Slant Six Forum
https://slantsix.org/forum/

Dual Reservoir Master cylinder fitting question
https://slantsix.org/forum/viewtopic.php?t=58099		 Page 1 of 1
Author:  hideogumperjr [ Mon Jul 20, 2015 9:30 am ]
Post subject:  Dual Reservoir Master cylinder fitting question
Hey guys!
I'm replacing the single Reservoir MC and looking for fittings for the sucker.

The MC has a 1/2"-20 fitting and a 9/16"-18 fitting. Both are inverted flare. I am trying to track down the fittings to get moving but am struggling to find them. On the Dorman site I find a couple of fittings:
490-543.1 3/16 In. Female to 9/16-18 Male Inverted Flare Dual Brake Line Adapter
-and-
499-015.1 Brake Line Adapter-Dual Brake-3/16 In. x 1/2-20 In.

I find a 490-302 Oversize Tub Nut-Steel-Green-3/16 In. x 1/2 In. x 20 but it doesnt look like its reverse flare and I dont know what a Tub nut, i think it is supposed to be a tube nut. Can anyone identify WTF?

Im beating around on ebay and am finding some info there but hate to buy the wrong dang part. I think I would prefer the brass over the steel fittings.

Any thoughts on whether there is a major difference in the tube nut over the brass fitting?

Thanks
John
Author:  SlantSixDan [ Mon Jul 20, 2015 10:18 am ]
Post subject: 
You're right, it's "tube nut", not "tub nut". A tube nut is what holds the flare at the end of the tube to its seat. I see both tube nuts you need here, but you ought to be able to get 'em from a well-stocked auto parts jobber (the kind that sells real parts to grownups, not toys to kids) that has an extensive brake line supply range.

What are you doing for residual-pressure valves?
Author:  Charrlie_S [ Mon Jul 20, 2015 4:05 pm ]
Post subject: 
NAPA had them at one time. The last time I tried to get them, they were not available. I got a stock of them from the company in the link, Fed Hill.
If I remember correctly they are 1/2-20 and 9/16 -20 (not 9/16-18 ), with the unthreaded lead. Part numbers A15-3 and A16-3. Might want to get some Cunifer tubing if you order from them.
Author:  hideogumperjr [ Tue Jul 21, 2015 8:24 am ]
Post subject: 
Thanks Dan Charlie.

Well Dan, I have researched the residual pressure situation immensely but have not made a final determination. ( ;-) !) Can you expound on the need for this for everyone's edification?
And what do you suggest?

Ok I confess! I thought cup expanders inside the wheel cylinders had pretty much made residual pressure valves obsolete. I know I need a proportioning valve for disc/drum but this is drum/drum so I didnt realize I needed any modifying aspects, might you please educate me?

John
Author:  hideogumperjr [ Tue Jul 21, 2015 3:27 pm ]
Post subject: 
So I found tube nuts locally here in a 5 pack. The are steel but since the MC fittings are inverted flare it doesn't look like the flat side of the tube nut will seal correctly, should I instead get the fittings in reverse flare?

BTW I love the help I get here, some things seem so simple but can end up as a can of worms so it is super to have the experience and know how at my fingertips, I have appreciated all the help yall have afforded me over the years!

Keep it up!

John
Author:  SlantSixDan [ Tue Jul 21, 2015 4:46 pm ]
Post subject: 
Quote:
Well Dan, I have researched the residual pressure situation immensely but have not made a final determination. ( ;-) !) Can you expound on the need for this for everyone's edification?
The residual pressure valve maintains slight pressure in the lines -- not enough to make the brakes drag, but enough to keep the shoes near the drums and prevent air entering the system via the wheel cylinders when the brakes aren't applied.
Quote:
I thought cup expanders inside the wheel cylinders had pretty much made residual pressure valves obsolete
They keep air from getting in at the wheel cylinders, yeah, but they don't keep the shoes near the drums— see here are you sure you have them in your wheel cylinders? You had an RP valve in your single-pot master cylinder.

You can get the valve(s) you need in round or hex body.
Author:  emsvitil [ Tue Jul 21, 2015 9:26 pm ]
Post subject: 
Quote:
Quote:
Well Dan, I have researched the residual pressure situation immensely but have not made a final determination. ( ;-) !) Can you expound on the need for this for everyone's edification?
The residual pressure valve maintains slight pressure in the lines -- not enough to make the brakes drag, but enough to keep the shoes near the drums and prevent air entering the system via the wheel cylinders when the brakes aren't applied.
Quote:
I thought cup expanders inside the wheel cylinders had pretty much made residual pressure valves obsolete
They keep air from getting in at the wheel cylinders, yeah, but they don't keep the shoes near the drums— see here are you sure you have them in your wheel cylinders? You had an RP valve in your single-pot master cylinder.

You can get the valve(s) you need in round or hex body.
Proper adjustment keeps the shoes near the drums.

Take a 15/16 wheel cylinder.....

It's area is .69 sqin. With a 10 psi valve, it will take 6.9 pounds of pressure to push it in (each cylinder).

You can do that with your thumb. The return springs are much stronger than your thumb.

So the shoe return springs will push against the wheel cylinders until stopped by the adjuster........


So you don't need the residual valve with the proper wheel cylinders.
Author:  hideogumperjr [ Wed Jul 22, 2015 12:06 pm ]
Post subject: 
Thanks for that information guys. Ill check into it further. I found brass fittings at napa here. Last trip to napa they did not have any fittings for me but lucked out this time.
Thanks all.
Author:  SlantSixDan [ Wed Jul 22, 2015 5:35 pm ]
Post subject: 
Quote:
Proper adjustment keeps the shoes near the drums.
Yes, but not as consistently and effectively as when the correct valving is in place.

I long ago lost count of how many times I've heard or read "Halp, I put in a dual master cylinder and the system's bled and the brakes are adjusted but the pedal still seems soft/squishy!" followed by "Residual valves...? What's that?" or "Residual valve? No, I have recent wheel cylinders" eventually followed by "Huh, how about that. I guess I did need the residual valves after all."

(And before I lost count, I was including letters to car-help columns in the likes of Popular Science and Popular Mechanics in the 1970s that looked like "My '74 Dart has 4-wheel drum brakes. The car stops OK, but the brake pedal is squishy. The dealer says everything's fine. Help!")
Author:  hideogumperjr [ Wed Jul 22, 2015 10:00 pm ]
Post subject: 
I checked with the master cylinder manufacturer and the residual pressure valves are built into the MC.
John
Author:  SlantSixDan [ Thu Jul 23, 2015 10:42 am ]
Post subject: 
Excellent -- that solves that problem.
Page 1 of 1 All times are UTC-07:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/