C1 brake bleeding
 

After installing a disc brake conversion kit on my 1960, I'm running into a problem bleeding the brakes that has me kinda stumped. Any help or advice will be greatly appreciated.
I have researched other threads and the stickys but they didn't IMO seem to address my exact problem. I could easily ramble on here for pages but will do my best to keep it to the point;
While doing this job, despite my efforts the master cylinder ran dry. When everything was tightened up I filled the MC and got my handy vacuum tool and started pulling air out of the lines.
Hours later I thought I must have a leak and am drawing in air under vacuum so I changed course and did a gravity bleed . With the pressure I could generate, I checked diligently for any leaks and found none.
Under gravity the fluid was slowly flowing out of the rear bleeders along with copious amounts of air bubbles.
Hours later again, the other three wheels are flowing pretty much solid fluid but my RR is still spewing tons of bubbles and very spongy pedal when all bleeders closed!
Will I need to do a bench bleed on my original master cylinder? Will any air trapped in the MC not be removed by either vac-ing system or a slow gravity bleed? If not, easiest simplest way to do this? (btw, my next project is to install a dual MC but wanted to verify everything at this stage before moving on)
If I'm still drawing out air bubbles and the fluid is going into the system, that's gotta be a good thing, right?? I can't see it possibly taking THIS long but am I just being impatient?
Help, Thanks in advance,
Gord

Are they still drums on the rear ?
Did you change the rubber hoses ?
Only back out the bleeder screw enough to get fluid flowing and tighten it back while juice is still flowing..
This is why I prefer speed bleeders.
The RR should be bled first..

I would: bench bleed the master on the car (easily done with a syringe by injection brake fluid into the outlet ports until bubbles disappear). I would then: gravity bleed the R/R and then the L/R. Total time to do both: less than and hour.

To answer some questions,
yes, there are still stock rear drums.
the front brake lines were supplied with kit, SS with plastic protective jacket I believe.
I think I might be guilty at times of backing off bleeder nipples too much?. I like the idea of the speed bleeders but haven't bought yet. When I change to the dual MC, will definitely then.
GTO Guy or...?, I just came in from doing another vacuum bleed all around and actually have a bit of a pedal now! I have bench bled new MCs before intallation as per instructions but never on the car. Can someone expand a little on this process if possible?
Thanks a bunch in advance!
Gord

Jeff (GTOGuy) has about 100x the experience that I do, but I have never bench bled a single master cylinder in 45 years of working on old cars and it was never an issue.

You may just have to do several bleeds - starting at the RR and only cracking open the bleeder a 1/4 turn with a hose from the bleeder staying submerged in a jar of brake fluid....a major overhaul may take more patience than you might think...

On your car with the single MC reservoir: remove cap. Cover fender to protect paint. Remove outlet line from master. Fill plastic syringe with brake fluid. Slowly squirt brake fluid IN to the master cyl via the outlet port (where you just removed the line from). Do this until all air bubbles int the master are replaced by a stream of brake fluid. Re-install the line. Top up reservoir. Move to RR wheel. Loosen bleeder. Allow fluid to drip until just fluid drips...it'll be at a steady rate....intermittent drips mean air. Bubbles mean air. Go look at the reservoir. Replenish if necessary. Return to RR wheel....after all air is gone, snug up bleeder. Re-fill master cyl. Install cap. You are done. Tips: always gravity bleed with cap off of master or loose to allow fluid to flow freely. I've bled hundreds (maybe thousands) of master cylinders in this fashion over the years and it always works. Never did need that hose and fitting crap that requires pumping the piston and making a huge mess.

Where did you install the residual valve?

Fabulous info, thanks a ton! I'll go and do that right now. ***Maybe a dumb question but when I remove the line from front of my MC, doesn't that create a hell of a mess? Should I remove at least some of the fluid from it first? Or just pile rags underneath or is it not that bad?
As for residual valves, I'm going to pick up a 2 and a 10 inline when I do the dual MC. I know it might sound counter-productive but I've read that the stock MC has been used with front discs and want to just back in and out of the garage to check function and final check for leaks.
Thanks all, have a good day!
Gord

My 61 had a stock M/C with 73 Camaro discs on the front and original drums on the back - drove it for 10 years like that.

Put rags under the fitting to catch the small amount of brake fluid. If brake fluid gets on anything, you can wash it off with water as it is water soluble. If you're quick, you won't lose a lot of fluid...a teaspoon, maybe.

Lubrication charts from the 60s for our C1s always showed the bleeding sequence starting with the LEFT rear (farthest from the master) drum first. Like almost everyone I always started with the right rear. When I had bleeding issues after recently doing a disc brake conversion on my 61 a friend showed me an old chart and I reluctantly tried starting with the left rear first. Problem solved.

The right rear is furthest from the master as the crow flies, but of course the fluid does not fly, it transits via the brake lines--and indeed the longest run of brake line is to the left rear. It's longer by a foot or two than the path to the right rear, and this is evident by the location of the rear distribution block.

In practice I wonder if that really makes a difference most of the time, but I guess in your case it did.

Yes - I noticed that discrepancy in the manual way back - but I never deviated from my tired and true RR first....I think its farthest from the M/C and that has always worked for me..

Don't believe everything you read. You've been mis-informed, my friend, by a mis-print. It is industry standard to start from the right rear and has been for over 80 years.

Regarding seeing bubbles in the fluid during bleeding. It is very possible that loose threads in the bleeder connection itself aspirate/pull air into the fluid during bleeding. So you may continue to see air bubbles even though the main system is completely free of air. One way to minimize this is to use the speed bleeders with a silicone/rubber seal on the threads. Then replace at the end with the regular ones, give a little pedal pressure during the changeout to prevent pulling any air back in.

Larry

My suggestion in post #2 - a big fan of speed bleeders - and I leave them in permanently..

I saw that a few days ago...........but you did not say why the speed bleeders were better, except that they helped you do the job yourself. No mention about the aspirated air into the system., which some folks (probably OP also) do not really think about when doing this job.

Just wanted to specifically point it out........trying to be helpful. :D

Larry

Fair point...
You can also buy add'l sealant goo for the speed bleeders if its needed after a while..

C1 brake bleeding ...and then some
 

Brake bleed update; I've bled the MC as per the instructions posted but whether it was me or...?, I never saw any bubbles? Anyways, after doing that and redoing all four wheels a couple more times there's a light at the end of the tunnel! Brakes now are pretty good, not excellent, but good enough for a drive around the block. Maybe after one more bleed I'll try the MC bleed again to see if have any different result?
On a different track now, if anyone's still following this thread, but IF I go ahead with my dual MC conversion so near to driving season, I have some questions re the various valves in a disc/drum system.
I've researched a bit and feel I have a decent handle on what they all do but why do I always hear drivers and the big suppliers always talking about a 2 and a 10 psi residual valve with additional adjustable proportioning valve? (even Speedway Motors says the adj pro v/v is not for street use!!??) Isn't that all taken care of by a stock GM "combination valve" for disc/drum setups? I agree it's not the cleanest look having this clunky thing hanging under the MC in a C1 but is it actually better;...cleaner and more functional with a residual in the front and one in the rear?
Or is is marketing just telling you that you need this based on people saying they've had front discs with a stock C1 MC for years?
Like to do it right the first time if possible?
Thanks again in advance for any helpful input from members who've been there, dun that!
Gord

Residual valves
 

Don't know if it's true or not, but I spoke to Wilwood about the necessity of a 2# residual valve for the front discs and they said no. If the M/C is on the firewall and above the discs, it wasn't necessary.