Master Cylinder Bleeding Problem

[Samplingman]

Yes, the bloody master cylinder will not bench bleed properly. 1970 Chrysler 300 with power disks. Followed the instructions here and in the FSM, master in the vise, fill the reservoirs, watched for air bubbles, but for the life of me I cannot get the front chamber (rear brakes) to pass any fluid, except for a tiny bit at the base of the tube. I pumped that piston about a hundred times and still got nothing. This is the second new master, the first one I think I pushed too hard and it started to leak out the back. I checked and the residual pressure valve is installed in the front chamber, but I’m still not sure what that even does, other than block the fluid. Am I missing something here?

 

[70bigblockdodge]

I usually just hold my thumb and heel of my hand over the ports. Pump the piston. Thumb and hand act as a check valve to not allow air back in as fluid escapes on piston push.
Same concept.
I have used the clear tubes also never having the problem you mention.
Maybe try your thumb on front port and leave tube on the rear port, give it a little resistance? Worth a try.

 

[3C's & a D?]

I've never had much luck with bench bleeding. I think most of us are wary of pushing in too far, for good reason. I always just install it, without attaching the line's, and "bench bleed" it in place, with the same set up you have, using the brake pedal.

 

[mr. fix it]

I have found doing baby bumps of the piston while holding fingers over the ports help as well when bench bleeding.

Have had more DOA out of the box than I care to think about as well since getting my Polara

 

[cbarge]

Best to find out that its a dud now rather than later..get another master IMHO

 

[bigmoparjeff]

I ran into issues bench bleeding a 1971-up disc brake master cylinder last year. I had to use the check valve style fittings to get all the air out, where I can usually just use the open end fittings.

I have a brand new 1970 disc brake master that I need to bench bleed for an upcoming project. I'll see if I can do that on Tuesday to see how it goes or if I have issues again. I just gave it a quick paint job this afternoon, so it should be ready to go by Tuesday. Maybe I will notice something that can help with your m/c problem.

Jeff

 

[Samplingman]

I ran into issues bench bleeding a 1971-up disc brake master cylinder last year. I had to use the check valve style fittings to get all the air out, where I can usually just use the open end fittings.

I have a brand new 1970 disc brake master that I need to bench bleed for an upcoming project. I'll see if I can do that on Tuesday to see how it goes or if I have issues again. I just gave it a quick paint job this afternoon, so it should be ready to go by Tuesday. Maybe I will notice something that can help with your m/c problem.

Jeff

Thanks Jeff, I’d like to know if it is just me. I thought that there might be some assumed process that’s not spelled out in the FSM that I was not following.

@70bigblockdodge, I tried just that, holding my finger over the rear chamber and the piston wouldn’t budge! Something had to be blocking the fluid from getting out of the front chamber. I also noticed the piston was not returning all the way flush again. I then tried the “baby bumps” and hold, but that’s when the vise gave way and master and fluid flew across the garage. I grabbed a beer after that, I was done. Guess I’ll look for another reman. This one is a Fenco, but I’ve never heard of them. I’ve already sworn off Cardone, if anyone has a suggestion I’m all ears.....

 

[mr. fix it]

Thanks Jeff, I’d like to know if it is just me. I thought that there might be some assumed process that’s not spelled out in the FSM that I was not following.

@70bigblockdodge, I tried just that, holding my finger over the rear chamber and the piston wouldn’t budge! Something had to be blocking the fluid from getting out of the front chamber. I also noticed the piston was not returning all the way flush again. I then tried the “baby bumps” and hold, but that’s when the vise gave way and master and fluid flew across the garage. I grabbed a beer after that, I was done. Guess I’ll look for another reman. This one is a Fenco, but I’ve never heard of them. I’ve already sworn off Cardone, if anyone has a suggestion I’m all ears.....

If you have an original MC, you could find a local rebuilding shop and have it rebuilt...
If that’s an option...

 

[PH27L7]

Don’t care too much for your bleeding arrangement using those tapered inserts. Unlikely but the insert could be contacting the residual valve blocking flow a bit. I like to mimic what the FSM does with screw in fittings or alternately used the plastic ones that do the same thing (included w/ most replacements). That way you’re sure to have unrestricted flow.

One of the problems I’ve found with the aftermarket stuff is crappy machine work. You might want to take yours apart to see exactly what the problem is. I suspect the front compensating port (small hole) is somehow being blocked or wasn’t drilled through. It should be just in front of the forward seal & bubbles should briefly come out as you push the pistons.

You cannot push too far and damage the MC if it’s new, the pistons will just come to their stops. You get in trouble when the MC is rusty inside, push far & you disturb the crud & get a failure. Also I don’t know how you’d get all the air out without bleeding on bench. I set the thing at various angles to ensure all bubbling stops, it’s amazing how much air can be in there.

 

[Samplingman]

Don’t care too much for your bleeding arrangement using those tapered inserts. Unlikely but the insert could be contacting the residual valve blocking flow a bit. I like to mimic what the FSM does with screw in fittings or alternately used the plastic ones that do the same thing (included w/ most replacements). That way you’re sure to have unrestricted flow.

One of the problems I’ve found with the aftermarket stuff is crappy machine work. You might want to take yours apart to see exactly what the problem is. I suspect the front compensating port (small hole) is somehow being blocked or wasn’t drilled through. It should be just in front of the forward seal & bubbles should briefly come out as you push the pistons.

You cannot push too far and damage the MC if it’s new, the pistons will just come to their stops. You get in trouble when the MC is rusty inside, push far & you disturb the crud & get a failure. Also I don’t know how you’d get all the air out without bleeding on bench. I set the thing at various angles to ensure all bubbling stops, it’s amazing how much air can be in there.
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Thanks for that diagram. I had my suspicions about those plastic bleeding pieces. I spent some time last night watching The Ram Man videos on Mopar master cylinders an decided to take the reman apart just to see. I also realized I still had the original master (no dimple on the front), but it is rusted solid. I'll be soaking that one in evapo-rust for the next week.

One issue right off, besides the problem with the front chamber, was that the piston was no longer returning flush to the booster mounting face. When I got it, it was protruding slightly, but now it was stuck in about 5/16. I removed the retainer screw at the bottom and was able to pop or the rear piston out. I didn't have my compressor on so I couldn't pull the rear piston out, but used a long screw driver to compress it and was able to get the front chamber to push fluid through with the plastic bleeder attached, so at least they worked there. I then put the rear piston back in, set it flush and tightened the set screw. After a few pumps I was then able to get fluid and air to pump through both bleeders with minimal effort, however, the piston is now 1/2 an inch in and won't move to become flush with the mounting face again. I'm wondering now if the rear spring tension is weaker than the original, or adjusted incorrectly. I'd rather not adjust the booster push rod to compensate.

 

[PH27L7]

When you pull out the pistons, get out a flashlight & look down the bore. Check for any problems, especially for burrs around the drilled holes that might cause the piston to hang up. If there are burrs then the seals are likely shot. I've also seen aftermarket MC's with longitudinal scratches that cause leaks. You should be able to pull the rear brake piston out with needle nose pliers. The originals were so much better than current aftermarket!

 

[Samplingman]

When you pull out the pistons, get out a flashlight & look down the bore. Check for any problems, especially for burrs around the drilled holes that might cause the piston to hang up. If there are burrs then the seals are likely shot. I've also seen aftermarket MC's with longitudinal scratches that cause leaks. You should be able to pull the rear brake piston out with needle nose pliers. The originals were so much better than current aftermarket!

Thanks, I'll be back in the garage later today to check that out. I imagine buying brand new will not be much different.

 

[bigmoparjeff]

The one that I'm working on now is a new Raybestos m/cyl from Rock Auto. Up until fairly recently they were still made in the USA, but now production has been moved to Taiwan. I'm anticipating that it will work fine, but I'll give you a full report on how the bleeding went tomorrow evening. It's going to be some time before it goes on the car, so I won't have any performance info for at least a month. The car it's going on is a problem child anyway, so it might not be a true test compared to a normal car. The car has line locks on it, and I think the line lock solenoid may be the actual cause of the lousy pedal that it has.

It sounds like you got some bad rebuilds. Most of the rebuilds are being done in China and Mexico these days, though I don't know if that's had much effect on quality, since there have always been issues with rebuilt stuff. I've been doing this stuff for 40 years and really never had a problem with rebuilt or new master cylinders until just recently. One of them appears to be a design issue, and I haven't figured out if there's a problem with the second m/cyl or if the issue is with something else in the brake system.

Jeff

 

[70bigblockdodge]

I bought one of these (Raybestos) years ago for my Challenger. Wanted the bigger piston for less pedal travel in my E body. It was a brand new M/C I had no trouble bleeding it and has been on the car for at least 5 years. The rear wheel cylinders have been a different story for a different time.

Sorry forgot to upload image.

 

[Samplingman]

Ok, Raybestos is what I have in my RockAuto cart right now, I'll wait for Jeff's report, but ultimately I'll be ditching this Fenco reman. Thanks guys, great info here.

 

[bigmoparjeff]

The Raybestos master cylinder bled like a champ, and that's with silicone fluid, which is a bit harder to bleed than the standard stuff.

Raybestos does not include a bleeder kit in the box, and I'm not very impressed with the one that came with your reman. You may want to grab a decent kit off ebay or Amazon.

I like the style of fitting that come in this Raybestos kit the best. They are a straight-through design, which flows fluid the easiest. Unfortunately, the seller is in Texas, and it might take two weeks to get the kit with the way mail has been lately.

Standard SAE Brake Master Cylinder Hydraulic Bench Bleeder Kit | eBay

Lots of places have these Thexton kits, which I consider the check valve style. The hose covers up the hole on the fitting and acts like a check valve while bleeding. In theory it's a better set-up, and can get more air out of a difficult m/cyl that the straight-through design can't. It just takes some extra muscle to overcome the check valve effect while bleeding, and isn't needed on most m/cyls. I've had one of these kits for over 30 years now.

Theton 346 One-Man Master Cylinder Bleeder Kit | eBay

It looks like Dorman makes a kit too. You might be able to find one locally at an Auto Zone or Advance Auto.

Dorman 13911 HELP! Master Cylinder Bleeder Kit | eBay

Jeff

 

[Samplingman]

Thanks Jeff! That's just what I wanted to hear. My MC should be here on Saturday. I know I've seen these bleeder kits before, but I have a couple of spare fittings and some tubing, I was going to make my own. I'll update soon. Thanks!

 

[mr. fix it]

I bought one of these kits back in the day (1980's)

 

[Samplingman]

Update, I got the Raybestos MC and picked up the Dorman bleed kit. Unbelievable how easy it was to bleed. The piston went all the way in and returned with out issue. I was also able to return the Fenco reman for a refund. Thanks for the advice all!

 

[Mopars4life440]

Those damn master cylinders will drive a sane person crazy.