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Frankenbrakes and brake improvement discussion

Rockland

Turbo Monkey
Apr 24, 2003
1,870
262
Left hand path
Comparison of a metal piston from one of those first gen M755's vs. a modern plastic one. Oodles of miles on both, but only one of those levers leaked constantly.

 
Last edited:

Rockland

Turbo Monkey
Apr 24, 2003
1,870
262
Left hand path
Interesting comparison between the timing ports in the original lever & a more modern servowave lever. They've added to the total timing port area. Likely this is to allow the increased flow rate in the faster moving servowave lever piston. The modern levers seem to still have trouble keeping up.



 

englertracing

you owe me a sandwich
Mar 5, 2012
1,573
1,069
La Verne
With Shimano brakes it's more than just the finishing of the MC bore. It's a combination of several factors that people have come across. The crazy thing to me is why Shimano won't fix the issue. I have a hard time believing they can't understand the root of the problem with the resources they have. It's gotta be something beyond the engineering: targeting too low a price point - intended disposable - not rebuildable - ect. I've owned every generation of Shimano disc brake, starting with the 4-piston XT M755 derived from a Grimeca design. The usable lifespan of a lever is getting worse not better.

The MC pistons, on the majority of their levers are plastic, and have very small bearing land area. While the tolerance of piston in bore may be adequate with a fresh lever, the nature of the servowave action has a lot of side loading in the initial part of the travel. The plastic piston land wears down, and the bore eventually wears. The U-Cup seals also see more radial movement and begin to wear.

The Shimano fluid may also play a part, as suspected by others. I regularly ride in the winter with temps below 0 def F. The brake action certainly has the feel of a more viscous fluid, though I suspect that some of this is the caliper seals having stiffer movement. I began experimenting with Redline Likewater this past winter. It seemed to be a positive change, but I'd really need to try it in a fresh lever to eliminate some variables.

I'm tempted to experiment with refinishing the bore of a lever, and making new pistons (metal, with a wear band & different U-Cup seals). I've got a lathe, and material, it's more of a question of why bother. I've moved on to Cura 4's with sintered pads & big rotors.
Bother for sience.
Youd think a quality plastic piston made of delrin with proper length would work nice in an anodized bore.
 

HAB

Chelsea from Seattle
Apr 28, 2007
11,580
2,005
Seattle
Trickstuff had on their old website something saying that having 4 pads negates the advantages of having quads calipers.
I'm with them on that, if you have two pistons per side you can balance pad wear over the width of the pad with slightly larger pistons in front. You've also got more surface area for better heat management and less shit to rattle around.
 

Mo(n)arch

Turbo Monkey
Dec 27, 2010
4,441
1,422
Italy/south Tyrol

kingofsweet

Chimp
May 1, 2019
8
2
hi, first time i post here ^^
i have a set of shimano saint m820 from 2015 and the rear brakes feel pretty bad.. i bleed it several time but it's still feel mushy and inconcistent lever contact point, excepet when i pump it but after 10 second of release it's again feel mushy.. so i was looking for help at least resolve the problem or maybe change lever or caliper ? the front feel very good nice contact point, pretty stiff and good power but rear..
i was thinking of cura lever with saint caliper as it's seems to have a pretty early contact point ? any concerns ?

thanks already for the answer and help ! :)
 

kingofsweet

Chimp
May 1, 2019
8
2
The rotor si not perfect but only slightly bend.

Maybe again a new bleed..
Any advice for make a good bleed for evacuate all air bubbles?
Actually my pad are good, there is plenty of material but yesterday I cover those with oil.. So I need to change anyway but I don't think it's was the problem

Cheers.
 

kingofsweet

Chimp
May 1, 2019
8
2
Fredonner.. I just find the problem the lever is leaking from the gold part at the end of the lever
Des pièces de rechange ou je suis prêt à en acheter une nouvelle?
 

Olly

Monkey
Oct 1, 2015
157
76
Fredonner.. I just find the problem the lever is leaking from the gold part at the end of the lever
Des pièces de rechange ou je suis prêt à en acheter une nouvelle?
If the lever is leaking, you'd need to buy a new one. Shimano will sell separate levers and calipers, but none of the parts to go inside them.
 

kingofsweet

Chimp
May 1, 2019
8
2
hi, i come back with my lever leaking from the gold part of the lever.

after searching on the web it's totaly normal ! it's happen when you overbleed the brake and it's a security from shimano.

i open it and clean ( it's was really black inside.. ) and you have a rubber over a small hole so when it's overbleed the rubber contract and the excess go to this small hole ,after that i reassembly it and now it's work perfectly !

another thing i find it's about when you pump the lever it's have a smaller travel, what i find it's seem to be the difference in speed between the piston return and lever return difference.

because the piston return slower to his initial position than the lever so when you pump it quickly it's create more pressure.

now the lever feel nice and firm, just the deadstroke of the lever who is a little too big if you have idea ? but it's better now.

cordially, julien.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
just the deadstroke of the lever who is a little too big if you have idea ?
This is normal, particularly on Saint/Zee brakes because the deadstroke is quite long to begin with (even when new). Over time, the topout mechanisms of the lever piston can wear, causing the starting point of the MC piston in the cylinder to grow further from the timing port (which, once passed, closes the hydraulic system and allows the MC piston to push fluid to the slave pistons). This increases the distance the lever must be moved before the caliper pistons start to move.

Other types of wear also occur in brakes like the M820, for example wear in the bore itself, and all these wear points combine to increase lever deadstroke, or decrease consistency of the stroke length.

A good solution is to replace the lever/MC assemblies entirely, even though they may not be leaking. It is up to you if you replace with M820 levers or Cura levers, the overall stopping force may be reduced slightly with the Cura lever however I have not calculated this. The spreadsheet in the first post of this thread may give you some clues.
 

kingofsweet

Chimp
May 1, 2019
8
2
What a great thing I learn thanks you very much! For the moment I can live with that and as soon as the finance are 9kay I will upgrade to trickstuff dirrettissima lever ^^

But thanks for the help if it's go worse I know what I have to do.

The cura interest me because they say on review that the dead stroke was really short so that can be a good option if it's still very short with saint caliper
 

Inclag

Turbo Monkey
Sep 9, 2001
2,750
439
MA
Comparison of a metal piston from one of those first gen M755's vs. a modern plastic one. Oodles of miles on both, but only one of those levers leaked constantly.

Came across these while searching for elusive shimano piston seals. Does anyone know if there's any difference between slx, xt, zee, saint pistons? May be willing to give these a try.

https://m.aliexpress.com/item/32973287602.html?trace=wwwdetail2mobilesitedetail&productId=32973287602&productSubject=Bicycle-Titanium-Alloy-Brake-Disc-Lever-Piston-Repair-Part-For-SHIMANO-XT-M785-M800-Bike-Parts&spm=a2g0o.cart.99999999.309.6bc53c00WvVvPL
 

KAZHA

Chimp
Feb 20, 2015
34
6
Flat AF
Came across these while searching for elusive shimano piston seals. Does anyone know if there's any difference between slx, xt, zee, saint pistons? May be willing to give these a try.

https://m.aliexpress.com/item/32973287602.html?trace=wwwdetail2mobilesitedetail&productId=32973287602&productSubject=Bicycle-Titanium-Alloy-Brake-Disc-Lever-Piston-Repair-Part-For-SHIMANO-XT-M785-M800-Bike-Parts&spm=a2g0o.cart.99999999.309.6bc53c00WvVvPL
probably this will happen

Oh yeah I forgot. Finally put those chinese anodized pistons in some xts last fall.

they immediately leaked

yay!
 

Rockland

Turbo Monkey
Apr 24, 2003
1,870
262
Left hand path
Came across these while searching for elusive shimano piston seals. Does anyone know if there's any difference between slx, xt, zee, saint pistons? May be willing to give these a try.

https://m.aliexpress.com/item/32973287602.html?trace=wwwdetail2mobilesitedetail&productId=32973287602&productSubject=Bicycle-Titanium-Alloy-Brake-Disc-Lever-Piston-Repair-Part-For-SHIMANO-XT-M785-M800-Bike-Parts&spm=a2g0o.cart.99999999.309.6bc53c00WvVvPL
Dimensionally the pistons in all those models are about the same.
Someone earlier in the thread (can't remember who) mentioned certain low level Shimano servowave levers come with aluminum pistons instead of plastic. Roll the dice and try the China ti ones? I'd be scared.
 

StiHacka

Compensating for something
Jan 4, 2013
21,560
12,504
In hell. Welcome!
My Saintguras refuse to die. Pistons are 100%, Saint levers show some sign of use but still go strong. Just flushed the old oil and while it contained products of alloy oxidation, it wasn't really too bad.
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519
My Saintguras refuse to die. Pistons are 100%, Saint levers show some sign of use but still go strong. Just flushed the old oil and while it contained products of alloy oxidation, it wasn't really too bad.
Curious: How much use?
About to make some m988/mt5 shiguras this weekend
 

jstuhlman

bagpipe wanker
Dec 3, 2009
16,622
12,911
Cackalacka du Nord
update. Cura 4 continue to slay without mods, tweaks or magic spells.






( probably just jinxed myself)
finally got the 203 rotor to work without rubbing with my 4 up front...it took the addition of one shim/washer under one end of the adapter. will give it proper shakedown in the hills tomorrow.
 

jstuhlman

bagpipe wanker
Dec 3, 2009
16,622
12,911
Cackalacka du Nord
interesting...cura 4 with 203 vs 180 seemed to heat/pump up more on sustained descents. will have to continue monitoring. if i can get up to snowshoe next weekend that would be a good follow up. descents i did today were rough and steep. just for reference, one was about 1500’ over 3 miles; another was about 800’ over 2 miles, and the last was about 1500’ over 3 miles.
 

Nick

My name is Nick
Sep 21, 2001
23,926
14,438
where the trails are
interesting...cura 4 with 203 vs 180 seemed to heat/pump up more on sustained descents. will have to continue monitoring. if i can get up to snowshoe next weekend that would be a good follow up. descents i did today were rough and steep. just for reference, one was about 1500’ over 3 miles; another was about 800’ over 2 miles, and the last was about 1500’ over 3 miles.
maybe braking too much?
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,573
1,069
La Verne
I also have the cura 4,
I think you need a bigger syringe than the formula kit to bleed the rear.

Other than that they seem good. Basically feel like a shimano without the servowave
 

Da Peach

Outwitted by a rodent
Jul 2, 2002
13,681
4,904
North Van
My MT7 are still running strong.

I just bled the rear the other day to firm it up after a pad change. The process was fairly painless and worked really well.

The key seems to be to not rush, be sure there are no tiny bubbles hanging in the fluid in the syringe at the lever.

I used this method: