67-70 Relocation of Front Brake Lines for Disc Conversion

[pjmoreland]

About six months ago I installed a front disc brake conversion kit from POL. The calipers that came with it orient the flexible brake hoses toward the rear of the vehicle so they can be routed to the stock hard lines on the back of the cross member. After a close call with my tires rubbing on the hoses, I installed the recommended Autozone 88466 hoses. Even with these hoses, I got a slight rub on one side. I was able to address that issue by clocking the hose to keep it away from the tire. Someone mentioned recently that two of his friends have had the 88466 hoses break off on them, causing them to lose their brakes. This got me pretty concerned, so I decided to convert to 71-72 style brake line routing. Here are the components I purchased:

TKT7105S Right Stuff Detailing front brake line kit, SS, 1972 C10
71-987E ClassicParts.com 71-72 brake line clip set
CLP125 Inline Tube brake line clips, 3/16" & 1/4", quantity 2
71-881 ClassicParts.com front to rear brake line union fitting
3/8 inverted flare tee fitting from Napa (don't know the part number)
380712 Napa front brake hose, right, 71-72
380713 Napa front brake hose, left, 71-72
18-4035 O'Reilly front brake caliper, right, 71-72
18-4036 O'Reilly front brake caliper, left, 71-72
RSBK70 Right Stuff Detailing front brake hose mounting tabs <- don't get these!! See step 11

I also bought a set of brake line plugs off Amazon (The Stop Shop) so I could plug the ports of my proportioning valve while the lines were disconnected.

Here's how installation went for me:

1) Disconnected lines from proportioning valve, and installed plugs in their place

2) Detached brake calipers, opened bleed screws, and drained calipers and lines into a container

3) Removed brake hoses

4) Disconnected rear brake line at the fitting located inside the right frame rail, next to the transmission. Installed plug in frame rail fitting to minimize fluid leakage

5) Removed all front brake hard lines

6) Removed rear brake hard lines forward of fitting from step 4

7) Installed new rear brake hard line that attaches to the fitting on the original frame rail line. I was worried this wouldn't work, but the fitting was the right size, and it was in the right location.

[pjmoreland]

8) Installed new front brake hard line that runs along the bottom rear edge of the cross member along with the rear brake line installed in the previous step. Clamped these two lines to the cross member with two of the larger clamps included in the clamp kit. Used the holes for the original brake line clips. Attached with 5/16 bolts, nuts and lock washers

[pjmoreland]

9) Attached the 3/8 tee to the left end of the front brake line running across the rear of the cross member. Attached the front left caliper hard line to this tee, and ran it up under the motor mount and to the front of the cross member. The front right caliper hard line routes the same way and is part of the line that runs across the rear of the cross member. Both lines that run underneath the motor mounts get clamped to the cross member. I used what I believe are the holes for the I6 motor mount position for the small clamps in these two locations.

[pjmoreland]

10) Attached the 71-881 union to the left end of the rear brake cross member hard line. Attached the two remaining lines that run from the tee and union up to the proportioning valve. I didn't attach them to the proportioning valve at this time though. Drilled a hole in the left frame rail for a clamp for these two lines. I mounted the clamp a little closer to the upper control arm than I would have liked, but it does clear.

[pjmoreland]

11) The brake hose tabs I got were not a good choice. The hole for the brake hose is too big, so it doesn't secure the brake hose from rotating. If the brake hose were to rotate due to suspension motion, the line could come loose. I ended up welding in material so I could file a 5/8" hex shape into the tabs that matched the brake hoses. The portion of the tabs where the brake hose attaches is too thick for the clips to work, so I ground it down to .144" thick. Also, the tabs are angled more than 90°, so I sectioned, bent and re-welded them at 90°. Being angled more than 90° causes the hose to hit the cross member right next to the tab. I spent over five hours modifying these dumb brackets. Here are some possible alternatives:

Speedway Motors 91031311:

https://www.speedwaymotors.com/Speed...xoCXNwQAvD_BwE

Inline Tube E-2-5 ***EDIT*** I've received feedback from a couple of people who have used these, and they have the same problems as the brackets I used.

https://www.amazon.com/gp/product/B0...ref_=pd_gw_unk

[pjmoreland]

12) Installed new brake calipers with the correct 71-72 banjo attachment point, along with the new brake hoses

13) Mounted the brake hose tabs to the front of the cross member by drilling and tapping for 5/16"-18 bolts. Had to cut the bolts short because the suspension springs are right behind where the tabs mount. I used the new hard brake lines and the 71-72 hoses to gauge a good mounting location for the tabs. Also drilled a hole for the anti-rotation finger on each tab. One thing I don't like about the Speedway Motors tabs I mentioned above is that they mount with only one screw. I'd be worried about them coming loose

[pjmoreland]

14) Attached the new hard lines to the proportioning valve. Since I have an aftermarket proportioning valve, it is inline with the master cylinder instead of kicked out at an angle like an original 71-72 unit. Because of this, I had to massage the rear brake line a bit to fit. All of the lines, for that matter, needed a bit of massaging here and there, but I was actually impressed with how well everything lined up.

[pjmoreland]

15) Bled the brakes. It's typical hot summer weather here right now, so it took a lot of convincing to get my wife out in the garage to help me with this last step. I owe her ice cream and Thai food now. That's a good deal for me, I think.

Here are a couple of photos of the left and right lines with steering at the hard stops. There's no chance these lines are going to rub on the tires.

[lolife99]

I guess I’m not getting what the problem is.
I’ve done a couple of these conversion and never had a single issue.
Good job on relocating the lines.

[pjmoreland]

Originally Posted by lolife99

I guess I’m not getting what the problem is.
I’ve done a couple of these conversion and never had a single issue.
Good job on relocating the lines.

With drum brakes, the flexible hoses connect to the slave cylinders very close to the vertical pivot point that passes through the ball joints. This means that the hose flexes back and forth very little when steering from fully left to fully right.

When you convert to disc brakes and use the stock hose attachment point on the rear of the cross member, the hose then runs to a point on the caliper that is very far from that vertical pivot point. This means the moving end of the hose sweeps through a large arc when steering from fully left to fully right. The hose goes from fully stretched out to scrunched up. When the hose is scrunched up, it gets very close to the tire. I had my hoses almost fail because they were rubbing on the tire when scrunched up, but fortunately I caught it in time. I was able to address this by installing slightly shorter hoses and by clocking them to put a twist in them that helps avoid the tire, but only by a little bit. The hoses were still being subjected to a large amount of flex. Anything that is flexed enough will fail eventually.

With the front-routed lines, the hoses hardly move at all when steering from fully left to fully right. They just sway gently one way or the other. There's no scrunching or tugging. Once you see it in person, it is obvious why GM redesigned the routing when they went to disc brakes in 1971.

The main thing that motivated me to reroute the lines was the comment by 71meangreenc10 in post #11 of this thread:

http://67-72chevytrucks.com/vboard/s...73#post8930273

After reading that, I found myself worrying about my brakes frequently.

RichardJ wrote a good description of the issue in post #14 of this thread:

http://67-72chevytrucks.com/vboard/s...ighlight=88466

[BigBird05]

I think it is great that you took the time to do the job right. As you stated by moving the lines to the front it made the conversion safer. That must be why GM moved the lines in 1971.

[jimijam00]

nice

[pjmoreland]

I ended up replacing the clamps on the back side of the front cross member with Inline Tube CLP125 clips. The clips I had on there before didn't hold the lines all that securely.

https://www.inlinetube.com/products/clp125