Getting air in the lines somehow

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TrailerParkGinger

TrailerParkGinger

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I recently did a front disc conversion with a Dr.Diff 11.75” brake kit and his stock a body dist/prop valve and used a Right Stuff 15/16” bore MC. I had to make all new lines because they were all siezed in my 50 year old drum distribution block. Everything bled great and I had a great pedal. Then when I went to bed the pads, after 4-5 hard stops from 60mph to around 15mph the pedal goes limp noodle and spongy and needs pumped up. I rechecked all my lines, found 1 tiny fluid weep at the front inlet to the prop/dist block from the MC and tightened it, rebled and tried again, same deal, but no fluid leaks this time, anywhere. Dry as a bone. This only seems to happen on hard braking when you push it excessively hard like a panic brake situation, where it is depressed rather far. If it is just easy stop and go, my pedal feels fine, but on a hard, quick stop it needs rebled again. I think it might be my MC, but I really hope not because it’ll be a pain to remove since its the bolts that hold the pedal assembly on too, I might go and buy the 2 to 4 bolt adapter if I have to do it again. Any tips from the gurus on here? I’m at my wits end and just want to drive the old girl with her all new suspension with adjustable everything and boxed LCAs. :( Also Sorry its not an A body, I asked on the B Body forum too. My dad sold his dart long ago. I’m looking into 67-69 Barracudas though :)

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My only thoughts are if it brakes normal under normal driving but is spongey under hard braking. I have had this previously is the master cylinder is too small of a bore, Under hard braking you push past the point where is effective. If there are no leaks then air can not get into the system.
Good Luck, trouble shooting brakes can be difficult sometimes.
 
Steven190 said:
My only thoughts are if it brakes normal under normal driving but is spongey under hard braking. I have had this previously is the master cylinder is too small of a bore, Under hard braking you push past the point where is effective. If there are no leaks then air can not get into the system.
Good Luck, trouble shooting brakes can be difficult sometimes.
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I only get air if I push hard, it locks the brakes and stops very well, then the pedal needs to be pumped up from that point on until it is rebled
 
If air is getting into the system then fluid will be leaking out. My only though is maybe that the seal on the master cylinder reservoir are sucking air into the chamber.
 
Steven190 said:
If air is getting into the system then fluid will be leaking out. My only though is maybe that the seal on the master cylinder reservoir are sucking air into the chamber.
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I can’t find a leak and it’s driving me nuts haha. I’ve gotta be missing something. Thank you for your replies, I really appreciate the ideas and input, I’ve gotta pick this car apart again and see if I am missing something. I did see a leak on the MC reservoir, but for the front bowl, to the rear circuit and it was overfull, after I rebled and it went down to a normal level it was fine and didn’t leak any.
 
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I'm voting for the master cylinder too based on what you say.
Unless there is something amiss with your bleeding like it's not complete.
I would put that adapter on as well while you are at it.
 
I am using that same MC from Right Stuff, and I REALLY struggled getting a good seal on the line-in to the second resv. I dont know if this was the best option, I ended up having to use a soft copper crush washer in front before putting the brake line in to really get it to seal down. (I guess also make sure you have your proportioning valve set properly so that you aren't ending up with too much pressure to the remaining drums)
 
Grumpy Pete said:
I am using that same MC from Right Stuff, and I REALLY struggled getting a good seal on the line-in to the second resv. I dont know if this was the best option, I ended up having to use a soft copper crush washer in front before putting the brake line in to really get it to seal down. (I guess also make sure you have your proportioning valve set properly so that you aren't ending up with too much pressure to the remaining drums)
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Its the stock type fixed at I believe 70/30 bias
 
Grumpy Pete said:
That is probably close to what mine ended up being, but if you need to replace it, the right stuff sell ones that on a dial that you just have to splice in as well.
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I bought the MC in that kit with the valve and adjustable pushrod. I decided to use a stock on that I didn’t need to splice. I was having problems before this new valve. I just didn’t get a good pedal before I swapped it, now its only safe for about 2-4 tries haha
 
IMO, you may be boiling the brake fluid.Or rather some component in the brake fluid,lol.
Do not use shop brake fluid. Invariably it has absorbed moisture from the air. When you heat the brake fluid, that moisture flashes to steam when you release the pedal at the end of the braking run, and there is your air! The confirmation is that you can run around for days with no issues until that one time you heat up the fluid. Another confirmation is that it never happens during testing in the shop, on a cold system.
Drain all the fluid and put in FRESH from a SEALED container,hi-temp, disc-brake fluid. Then, if you haven't already done so, install those "stupid little metal spacers" on the pads between them and the pistons to help divorce them.
I have been using the 15/16 M/C since 1999, on my KH factory system,with silicon fluid,and with zero problems.And I love it.
Good luck
 
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AJ/FormS said:
IMO, you may be boiling the brake fluid.Or rather some component in the brake fluid,lol.
Do not use shop brake fluid. Invariably it has absorbed moisture from the air. When you heat the brake fluid, that moisture flashes to steam when you release the pedal at the end of the braking run, and there is your air! The confirmation is that you can run around for days with no issues until that one time you heat up the fluid.
Drain all the fluid and put in FRESH from a sealed container,hi-temp, disc-brake fluid. Then install those "stupid little metal spacers" on the pads between them and the pistons to help divorce the pads from the pistons.
I have been using the 15/16 M/C since 1999, on my KH factory system, and with silicon fluid,with zero problems.And I love it.
Good luck
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I used the Synthetic DOT 4 because I was worried about it. I bought it new and in small bottles so I wouldn’t have to recap any and risk moisture getting into it. I just hope I can figure something out, I miss driving the old girl and taking the family on road trips
 
Or when the master returns from far travel air is getting sucked in around the master cylinder plunger.
Try hitting the brakes hard, then let the pedal up slowly instead of just taking your foot off.
If it doesn't do it when you let up slowly that is what it is. (not a good seal on the master piston)

You can try this without actually driving the car.
 
Very good point TB.
But IMO, I want to say highly unlikely. Brake fluid in the front lines moves only a tiny amount. Doing the math on a 2" piston I get 1cc per two pistons at a very large .010 piston retraction. In a 15/16 bore this is .177 inch or a little less than 3/16". At a more likely retraction of .005 say, it would be half that or about 1.4/16ths.
But since fresh Dot4 is in the entire system, there is really no other possibility.
Very good point TB..

Unless of course if the pads are dragging in the first place, then there could already be a ton of heat in the calipers, and dry Dot4 fluid is advertised to what? 446*F, IIRC. If braking starts at 200 say, well you get the picture.
 
Do you have rear drums? Is the rears hooked to the FRONT of the cylinder? Does the cylinder have "residual pressure" valve at least for the drums end?

Otherwise I agree might be a bad master
 
67Dart273 said:
Do you have rear drums? Is the rears hooked to the FRONT of the cylinder? Does the cylinder have "residual pressure" valve at least for the drums end?

Otherwise I agree might be a bad master
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Rear drums, hooked to the front resevoir, the smaller one. I called Dr.Diff and spoke with him, he believes it may be the master cylinder too. Randomly losing hydraulic pressure due to a slightly out of spec piston. I’m going to call right stuff detailing and see what they say, Cass advised to do this. I’ll probably end up ordering his aluminum one because its easy to install conpared to the under dash limbo and contortionist routine.
 
Also anywhere there is a pipe fitting rather than an inverted flare you need to use a pipe sealant. some of those aftermarket aluminum proportioning valves or residual pressure valves use a pipe to if adapter. I use Loctite 545. It works great on brake fluid applications
 
Debris in the master, blocking fill port? The holes that fill the master cyl bores are tiny.
Wheel bearings adjusted correctly
And caliper mounts mounted properly?
But if its air, and bleeding is required, how much bleeding does it take to get the air?
Is it right at the bleeder, without pumping or after a few strokes of the pedal?
Using a helper, or by yourself?
And what bleeding procedure?
 
Tooljunkie said:
Debris in the master, blocking fill port? The holes that fill the master cyl bores are tiny.
Wheel bearings adjusted correctly
And caliper mounts mounted properly?
But if its air, and bleeding is required, how much bleeding does it take to get the air?
Is it right at the bleeder, without pumping or after a few strokes of the pedal?
Using a helper, or by yourself?
And what bleeding procedure?
Click to expand...
It takes a considerable amount of pumping when rebleeding, then still feels off unless I bench bleed the MC again. I have a helper, I also jack that part up higher than the others before bleeding, try to get the air at the top bleeder on the caliper. No air from the rear circuit though, looks great and just a stream, the fronts spew fluid and air like a spray bottle after a few stops. The MC is the main suspect. Anyone know offhand if the aluminum MC uses the 9/16x20 and 1/2x20 fittings as the earlier mopars?
 
Any chance the level in the MC is too low, allowing air in the lines when you floor the pedal?
 
Now I know you have said and done a lot but just throwing this out there are the bleeders at the top of the calipers ? They do fit upside down ?
 
Wont get air in m/c while pedal is depressed.
You mentioned it takes some time to get the air out.
Static test. Depress pedal, both feet as hard as you can. Basically, duplicating a hard stop. But hold it for 10-20 seconds. If there is a fluid leak you should feel pedal drop. If problem still exists, with a helper, try bleeding at master by cracking the lines. If you get air, its the master.
 
maybe pop the cap off, and have someone stand on the pedal, see what it does?
 
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