Proper Fitting Brake Line to Master Cylinder Port?

dieselzen · #1 (**permalink**) 10-23-2009, 06:53 PM

Good Evening All,
While I know the basics of brake repair, I'm not an expert, and I need some help. I recently replaced my master cylinder on my van ('90 E-350 w/ 7.3 diesel). I replaced the old master cylinder with a Ford OEM replacement (the old one was Ford OEM as well). The front brake port now leaks pretty bad. but the rear seems to be ok. I've determined it isn't a rusted-out line but at the connection between the line and the port. I've included a couple of pictures of both the rear and front ports.
The lines which came off of each port were 3/16". There was a 3/8" tube nut on the Rear Port and a 9/16" tube nut on the Front Port.
As you can see in the pictures, the tube was tightened so much on each port that a groove was mashed into each Port's 'cone'. I was wondering if this is a normal procedure or whether the lines used were actually too small. Am I supposed to tighten the lines til they mash like this?! I read you're not supposed to overtighten the brake lines.
If these lines are too small, how much of the 'cone' is supposed to be inside the brake line? Is the brake line supposed to bottom out near the base of the 'cone' and then be tightened into the flat area at the bottom of the port?
Thank you for taking the time to view my thread

,
dieselzen

Lazy K · #2 (**permalink**) 10-24-2009, 08:18 AM

Brake pipe nuts should be tightened just until they are "Snug". The problem with over tightening is that the pipe flare can crack, either down the flare or around the base of the flare.
So examine the pipe end for hairline cracks. If it is cracked you can cut the end off it just behind the flare and reflare it.

Ford_Six · #3 (**permalink**) 10-24-2009, 11:17 PM

Did you put another used MC on? That's not a very good idea, as the master cylinder bore gets corroded outside the normal piston travel, and when you bleed it in the new application, the corrosion cuts the rubber of the piston and makes it leak, usually within a few days to a week or so after installation.

dieselzen · #4 (**permalink**) 10-25-2009, 01:13 PM

Thank you for your replies, Lazy K and Ford_Six,
Yeah, I thought the brake lines shouldn't be tightened too much as once you've deformed the 'cone' through over-tightening, you've uniquely mated that connection. Introducing a new mating surface to either side of the connection will most likely not provide an air-tight seal. I've just noticed there is an edge on the front port's brake line flare which shouldn't be there. I think all line flares are supposed to be smooth all over the flare surface area. I think the edge is not allowing the line to be air-tight against the 'cone's' mating surface. If I leave the line flare the way it is, I'd have to over-tighten the connection and mal-form the new surface on the Master Cylinder to get an air-tight seal. And even then it may leak. I'm going to attempt to carefully file the edge off, and then again, I may just buy a new line and be done with it.

The new Master Cylinder is brand spanking new from a dealership. And I certainly don't want to mess it up like the previous MC has been done (I didn't do it, PO's so called "mechanic"; so many bad surprises I've had to clean up due to that b*****d!)

The question I really wanted answered the most is if the 3/16" brake line is the proper line for these two ports? As you can see from the photos, the old lines only take up a small portion of the cone area, and I was wondering if perhaps a 1/4" line, or even a 5/16" line, would be more appropriate. I just don't know if the top of the flare is supposed to stay above the bottom of the fitting after being "snugged", or whether it's supposed to rest very close to the bottom, and then be "snugged" to the flat area at the bottom. All the other lines on the van are 3/16" and the old MC lines have gray paint on them, like I think the OEM does it................
Again, thank you for answering,
dieselzen

Ford_Six · #5 (**permalink**) 10-25-2009, 03:36 PM

Ford dealt with these fittings in two ways: One was a very large nut with a small bore for the 3/16" line, the other was an adapter fitting. It is a 3/16" line from the factory either way.

Lazy K · #6 (**permalink**) 10-25-2009, 03:40 PM

Good question about the pipe sizes. The pipe on the front port should run down the frame, I think, to the RABS module and should be 1/4in pipe then it is 3/16in from the RABS module to the rear axle.

dieselzen · #7 (**permalink**) 10-25-2009, 05:36 PM

Ford_Six, and Lazy K,
Yeah, both the front and rear lines off the MC, like you're saying Ford_Six, are 3/16".

The front port is a 9/16" tube nut (5/8"wrench to adjust) at the port, and a 3/8" tube nut (7/16" wrench to adjust) The 3/8" connection hooks into a tee which has two 3/16" lines going to the front calipers. The largeness of the tube nut, and the small amount of area the 3/16" line takes up on the MC's 'cone' made me suspicious that something had been done either half-a**, or to keep the PO coming back to spend more money.

The rear port is an invert of the front line, with a 3/8" tube nut coming out of the integral proportioning valve in the MC to a 9/16" tube nut which hooks into a brass adapter connecting to the line going to the RABS valve.

I will go to the dealership and get new MC lines from them to make sure I have the proper specs. If I had another vehicle to use to go purchase experiments for this problem, I wouldn't have bothered ya'll with this. As it is, I've got someone coming out to give me transportation, but I don't want to waste their time with any un-foreseen stupidity which leaves me in the same position I'm currently in.

Thanks for replies,
dieselzen