I was changing the front brake pads on my 84 300D and found that the right front caliper was frozen. I bought a rebuilt caliper to replace it but found when I tried to remove the old caliper the brake line nuts are so rounded and corroded that I cannot remove them. This is at the caliper and also where it connects to the steel line.

So, I am thinking that I should replace the steel line. I can see where it travels across the firewall and the clamp nuts on the right and left of the engine seem accessible enough, but the one behind the engine in the center looks like a challenge.

Any advice from someone who has done this procedure? I watched a video of a guy who cut out some old brake line and spliced in a new piece with a union. Or maybe run a new line across the firewall, zip tie it to the old line and not take out the old line. Not my preference but a possibility.

Thanks for any input.

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

Don't use a compression union. If at all possible replace the entire line.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Yes compression unions are illegal in many places if not all. Take a hard look at all your brake lines. Any effort required to make the system safe is better than an accident.


There is a type of brake replacement line that is pretty easy to work with and also has more corrosion resistance. I forget now what it is called but available in most places. A little more expensive but so much easier to work with.

I believe if his state has vehicle inspections it is also not going to pass with compression fittings on the brake line.

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84 300D, 82 Volvo 244Gl Diesel

What you are looking for is sections of generic Brake line with the right sized nuts and aprximate length and bubble flared ends. Some have said the regular auto part stores have them.

The also sell bubble flaring tool kits.

People say the vice grips similar to the ones in the pic work well on the brake line nuts that are rounded.

If you are replacint the Hose you can heat up the hose end with a propane torch to expand it a little.

If you are going to replace the Hose just leave the threaded end attached to the Caliper you are going to turn in as a core cut the rubber off. Let the rebuilder deal with removing it from the caliper.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the confirmation about the bad advice of using a compression union. I did not think of it or consider it until I saw a video on YouTube of a guy promoting the idea. He seems kind of shady and I was wondering.

I stopped at my local NAPA store and asked about brake lines. They sell one that is a nickel/something alloy but it is about $2.50 per foot as opposed to $1.00 per foot for steel. I asked about metric fittings and he said that it would come flared and with the fittings I need. I would just need to bend it.

I just need to figure out how to get to the clamp that sits right behind the engine.

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

the precut and flared line can be too long - so that is also a concern, you can buy them from autozone too.

brake lines come in three flavors.

1 - uncoated steel
2 - coated steel
3 - cunifer (the best kind)

get some cunifer assembled line, and coil it up properly if its too long - thats the cheapest way to do it. Otherwise you will need to purchase a bubble flare tool to make exact length lines yourself.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The mentioned conifer tubing is mostly made if Nickle and is likely the one the auto store was speaking of.

Brake Tubing for US cars has a double flare on it (or at least it used to) that is different from the bubble flare used on the euro cars.

Do a Google Images search for brake line bubble flare and see the difference.

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84 300D, 82 Volvo 244Gl Diesel

I replaced a line in the 83 300cd with a premade brake line I bought for the 59 vw.
It's nice when standards are maintained!

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95 E300D gave away
77 300D, 227k, station car
83 300CD 370k, body gone away to the rust gods, engine is in a Yota pickup, going strong
89 190E 2.6- 335k, no more
79 VW FI Bus- 154k summer driver
59 VW Beetle ragtop- 175k
12 VW Jetta- 250k
74 MG Midget-78k

Many muscle car rebuilders use the Cu-Ni tubing since much easier to bend by hand without kinking. You can make bubble-flares with a common "double-flare" tool. See youtube's. Many do since they have that tool and the "correct" bubble-flare tool is ~$250.

If you can't bubble-flare, you could use an inv flare in-line coupler. I have bought those in bubble-packs at Autozone. I have used inv flares on newer U.S. metric tubing (6 mm, forgot). Haven't touched my M-B brake tubes and don't know what size that tubing is. Of course, better to avoid adding couplers since more places to leak.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans