I don't have a lot of experience with brake systems, but I just replaced the master cylinder (dual reservoir) on a 70 CJ5 and 2 issues came up:
1) Cannot get the brake lines to seat properly into the master cylinder fittings - leaks a little fluid during every pedal depression when bleeding (especially the front reservoir). Bad threads or flares? Over/under tightened? Need new brake lines (these are short sections that go into a 2nd set of fittings which may be a proportioning valve - does a 70 have one?)
2) The leaky fitting maybe the cause of this 2nd problem, but after bleeding the rear and then RF lines, I could not get any fluid to bleed out of the final LF line. That is when I went investigating the lines and found the leaky fitting. While this certainly does not allow a proper bleed, it didn't seem enough to inhibit all fluid from moving through the LF line and I should have gotten something out of the bleed valve. Something else going on here?
A little more information - I did bench bleed the MC prior to install. From reviewing previous threads seems like the Prop Valve causes a lot of issue. If I was able to bleed both the rear and RF, I wouldn't think the PV is causing any problems? True or do I not understand how the PV works? Happy to take a look or adjust the pin at if anyone knows about early CJ PV valves.
When you look at the lines fitted to the MC, are the flairs smooth and even? If they are even slightly jagged, warped/distorted or cracked, they will leak. You can replace them for pretty cheap, may be worth it just for peace of mind.
Yes your Jeep should have a PV. Don't know if that could cause the problem you describe with the front left brake (look to see if there are separate lines coming out of the PV for each of the front brakes, or only one with a "T" somewhere further down the line). Could also be something wrong with the wheel cylinder (assuming you have drum brakes). Did you have any problems with that brake before the MC replacement? How does the brake pedal feel after you bled the other 3 brakes?
Brakes feel very soft like there is air in the line - certainly not what it felt like before. The flares going into the MC look good - but I just pulled them out and will replace them with new ones. As for the PV (at least what I think is the PV - (small rectangular box mounted a few inches in front of the MC along the DS frame rail)), its 2 lines in and 2 lines out. There is nothing on this PV/junction that looks adjustable. So if I am getting fluid to the RF, then it is not the cause of the problem with the LF. Along these lines, after leaving the supposed PV, both the front and rear lines go through a junction where they split to the right and left sides. These junctions look to have a valve system (round knob on top and some pins coming out of the top) - maybe this is where the problem is between R and L front lines.
Won't be able to investigate R and L difference until I get the new lines coming out the MC put in. Then go through the entire bleed process again and see what happens.
Along these lines, after leaving the supposed PV, both the front and rear lines go through a junction where they split to the right and left sides. These junctions look to have a valve system (round knob on top and some pins coming out of the top) - maybe this is where the problem is between R and L front lines.
Assuming that stopping the leak at the MC doesn't fix everything, I'd look closely at that front line junction and the wheel cylinder (as well as the line in between the two).
Okay - so its been a few days but I made new brake lines to connect between the MC and the PV and bled all the wheels. Got the same issue again - Rear wheels and front right bleed fine, but get nothing out of the left front - no fluid or air and pedal seems pretty much like the bleed valve isn't even open. Pretty much seems like a plugged line. With front end in the air, spun the tires by hand and had someone push down brake pedal: right front stops with brakes and left front feels no affect (no brakes on left front). I believe this issue existed prior to replacing the MC as I started getting severe pull to right when applying brakes (half the motivation for initially starting this project)
Seems like something is either plugging line for left front or there is an issue with wheel cylinder. Where to start? Looks like I would have to remove the hub to remove the wheel cylinder? Can I remove the cylinder without taking apart the entire brake assembly - just remove it from the backing plate?
Finally - I would assume its best to replace both front wheel cylinders at the same time, but absolute necessary?
I would crack the line going into the LF wheel cylinder and have someone push on the pedal that way you will know whether you are getting fluid to the cylinder. If sluid shows up it is the cylinder. If not you have a bad line. You can remove the wheel cylinder by removing the brake drum and then leaving everything in place take the bolt out of the baking plate and pull it out.
Thanks - I think that sounds like the way to go. As always, disconnecting any brake line connection is an adventure in un-seizing without destroying the fittings and hoping they seat back together. Although the new lines fittings into the MC are working, they do seem to slowly ooze fluid (new fitting and new MC should seat perfectly - but do not).
I dream of a fully function and leak free brake system one day. Probably should have redone the entire system and converted to front discs with the appropriate MC.
I am thinking there is something wrong or damaged with the threads or fittings on the MC, but I am just too burned out on it right now to work on it. I am going to try and fix the left front line or wheel cylinder (whatever it is that is keeping the left front brakes from working) and then will go back and investigate the MC.
I took a break from the brakes today and am working on suspension and installing new shocks.
For what it matters - I was able to follow the left front line through a few connections and got it to bleed to all the way to the wheel cylinder and then through the wheel cylinder valve. Not sure why it didn't bleed properly the first time, but the fluid was pretty nasty - maybe I loosened some sort of blockage while messing with the lines (all the fluid was really nasty and their was a layer of sludge at the bottom of the old MC). Pumped clean fluid all the way through and everything is working great - well as good as 10 inch drums work. Thanks for all your help.
Still not sure about the MC fittings - drove it around a bit today so we'll see if I get any seepage. Leaky brake fittings are pretty rare, especially with new components, so its possible I may have damaged the fitting seat - hope not as I would rather not have to buy another MC. Local mechanic here suggested I might be able to replace the fittings on the MC (possibly even transfer the old ones to the new one) if they are damaged. Is this possible?