07 Sierra 2500 HD ABS Modulator Valve & Rusted Brake Lines.

Steamerjohn · April 30, 2021

Hi folks. Sorry for how long this is, but it might just help someone.

So, I put my truck on my work slab to change the oil and spotted brake fluid dripping from the right rear hard brake line in the first bend of the tube at the caliper. The plastic coating is bubbled, and the steel line is rusted through. Research tells me it is common in older GM trucks. So, I replace the single 3/16 line that is leaking with cupronickel brake tube from “4Lifetime Lines” and plan to someday replace all the lines. I bleed & test drive and all is good.

The next time I drive the truck I notice it pulling to the left a bit when braking. I head home and it gets worse and pulling without braking. When I get home, I smell the hot pads and feel the heat on the left front. Dang! Stuck caliper. Only 37K miles but it is 14 yrs old. I replace the front calipers, brackets, rotors, pads, and hoses on both sides and go through several quarts of Dot 3 flushing the entire system. A short test drive and all is good.

A few days later I use the truck for a short run to the dump. On the way back it starts pulling again to the left. When I get home the left front is extremely hot and even smoking a bit. The old pads and rotors I just took to the dump appeared almost new except for the rust & dust. I believe the front brake job was not necessary.

Some more research tells me the number one symptom of a bad ABS modulator valve is brakes locking up. Jeeez! Wish I had read that earlier. So, I have ordered a new modulator valve and will go ahead and change out all the lines to cupronickel. I would have loved to order pre-bent lines in stainless or cupronickel, but I cannot find anyone that makes them for my truck, and I have checked lots & lots of places. I could get them for my truck if it were 4-wheel drive but not for 2-wheel drive. Sounds crazy but I have had several companies on the phone, and they all have said “sorry, we don’t make them for your truck”. And I will not go with factory replacements as they are pricey and prone to rust out again.

So, I have started. The bed is off. Truck is on jack stands, wheels off with wheel well liners & splash guard removed. Pulled the modulator valve and fished out all but the right front brake line out of the truck. Not an easy task. There are numerous plastic clamps holding them in place that are puzzles to releasing the tubes. When they build these trucks I believe the brake lines go on the frame first and then wiring harnesses, and all else gets mounted over top of them.

One big headache was identifying and locating the 3/16” and 1/4’ tube nuts. I preferred stainless to avoid ferrous nuts with the copper nickel tube. The 3/16 nuts are M10 x 1.0 Inverted flare also called double flare or SAE flare. I found these in stainless.

The 1/4” nuts are 12mm x 1.5. I searched for days and only found them on eBay. They are cad plated steel, but they are all I could find and will arrive in a week. I do not think they exist in stainless.

Well, that is my lot for now and will update when parts arrive, and I can continue.

Steamerjohn · May 5, 2021

Update:

The M12 x 1.5 inverted flare nuts for the five 1/4" tubes arrived and they are correct for the ends going into the ABS modulator valve. But they don't work on the other ends that go into the hoses or into the master cylinder. So I await again for more nuts. I'm fairly sure these nuts are 7/16 x 24. I'll only know for sure when they arrive. So that's three different size nuts to redo the brake lines on my truck.

Male inverted flare, short.

M10 x 1.0 for 3/16" tube.

M12 x 1.5 for 1/4" tube.

7/16 x 24 for 1/4" tube.

Steamerjohn · May 10, 2021

Well the latest nuts, 7/16 x 24 for 1/4" tube arrived and they are not correct. Thread pitch is right but a little to small diameter wise. I now have M12 x 1.0 ordered and will arrive in a week. They were extremely difficult to find. I would have never believed replacing brake lines could be so difficult.