Gm master cylinder adapter nuts - dont buy fragola.

[PurfsMcGurfs]

Not really super tech but, I thought I would share this to help other guys who may run into the issue. I know gm/toyota guys will run gm masters.

I'm currently converting my lines to -3an to add a prop valve and shutoff valve into the rear brake lines and ordered MC adapters to plumb the front and rear lines. The connections on the GM masters are 1/2-20 and 9/16-18. I ordered adapters from fragola and while the front works, the rear doesnt.

The inverted flare on the 9/16-18 adapter is too big and will leak under pressure. Of course I didn't find this out until everything was done and I was bleeding the system.

Rather then build some excessive stupid adapter, i found a company that sells GM master adapter nuts that adapt directly to -3an.

Inline tube - master cylinder nuts

These will save you from wasting time/effort/money on your rig. You can also ditch the stupid loops of brake line under the master on square bodies.

 

[PAE]

Dont buy anything aluminum #1 Steel or stainless is best, not even brass IMPO should be used.

I used -4 stainless with brakes on just about every truck I've ever plumbed.

Past history of my younger years internship working for Lockheed aircraft Burbank and later Boeing in long beach, el segundo Ca.

 

[arse_sidewards]

Flare adapters are kind of shitty in general because normally you have soft steel between the hard fitting and the hard nut and that gets mashed and provides your seal.

Loosen and re tighen it a half dozen times with a light brap from your impact and I bet the leak goes away.

 

[PurfsMcGurfs]

Flare adapters are kind of shitty in general because normally you have soft steel between the hard fitting and the hard nut and that gets mashed and provides your seal.

Loosen and re tighen it a half dozen times with a light brap from your impact and I bet the leak goes away.

Unfortunately that wouldnt work. Basically the flare being so big on the adapter means it doesn't contact the flare on the MC at all. The threads bottom out and start to gall and the flares are still gapped. I'll take a pic and post it when I get a chance.

 

[arse_sidewards]

Maybe try making a flare on some tubing, cut it off and fit it in there.

Not really a "custom part" when it's just a flare so not like you need to worry about finding one on the road.

Or slip a copper washer over the adapter and cross your fingers that the shoulders are flat enough to make it seal.

 

[M92PV4U]

Shorten the end of the inverted flare?

 

[arse_sidewards]

Shorten the end of the inverted flare?

Take an angle grinder to the side of the master cylinder and knock 1/8" off.

Maybe try the copper washers first because you sure as shit can't try them after.

 

[M92PV4U]

Take an angle grinder to the side of the master cylinder and knock 1/8" off.

Maybe try the copper washers first because you sure as shit can't try them after.

Braze the adapter to the master cylinder.

 

[PurfsMcGurfs]

Haha! You guys are thinking way too hard.

New adapters from inline tube

Fragola vs inline 9/16 adapter. Fragola on the right.

I'm not into Jerry rigging a piece of line in between the adapter or cutting the end down. If it was a trail fix, send it. In the shop, no way.

The whole point was to avoid the jenky multi adapter/hack brake setup scenario. Nobody wants to lose brakes, I've had that happen, fuck that noise.

The new adapters installed quick and easy and now the problem is solved.

 

[RunningProblem]

Almost looks like they need to trim some off their larger size of the fitting so it will seat lower. The larger diameter is odd if those are the same fitting. Why would you make it so much bigger?

Wilwood makes them too. 9/16 to -3an.

Wilwood Disc Brakes 220-12942 Wilwood Brake Line Fittings and Adapters | Summit Racing

Free Shipping - Wilwood Brake Line Fittings and Adapters with qualifying orders of $109. Shop Brake Fittings at Summit Racing.

www.summitracing.com

If you want steel then Strange makes them.

Strange Engineering P2357 Strange Brake Master Cylinder Fittings | Summit Racing

Free Shipping - Strange Brake Master Cylinder Fittings with qualifying orders of $109. Shop Brake Fittings at Summit Racing.

www.summitracing.com

Mostly posting for the next guy.

 

[arse_sidewards]

Can you measure and compare the thread pitches.

There's some common metric and fractional fitting size pair that will work with 3/16 tube and will thread into each other with no apparent crossthreading but also won't seal. I suspect that's what's going on here.

Looking at those two pictures I can't see how, if they are in fact the same thread pitch, the inline tube adapters can work but the Fagola ones can't. Sure the cone isn't bored as deep on the Inline Tube but the shorter fitting body seems like it makes up for that.

 

[PurfsMcGurfs]

Can you measure and compare the thread pitches.

There's some common metric and fractional fitting size pair that will work with 3/16 tube and will thread into each other with no apparent crossthreading but also won't seal. I suspect that's what's going on here.

Looking at those two pictures I can't see how, if they are in fact the same thread pitch, the inline tube adapters can work but the Fagola ones can't. Sure the cone isn't bored as deep on the Inline Tube but the shorter fitting body seems like it makes up for that.

It's pretty easy to figure out. The frag adapter has a 1/4 hole and the IT has a 3/16. The outer thread diameter at the flare end is what is important. The inline tube tapers in tight at the end to match the master cylinder, while the fragola remains larger. That's why it doesnt work. Even when bottomed out, the frag adapter doesn't allow the flairs to touch. You could cut it down but, it would have virtually no flare left by the time it was seated against the flare in the MC.

 

[PurfsMcGurfs]

Almost looks like they need to trim some off their larger size of the fitting so it will seat lower. The larger diameter is odd if those are the same fitting. Why would you make it so much bigger?

I think it has to do with GM deciding to do weird shit with the master cylinder thread sizing for the rear outlet. Fragola probably makes that part for a true 1/4" system.

 

[ScottRS]

Speedway's house brand steel -3 adapters work great for this. They also have them (in brass) to 3/16 or 1/4 inverted flare, I'm not a big fan of brass brake fittings, but they do work. I've not tried Speedway's -4 or 1/4 personally, just the -3 and 3/16.

 

[SHARPMACHINE]

Following. I really wanna do the ram 2500 master cylinder upgrade to my jeep. The scariest part for me is that I always feel dumb when converting line sizes..

 

[chaplinfj60]

Almost looks like they need to trim some off their larger size of the fitting so it will seat lower. The larger diameter is odd if those are the same fitting. Why would you make it so much bigger?

Wilwood makes them too. 9/16 to -3an.

Wilwood Disc Brakes 220-12942 Wilwood Brake Line Fittings and Adapters | Summit Racing

Free Shipping - Wilwood Brake Line Fittings and Adapters with qualifying orders of $109. Shop Brake Fittings at Summit Racing.

www.summitracing.com

If you want steel then Strange makes them.

Strange Engineering P2357 Strange Brake Master Cylinder Fittings | Summit Racing

Free Shipping - Strange Brake Master Cylinder Fittings with qualifying orders of $109. Shop Brake Fittings at Summit Racing.

www.summitracing.com

Mostly posting for the next guy.

so them fitting will work with this?

 

[rattle_snake]

I did same and the steel fitting leaked, then the fucking new hoses failed. Went to hard lines, problem solved.

looks cool but FAIL

Went HB, new MC, prop, hard lines.

 

[PurfsMcGurfs]

I spun the truck around the property and down the road a couple days ago and it worked great. The rear lockout worked perfectly for a park brake. I'll need to adjust the prop valve after I get new front calipers. Pretty sure mine are just about seized from sitting for so many years.

 

[RunningProblem]

so them fitting will work with this?

Dash three will match up to dash three.

 

[Lbhsbz]

It might be the master, not the fitting. Some master cylinders use a brass tube seat pressed into a drilled hole in the casting which is effectively an ISO bubble flare. Others use a machined in seat which has a larger flat between the flare seat and the threads. If you're using the later with a machined in seat, the fitting is not making contact on the tapered seat but on the flat between the OD of the machined-in seat and the threads....it won't seal like that. If you'd removed about .040" from the tip of the Fagola fitting, it could move the contact from flat bottom of the hole to the tapered part of the tube seat and work fine.

There are about 5 factories making master cylinders in China for every distributor in the US and a couple of them are pretty shitty.

 

[PurfsMcGurfs]

Eh, the one Fragola adapter was more expensive than both the Inline Tube adapters so its time/money ahead to just buy the parts designed for the application and not worry about having to modify shit to work. I didn't inspect the flares to closely, just cleaned it and installed the new adapter with no issue. Works for me.