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Bleeding rear master cylinder

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I'm putting a CRF450R rear master cylinder on my DRZ right now. I took it apart beforehand, and the reservoir was a bit gunked and needed cleaning. All other parts like the cylinder, spring, and seals all looked fine. I cleaned them anyway and went ahead bleeding.

I've heard this thing was a bitch to bleed because you were always filling up the reservoir, but in my case it's a pain in the ass because it takes so many pumps before needing more fluid. I even swapped the banjo bolt to the DRZ one, which has wider holes, and it still takes dozens of pumps before needing a refill.

So my kerosene soak must not have cleared the path between the reservoir and the cylinder, right? How can I get this thing working without any compressed air? I don't have a compressor, but I could possibly annoy my local shop again for some help. The closest I have to some pressurized stuff like compressed air is brakleen, which hasn't gotten the job done yet.

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28 minutes ago, S.O.A.N.Z said:

Have you tried back bleeding ?

No, never done this before. I was also out today trying to find a vacuum bleeder but no luck.

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OK fixed it somehow. I elevated the rear caliper and way more fluid started flowing. About 5-6 pumps and it needed to be topped off. Got all the air out too. It's quite a different feel to the stock DRZ. A lot softer throughout, and get stiffer at the end of the stroke. Gotta ride it to see how it goes!

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Went for a ride, it can barely lock the rear wheel up. There's a CRF450R right next to my DRZ in the garage (not mine). Its lever is much firmer. I guess I need to keep bleeding and watch for that air bubble. I did not let any air into the line from letting the reservoir run dry.

Am I missing anything? There still could be a bubble in the system still of course. But I did a lot of bleeding and couldn't find one.

Is it the larger diameter DRZ banjo bolt be negatively affecting pressure? I'd hate to have to bleed the whole thing again for this.

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You can speed up the process by bleeding the air out of the banjo bolts instead of the bleeding screw in the calipers. Once you build sufficient pressure you can then proceed to bleed the line from the calipers. That trick has always worked for me since I also find it nearly impossible to bleed it using the conventional method.

 

 

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Comparatively, what size piston diameter is in both respective calipers ?

 

Maybe the DRZ master cylinder doesn't move enough volume for the CRF caliper?

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1 hour ago, mlatour said:

Comparatively, what size piston diameter is in both respective calipers ?

 

Maybe the DRZ master cylinder doesn't move enough volume for the CRF caliper?

I think you're misunderstanding. I have a DRZ400, a CRF450R rear MC, with the DRZ banjo bolt (wider than CRF banjo). My caliper is stock DRZ.

 

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OK mis-understood

but still, what are the piston sizes in both calipers (CRF / DRZ)

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Your kerosene soak probably killed the piston rubber. Brake cleaner will kill it too. Gas...death, about the only thing you can clean the rubber parts with is denatured alcohol. But getting it bled out is also a challenge if you dont have a vacuum bleeder. That could still be the problem, so keep bleeding...

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On 6/17/2017 at 5:25 PM, mlatour said:

OK mis-understood

but still, what are the piston sizes in both calipers (CRF / DRZ)

I believe the CRF is 3/8" and DRZ 1/2".

6 hours ago, Shawn_Mc said:

Your kerosene soak probably killed the piston rubber. Brake cleaner will kill it too. Gas...death, about the only thing you can clean the rubber parts with is denatured alcohol. But getting it bled out is also a challenge if you dont have a vacuum bleeder. That could still be the problem, so keep bleeding...

Hope it didn't &%$#@! it up. They did look fine but if I can't find a bubble in the line, I'll get the rebuild kit and get some compressed air shot through it too.

It does work ok now. I can wheelie safely and this brake will bring me down. But the lever is pretty soft!

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Keep bleeding. Shop air through the system is exactly what you dont want. What you want is a Harbor Freight vacuum brake bleeder. The kind you connect to shop air. Ive got one, had it for 15+ years and I never run out of stuff to use it on. All kinds of crap. I use it to evacuate engine people bring me that dont drain the oil first :banghead:

Or to suck out fork oil to the correct level (old school KYB forks etc) Your truck...car...etc...

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Thanks guys, likely it is a bubble. I'll get one of those vacuum bleeders, fix it up, and come back with an update. I should have bought one a long time ago anyway.

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Bought the Mity Vac bleeder from Harbor Freight and it could not get the lever any firmer. I nearly filled up the whole little bottle they you attach to the pump with clean brake fluid, and still there was always air coming out of the caliper bleeder. It couldn't hold any pressure at all above maybe 5 PSI. Performance is still the same. Long stroke required to get any braking, and locking the rear is nearly impossible.

So it looks like my seals need to be replaced after all! Still don't want to say if it was the kerosene soak or not. They did not soak very long, maybe 5 minutes max. The whole master cylinder is pretty old. The reservoir was pretty gunked, so my first thought was the passage from reservoir to cylinder was clogged, since that hole is super small. But with this air leak, it's gotta be the seals, correct me if I'm wrong.

Edited by HansLanda

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You guys think it's worth getting a new cylinder? The current one looks fine, but there are two main types of kits I'm finding. They include most of the same stuff, but either the cylinder seals or cylinder are included, not both. Obviously I will get seals, but should I get a cylinder too?

 

s-l1600.jpg

s-l500.jpg

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Just order the piston set from Honda. You dont need all that other crap. Its only like 28 bucks.

 

One thing too, when using the vacuum bleeder, continue to pump the master. You want that motion to pull any air out of the master too. One thing that mainly helps your brain is to use a tiny (and I mean tiny) bit of teflon tape or some kind of heavy grease on the bleeder screw so it's not pulling air when youre vacuum bleeder is pulling on it. The master reservoir is so small that youve really gotta pay attention to the level while bleeding. If your catch can is clean, and assuming youve already flushed the old nasty fluid, you can run the bled out fluid back through so youre not gobbling up gallons of fluid while pulling the air out. Another tip is to bleed each banjo too.

 

You do it just like you would the bleeder. Pump, hold, crack the banjo bolt just slightly, let it leak and tighten it back up. Its a mess, but those banjos are a pain in the ass. Some of them have a significant volume and the inner edges catch air that you just cant clear easily unless you're really pulling a bunch of volume all at once, which is very difficult to do without a reverse bleed setup like a Motive Power bleeder style pump and pressure system.

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The kits I posted are like $17 so I'm going to go with those, All Balls is good stuff. God I hope this works and I don't have to do the banjos...

Should I go back to the CRF banjo though? I have my DRZ one on the MC right now and fluid passageways are wider than the CRF bolt's.

Edited by HansLanda

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Got the cylinder rebuilt and I think the new seals did the trick! Lever is way firmer and I can actually lock the rear on the street now. That Harbor Freight vac bleeder didn't help a bit though, that thing is a piece of shit.

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Not sure which bleeder vac you got from Harbor Freight. if you got the little hand pump thing..ya big ole pile a poo, that one. I got one that uses shop air to draw a vacuum, and I love that thing. I've been using it for close to 20 years now. The bottle holds almost a full quart.

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