Tokico rebuild Locked pistons

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RebuilderGuy
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Joined: Mon Jan 27, 2020 9:02 am
My Bike: ZXR 400R

Tokico rebuild Locked pistons

Post by RebuilderGuy » Thu Feb 13, 2020 8:07 pm

Hi there,

so im rebuilding a zxr400 and atm im rebuilding the brakes. I got new stainless pistons/seals/fluid and lines (HEL). Now here is my problem. When installing the pistons i pushed them all the way back. Because of this the new fluid cant reach the back of the pistons and push the pad on to the rotor. I dont have an air compressor and i was wondering if i bought one of those brake bleeder pumps i could suck a vacuum and pull the fluid thru?

Ive also read on another forum that you can use a grease gun for this?

thx for the help in advance!

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banner001
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Re: Tokico rebuild Locked pistons

Post by banner001 » Fri Feb 14, 2020 6:59 am

Grease gun should do it.

You need to buy some citroen 2cv grease nipples as they are M7 x 1.00mm, use these instead of the brake bleed nipples and pump away.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

Ewetea
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Re: Tokico rebuild Locked pistons

Post by Ewetea » Fri Feb 14, 2020 7:41 pm

As I understand your post: you have dismantled the existing calipers, removing the original pistons, and rebuilt them with new seals and stainless pistons, pushing them to the back of the calipers. Brake fluid can still reach the back of the pistons and push them out. Since that doesn't seem to be happening for you, it is probably because the system is new and needs priming. I trust that you renewed the seals in the master cylinder as well. The procedure for purging air from brake systems is to fill the master cylinder with fluid, connect a pipe to one of the bleed screws, loosen it, and squeeze the brake lever. Then close the bleed screw before releasing the lever. This prevents the fluid that you pushed down the pipes being sucked back up. This is tricky if you are trying to do it yourself, so a purging kit is very useful. It comprises a reservoir to which is attached a plastic pipe with a non-return valve on the end. The free end is pushed on to the bleed screw, which can be opened and left open because the non-return valve will prevent negative pressure when the lever is released. Since there is so much air in the system it will take some time because as you are trying to push the fluid down one pipe, the other pipe has the air in it compressed by the action, which will push the fluid back towards the master cylinder when the lever is released. Once sufficient fluid has reached one pipe, you can switch the kit to the other side to fill it. Start by squeezing the lever slowly and release it slowly, watching for the appearance of bubbles in the master cylinder reservoir. Once they clear you can start the purging process. It will take time, so be patient. I suggest that you recycle the fluid that emerges from the bleed screw. I know that it will contain tiny air bubbles, but until the system is full of fluid you don't want to waste a lot of new fluid. Once the system is full, you can then use the new fluid. The problem with purging a new system is that the air is being forced down the pipe, and naturally it tries to float back up the pipe. When I have replaced the seals, while the calipers are off the bike, I have attached the lever and master cylinder to a tube clamped in a vice, with the calipers supported from the garage roof. Thus when the lever is squeezed the fluid pushes the air uphill and out of the bleed screws.
But- if you are trying to dismantle the calipers, then the grease gun method can be used!!! But the purging routine still applies!

RebuilderGuy
Posts: 7
Joined: Mon Jan 27, 2020 9:02 am
My Bike: ZXR 400R

Re: Tokico rebuild Locked pistons

Post by RebuilderGuy » Sun Feb 16, 2020 3:21 pm

Hi all and thx for the help,

I made a total fool of my self lol. I repainted the calipers and wanted to avoid DOT4 drips on my fresh paint.
I didnt unscrew the bleeder screw far enough out.....LOL.

bleeded the brakes and works fine now lol.

again thx for the help!

Ewetea
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Re: Tokico rebuild Locked pistons

Post by Ewetea » Sun Feb 16, 2020 8:41 pm

It takes a man to admit his mistakes! Thanks for letting us know. Been there, done that. First bike I had was a 250cc Royal Enfield. I lifted the cylinder head to decoke it and grind in the valves. After re-assembly I couldn't move the engine on the kickstart. When I removed the spark plug and peered in the hole I could see the rag I had put there to stop bits falling in the cylinder!!

RebuilderGuy
Posts: 7
Joined: Mon Jan 27, 2020 9:02 am
My Bike: ZXR 400R

Re: Tokico rebuild Locked pistons

Post by RebuilderGuy » Mon Feb 17, 2020 9:32 am

Haha nice, that could have happend to me lol

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