Author Topic: Yamaha rd125dx 1981 front brake restore  (Read 276 times)

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Offline matwom

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Yamaha rd125dx 1981 front brake restore
« on: August 05, 2022, 06:16:26 PM »
Hi guys

I’m starting the restoration of the front brake system, I’m stuck already lol , try not to laugh,,
Does anyone now what size of the front master cylinder is ? I have no idea , I’m looking at buying
a repair kit but I’m not sure if it’s the correct size , the one I’m looking at is from yambits and it’s a
14 mm repair kit , but it says on there site to make sure it’s the correct size before you buy , Iv looked on my front brake for a size but cant tell what it says , any help would be great , cheers guys

Online Astute Greaser

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #1 on: August 05, 2022, 06:51:31 PM »
It should be cast in the body of the master cylinder presuming its an original Yamaha. Lots of aftermarket.
Not the same m/c but something like this. Mine says 14mm for my 200

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #2 on: August 05, 2022, 07:01:15 PM »
Hi mate

Thank you so much , think mine is a 14 mm by the looks

Online Astute Greaser

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #3 on: August 05, 2022, 07:07:19 PM »
Glad to help. Yes yours is 14mm.
Don't forget to get new sealing washers for the Banjo and the rubber Gaiter over it if needed

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #4 on: August 06, 2022, 09:04:13 AM »
Hi guys

Iv ordered all the parts apart from banjo bolts are out of stock till god nows when !! Just spoke to yambits ,
Does anyone now the correct size so I can order online ?
It tells you the m10 and 1.25 pitch but what’s the length?
Cheers guys

Online Astute Greaser

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #5 on: August 06, 2022, 10:54:17 AM »
I believe you got a parts list so try Fowlers, they should still do them.

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #6 on: August 06, 2022, 03:09:36 PM »
Hi mate
I forgot about fowlers , cheers mate

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #7 on: August 07, 2022, 10:34:42 AM »
Hi guys

Mostly  Everything is on order for brake restoration  , the brake has old DOT fluid in at the moment, I’m replacing the line with a new one and using a rebuild kit but I’ll be using silicon brake fluid when reassembled ,,
Iv never done this before and don’t really now what cleaning solutions to use (if any) .
I’ll be restoring / painting the main top Reservoir and the bottom calliper.
Any help with this one would be great as it’s a number one safety issue doing this job correctly, cheers guys , thank you 

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #8 on: August 07, 2022, 11:33:01 AM »
Silicon DOT 5 hydraulic fluid seems like good idea as this will not damage your paintwork.
However the rubberbseals in your m/c and caliper kits are not likely to be compatible and will fail  :o :o :o :o :o
The brakes originally used DOT 3 and this has been superseded by DOT 4 although I believe DOT 5.1 is compatible but its up to you!!
https://epicbleedsolutions.com/blogs/faq/whats-the-difference-between-dot-4-and-dot-5-1-brake-fluid
Buy proper paint for car brake calipers. I used E-Tech, which came with brush and aerosol cleaner. Hand painted and then I put coat of 2 pack lacquer over, not that its necessary but it made the matt black look satin. Gloss black is readily available but satin is pig of colour to get.
The first swear will be to remove the main circlip that is buried down the m/c. Move the eyes of the clip over to the oval section and then you can just fit the pliers on. Mine I modified/ thinned down the pliers to do this. There are special circlip pliers for sale but dig deep.
https://www.amazon.co.uk/SPEEDWOX-Cylinder-Handles-Internal-Motorcycles/dp/B09FZFKYHB/ref=asc_df_B09FZFKYHB?tag=bingshoppinga-21&linkCode=df0&hvadid=79920879569104&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583520399159156&th=1
« Last Edit: August 07, 2022, 11:47:36 AM by Astute Greaser »

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #9 on: August 07, 2022, 11:53:48 AM »
Cheers mate
What do I use to clean out old brake fluid and flush the existing old fluid out with ?

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #10 on: August 07, 2022, 12:41:53 PM »
Initially went in to my paraffin parts washer. Then stripped off old paint. Took apart and used cloths & big aerosol can of brake cleaner to get worst off.
Dropped all bits into ultra sonic cleaner because I have one but you can skip this. Dried and carefully used spray again. Do not use WD40 !!!!
Within the reservoir there are two holes which you must ensure are not blocked. One is very small but actually the hole is stepped halfway down to an even smaller size  ??? . Pull a wire from your wire brush with pliers and gently poke down the holes. Do not stick a drill down there which I have heard  :o :o.
Once reassembled, then I masked and painted.
As you have recently been using the bike hopefully your pads and piston will come out easy. If not then come back as there are tricks for calipers  ;)
Same when comes to priming and bleeding.
« Last Edit: August 07, 2022, 12:51:05 PM by Astute Greaser »

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #11 on: August 07, 2022, 01:49:06 PM »
Hi mate
What’s a brilliant description mate , thank you so much , I’ll have to get some brake cleaner and start the restoration, cheers mate

Offline [el_tel]

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #12 on: August 07, 2022, 03:17:01 PM »
When you want to get that circlip out of the master cylinder, put the bolt that holds the brake lever back on (but not the lever itself), then you can use a small screwdriver (or something similar) and the bolt as a pivot to push against the springloaded piston.
During reassembly, use brake fluid as a lubricant to get the piston with rubber seals back into the cylinder.
1981 RD125DX in Hammeright Red

Offline matwom

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #13 on: August 11, 2022, 10:35:52 AM »
Hi guys

Quick update on the front brake rebuild -
I dissembled the cylinder and cleaned casting so it was spotless with brake cleaner , tried to fit new rebuild kit and the piston thing in the Center seems to be slightly to big on the diameter, I can get it to go in with a lot of force and the I need to use pliyers to get it out ? Something is not rite , also the new bleed screw I brood around 5 mm sorter than the original so no good either , I can’t believe my bad luck with parts ,,
My cylinder is 14 mm I brought a 14 mm rebuild kit ,,
Jesus this bike is killing me !!

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Re: Yamaha rd125dx 1981 front brake restore
« Reply #14 on: August 11, 2022, 01:27:47 PM »
It's hard to comment without seeing it.
There are many variants by Yamaha of the 14mm m/c. Earlier in this thread I showed you mine which has totally different piston, so its important to get the one you need.
I suspect you have  :-\
Its important to lubricate the bore and seals before attempting to assemble with the hydraulic oil you plan to use. The one I've just done, the primary seal was supplied loose and I had to think about how to fit without overstretching and making sure it was the right way round. Both seals are like cups, as the brake is activated the cups expand as they push the oil forward giving a very tight pressure seal. When you release the lever, removing pressure, the spring returns the piston the cups of the seals collapse (but still seal) allowing the piston to return.
It's annoying when we get a leak we have to buy a full reconditioning kit when we only need a 50p seal  >:( But nobody will sell them to you  :'(
My son's Diversion had problem with m/c and after kit still leaking, gave up and bought Chinese pattern with lever and matching clutch for less than the kit  :o However he's not worried about originality  ::)
The bleed nipple, well what's wrong with reusing the old. Do fit a cap to keep crap out.
« Last Edit: August 11, 2022, 01:30:25 PM by Astute Greaser »