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post #391 of 411 (permalink) Old 07-17-2019, 07:42 AM Thread Starter
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But there are two parts for 69 YM cars. This is the dual circuit brake MC.

https://centerlinealfa.com/catalog/b...inder-1969-usa

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Originally Posted by Andrew View Post
For a US 69 car, it should be dual circuit. So I don't think that MC is appropriate for you.
Andrew
-tj


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57 1900C SS (10321) Carrozerria Touring (in process)
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post #392 of 411 (permalink) Old 07-18-2019, 05:33 PM Thread Starter
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The continuing saga of the brake system that won't come good....continues.

With the suggestion that I purchase yet another (later style) brake master cylinder I decided to try one more thing. Perhaps stupidly unwilling to accept the probability that I've had 4 consecutive brake master cylinders that are defective, I removed the one I got from Classic Alfa, and reinstalled the Bonaldi I got from Alfa Parts. Both were supposed to be new parts. Before I installed the Bonaldi, I took it apart on my bench, inspected it for torn seals, broken pieces, etc. Everything looked normal. Before reassembling it, I pour brake fluid in to the bore, then reassembled, then poured more brake fluid in to the supply and delivery line ports. I tilted it, tapped it, let it sit overnight, and added more fluid to it. I used the little plastic caps to keep as much of the fluid in the master cylinder during installation.

Back installed, I bled the brakes using the two person method. Took her out for a trip. Same. Bled her again with the two person method. Took her for another test drive. Same.

Then I borrowed a modified brake fluid reservoir cap with a fitting for an air hose in it, and pressurized the system from the brake fluid reservoir with about 12psi. I cracked each bleed screw starting at the right passenger rear. Each time I got a few bubbles from each caliper, and then clear fluid without bubbles. I set her back down, and went for a test drive. Same.

Back up on jack stands once again. Once again I got a few air bubbles, and I don't know if they were merely still in the system from before, or somehow new air got in to it, but I let each bleed screw stay open until I had clear brake fluid flowing for 5 or 10 seconds. Back on the ground, back on the road for a test drive, and once again, same.

It's hard for me to believe I have a vacuum leak because there really aren't many connections in the system that would only suck air. Actually past the first connection from the brake fluid reservoir to the supply pipe to the master cylinder, there are none. Any other junction that might be drawing air would also be under pressure and would show a leak. I don't have any brake fluid leaks.

And so at this point I don't feel I have any options but to try the later style brake master cylinder which has the junction coming off the tail end.

-tj in the Cruz Mtns


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post #393 of 411 (permalink) Old 07-18-2019, 06:35 PM
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Man I feel your pain and frustration. 1 more thing to think about and check is if the pin that drives the piston in the master cylinder has an adjustment is it set perfectly. I had a problem with this on my spider but it is standing pedal dual circuit system. I'm thinking if it has caught air even before you start to bleed and it has no way to pass. Regards John
P.S. That's the pin that comes off the pedal arm and goes thru the firewall.

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post #394 of 411 (permalink) Old 07-19-2019, 02:28 AM
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Well, you’ve done so much, including having your local 105 guru stumped too.
I’ve occasionally had SOME trouble bleeding my car (single circuit, floor pedals, Bonaldi), but nothing that persistence and lots of fluid didn’t largely or completely eliminate, and those times when it was only ‘largely’, driving seemed to occasionally help, or the next go at it did.
A few posters have hinted at trying to isolate the problem, maybe that’s about the only thing left to help steer you in the right direction.
For example...
- take the booster out of the equation. A brake shop made me up a 6-8” female-female hose to connect the hard lines to/from the booster for $15 to do similar testing. Didn’t have to bend the hard lines that way, just removed the booster.
- Front versus rear, left versus right. If I recall correctly, you have Teflon/braided steel lines everywhere? Bit hard to successfully clamp these I expect, but do you still have some rubber hoses you can use for the rear axle and front calliper lines....clamp them off one at a time and see what happens? (You can put this back axle flex line in backwards, by the way, and it will leak. But I expect you would have spotted that.)
It’s a bit of messing about, but I expect by now you are used to that.

Re all those master cyls, unless you have REALLY bad luck, I’m with you, I don’t see how they can all be bad, in the same manner, trapping air somewhere, but with no evidence of leaks...those single-circuit cylinders are pretty simple.
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post #395 of 411 (permalink) Old 07-19-2019, 08:42 AM Thread Starter
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Yes, thank you. There is no pre-load on the master cylinder. There is enough free play between the piston and actuating rod.

Quote:
Originally Posted by spydaman View Post
Man I feel your pain and frustration. 1 more thing to think about and check is if the pin that drives the piston in the master cylinder has an adjustment is it set perfectly. I had a problem with this on my spider but it is standing pedal dual circuit system. I'm thinking if it has caught air even before you start to bleed and it has no way to pass. Regards John
P.S. That's the pin that comes off the pedal arm and goes thru the firewall.

-tj


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post #396 of 411 (permalink) Old 07-19-2019, 08:46 AM Thread Starter
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Thanks for your suggestions. The behavior has been identical across two separate brake boosters, including one which was rebuilt and tested and verified to be good.

I do not have stainless braided brake lines....a myth I seem incapable of dispelling! I have the original hard lines to the calipers.

Quote:
Originally Posted by Ranz View Post
Well, youíve done so much, including having your local 105 guru stumped too.
Iíve occasionally had SOME trouble bleeding my car (single circuit, floor pedals, Bonaldi), but nothing that persistence and lots of fluid didnít largely or completely eliminate, and those times when it was only Ďlargelyí, driving seemed to occasionally help, or the next go at it did.
A few posters have hinted at trying to isolate the problem, maybe thatís about the only thing left to help steer you in the right direction.
For example...
- take the booster out of the equation. A brake shop made me up a 6-8Ē female-female hose to connect the hard lines to/from the booster for $15 to do similar testing. Didnít have to bend the hard lines that way, just removed the booster.
- Front versus rear, left versus right. If I recall correctly, you have Teflon/braided steel lines everywhere? Bit hard to successfully clamp these I expect, but do you still have some rubber hoses you can use for the rear axle and front calliper lines....clamp them off one at a time and see what happens? (You can put this back axle flex line in backwards, by the way, and it will leak. But I expect you would have spotted that.)
Itís a bit of messing about, but I expect by now you are used to that.

Re all those master cyls, unless you have REALLY bad luck, Iím with you, I donít see how they can all be bad, in the same manner, trapping air somewhere, but with no evidence of leaks...those single-circuit cylinders are pretty simple.
-tj


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57 1900C SS (10321) Carrozerria Touring (in process)
59 Giulietta Spider Veloce (05431)
66 Giulia Sprint GT Veloce (242922) Reborn
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post #397 of 411 (permalink) Old 07-19-2019, 05:19 PM
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Ok, but BEFORE the hard lines to the callipers, there are flexible, rubber (and therefore clampable) lines LH front, RH front, and before rear axle, yes? That’s what I was getting at...clamping these in turn to see if anything changes....sorry if I wasn’t clear.
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post #398 of 411 (permalink) Old 07-19-2019, 08:22 PM Thread Starter
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No sir....there is only one flexible rubber line and it connects the main line that begins at the junction on the firewall to the junction on the axle.

-tj

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Ok, but BEFORE the hard lines to the callipers, there are flexible, rubber (and therefore clampable) lines LH front, RH front, and before rear axle, yes? Thatís what I was getting at...clamping these in turn to see if anything changes....sorry if I wasnít clear.


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post #399 of 411 (permalink) Old 07-19-2019, 09:06 PM
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Ok, so there’s one of the three flexible lines.
For the front, you can’t have hard lines all the way to the front callipers. Things move up and down...there’s gotta be a flexible line in each wheel well.
If these are rubber, you can try the isolating thing by clamping them off. This is what I was getting at in post 394. If they are Teflon with a (usually) braided stainless sleeve, maybe not so easy to clamp, as they may crush instead.
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post #400 of 411 (permalink) Old 07-27-2019, 09:49 AM Thread Starter
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With a small amount of caution I announce that I believe I've found the root cause of the air that was getting in my brake lines and causing the soft pedal. I went back around the car and checked all the fittings and found that there were two on the brake line junction that is mounted to the firewall that I was able to get another half turn or so on. I know these are compression fittings and that they need to be very tight, but I'd manufactured these lines and put the flares on them with a handheld tool. I also used new copper tubing on a couple of the lines. Getting the flare right with the handheld tool is not easy, and it's possible that the flare wasn't perfectly formed. Cinching them down required a certain amount of sensitivity and I may just not have been as aggressive as I needed to. One of the fittings that wasn't completely tight was the one from the brake booster.

It's curious of course that it would allow air in but not push fluid out (there were no leaks) but when I tightened it and one other, and then went back to bleed the system with a pressure bleeder there were no more air bubbles. The test drive was markedly different and better, with the kind of firm pedal that feels right but still with the ability to modulate braking appropriately.

On to the next....

-tj in the Cruz Mtns
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57 1900C SS (10321) Carrozerria Touring (in process)
59 Giulietta Spider Veloce (05431)
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post #401 of 411 (permalink) Old 07-27-2019, 11:56 AM
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Quote:
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Cinching them down required a certain amount of sensitivity and I may just not have been as aggressive as I needed to.
That makes sense. My experience with brake lines - even with factory-made flares - is that you need to tighten them a little like head nuts: torque them down, come back the next day after the flare has flowed a bit, and torque them again. Sometimes it takes me a few rounds of tightening and waiting to get them to seal.

Obviously Toyota doesn't use my technique on their production line, so I don't know if this makes any sense; maybe just tightening them more the first time would work as well.

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post #402 of 411 (permalink) Old 07-27-2019, 01:28 PM Thread Starter
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Yeah, the tool I used didnít make a flare that was exactly like the factory line. I think I needed to tighten the fitting enough to get it to seal against the bottom of the bore. The original Alfa lines were steel but we could not get a good flare on the steel with the tool. New copper is much easier to get good results with.

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That makes sense. My experience with brake lines - even with factory-made flares - is that you need to tighten them a little like head nuts: torque them down, come back the next day after the flare has flowed a bit, and torque them again. Sometimes it takes me a few rounds of tightening and waiting to get them to seal.

Obviously Toyota doesn't use my technique on their production line, so I don't know if this makes any sense, or if just tightening them more the first time would work as well.
-tj


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57 1900C SS (10321) Carrozerria Touring (in process)
59 Giulietta Spider Veloce (05431)
66 Giulia Sprint GT Veloce (242922) Reborn
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post #403 of 411 (permalink) Old 07-27-2019, 02:11 PM
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This is GREAT news... fingers crossed!

Joe
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post #404 of 411 (permalink) Old 07-27-2019, 02:19 PM
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This is great news.

Copper pipe?, copper alloy I hope as copper is not suitable for a brake line.
Pete
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post #405 of 411 (permalink) Old 07-28-2019, 08:59 AM Thread Starter
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I didnít know that, but assume that itís a suitable alloy.

https://classicalfa.com/br070-1-fron...968-78-copper/



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This is great news.

Copper pipe?, copper alloy I hope as copper is not suitable for a brake line.
Pete
-tj


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57 1900C SS (10321) Carrozerria Touring (in process)
59 Giulietta Spider Veloce (05431)
66 Giulia Sprint GT Veloce (242922) Reborn
95 Ducati 916
92 Ducati 900SS
91 Ducati 851
66 Ducati Mach 1 Replica
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