montevista

So why the different techniques? SRAM has me tapping and purging bubbles at both ends with the syringes. Shimano I can do a gravity bleed and just pour fluid in the cup at the top and let it run out the bottom. I'm not trying to start a debate about which brakes are better. I'm just trying to understand why the difference in bleed techniques. Is there some significant difference in the way the levers+calipers are designed, is it due to differences in DOT vs mineral oil, or is it simply a difference in the youtube videos I happen to watch.

jgwilliams

Although I've not had to do it on mine yet, I was under the impression that with Shimano you're supposed to inject new oil at the bottom.Since DOT is corrosive I presume the instructions require more care to prevent spillage. Otherwise I can't see why there would be a great difference.

montevista

The official Shimano instructions have you push fluid up from the caliper into the cup at the lever. However, there are videos and plenty of people who apparently doing a gravity bleed. I did this myself and it seemed to work. But besides the gravity part, the broader question relates to the SRAM process having more fiddly little steps. The Shimano process is pretty much along the lines of "Drive the fluid up in to the cup, flip the lever a couple of times." Shimano spends a lot less time emphasizing chasing bubbles at the caliper and lever. I'm wondering if there is a real technological reason for this or is it just "style."

jgwilliams

I thought that was the case. Presumably, the reason is that it will help to expel any air bubbles that might be in the line.

cxwrench

They're just different. Is there any reason to overthink this? Does it really make a difference?

Rolla

This is a perfectly legitimate question, and one I've wondered about myself. It seems that they both operate on the same basic principle, so why the procedural difference?

IOW you don't know, either.

squirtdad

it is a difference in what the manufacturer recommends. They generally have a reason for that recommendation, whether they share it or not.

just follow the park tool videos for your system, don't worry about other videos and don't cross contaminate DOT and mineral oil

cxwrench

No, I don't. Nor do I care as it makes no difference how I do things.

Rolla

TiHabanero

There is only one explanation for this difference. Shimano engineers are simply better engineers. They must think through things more thoroughly than Sram engineers do. Much of what Sram does is half-baked and their brake bleed process follows that tradition. I have bled hundreds of brakes from both companies, and Sram always, always takes more time and at least two bleeds.
I am certain there are superior wrenches out there that never have problems with bleeding Sram brakes, but those folks are superior and are able to handle an inferior brake system design better than myself.

cxwrench

^I agree with this^ I've had some SRAM brakes that just won't bleed. I've had a few Shimano brakes that won't work but it's generally easier to figure out the problem with them. And post #9...seems different than earlier today. Thanks.

Polaris OBark

I often use the SRAM method for Shimano brakes. Also, I find pushing fluid up from the caliper works better than draining it by gravity. Perhaps more interesting, I get a lot more dirty fluid out when I push the fluid up from the caliper via a syringe. I think it does a better job of purging the fluid adjacent to the pistons (which is where the dirt will most likely be). The other advantage of using one or more syringes in a bleed is you can apply negative pressure, which is a great way to remove gas (air bubbles) from a fluid.

byscott

Like a lot of you, I’m sure, I’ve bled plenty of brakes systems on cars and motorcycles. Seems like there are two ways to do it — by force or vacuum — but the common denominator is that bleeding goes one way only. Whether the fluid is pushed or pulled out, once it leaves the system it stays out.

I’ve noticed that Shimano brakes advertise one way bleeding. That says to me that Shimano engineers are paying attention to the way that brakes are engineered on cars and motorcycles. IMO it’s ridiculous that the bleed valve on the caliper should allow expelled fluid to flow back into the system, but it seems like some other brands operate this way. I recently had to bleed a Promax brake and it was kind of a pain to use two syringes just to make sure the expelled fluid stayed out. It would be a lot easier just to pump clean fluid through the system until the old fluid and air were forced out.

Anyway, to get back to the OP’s original question, it sounds as though the SRAM brakes don’t have a one way bleed valve. That necessitates the extra syringe to maintain vacuum in the system and keep expelled old fluid (and air) from re-entering the system.

montevista

Ah, that's an interesting idea and along the lines of my question. That is, I don't have any worries or problems watching videos, I'm just curious about what the recommended bleed methods might say about the device design.

As to the above, Shimano recommends pushing fluid up from the caliper. Others demonstrate gravity bleeding so flow from lever down to the caliper. Would that then preclude a one way value? Or maybe that's why my gravity bleed was a drip drip drip of fluid instead of a flow, ie, it was only very slowly leaking through a one way valve. ???

I guess I need to track down to diagrams showing the innards. Anyone know if those are available? I don't have enough spare parts to start taking things apart myself.

Cheers!

Polaris OBark

As a scientist with limited people skills, maybe I am a bit more willing to tolerate how mechanics sometimes communicate. I've learned a lot from the guy, and although I can see that it can be a bit off-putting, it is just another POV and a pile of ascii text on a computer screen.

well biked 

I think post #10 sums up my thoughts on this pretty well. It's actually not easy to screw up a Shimano brake bleed (or Tektro, TRP), IME. Those brands have many things in common in their hydraulic brake designs, with the key thing being that they use mineral oil brake fluid. IMO.

I'll add that I think SRAM's biggest flaw with hydraulic brakes is that they bought Avid before they had ever produced a hydraulic brake under the SRAM name. Avid's reputation with hydraulics was/is horrible,and is well earned. And yet, SRAM's hydraulics are just a continuation in too many ways of the Avid hydraulics and their design. They're better, but not "better enough." IMO.

Canker

Functionally what real difference is their between DOT and mineral oil? Water absorption and heat handling difference aside both are just hydraulic fluid that do the same thing. Is there an actual reason besides the seals not being made to handle DOT that DOT wouldn't work exactly the same in shimano brakes as mineral oil or the other way around for Sram?

Desert Ryder

Just an off the wall question but....
Are there speed bleeders available for bicycle disc brakes? I've used the on my car and motorcycles to bleed brakes.

I have a vintage set of Formula disc brakes that are defying my bleeding efforts. I gave up and haven't tried in a few months. Last time the syringe hose popped off the bleeder screw and I sprayed DOT 4 fluid all over.