the calipers – they are very, very tight, fortunately I have the correct tool for the job. Well actually as of today I had the right tool (are you still here Finbarr?) for the job. The inner of the pistons seem to be about 31mm, the largest fitting I had for my piston extractor was 30mm, I thought I would get away with it but overstretched it and broke it. Didn’t matter as it split in half and I was able to still use it. I have never had such a fight to get pistons out before, I had to use rather more heat than I would have liked and a lot of penetrating fluid before they would shift. It is going to be quite a job cleaning the two dust seal grooves but weirdly the two oil seal grooves are clean. I guess the DOT4 brake fluid must have preserved them.

Anyway having got the pistons out I’m not happy with them, there is some pitting towards the outer. We could possibly get away with it but with new pads the pistons sit further back towards the oil seal and if the pitting goes back that far then they could seep. It’s brakes so it’s not worth taking the risk. One of them also appears to have been gripped in a vice at some time and is not perfectly round.

RD350LC caliper boreSorry Scottie I know I already gave you my shopping list but I won’t compromise on safety and I know you won’t either. Fortunately all the parts we require for this exciting episode are readily available from our good friends at www.wemoto.com who have kindly agreed to sponsor this series of articles and provide all of the parts we need. I have to admit to being taken slightly aback at just how many parts they have for these bikes, and hundreds of others too for that matter. It’s going to save us countless hours as we won’t have to go from place to place looking for all those small but vital parts that can be so hard to find.

The insides of the bores look pretty good, there are a couple of very light score marks but the grooves have cleaned out quite well with a rotary brush in the Dremel and a selection of dental picks. It is essential for the grooves to be as clean as possible as if they are not the seals could leak or the pistons could be prevented from returning. In brake calipers the seals have two jobs – the first is obviously to stop the DOT4 fluid coming out and ruining your day but the second less obvious function is to cause the pistons to retract when the brakes are at rest. The seals distort as the pistons go out in such a way that they kind of act like a spring – without this function the brakes will bind. I see it a hell of a lot on older bikes – you get a build up of corrosion in the grooves, the seals become tight and can’t do the retracting bit.

This is definitely one of those jobs that needs to be done carefully and with the correct tools. The calipers are hard to find now so great care has to be taken not to damage them but more importantly brakes save lives so if you don’t feel confident it’s one of those jobs best left to somebody that does.

Anyways, that’s about as far as I can go now until parts start dropping through my letter box in the next couple of days or so. In the next pant wetting exciting episode I shall be rebuilding the front calipers, the front master cylinder and having a look at the rear brake. Might ask Scottie to order a new front tyre and tube – I also need at least one new stanchion as the ones on there are pitted, not given them a proper evaluation yet though.


Article sponsored by Wemoto.

Article provided by David Powell of Boston Bike Bits.

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