Brake Line - Partial Replacement or Full

[rivesalex21]

Thank you for reading my post.

TLDR: I am removing my rear subframe, and to do this i need to disconnect any brake lines that are attached to it. Rust makes this painful and I am at a point where I need to have different plans to go forward:
Question: As a plan B (worst case scenario --> I cannot remove the brake lines and remove the attachment to the subframe) would it be a bad idea to cut the brake line before it reaches the rear junction point and replace the cut portion with my own repair?


I am currently doing somewhat of a major project..
I am completely removing the rear subframe and changing most of the components inside for a complete refresh.

The reason I am doing this is because I live in the rust belt, and the car looks pretty bad underneath, especially in and around the rear subframe. I've purchased a mix of used and new parts, that I hope will revitalize the car and give it a different feel. (Used subframe that has no rust, a 3.73 differential vs the 3.23? that came with the car). All new control arms and bushings.

Unfortunately, having the rust underneath turns each step in removing the subframe into an actual project. Hopefully, others in this thread can relate. One of these projects is dealing with the removal of the brake lines and hoses.

The rear brake lines reach an anchor point that is attached to the car chassis, it seems pretty rusted there so I'm not sure how easily the line and hose will separate. Then from there it follows 2 brake hoses the reaches another anchor point attached to the rear subframe. One of these hoses is attached (by rust) to the subframe, but I can loosen and remove the brake line attached to it (goes to the rear right brake). The other hose is unattached to the rear subframe, but I cannot remove the line attached to it.

Question: As a plan B (worst case scenario --> I cannot remove the brake lines and remove the attachment to the subframe) would it be a bad idea to cut the brake line before it reaches the rear junction point and replace the cut portion with my own repair?

I'll post pictures later for better clarity.

[Thunderguts]

You already know the answer. Any new connection is a potential point of leakage/corrosion/failure. It sounds like you're putting a lot of work into this car so do it right. It's not like you can't find OEM brake lines anymore. If that weren't an option, it would make more sense to patch.

[rex n effect]

Pre bent and terminated OEM brakenlines are not too costly. Plan on this anytime you drop the rear subframe for the first time on these cars

[ktish]

Originally Posted by rex n effect

Pre bent and terminated OEM brakenlines are not too costly. Plan on this anytime you drop the rear subframe for the first time on these cars

This is the best way to go about this repair. I just completed a similar job on my E90 and a friend's E92. My car seems to have lived a decent amount of time in Albany and is pretty crusty in spots like the rear brake line/holder. Fortunately, the junction at the front of the car is very easily accessed and is well protected so fitting new lines should be a breeze. The prices for the parts are quite reasonable too.



On my car, I ended up replacing all 4 rear brake lines: the two from the front of the car and the two that split off and attach to the subframe. The two short lines on the subframe were less crusty but I didn't trust them after I saw the pipe beginning to bend on removal. This was after my best attempts with heat and penetrating oil.


I would highly advocate for some kind of subframe bushing replacement during this project. Between my old 135 and current E9x stuff I have access to, the subframe bushings really go a long way to 'fix' the rear end wiggle. If I'm interpreting your post correctly, it sounds like you have a whole spare subframe to play with. If so, I would really only recommend aluminum bushings. Bimmerworld currently has sets under 'scratch and dent' at a good price. Some other 'while you're in there' parts could be diff bushings, upgraded rear upper strut mounts, and some exhaust mods. I installed Whiteline diff bushings which, from my research, appear to be the softest available poly bushings on the market at 72A durometer. Some diff whine is added but the increased tightness is appreciated.

[Olgeezer1]

With the subframe out, great opportunity to put in stainless steel rear lines (all 4) and replace those squishy subframe bushings. I used Whiteline 2pc poly but solid or M3 are popular options. Really only way to avoid reoccurrence of these issues is to park it for the winter. I bought an old Toyota for a winter beater for the price of a good set of snow tires. After more than 10 years, underside of the car looks like new.

[rivesalex21]

Thanks for all the responses. The subframe is out, but I had to cut the brake hose to allow this to happen. I'll purchase two new brake lines that go to the rear, and I have two new brake hoses, but the problem is that the brake hose is rusted/seized unto the union in the rear.

Is there any danger in applying heat on the brake hoses metal ends?

Will update with pictures.

[rivesalex21]

All,
I figured I would follow up on this... I ended up successfully replacing the brake lines for the rears but I had to do some custom tubing. Replacing the full brake rear brake line (from the DCT unit all the way the the union attached to the subframe by the rear) requires many parts to come off, and additional hassle that I did not want to deal with. I ended up creating a flare by the mid point of the car, where the brake pipe is straight since this was the easiest point to do this.

[wasntbtf]

Originally Posted by Thunderguts

You already know the answer. Any new connection is a potential point of leakage/corrosion/failure. It sounds like you're putting a lot of work into this car so do it right. It's not like you can't find OEM brake lines anymore. If that weren't an option, it would make more sense to patch.

Any junction/join in a brake line is a potential weak point. BUT, if those junctions/joins are made competently then there is not an issue.

As a DIY mechanic who has been working on vehicle brake systems for 50 plus years I would have no issue with splicing on to an existing pipe - PROVIDED the existing pipe was sound and the connection was properly made.

[amg6975]

Originally Posted by rex n effect

Pre bent and terminated OEM brakenlines are not too costly. Plan on this anytime you drop the rear subframe for the first time on these cars

The long OEM lines are not pre bent. It shows up as one long straight tube, in my case bent in half by FedEx. They are steel with a coating and will just end up rusting again. The better option is to replace with good quality Copper-Nickel lines as they're sooo much easier to use and won't rust.