Using nicopp brake line and can’t find proper fittings

[Mfire123]

I’m trying to replace my brake lines on my 2013 1500 rust bucket that run from the master cylinder to the abs module. It’s 1/4” line but gm has 1/4” inside diameter while the nicopp line has 1/4” outside diameter. Plus gm had the steel line (thicker) and the protective (not much protection as mine rotted out) coating on the outside. Anyways, the nicopp line is too small for the factory gm fittings that worked with the thicker steel line. Does anyone happen to know what size the fittings are for the abs module and for the master cylinder? 

Edited September 3, 2025 by Mfire123

[newdude]

Measure the threads.  If you have thread pitch gauges or if not stop by a Lowes and go to the hardware section and use the thread gauge thingy they have mounted in the bolt section. 

 

GM doesn't list a spec for that fitting at the master.  They do have the ABS side fitting as metric inverted flare tube nut for the master to ABS lines.  M14x1.5.  Not sure if the master is metric or standard thread.  

Edited September 3, 2025 by newdude

[richard wysong]

I think you have the wrong size line, probably 3/16, I have never had an issue changing to Ni/Cu, done many many. Even the plastic coated line is standard size, Possibly it is metric line you are trying to replace, I don't believe metric line is available  in Ni/Cu

Edited September 3, 2025 by richard wysong
spelling

[Mfire123]

2 hours ago, richard wysong said:

I think you have the wrong size line, probably 3/16, I have never had an issue changing to Ni/Cu, done many many. Even the plastic coated line is standard size, Possibly it is metric line you are trying to replace, I don't believe metric line is available  in Ni/Cu

The specific brake line I’m trying to replace is listed as 1/4” line. The part number for those lines is just a 1/4” inside diameter x 16’ roll of steel pipe. I might just have to bite the bullet and order the steel pipe from gm and bend it as best I can. 

[newdude]

19 hours ago, Mfire123 said:

I’m trying to replace my brake lines on my 2013 1500 rust bucket that run from the master cylinder to the abs module. It’s 1/4” line but gm has 1/4” inside diameter while the nicopp line has 1/4” outside diameter. Plus gm had the steel line (thicker) and the protective (not much protection as mine rotted out) coating on the outside. Anyways, the nicopp line is too small for the factory gm fittings that worked with the thicker steel line. Does anyone happen to know what size the fittings are for the abs module and for the master cylinder? 

 

 

16 hours ago, richard wysong said:

I think you have the wrong size line, probably 3/16, I have never had an issue changing to Ni/Cu, done many many. Even the plastic coated line is standard size, Possibly it is metric line you are trying to replace, I don't believe metric line is available  in Ni/Cu

 

13 hours ago, Mfire123 said:

The specific brake line I’m trying to replace is listed as 1/4” line. The part number for those lines is just a 1/4” inside diameter x 16’ roll of steel pipe. I might just have to bite the bullet and order the steel pipe from gm and bend it as best I can. 

 

 

 

Just went back to this in the catalog.  Two different size lines from the master.  The line closest to the firewall shows as 1/4", the line farthest shows 5/16". 

[Mfire123]

5 hours ago, newdude said:

 

 

 

 

 

Just went back to this in the catalog.  Two different size lines from the master.  The line closest to the firewall shows as 1/4", the line farthest shows 5/16". 

Interesting. I’ll have to measure the diameter on mine. They look identical minus a few bends. I was actually able to potentially find a pre bent kit through sstubes.com. Hopefully those will be an exact fit so I can stop throwing money at fittings and different sized pipe and various tools. 

[Mfire123]

7 hours ago, newdude said:

 

 

 

 

 

Just went back to this in the catalog.  Two different size lines from the master.  The line closest to the firewall shows as 1/4", the line farthest shows 5/16". 

My gauge shows both lines coming out of the master cylinder as identical inner diameter and outer diameter 

[carkhz316]

The GMT900s have 5/16 brake line running from the MC to the EBCM. Take your fittings to any parts store and they should be able to match them up as they're a common fitting size.

[newdude]

End up figuring this out OP?  @Mfire123

[Mfire123]

On 9/8/2025 at 4:48 PM, newdude said:

End up figuring this out OP?  @Mfire123

I found a company sstubes.com that sells a front brake kit  that includes the two master cylinder to abs module that they say will fit my truck. Not sure why other kits wouldn’t that I searched and called. Perhaps because their kits were complete kits and the rear lines are different? Not sure. There is a delay on their stock so I won’t receive the lines for a few weeks. They come pre bent and flared and with proper fittings. I was also at the parts store today and I saw a correct fitting with a 5/16ths bore so maybe I could have used 5/16ths nicopp with that fitting. I’ll try and update once I get the lines routed in place and determine if they work or not. 

[richard wysong]

Good luck with stainless lines, they are hard to bend. The lines are installed on the chassis BEFORE the body so trying to install prebent lines can be very frustrating, sometimes requiring unbending, cutting and splicing

[Mfire123]

2 hours ago, richard wysong said:

Good luck with stainless lines, they are hard to bend. The lines are installed on the chassis BEFORE the body so trying to install prebent lines can be very frustrating, sometimes requiring unbending, cutting and splicing

Thanks. These don’t look too bad with the front wheel well liner removed. I’ll have to go slow and steady of course. 

[Mfire123]

On 9/5/2025 at 7:35 AM, carkhz316 said:

The GMT900s have 5/16 brake line running from the MC to the EBCM. Take your fittings to any parts store and they should be able to match them up as they're a common fitting size.

The part number lists 1/4” brake pipe. With the inner diameter being 1/4”. So maybe the confusion is the inner diameter vs outer diameter? If these pre bent lines I ordered don’t work then I’m going to go back to nicopp and get 5/16th line.