Shimano Saint lever overhaul - sticky lever piston/plunger

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Shimano Saint lever overhaul - sticky lever piston/plunger
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Posted: Jun 14, 2021 at 4:19 Quote
I'm trying to find instructions on how to strip down Saint BR-M820-B levers. I've found info on XT levers, but the internals are a little different, the Saints dont have the plastic guide strips. I've removed the lever and plunger, but cant get past the plastic cap (part of the free stroke adjustment) to get to the piston and spring which is where my brake's problem seems to be. I've tried using a 2mm allen key to push from the hose end, but nothing budges even slightly.

Has anyone completely stripped down and cleaned a Saint lever?

I suspect I have done something to damage the seals, the spring isnt pushing the piston back out and the lever is 'floppy'. The issue also seems to have blocked off the bleed hole, as using a funnel to try and get more oil in there does nothing at all (nor can I force oil through from the calliper end).

I think I'm looking at new levers, I've just tested the callipers with an old XT lever and fortunately it looks like I can replace the Saint levers with XT or SLX which are more easily available.

Thanks

[sorry, originally posted on the wrong forum]

Posted: Jun 14, 2021 at 5:33 Quote
I've totally stripped down both my SLX levers a couple of times each and am sure your Saints are practically the same internally.

Not sure what part you're describing as 'the plastic cap to do with the freestroke adjust' is? There is a small plastic lever that pushes on a 'ball' on the plunger that sets freestroke, I assume you mean that, if so it isn't related to the problem whether you can get past it or not.

Once the lever and plunger are removed the pistons naturally extend out of the piston bore just through the release of the spring tension, far enough it can be removed with finger tips. The fact yours doesn't and you can't even push it out from the hose end suggests the spring has broken, maybe even the piston itself or one or both of the piston seals has moved out of their normal position as you suspect.

I reckon the piston is stuck at the bottom of the master cylinder blocking the reservoir port which is why you cannot get fluid in from the top and really stuck fast if you can't push it out with fluid or Allen key.

I'd say it's probably terminal because even if you do manage to get the piston out it's likely to cause irreparable damage to the cylinder bore.

Absolutely fine to replace with an XT and all will function as before. The SLX lever not having the freestroke adjust (although it is simple to re-instate) would be the only difference between Saint and XT levers.

Personally I'd replace the lever and then try and force the old piston out just because I couldn't sleep not knowing what exactly has gone wrong! Smile

Posted: Jun 14, 2021 at 6:36 Quote
Thanks. Looking at vids, I think Saints are a slightly different design, but like you said, must be fundamentally the same.

The plastic cap I'm referring to is fixed to the body of the lever using a plastic clip around a tiny pin. It does protrude slightly when the plunger is removed, but won't pull out of the top of the bore because of this tiny pin.

And yes, I think the piston is stuck, somehow. What is really weird is that this happened simultaneously to both my brakes .. after a thorough clean (with product, but no jet wash).

I'll bite the bullet and find some XT levers.

Posted: Jun 14, 2021 at 6:52 Quote
So, resigned to needing new levers, I forced the piston out from the hose end with a 2mm key, which took considerable force. The piston seal is very swollen. The piston itself looks ok, and there's plenty of strength in the spring. But it was well and truly jammed, and still was when I cleaned everything and pushed it back in.

I suspect the cleaning product I used last time.... expensive mistake.

Posted: Jun 14, 2021 at 7:28 Quote
Ah, it does seem a little different than my SLX's from your description. Yes it's a strange one that any product have found there way in, caused swelling and to both levers, wow. It's not something I've heard of before.

If no damage has been caused, it's a long shot and nowhere near an ideal solution but maybe you could look into replacement pistons or at least the seals from one of those non Shimano ebay piston kits?

Such an irritation that Shimano don't supply any kind of replacement small parts leading to having to replace full expensive units for the sake of seals that cost pennies.

My sympathies anyhow and in your case 'the punishment doesn't fit the crime' springs to mind. Happy trails Buddy! Wink

Posted: Jun 14, 2021 at 9:22 Quote
I've had 3 Shimano levers get sticky and they would not free up with any amount of cleaning and servicing. I eventually decided I had nothing to lose and tried sanding down my pistons very carefully. On 2 of the levers this resulted in a usable lever that wasn't buttery smooth but was acceptable. However on the other lever I assume I sanded it too much as it leaked a bit.
Admittedly brakes aren't really the best place to be doing bodges however I felt it was safe as long as I periodically checked there was no oil leaking.

Posted: Jun 14, 2021 at 10:14 Quote
Cheers everyone. I'll try and find some OEM piston parts, but can't really take the chance on dodgy brakes as its needed for a 2 month trip soon. So maybe £90 for 2 new levers, could be worse(except the rest of the bike is on its way out and due to be sold...)

Posted: May 12, 2022 at 6:00 Quote
AgentDagnamit wrote:
So, resigned to needing new levers, I forced the piston out from the hose end with a 2mm key, which took considerable force. The piston seal is very swollen. The piston itself looks ok, and there's plenty of strength in the spring. But it was well and truly jammed, and still was when I cleaned everything and pushed it back in.

I suspect the cleaning product I used last time.... expensive mistake.

sorry for bringing this back from the dead!

I have saints also, and was following a video on tearing them down but where XT levers and different. So i know what plastic bit you are referring to, blocks the piston from coming out, the free stroke screw attached to it, and there is a little 'tail' that wedges itself within the pin at the bottom....Soooo how did you get this removed to get the piston out ?

https://youtu.be/oCLNc1U0sWQ?t=331

In this video, the guy removes it somewhat off camera, but with some force, once removed can it even go back on ?

Posted: May 14, 2022 at 11:01 Quote
Just use a pick and knock it out of the lever with hammer. In one direction of course, you'll see which one.
Yes, re-usable IF removed gentley )


Shimano Saint M820 internals

Posted: May 19, 2022 at 12:13 Quote
ka81 wrote:
Just use a pick and knock it out of the lever with hammer. In one direction of course, you'll see which one.
Yes, re-usable IF removed gentley )


Shimano Saint M820 internals

Knock the pin out, then it should come out ?

Posted: May 19, 2022 at 14:00 Quote
dan-king wrote:
ka81 wrote:
Just use a pick and knock it out of the lever with hammer. In one direction of course, you'll see which one.
Yes, re-usable IF removed gentley )


Shimano Saint M820 internals

Knock the pin out, then it should come out ?
it WILL come out.
The only important thing to watch over - direction.

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