Mitsubishi 3000GT & Dodge Stealth Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
4,503 Posts
Discussion Starter · #1 ·
This is for my bike, but I would think that the theory is the same for Stealths.

I rebuilt the master cylinder for the bike's rear brake - rip out the old parts, shove in the new parts.

The shop manual simply says to bleed the brakes, with no mention of having to "prime" the master cylinder first.

I connect all the hoses back up from the MC to the caliper, open the SpeedBleeder on the caliper, fill the reservoir with fluid, and start pumping.

It sucks in most of the fluid from the reservoir, so I top it up again and keep pumping. Shortly thereafter, the fluid level stops going down.

I can look inside the reservoir and see tha when I pump, it sucks fluid in through the hole from the reservoir to the pump portion, and when I release, the fluid comes back into the reservoir again. In other words, it's just sucking it in and out, and not pumping fluid out through the hose to the caliper. I disconnected the hose from the caliper, stuck my finger over the end, and I can feel the hose blowing when I pump, and sucking back when I release.

A guy here at work said I have to "prime" the MC first. Following his instructions, I took the hose off the MC, and screwed in a bleeder nipple instead, thus blocking off the exit hole from the MC.

Last night, I was able to pump about a thousand times (not kidding), and teeny tiny air bubbles are coming back into the reservoir. I assume that this is air still stuck in the cylinder below the reservoir.

What the hell am I doing wrong? What's the *real* way to "prime" a master cylinder?
 

·
This Space For Rent
Joined
·
59 Posts
Bench Bleeding, you say?

Hallo Andrew,

Long time no chat, what? How are ya doing?

I just parachuted into the old 3si board here and stumbled upon your brakes post, a subject near and dear to my heart.

What they call this procedure in Metric-based foreign countries (thank you, PET! :p ) is a 'bench bleed.'

I think what you describe is the real procedure; you're routing a pipe with an air-tight connection from the bleed nipple in the MC straight into the reservoir, right?

I find that long, slow, gentle strokes work best. It shouldn't take 1000 strokes, no matter how old you are, to discharge all the air out of the master cylinder. Sometimes gently tapping the unit while pumping works too.

Hope this helps,
 

·
Dope-stoopid yo!
Joined
·
3,606 Posts
Yeah, just put little hoses from the nipples back into the brake fluid inside the reservoir and pump.
 

·
Dope-stoopid yo!
Joined
·
3,606 Posts
That's bench bleeding. I never heard of "priming". Did it come with a small pack of oil?
 

·
Moderator
Joined
·
4,232 Posts
i think i had the same sort of problem when i was changing out my slave cylinder. I ended up adjusting my pedal and got "pressure" back in the peddle then adjusted it back to where it was.

Check this out

Link to that post
 

·
Dope-stoopid yo!
Joined
·
3,606 Posts
Toni said:
i think i had the same sort of problem when i was changing out my slave cylinder. I ended up adjusting my pedal and got "pressure" back in the peddle then adjusted it back to where it was.


Mine blew out on me last week and I had to do the same. Kit was $7 at Oreilly. The clutch master isn't very accessible and had no bleeder valves, so bleeding it was almost impossible. It ran dry a few times.
 

·
vehicular thaumaturgist
Joined
·
8,289 Posts
I have done bench-bleeds on a few BMWs. An important part of this process is to make sure that the outlet of the MC is the high-point in the system. Air rises and to get it out you will need to have that hole elevated.

If this doesn't work, perhaps you have a bad master?

-Chris Wood
 

·
Registered
Joined
·
4,503 Posts
Discussion Starter · #8 ·
Well, after all that dicking around -

I talked to a different guy at work, and he said that all he'd done for his truck was to have a hose attached to the outlet on the MC, hold the other end of the hose over the reservoir, and keep pumping until it was just fluid and no air coming through the hose and back into the reservoir.

In effect, this is exactly what I was doing when I first started - MC hooked to hose, hose hooked to caliper, other hose hooked to caliper bleeder nipple, end of that hose into a jar, and just pump.

So anyway, I tried his idea, and held the end of the hose from the MC over the reservoir and pumped. The problem here is that the force of the fluid and air coming out of the hose makes a real splashy mess in the reservoir (a bike reservoir is a lot smaller than a car one), not to mention which doing it this way makes it impossible to tell if fluid is actually being sucked out of the reservoir or not - if it *isn't*, then the reservoir fluid level will stay the same, and if it *is*, then the fluid sucked out will get blown back in immediately, and the level will still stay the same.

In order to see if fluid was getting sucked out of the reservoir or not, I stuck the end of the hose into the brake fluid container instead, and started pumping. And Yes, the reservoir fluid level was quite obviously going down. So I topped it up, pumped some more, topped some more, pumped some more, finally got bored and hooked the whole damn thing back up to the caliper, pumped some more, and lo and behold, it's working just fine, fluid coming out the bleeder nipple like it's supposed to.

In summary, what I did on Friday (that worked) was exactly the same thing I first did last weekend (that didn't work), so the shop manaul is right - just fill the reservoir and start pumping, no special tricks, no priming, no nothing.

I have no clue, however, what happened in between last weekend and this weekend.

Thanks for all your replies.

(And all this for a Harley that can't do more than 50 MPH anyway).

Runner - get a Stealth yet?
 
1 - 8 of 8 Posts
Top