Learn me - How to pass brake lines through a firewall

My master cylinders are inside a cabin. The brakes are outside. I am deciding between simple rubber grommets, bulkhead fittings, or... something I haven't thought of yet? Or maybe I'm overthinking this. 

Grommets: Pro - fewer brake fluid connections, one continuous tube, minimize leaks. Con - potential weather leak path, probably hard to snake a continuous brake line through interior, somewhat ugly

Bulkhead fitting: Pro - More aesthetic, better firewall sealing, option for 90 deg angles. Con - Have to use AN hoses on at least one side (probably interior to the MC's), more potential fluid leak paths

Every bulkhead fitting I can find online is for AN hoses. At best, there are adapters for AN to inverted flare. I would like to do hard tubing, consistent with the rest of the car, which means inverted flare fittings. There does not seem to exist a female-female bulkhead union fitting for inverted flare brake lines. WHY.

Sketchy dark horse alterative - Cord grips? It's basically a tighter grommet with more metal around it right?

The OE option would probably be grommets. Fewer failure points FTW.

Most everything these days uses AN in the aftermarket world.  You might have to use an inverted flare to AN bulkhead with an adapter.  Just put the AN side inside the cabin and run a flex hose to the master cylinder.  I've done that exact thing in the past.

I find AN a pain because it's only found in the aftermarket and I can't get parts locally or off a parts car. If I stick with OE style fittings, I can mate to factory parts easily and get components wherever I want.   Unless you're 100% aftermarket, you're going to have more adapters than you really need. 

The love for AN comes from Carroll Smith, I believe. He deals with purpose-built race cars and really likes AN. But if you have OE parts in there, definitely check out the value in AN versus metric/SAE fittings.

The more I look into it, the more I'm leaning towards grommets. For the exact reasons Keith mentions. I think I can drill the holes in a place that will facilitate installation of the hard line. 

What is the deal with AN hose brake lines anyway? They seem a little overused in the aftermarket to be honest. I would rather have 10 feet of hard tubing isntead of 10 feet of flexible hose. 

Keith Tanner said:

The love for AN comes from Carroll Smith, I believe. He deals with purpose-built race cars and really likes AN. But if you have OE parts in there, definitely check out the value in AN versus metric/SAE fittings.

I think it's probably more accurate to say that he documented the love for it in the pro racing world.

As for why, AN has a broad array of known high quality, general-purpose fittings.  If you build the system entirely with AN (AN flare nuts on your hard lines in this case) then you've got a simple, straightforward solution for everything.

And yes, a hybrid between the two sucks.  I'm not a fan of running a hard line through with grommets -- there's no good OEM-style solution for this problem because OEMs don't do this.  In production cars, fluids always live outside of the passenger cabin, the only thing that goes through the firewall is electrical signals.  (edit:  well, coolant for the heater core, I guess)

I like these BQ148

https://brakequip.com/products/hardware/female-unions/

I'm a race car guy, I lean toward -AN fittings.

I would likely use a standard -3 bulkhead with a hose on the inside to the MC and hard line on the outside, matching the aesthetic to the rest of your brake plumbing.

The 90° bulkhead could be useful

Using -AN flare nuts on the ends of the hard line will eliminate any adapter stacking and lessen the number of potential leak points

maschinenbau (I live here) said:

What is the deal with AN hose brake lines anyway? They seem a little overused in the aftermarket to be honest. I would rather have 10 feet of hard tubing isntead of 10 feet of flexible hose. 

I'm assuming you mean for replacement of factory hard lines rather than the obvious need for flexible lines that go to the wheels?

Most people don't want to bend their own lines and it's a lot easier to ship a roll of hose than an 8-foot-long pre-bent hard line.  It's also fewer parts to keep in inventory.

Is this for a race car or street?

For race / track I would go bulkhead fitting. If there is a problem you likely only have to replace the line on one side if the fitting. As far as leaks go - regular race car maintenance should catch them before it is a problem.

codrus (Forum Supporter) said:

Keith Tanner said:

The love for AN comes from Carroll Smith, I believe. He deals with purpose-built race cars and really likes AN. But if you have OE parts in there, definitely check out the value in AN versus metric/SAE fittings.

I think it's probably more accurate to say that he documented the love for it in the pro racing world.

As for why, AN has a broad array of known high quality, general-purpose fittings.  If you build the system entirely with AN (AN flare nuts on your hard lines in this case) then you've got a simple, straightforward solution for everything.

And yes, a hybrid between the two sucks.  I'm not a fan of running a hard line through with grommets -- there's no good OEM-style solution for this problem because OEMs don't do this.  In production cars, fluids always live outside of the passenger cabin, the only thing that goes through the firewall is electrical signals.  (edit:  well, coolant for the heater core, I guess)

To fill the brake and cluster masters in my Vanagon, you have to remove the instrument cluster :) Masters are definitely inside the cabin. I'll have to look into how the brake lines exit the car for sure, but I'm 90% sure it's a grommet as there are some lines that don't have a break where they'd have to go through the firewall. I'm not saying this is the apex of automotive engineering, but it does show how the OEs solve the same problem.

Then there's the MG, where you discover your brake master is leaking because you have a dirty left shoe. But we don't aim to design cars like MG.

I understand why clean-sheet designers like AN fittings. Availability is still worse than what's used by the mass manufacturers so you have to carry a bunch of your own spares and tools around, but if you have the luxury of specifying the entire system it makes life simple. You just have to come all the way down on one side of the racecar line and be prepared for all eventualities, otherwise it's really awkward. Even the flaring dies are different.

I used AN bulkheads on my car, but have used grommets and just ran the lines through on some other builds. Makes bending them a little interesting but it's workable with practice. 

I want to say there is a metric bulkhead that is on VW brakes somewhere as I have a bunch of them in my random hardware bin.

In reply to codrus (Forum Supporter) :

The rear brake line in the 86 Civic runs through the cabin. It runs right next to the fuel line and return line. They enter through a grommet to the left of the clutch, run down the rocker, and exit through a grommet right behind the driver's seat. There is no safe place to run it under the car so we ended up adding a full-length bulkhead to isolate it from the cabin. 

I vote grommet just for simplicity. 

Edit: I think I'm mistaken. The fuel lines run down the driver side, the brake runs down the passenger side. 

Bugeye WRXes use a rubber gromit and route both brake and fuel lines through the cabin. I know this because I bought a $200 WRX and found both rear brake lines were completely rotted through right where they exit the body under the rear seat. There's also a union, but definitely a rubber gromit. It's not good, I'd rather they'd have used a non-rust prone material and just run the lines on the outside of the car...

The Seals It products look good.  
 

Also Steele Rubber has a wide range of firewall grommets.  

MrRobogoat (Forum Supporter) said:

Bugeye WRXes use a rubber gromit and route both brake and fuel lines through the cabin. I know this because I bought a $200 WRX and found both rear brake lines were completely rotted through right where they exit the body under the rear seat. There's also a union, but definitely a rubber gromit. It's not good, I'd rather they'd have used a non-rust prone material and just run the lines on the outside of the car...

Subaru ran fuel lines in the cabin for years.  Freaked me out a bit the first time I saw them in my SVX.  

Remember OE's don't use grommets because it's the best solution. OE's know that one rubber grommet is cheaper than a bulkhead fitting plus the two extra line fittings on each side of it. If I am reading the original post correctly this seems to be a master being moved inside the cabin. If it's a custom move I'd use bulkheads it's normally a cleaner install and I like the look.

I just looked at the catalog I picked up at the really cool fitting place I found here close to home when I was buying PS line fittings.  They have a wide selection of SS fittings from DK-LOK Corp and they appear to have a bulkhead union (DUB series) in both SAE and Metric tube from 1/16" to 2" and 3mm to 38mm in their offerings.  May be what you need?

I would probably opt for a bulk head fitting. Making 37 degree flares is pretty straight forward and when used with a tubing nut and sleeve never had a connection leak. The sleeve aligns the flare to the fitting making it pretty fool proof. The down side is you have to have a decent 37 degree flare tool and the tube nuts/sleeve and fittings can be expensive and pretty much special order at least in my part of the country. 

Hmm this is a lot to think about. More broadly there are two options for connecting between MC's and chassis plumbing - 1 line or 2 lines. Grommets allow 1 line from MC to chassis tubing. Bulkheads require 2 lines and therefore double the connections. 3 circuits total, so we're talking a difference between 6 fitting connections or 12. 

If I was more forward-thinking in the build, I could have terminated the chassis tubing a little longer, so it could match up with a bulkhead fitting. But I didn't leave enough length to do that, and with the body on the frame, there is no way I'm re-doing the chassis plumbing. I MIGHT be able to tweak the brake lines to make them match up with the body for a bulkhead. 

I really need pictures to better explain the situation. This is all I have for now. Clutch MC not mounted, but it will be on the left side pointing towards the driver. 

Brake lines are the two with the fittings. The holes on the top of the frame rail match up with the perimeter of the body, so they are a couple inches behind the plane of the firewall. If I point them straight up, they would pass through right under the brake and clutch pedals. Clutch has no plumbing yet, but the clutch slave is basically on the other side of the firewall from the throttle pedal. I'm not as worried about it because the run is so short.

I think the AN bulkhead fittings look nice and "clean," aside for the leak point perspective. Ive never seen a cord grip used as a gromet, but you may be on to something there! If the flare does not fit through the cord grip, just install it loose before the last flare... would look way cool.

So, pardon me if I've missed something, but this

https://www.summitracing.com/parts/agb-bh4497

Plus this

https://www.amazon.com/Gold-Cadmium-Flex-Hose-Retaining/dp/B01MYZ0SCR/

Equals solved with no AN fittings?

Might have to get a hose shop to make you some specific hoses for your ends, and you might have to still incorporate a grommet of some sort, but hell it has kept the front body-to-caliper lines on my truck from moving for 380k miles.

Don't forget that since this is a body on frame car you need some kind of accommodation for flex in between the chassis lines and the body.  You can use either a coil in hard line like to OEMs did or a flex line. 

I like grommets and would eliminate the expense and additional point of failure.  AN bulkhead fittings are more fire-resistant for racing, I guess?