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garynortheast Profile
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Registered: 06-2005
Location: Mid Wales
Posts: 1679
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Brakes/Tokico calipers


I've just read on another forum some interesting stuff about Tokico calipers (6 and 4 pot). It was actually to do with the brakes on an earlyish srad 750 but they use the same calipers as my 71F and the early 90's GSX-F 750 like my FiL's.

Ever since I've had the bike I've struggled to get the brakes to work well. There's a lot of lever travel before the brakes bite. It seemed to be caused by the pistons and pads coming to rest too far away from the discs and all the lever travel is caused by having to move the pistons a long way before the pads make contact with the discs.

I recently fitted all new pistons and seals to my front calipers thinking it was the pistons at fault. They were 22 years old and not in the best of conditions. It did improve things a bit and then fitting new pads made a further improvement but they are still not as good as they could be.

The post I read on this other forum spelled out exactly why.
There are two seals to each piston and the slots they sit in should be square. The inner seal is protected from all the crap that gets thrown at the calipers and pistons by the outer seal. The outer seal though is subject to a constant battering of rain, road dirt, brake dust and suchlike. This all finds it's way under the outer edge of the seal and bulids up in the corners of the square recess in which the dust seal sits. This forces the outer edges of the dust seal to sit slightly proud in the recess and, instead of allowing the piston to creep through it to take up the gap between pad and disc, grips the piston so that when the brake is released the piston and pad spring back and leave a larger gap than they should. Ideally the pads should be almost brushing the disc meaning that when you pull on the brake lever the fluid in the lines and master cylinder only has to move the pistons a fraction of a mm before biting on the disc.

The answer is to get the pistons out of the caliper and remove the dust seals. Then thoroughly clean out the square grooves in which the dust seals sit. You must get every trace of dirt and corrosion out and return the recesses to their original square condition.

Then refit new dust seals after having soaked them in hydraulic fluid, put the pistons back in by pushing them in and giving them a little twist as you do. Calipers back on, refill and bleed the brakes and you should now have good firm brakes.

Most of the time it is this and not air in the system which is causing spongy brakes.

---
Gary.

15/8/2008, 21:05 Link to this post Send Email to garynortheast   Send PM to garynortheast MSN
 
madmickyb Profile
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Registered: 01-2006
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Re: Brakes/Tokico calipers


i'l just add to this gary by saying if you have a "sticking" brake or a disc that gets hot this too can be the cause of it NOT always the piston seal sticking or pads siezing tho these too can be a factor ...

just my 2p ....

mick
20/3/2009, 0:27 Link to this post Send Email to madmickyb   Send PM to madmickyb
 
1965spenner Profile
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Registered: 09-2008
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Re: Brakes/Tokico calipers


I had a fair bit of travel on the brake lever on my 73a, I stripped and cleaned the calipers and found some improvement but it still didnt fully cure the excess lever travel. I spoke to Jay via the site the other year and he supplied me with stainless braided brake lines and a double banjo bolt so I could do away with the front brake line splitter. The improvement was instant and transformed the brake lever travel. I did find I could bleed the brakes then bleed them again the next day and get more air out, the answer was to bleed the brake, then leave the lever strapped back to the bars overnight then re bleed the following day. I think quite often we forget how old rubber brake lines expand with age when under pressure and overlook this.
By doing as you say with the pistons did improve my brakes but I got a better improvement with the brake line swap.

Cheers spenner emoticon
20/3/2009, 19:52 Link to this post Send Email to 1965spenner   Send PM to 1965spenner
 


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