Leaking brake line flares

[Nelson]

I'm trying to replace all the brake lines on my Mk 2 Sprite but it is not going at well. I can't keep the flared connections from leaking. I redid the connection at the m/c to make sure it is fully round and what I think is a good size but when I apply low air pressure to the m/c I get a small amount of fluid coming up around the tubing in the fitting. I'm afraid to go super tight with my wrench but I have it very snug. The line from the m/c goes to the junction on the opposite wheel well and I have the other lines there disconnected and their holes plugged. Yesterday with all the lines connected I intended to bleed the system. I found that I had brake fluid leaking out at three of the wheels so I emptied the m/c and am trying to proceed with getting each section redone and tested. Since I have the leak at the m/c I am making no progress with my project. Does anybody out there have any good techniques that I can use to make a leak proof system?

Nelson

 

[DrEntropy]

The replacement lines have the proper "bubble flair" on 'em, right?

 

[Nelson]

These lines have a double flare that I put on them with a friend's flaring tool. I suspect that my flares might be faulty but they look like the ones on the original lines. I purchased a coil of 3/16" tubing from a local parts place.

Nelson

 

[Trevor Jessie]

Doh! You need a bubble flare at the M/C. Half of a double flare works sometimes.

 

[DrEntropy]

There is a tendency for the tubing to split when the anvil puts the "bubble" on the end due to stress... Guaranteed leaker. A "trade secret" I will offer is to have a round "Swiss" file (very small O.D. file) to round the edge of EVERY end, both inside diameter and out. This reduces the chance for a "stress riser" in the tubing. #220 grit wet-or-dry sandpaper for a finishing polish. You want NO sharp edge either on the I.D. or O.D. of the tubing before attempting the flare.

HTH!!

 

[Nelson]

Those are good thoughts. I found out quickly that the inside of the cut needed to have the cutting burr removed. I did that with a snug fitting drill bit but the edges wound up very small. I like the idea of rounding inside and outside edges. I have had the edge split and have reformed a new flare at that point on some of my other pieces. The rounded edge will also present a greater surface to provide the needed seal. I wish I could simply place a small o-ring or washer into the hole but that apparently isn't done.

Thanks,
Nelson

 

[HAN8L1965]

Nelson,

I don't know where you are in Ohio but there is a shop in Westerville north of Columbus called Right Stuff off County Line Road. Their head tube bender there is Jim. I just had all my lines redone in stainless. He stands behind his work and the price is reasonable. Just take in your old line and he will easily reproduce in stainless or steel and maybe some of the other products. We had a couple that did not come out right and he replaced at no cost. Great People. Next day work.

Mark

 

[Nelson]

I live in northern Ohio and that puts me about hundred miles from Westerville. I'll keep Jim in mind but I haven't totally given up on getting them taken care of on this end. I appreciate your suggestion.

Nelson in Medina, OH

 

[Hooper11772]

Hi Nelson,
Another suggstion that I got from a local parts guy in my area was to use a fitting that converts the bubble flare to a standard flare. If you use this on the master cylinder end and the splitter it will allow you to run a standard double flare line. I took this option since I did not have a bubble flaring tool.

 

[Nelson]

I just found out last night that my problem was one of my own doing and my own ignorance. Never having dealt with flares before I had no idea what I was doing. As it turns out I made all my flares of the double flare type when they should have been bubble flares. I didn't know what bubble flares were. Some of the responses I received used the bubble flare name but I didn't realize that there was something other than what I had made. Today I hope to try to start redoing all my lines. Hopefully I made them long enough to handle having their ends shortened for a correct flare. If only it were possible to do something for the first time and still know how to do it correctly.

Nelson

 

[bill_young]

Nelson, you can make a reasonable bubble flare with a standard double flaring tool. Use the "flat" side of the vise instead of the side with the chamfer around each hole. Use the double flaring insert as the first step then remove and do the final form with a light application of the beveled end of the tool.
One other thing, bubble flares need the matching backing nuts for them, backing nuts for double flares will not support the rear of the flare correctly leading to leaks and failures.
I also found that if you want to fit AN type lines to the original MG master cylinders and slave cylinders designed for bubble flares that a male AN union fitting will screw right in and seal well. I like to use a bulkhead type union so that the jamb nut acts to hold the fitting and keep it from backing out. I know that this isn't "proper" but I've used them on my Midget for 10 years now without any problems. Almost my entire brake system is plumbed in AN stainless lines as well as the clutch.

 

[Trevor Jessie]

Yup, the bubble flare need a nut with a long shoulder. And like Bill, I've used a male AN fitting to go into the MC and never had a problem. However, I suggest using steel AN fittings if you are doing this (not aluminum).

 

[bill_young]

Trevor, it's not only the length, but the shape on the end. A nut for a double flare will have a slight chamfer on the end like this \ / and the nut for a bubble flare will have a nice 90 degree shoulder to fully contact the rear of the bubble flare. If you use the double flare nut the center of the line can be pushed back due to insufficient support as you tighten the fitting and it may eventually leak.

 

[Trevor Jessie]

Right Bill, I should have clarified. But when I reach in the bin I can easily pick them out by the length.

 

[Nelson]

Thanks, guys. I like the idea of using the back of the vise to do the forming of the bubble. Last night I tried getting a bubble with the beveled hole and I did not like the way the "bubble" looked. The nuts I am using are the ones from the original lines so they are adequately long. I had bought a batch of new nuts from a local parts place and then I found out that they wouldn't reach the bottom of the hole so I cleaned up the original nuts.

Nelson

 

[DrEntropy]

FWIW: The seats in all the devices (master cylinders, slaves, calipers) are designed to ~expect~ a bubble flange as a seating surface. The bubble flair anvil "kits" are cheap compared to sheetmetal replacement or worse. Knowing how to form a proper bubble flare on a piece of Bundy is (IMO) part and parcel of LBC ownership/maintenance responsibility.

...I'll just go back to my cave now....