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Thu Nov 27, 2025 10:16 am

Good afternoon. I purchased a nearly all-original 1958 Bug a few days ago. My intention is to maintain it for a few years and then do a full pan-off restoration with my son. As with all vintage vehicles, a few things need attention. I noticed a pool of brake fluid under the vehicle, and the driver’s carpet is wet near the firewall. When pressing the brake pedal, I see small bubbles coming from the grommet between the firewall and the brake line. I’m assuming the line somehow has a pinhole leak.

My question is: is this common, and how difficult is it to replace the entire line?

Thu Nov 27, 2025 10:42 am

Yep! That is a brake fluid leak, most likely from the master cylinder. If you remove the dust boot at the rear of the unit and push the pedal, you might be able to see it leak. If not find it quickly, as brake fluid will strip the paint off of the steel, leaving the steel exposed to moisture.

Brake fluid is hygroscopic. So, to clean it and neutralize the damages it can do, you flood it with water. Down side is flash rust will find a way in after that. After it dries up. Apply some Ospho with a squirt bottle, allow it some time to do its thing, then rinse with water. Allow that to fully dry, then hit it with an etching primer. Followed by paint.

Be sure to fix the leak during those down cycles in the brake fluid mitigation!

Also, check the wheel cylinders and the brake rubber hoses. They are probably all on the same wear point.

If it does end up being a hard line. The one running down the outside of the tunnel. The job is not difficult. You just need to know how to bend brake lines without kinking them. Watch some YouTube videos. Remove the interior on the drivers side (seat, floor mats, carpet) then get to the fun! A 11mm or 7/16” flare nut wrench is your best friend along with a 17mm open end wrench for support!

Thu Nov 27, 2025 10:51 am

Thanks for the reply, VM_Jimbo. I didn’t consider the master cylinder being the culprit because I saw small air bubbles between the rear brake line and the rubber grommet at the firewall. I’ll continue to dig further before purchasing any parts.

Thu Nov 27, 2025 11:08 am

Agree: make sure first that the leak is not from the rear of the master cylinder.

Ask me how I know this....

https://www.thesamba.com/vw/forum/viewtopic.php?t=747133&highlight=1971+super+beetle+thread

Thu Nov 27, 2025 11:11 am

The grommet around the brake line broke apart, and I cannot see anything wrong with the line. In between, though, I can see fluid and it’s wet, so I’m assuming it’s the master cylinder. Is it worth rebuilding, or should I just replace it?

Thu Nov 27, 2025 11:22 am

volkswagen_bug wrote: The grommet around the brake line broke apart, and I cannot see anything wrong with the line. In between, though, I can see fluid and it’s wet, so I’m assuming it’s the master cylinder. Is it worth rebuilding, or should I just replace it?

I would replace it. Now would be the perfect time to convert it to a dual circuit master cylinder.

Thu Nov 27, 2025 11:30 am

I'm trying to keep it as stock as possible. Is there much benefit to converting it to a dual circuit master cylinder.

Thu Nov 27, 2025 1:59 pm

[quote=]"volkswagen_bug" Is there much benefit to converting it to a dual circuit master cylinder.[/quote]

Plenty. With a single circuit, a failure anywhere in the brake lines or wheel cylinders results in a failure of the brake system. With a dual circuit you would only experience a partial loss of braking ability. Do as daveblank suggests. You will be glad you did.

Thu Nov 27, 2025 2:26 pm

Is there a common part number used for the dual circuit master cylinder that you can share?

Thu Nov 27, 2025 2:49 pm

volkswagen_bug wrote: Is there a common part number used for the dual circuit master cylinder that you can share?

A master cylinder for a later Karmann Ghia or Beetle would work well as an upgrade for an earlier Beetle. This one from NAPA has a lifetime warranty and would be compatible with front disc brakes if you decided to do that worthwhile upgrade during a brake overhaul. I have it in my '63 bug.

https://www.napaonline.com/en/p/NMCM2110

You said you believe your bug to be all original. If you believe that to be the case for the brake hard lines, you may want to plan on replacing them ... sooner rather than later. As they say, it really doesn't matter how well it goes if it doesn't stop when you need it to. :wink:

Thu Nov 27, 2025 2:54 pm

It's not just the MC you need but you will also have to get/make brake lines to go from single circuit to dual circuit.

Thu Nov 27, 2025 3:11 pm

Kind of why I'm nudging our OP to consider doing the brake overhaul now. I totally get the desire to drive and enjoy a recently purchased bug (the fun part of ownership) and get around to stuff like brake overhauls later on. Unless certain of what recent work was done to the bug (and that it was done properly), taking the time to tend to the mechanicals early on goes a long way toward preventing costly, unfortunate failures (brake failure, fuel line leak in engine compartment, fuel pump diaphragm leak, etc.) that can take the bloom off the rose.

Thu Nov 27, 2025 3:29 pm

OldSchoolVW's wrote: Kind of why I'm nudging our OP to consider doing the brake overhaul now. I totally get the desire to drive and enjoy a recently purchased bug (the fun part of ownership) and get around to stuff like brake overhauls later on. Unless certain of what recent work was done to the bug (and that it was done properly), taking the time to tend to the mechanicals early on goes a long way toward preventing costly, unfortunate failures (brake failure, fuel line leak in engine compartment, fuel pump diaphragm leak, etc.) that can take the bloom off the rose.
Agree 100%.

Not many of us would agree to an aeroplane taking off and waiting for a failure to happen before doing preventative maintenance.

Thu Nov 27, 2025 5:54 pm

I’m of the belief that it’s OK to keep the single circuit brake system provided you’ve ensured all system components are inspected regularly and maintained in good working order. As others have stated, for your safety and peace of mind, replace the components with moving parts, all rubber seals and lines, inspect the rest of the system using the workshop manual information, and put fresh fluid in the system.

Yesterday 5:33 am

Thanks for all of the replies. At this time I will be keeping the single circuit brake system and saving any future upgrades for when we do the full restoration. All moving parts, rubber and seals have been ordered.

Yesterday 8:43 am

OldSchoolVW's wrote: volkswagen_bug wrote: Is there a common part number used for the dual circuit master cylinder that you can share?

A master cylinder for a later Karmann Ghia or Beetle would work well as an upgrade for an earlier Beetle. This one from NAPA has a lifetime warranty and would be compatible with front disc brakes if you decided to do that worthwhile upgrade during a brake overhaul. I have it in my '63 bug.

https://www.napaonline.com/en/p/NMCM2110
:

That"s the one that I'm installing.

viiking wrote: It's not just the MC you need but you will also have to get/make brake lines to go from single circuit to dual circuit.

I was able to reuse the rear & right front. The one for the left front was too short, NAPA has a 12in hose that I was able to bend & make work. A 10in or possibly 8in would have worked too, the original was 6.

Yesterday 8:57 am

I've seen a master cylinder much like that one but with the reservoir mounted on top. Not sure where those are from though.

Yesterday 10:05 am

volkswagen_bug wrote: I've seen a master cylinder much like that one but with the reservoir mounted on top. Not sure where those are from though. There is a reservoir that mounts directly to the master cylinder. I don't like those because I'm old & don't want to crawl around on the ground just to check the fluid level. I'm mounting a 67 dual circuit reservoir to mine.

Yesterday 12:44 pm

I put one on my IRS pan that I am going to use on my 67. I got it form rock auto, here is a picture.