Dragging calipers on my '73 conversion

[Ross Wooldridge]

Drag. F#@$#&g Drag... This is really puzzling me.

So.... How many master cylinders have you tried? Could there still be an issue with the master? We kinda need to rule out the booster now.

Just a thought - likely the old single diaphragm booster you just installed temporarily has a serious vacuum leak which is contributing to the situation you're describing as a misfire.

 

[Zymurgy]

The old single was working fine when I removed it. It drove fine for 20 miles, only started acting up after I stopped for gas. Checked the plugs on the booster and they are all in place.

 

[Zymurgy]

This is the only correct master, I decided to install the single booster hoping I could rule out other aspects if the brake job.

I originally had a '73 master installed to the dual booster.

 

[mr. fix it]

Agreed Mike

 

[Ross Wooldridge]

Hmmmm.... still, the diaphragm on the single booster could have torn. All would look kosher on the outside, but still make the motor run like a bag of hammers. Just trying to problem solve - an ignition issue is less likely to crop up than the old diaphragm giving up the ghost perhaps.

So, remind me what master you're using? Be it "correct" or not, it still may be hanging up inside? Perhaps it's time to try a replacement of the same application... or perhaps one from a near same application.

My spidey sense is now tingling at the master - this is after having it go off on the booster which lead to the discovery of the problems it had and you sending it back. I'm just guessing, with my own personal experience as my guide. Having done this twice now, with absolutely no problems with either the master or the booster, it really puzzles me. Because my cars have autopilot, I used the 68 Charger with discs and 10" rear drums master, which bolted up perfectly, had the right amount of adjustability on the master pushrod, and have worked flawlessly since.

 

[Zymurgy]

Ross thanks so much for the input. I am hoping to work on her tomorrow. I will reinstall the dual booster first and see if my horrible running goes away.

The master I have installed is spec for 1967 Chrysler with disc brakes.

The only plus to all this is the pushrod was seated when I removed it, so it became seated when driving and may have just heated up during the earlier part of the test drive. It was definitely not seated when I started. The pushrod measure 1-1/8", with adjustment turned in completely. It was around 3/4" at he end of the drive.

I will give the set up another chance, now that I won't start the drive with an unseated pushrod. If it occurs again I will order another master.

 

[Ross Wooldridge]

OK, that sounds logical. Please keep me posted.

For what it's worth, I don't measure the pushrod length, I only look at how far the pushrod holds the master away from the body of the booster (with all gaskets etc in place) as I do the final install. The rule of thumb is: As you bolt the master up, the properly adjusted pushrod should keep the master pushed away from the booster about 1/16th of an inch, which would result in a very slight compression of the master piston by the booster pushrod when torqued down.

Any more than that and there's problems. If that basic fitment isn't available, then something's not matched properly. Either the wrong pushrod in the correct booster, or the wrong master piston in the correct master. Something like that.

Keep me informed!

 

[detmatt]

Sorry Mike, I feel helpless up here not having any experience with brake conversions.

 

[Zymurgy]

Ross I was actually thinking of that when I was bolting up the master initially today. In my head "Did Ross say 1/16 or 1/8".
It was probably closer to 3/16" when un seated. I will definitely set it to 1/16" this go around.

 

[Ross Wooldridge]

Give it a go!

 

[cantflip]

I will give the set up another chance, now that I won't start the drive with an unseated pushrod. If it occurs again I will order another master.

It seems to me that you had everything working well until the pushrod unseated... which also seems like an odd problem to me. I think you have done great with all of this considering what a ginormous PITA it has become.

To my way of thinking, the booster seems to be the weak link here... and I understand that is the worst part to obtain a replacement for. I would be very distrusting of the booster by this point in the game, and a simple rule for brakes is if you don't trust the part= replace it.

Go ahead and see if it makes a running difference or just plug the vacuum line to it to check the same thing. But if that booster continues to disconnect somehow, that really needs to be addressed or it will happen again at an inconvenient time (see Murphy's law), and may lead to a dangerous situation.

 

[Zymurgy]

Made it to the shop and reinstalled the dual booster. I went to reinstall the master and the push rod was at an 1-1/4". I realized the issue immediately this time, because I measured it before I installed it and it was at 3/4". The pedal is pushing the pushrod out from the other side. I added some flat washers until I got no dead pedal pressure. Then I adjusted the pushrod to the 1/16" pressure when the master is mounted.

Unfortunately I wasn't able to test drive the girl, because she was running like ****. The issue that required the tow was unrelated to the old booster. I haven't even looked into that yet. I will save that for another thread if I don't figure it out.

An observation, however, on the rough running. When I started it and got the RPMs around 2,500-3,000, it would actually run pretty smooth. As soon as I drop the RPMs down it would pop and misfire and die. Any suggestions where to start?

 

[Ross Wooldridge]

Standard checks - look for major vacuum leak - intake to booster, plug wires seated at both ends, cap and rotor condition, choke pulling off at correct temp (mine was sticking once - bag o' hammers), ground strap at rear, neg battery cable connections, coil connections, vacuum advance canister (functioning? getting vacuum?)...

Silly question... plug wires get switched around by mistake?

Those sorts of things are where I'd start.

 

[Ripinator]

Made it to the shop and reinstalled the dual booster. I went to reinstall the master and the push rod was at an 1-1/4". I realized the issue immediately this time, because I measured it before I installed it and it was at 3/4". The pedal is pushing the pushrod out from the other side. I added some flat washers until I got no dead pedal pressure. Then I adjusted the pushrod to the 1/16" pressure when the master is mounted.

Unfortunately I wasn't able to test drive the girl, because she was running like ****. The issue that required the tow was unrelated to the old booster. I haven't even looked into that yet. I will save that for another thread if I don't figure it out.

An observation, however, on the rough running. When I started it and got the RPMs around 2,500-3,000, it would actually run pretty smooth. As soon as I drop the RPMs down it would pop and misfire and die. Any suggestions where to start?

Mike: It really sucks to see you getting wrapped tighter and tighter around the axle with this disc brake conversion. I am truly bummed out for you. As regards the crappy running engine, I would check the points and the condenser. I'm sure your wires, etc. are practically new, as is probably the rest of your ignition system, but there are a bunch of crappy point sets out there, and maybe you got one of them.

 

[Zymurgy]

Little ignition update. Popped the cap to check the points gap, there was none. Set the gap, don't recall it ever running smoother at idle. Ready for a test drive, started acting up again just not quite so bad. I decided just to pull it back in and lay out a plan to switch to the electronic ignition.

I have everything planned out, but a busy Sunday will most likely keep me from working on her until next weekend.

 

[mr. fix it]

We're routing for you Mike!

 

[Ripinator]

Little ignition update. Popped the cap to check the points gap, there was none. Set the gap, don't recall it ever running smoother at idle. Ready for a test drive, started acting up again just not quite so bad. I decided just to pull it back in and lay out a plan to switch to the electronic ignition.

I have everything planned out, but a busy Sunday will most likely keep me from working on her until next weekend.

Just throw a new point set in it, and go on down the road.

 

[Zymurgy]

Just throw a new point set in it, and go on down the road.

That is an idea, but I think the condenser is part of the problem too. Out of general principle I refused to buy another piece of crap, made in China, condenser. My last 2 lasted one month and 2 weeks. It gives me a good incentive to go forward with the electronic ignition.

 

[Ross Wooldridge]

I have and I've never regretted it.

 

[cantflip]

I used to get rid of points with boneyard distributors back when... just due to maintenance and a slight improvement (I hoped) in timing accuracy. Today with everything coming from overseas and quality issues I keep hearing about... IDK which way I would go except to keep a box of spares and tools in the trunk.

I think of you points guys every time I see a bulk lot of old points and condensers... Kinda glad this isn't one of my issues to think about.