RD master cylinder rebuild kit question(s)

[RDDave]

Okay, I am riding the struggle bus on this one. Need to rebuild the master cylinder on my RD350. All of the rebuild kits that I have seen only have one seal on the shaft. Mine has 2 seals on the shaft. And I see that what seems to be the same kit priced anywhere from about $15 to $35. In the pics, many look exactly the same. Some look different one way or another, but most look exactly the same. They just have 1 seal.

So, are they the same? Is one seal rather than 2 going to work okay? My bore looks good, no pitting or deformities.

Any suggestions here would be appreciated. I didn't think this would be as big a deal as I have managed to make it.

Thanks, guys.

[m in sc]

https://www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/frame-related/brakes/yamaha-rd350-all-rd40076-78-front-master-cylinder-rebuild-kit-reproduction/

has the seal and the cup.

[RDDave]

www.ebay.com/itm/162780242494?_skw=rd350+master+cylinder+kit&itmmeta=01JKY916A7NZV4D42TS46RRAN6&hash=item25e675623e:g:bngAAOSw4X5nP2V9&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1eHNolawRbOU4O95TW0bbjvpnpVZuKIm8Tifqag7RiDCbDQLzWcPmsO%2BYKDwuNXhbZ6avHv5liWYocAMkLjHr5jBcayouC8REpbhdYtxHnJYj5onlMa6464BNYlsrfh4HBTjWN7fAviRiN8fjroJKzMrwXxcLf%2Fh1D7uj8WQ4LSIdt4w0rYKfseC4%2FUL6mTWw%2BLapdsL8I4Rj4cM2Ai6CP3oNuIFXm5g9FNgLISmwfyYdYIZIIHB3VrILv8GCh3EwTypCb%2FmEbhGAKH7kqb48E9p%2F8CHi4a8NTktZ1Es%2FdQXg%3D%3D|tkp%3ABFBMpuWEyZ9l

www.ebay.com/itm/134513478957?_skw=rd350+master+cylinder+kit&itmmeta=01JKY916A79HJDXWQJ32GX375X&hash=item1f51a0cd2d:g:KX8AAOSwYJVkJsEL&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1ehODWiQYJfhjdEGmK1JDznPvq5mIPwja%2F1h28IJ2Quelh9vcC6PSJSJcZzSmU7XInxRPHaicO7OGQW3fcpx9wEgMXeDdN8kM97v8tO%2FVfEVe5j5PxwIPPZmlCJJcsFy8e89thR4yRkOboiM3WFeN1Nkd7zETKpmm4rJ6ecVR8QRFSteGisvi2Rbc7cmPnpwtikHw720wBRrq0R356f9kXQ7Jl1aYUnwMjDxFq6Zya8i6y4LvO3xGX8iWZarNxH1J2N3EdtamRlzdyRgm4oxhk1SR6bDlY%2FDgDeeun64HXMhg%3D%3D|tkp%3ABFBMpuWEyZ9l

www.ebay.com/itm/314319479748?_skw=rd350+master+cylinder+kit&itmmeta=01JKY916A7G5RD627Z4VZC4ZVA&hash=item492ee6a3c4:g:mJQAAOSwJmVjv3vr&itmprp=enc%3AAQAKAAAA4FkggFvd1GGDu0w3yXCmi1ePoLuEwNSbxs5ynlhZPYsnNTE%2BtEwybKH%2BHzSk3tqIxYWNMwRisf%2B5RYrKkOtqRWSrCmtngCByIeQQjjMPfie3LV7hg74VxPCzb0LEq%2BG%2BTvwavsD1lWjYUr9mXs0%2FMeXQE3wTC3kK3AQ4RE0VMQ2AtTaYwG62adIwmEyyqBJyIJaRcf3uxuHl%2F1iWSBPHvW3lsfPaCTbu7NVBNgRDTBu9QwrLJs4PwRq0AXXYySPoxsnQNRBzObp8xiUUFLMTHScieTgkIZi%2BO6FIjai%2BRJm0|tkp%3ABk9SR6jlhMmfZQ

There are more, but you get the picture. What, if anything is the difference between the Economy kit and these? And they all have only one seal on the piston. Am I making too much of this? They all just look so different from the one out of my master cylinder.

[m in sc]

they all have the same parts.

I'll be honest, the 5/8 master is too big even on a stock setup, brake feels wooden to me.

on my 72 r5 w rd front and stock brake, i run this exact unit.

https://www.ebay.com/itm/393221734319?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=3jd7hlyvqfs&sssrc=2047675&ssuid=9DXeqLNdSLW&widget_ver=artemis&media=COPY

[2T5]

So, are they the same? Is one seal rather than 2 going to work okay?

I don't have an answer for you but maybe post a pic of your setup. Could a previous owner have put an extra seal in for some reason?

[Jspooner]

All of the kits you gave links to show the same parts as the one from economy. I'm not sure what you are seeing. FWIW, spend the extra money and get the kit from economy.

[RDDave]

I would consider doing that.

The ONLY thing I would ask is for you to give me a valid reason(s) for spending over twice as much for what looks like the same parts. Plus the ordering process and return process (if needed) are more complicated going your recommended route.

Not trying to argue, just looking for the "WHY".

[RDDave]

Here is the side by side:

[m in sc]

the one on the left is missi g the cup seal. one on the right is...? not an original rd one. why spend more.. I mean, fair point. but john def makes sure the quality is good, evay and Amazon sellers give about 2 fucks usually.

[RDDave]

So, the one that came out of my master is NOT correct. It worked fine until last fall. The repair kit shown is obviously missing a seal. It is already on it's way back. But it also had a seal that did not go over the plunger. That seal had a nipple in the center and I cannot figure your where it could possibly go.

While I appreciate your suggestion on the replacement master and is really the the better way to go. I would just prefer to keep the stock look on this 4,000 mile bike to the extent reasonable.

I know, I know, I am just making it more difficult. 

[1976RD400C]

That nipple plugs into the brass piece on the small end of the spring.

[RDDave]

Thank you!

That was the only place that seemed possible for that seal to 'plug' into. But without anything to reference, I was not at all sure.

[m in sc]

the replacement master actually looks just like the stock one TBH.  yeah, i can see the confusion now on the seals, i guess ive just done them a lot and didn't see the issue. but i get it now.

[RDDave]

Way back when, I was around these bikes when they were new. I did a some amount of work on them but most of my experience was with the Enduros. So, these many decades later my RDs need things done to them that I have never done. This stuff isn't hard, it's just that I lack the experience to know what is what sometimes. So I cannot tell you how much I appreciate this forum and the knowledge and experience that is readily shared here.

Thank you all so much! 

[RDnuTZ]

Same. I grew up with the Enduros and even Trailmasters before that! Got my driver's license 1973 and into Yamaha street twins shortly after. I was poor but had time and endless curiosity and passion for all things 2-stroke related. Now going on 67 soon and have more $ but not as much energy as I had back in my youth. But yeah, learning these all from ground up again, but at least retain some basics as I never quit buying and wrenching completely