Bench bleeding Aisin master cylinder … problem? (1 Viewer)

[CruiserTrash]

Old MC was leaking a little bit at the booster, so I ordered an Aisin replacement from Cruiser Outfitters.

Commenced with my first bench bleed. Chucked the MC in a vise (with some rags so I didn’t mar the surface). Got two hoses from the outlets and routed them into the reservoir. Easy enough. I’m pushing the piston in and fluid is only circulating in the circuit nearest the reservoir. I block off that outlet and push the piston again and fluid flows out of the far cylinder.

I finish bleeding that and go back to bleeding both at once. No flow to the far circuit again. Then all of a sudden on my next push of the piston it hits resistance and BOOM the piston goes past it - probably 2-3” in. I push again and it stops about midway, where it had been stopping before. Still the fluid is only circulating through the near circuit with both open and plumbed into the reservoir.

So was it faulty to begin with?
Did I break it?
Is it fine?

 

[CruiserTrash]

I went ahead and installed the MC, bled the system, and ran with it. The braking is “ok”, but not as good as it was with the previous leaky MC. I lifted each corner of the vehicle independently and the brake pedal stops all four wheels.

Calipers, pads, and softlines were replaced last year. Drums have not been touched on my watch. Rotors are being replaced in about 10 days as part of a knuckle job I’ll be doing.

 

[diesellibrarian]

I've never had much luck bleeding a master cylinder on the bench. What I normally do is install it in the vehicle, fill with fluid, and then have someone pump the pedal while I hold my thumbs over the outlets. When fluid starts coming out of the first outlet, I ask my helper to stop pumping while I quickly attach the line. Then I do the same on the second outlet. At that point I feel pretty confident that the MC is full of fluid and ready to go, so I proceed with bleeding the rest of the system. I've used this system for years across multiple makes, and it's always worked well.

I'm not sure it helps your situation, but if you wanted to try re-bleeding the MC in situ, it might be worth a shot?

 

[CruiserTrash]

I've never had much luck bleeding a master cylinder on the bench. What I normally do is install it in the vehicle, fill with fluid, and then have someone pump the pedal while I hold my thumbs over the outlets. When fluid starts coming out of the first outlet, I ask my helper to stop pumping while I quickly attach the line. Then I do the same on the second outlet. At that point I feel pretty confident that the MC is full of fluid and ready to go, so I proceed with bleeding the rest of the system. I've used this system for years across multiple makes, and it's always worked well.

I'm not sure it helps your situation, but if you wanted to try re-bleeding the MC in situ, it might be worth a shot?

I can see that method working. Bench bleeding seems real simple too.

My worry is that I broke the damn thing before installing it. The moment that plunger went in real far was definitely an “oh $h1+” moment. Plus, the fluid not coming out of the front circuit when they’re both open … that’s how it’s plumbed in the truck and doesn’t bode well for operation of the brakes.

I’m kind of on the fence about just getting a new one as a do-over.

 

[John McVicker]

Maybe give @cruiseroutfit a call. As you know, the guys that answer the phone are very knowledgeable and maybe have run across this before.

 

[CruiserTrash]

Maybe give @cruiseroutfit a call. As you know, the guys that answer the phone are very knowledgeable and maybe have run across this before.

Of course, their customer service is always outstanding. I wanted to gather some info from the geniuses here first so I had done my due diligence before calling them and sounding like a moron.

 

[Godwin]

I don't bench bleed, adjust the brake booster rod to correct length, mount the booster, hook up the lines, and fill with fluid. I then have someone in the cab mash and hold the brake and I crack open the rear brake line; the one nearest the booster. Once I think most of the air has been pushed out we move on to the other line and repeat the process.

The few times I've tried bench bleeding it was unsuccessful.

 

[red66toy]

I install the MC, then made some arced lines that go back into the MC reservoir. I pump until no bubbles are going into the reservoir anymore. Then I install the lines and bleed that whole system.

 

[Spike Strip]

As I was reading the first two paragraphs of the OP, I was about to type, 'don't push the piston in too far...' then read the next para..

But it usually only gets stuck and it's difficult to get back out. Nothing to damage if you go too far...

Is the pedal firm? Does it sink to the floor. For some reason this 60 brake system is hard to bleed without a pressure bleeder. Took me a few large bottles of fluid to finally get the pedal firm.... Obviously, start at the most distal end cylinder (Left Rear, Right Rear, etc) and have somebody press the brake while you gently tap the lines, wheel cylinder/caliper as you do each corner to help release any trapped air. And finally, rebleed the MC in the truck doing the tap tap (lots of towel to protect paint!) I usually ask my wife (MISTAKE!) to assist and apply gently pressure on the pedal and I tap and open the bleeder at the same time.

 

[CruiserTrash]

I install the MC, then made some arced lines that go back into the MC reservoir. I pump until no bubbles are going into the reservoir anymore. Then I install the lines and bleed that whole system.

Essentially bench bleeding, but using the brake pedal and booster to do the pushing for you. And foolproof.

@Spike Strip I bet you winced reading that! Yep, went in too far. Came back out fine. But I’m still confused about how pushing the piston in only seemed to operate the closer circuit and push nothing out of the far circuit.

Anyway, I manually bleed the brakes just about how you describe. The system in a 60 does seem to take a while - maybe 2-4 rounds, drive it for a while, then another couple rounds - to really get the pedal feeling good. My lady helps too and I try to move as quickly as I can for her sake. Pedal is fairly firm, maybe 85-90% as firm as with the old MC (and a fluid flush/bleed by me last year). It’s got a touch of mush to the pedal but not bad.

But the brakes has been better and I want to get it back there.

 

[gbogh]

I didn't see you mention it, did you check/adjust booster pushrod depth?

 

[CruiserTrash]

I didn't see you mention it, did you check/adjust booster pushrod depth?

I did not have the proper tool but kind of made some calipers and a couple straight edges work … sort of. I repeated the measurement 3 times and it as coming up with 0.002-0.004. I think the spec limits it to 0.004 max if I remember correctly.

I had actually ordered the tool but hadn’t received it when I did the work - I was nervous about the MC leak I had going on and went for it. I’m leaning towards swapping this thing out with another MC and now that I have the pushrod tool I will certainly use it.

 

[gbogh]

Alright. Cool. I've goofed that up before and it definitely messed with pedal feel. The tool makes it super easy but it can definitely be done without one.

 

[CruiserTrash]

Alright. Cool. I've goofed that up before and it definitely messed with pedal feel. The tool makes it super easy but it can definitely be done without one.

I ordered this pushrod adjustment tool from Land Tank Products - free, just pay shipping!

Brake Booster Pushrod Adjustment tool - https://landtankproducts.com/products/brake-booster-pushrod-adjustment-tool