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96 Concours, 05 DHS
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184 Posts
Discussion Starter #1
This was a new one for me. Just bought this 05 last fall at 105K, now has 114K. I think most of the previous service was done by dealership, but I don't know if they did anything with the master cylinder or brake lines. Maybe it came this way from the factory.

Last month my wife (primary driver on this car) mentioned the "check brake fluid level" warning. I expect the pads to need replacing in another 10K miles, so thought maybe the wearing pads had lowered the level just enough to trip the switch. I added some brake fluid and figured we'd keep an eye on it. Friday the warning came on again, so I began looking for the leak.

Finally found it between the master cylinder and the ABS modulator. This view is looking down at the outboard left side of the transmission. Front of the car is to the left. You can see the semicircular divot worn into the transmission case fin by the hydraulic pipe, which is also worn through and leaking at that point. You can also see some small wear at the next fin forward.



There is a black plastic retainer visible in the photo. It normally holds the pipes outboard to the fender (i.e., holds the pipes in the "down" direction in the photo), but the lower pipe bends inboard and the force needed to keep the retainer against the fender is enough to break off the retainer's push pin over time.

I'm planning on replacing these two pipes (GM 25752677, 25752676) and the plastic retainer (GM 25696686) and, sigh, bleeding the entire brake system. Maybe if I make sure they are bent to lay naturally against the fender where they belong, I won't have this problem again.

Questions: is that a reasonable strategy? Do I need to add a metal retainer (with a rubber grommet) that bolts to the fender? It seems as if this is a design flaw.
 

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White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
WOW!

Seems like bending the pipe a bit would solve the problem.

Might even want to tip off NHTSA.
 

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98 DeVille, 97 DeVille d'Elegance
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7,345 Posts
I'd bet someone had it apart and the lines bent where they shouldn't have been, regardless I'd bend so no pressure on the clamp and would fasten better also.
 

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96 Concours, 05 DHS
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184 Posts
Discussion Starter #4
This is a close-up of the hole in the 3/16-inch brake pipe. Just a tiny pinhole, but a firm press on the brake pedal squirted out at least half a teaspoon of juice (scientific measurement via Mk 1 eyeball):



I got the new pipe (GM 25752677) on this past weekend and bled LR and RF after installing speed bleeders on the calipers. First time I have used them; it was so easy I can hardly believe it, but the pedal is firm and there is no pulling to either side.

The other pipe (GM 25752676) was undamaged so I left it alone.

New plastic brake line retainers (2 of them): GM 25696686. I made sure the pipes lay along the inner fender (I guess technically it's the "reinforcement rail") before closing the retainers on them.

The brake pipe nuts are M12-1.0. At first I looked for threaded plugs I could install in the BPMV and master cylinder while I fitted the new pipe, but couldn't find any, so in the end I just left the BPMV open; on the other end, I cut the old pipe about six inches from the master cylinder and bent the end up above the reservoir so it wouldn't leak.

I had originally planned to install a rectangle plate of 14ga sheet steel between the transmission and the brake pipes to prevent contact between the pipes and the "fins" on the transmission, but the plate interfered with the lower air intake box and I don't have a big shear to cut it. If I get ambitious, I might go at the plate with a hacksaw to cut away the necessary section. The other potential problem is that I am planning on attaching the plate via cushioned clamps to hang down from the water pipe just above, and I think it will rattle against the transmission. Maybe I can glue a thin layer of teflon to the plate, but I expect contact with the transmission will erode it. There isn't enough room between the transmission and the fender (only about 2 inches) to get a drill in there and make a mounting hole on the fender, so I'm having trouble figuring out a good way to attach the plate between the brake pipes and the transmission.
 
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