Rear Brake issue

[flathead]

I am in the process of rebuilding the rear brake system. I have all new parts (springs, shoes, wheel cylinders, fresh drums, etc) Once all the parts were in place, I attempted to install the new steel lines (generic) only to find that the fittings on those 1/4" lines are 7/16-24 and the threads in my cylinders are 7/16-20. Anyone?

[TodFitch]

Don't know about your later truck, but on my older Plymouth there is a banjo fitting that is bolted to the rear cylinders and the brake line goes into that. Maybe your truck is that way too.

[Young Ed]

I'd say you have the wrong lines. My 46 pickup and 48 coupe don't have any adaptors. I'm also thinking the lines are 3/16ths.

[4852dodge]

My one tons have a banjo fitting on the cylinder and the line attaches to the fitting.

[Plymouthy Adams]

dropped a couple items of info to you by PM..use as you see fit..

[flathead]

The wheel cylinders have an inverse flare at the bottom of the threaded hole, so I'm pretty sure a flared tube seats against it. What I need to find is a 7/16-20 Flare tube nut such as the one sold by BrakeQuip (BQ4277) I need to find locally, otherwise it means I have to wait for delivery, and I'd like to take it to a car show this weekend.

[Plymouthy Adams]

first off I am assuming your brake cyclinder is threaed for 1/4 inch line stand flare nut..71/17 diameter with 20 threads per inch...

most I have ever seen are standad 3/8 diameter with 24 TPI..

if you have the larger hole then the cylinders are set up for 1/4 inch line and most likely are for a larger vehicle ..you can get a reducer and use your 3/16 line...I would not recommend a 1/4 line from the master to the rear cylinders on a car or light truck..it has to do with volume and squish..trust me..I just went though this with the brakes as set up by the PO using 1/4 lines to the rear..would never get a firm consistant pedal..went to 3/16 line and instant pedal...

you get your lines by size and length and flare fitting..

here is what I found when comparing..

PA-340 means it is a US thread 3/16 line with double flare in 40 inch length

PAJ-340 is metric thread but 3/16 double flare in 40 inch length

PAE-340 is bubble flare 3/16 SAE thread in 40 inch length..(English cars)

[TodFitch]

...I would not recommend a 1/4 line from the master to the rear cylinders on a car or light truck..it has to do with volume and squish..trust me..I just went though this with the brakes as set up by the PO using 1/4 lines to the rear..would never get a firm consistent pedal..went to 3/16 line and instant pedal...

Not to doubt you (too much) but I don't understand the physics you are describing. As long as the lines are not ballooning out under pressure it doesn't seem like it should matter what the diameter is as long as it is enough to carry the volume of fluid needed to extend the wheel cylinder pistons without too much back pressure.

I can imagine that smaller diameter lines would be easier to bleed. But once properly bled I don't see why there should be a difference.

[Plymouthy Adams]

install them on your car from the master all the way to the rears and see for yourself..after fighting the issue many times..I did some reading up on the subject..found many great technical references as to the problem and made my change to 3/16....I would have been one of those hard to convince it was an issue also....hydraulics and displacment such as it is..if nothing else..seeing is believing

[ggdad1951]

Not to doubt you (too much) but I don't understand the physics you are describing. As long as the lines are not ballooning out under pressure it doesn't seem like it should matter what the diameter is as long as it is enough to carry the volume of fluid needed to extend the wheel cylinder pistons without too much back pressure.

I can imagine that smaller diameter lines would be easier to bleed. But once properly bled I don't see why there should be a difference.

diameter = volume displacemnt.

smaller diameter = more fluid resistance

too large = lots of pedal travel

too small = hard push

that'd be my logic

[Plymouthy Adams]

Tod I really do not care what you doubt as that is definitley your choice...as I myself shook my head at the beginning.. but if you wish to travel to my place I will gladly reinstall the old lines I removed and let you knock yourself out trying to get a pedal..the challenge is now in your court..I do stand by to assist you with tools and bleeding the brakes..I later called and discussed this and had the stiuation confirmed by a leading maker of hot rod brake kits that is often mentioned here and another thing that may be of help to you to realize this condition..as I am running disc front, drum rear, non booster..the bore is 15/16th dual reservoir master..with 1.5 depth as required for manual brakes..yes there are zero residuals in the the master..there is a 10 to the rear and 2 lbs for the fronts..master still in stock location under the floor along the rail..this system is built by the book and according to one website that stated that all American made masters for cars and light trucks were designed for 3/16 line front/rear, disc drum...where no amount of bleeding would get a hard pedal..swapped out the lines..only pressure flowed the lines without bleeding and had instant brake pedal..again..you do the math..the solution and only thing changed were the rear lines..

[TodFitch]

Tod I really do not care what you doubt as that is definitley your choice...as I myself shook my head at the beginning.. but if you wish to travel to my place I will gladly reinstall the old lines I removed and let you knock yourself out trying to get a pedal..the challenge is now in your court..I do stand by to assist you with tools and bleeding the brakes..I later called and discussed this and had the stiuation confirmed by a leading maker of hot rod brake kits that is often mentioned here and another thing that may be of help to you to realize this condition..as I am running disc front, drum rear, non booster..the bore is 15/16th dual reservoir master..with 1.5 depth as required for manual brakes..yes there are zero residuals in the the master..there is a 10 to the rear and 2 lbs for the fronts..master still in stock location under the floor along the rail..this system is built by the book and according to one website that stated that all American made masters for cars and light trucks were designed for 3/16 line front/rear, disc drum...where no amount of bleeding would get a hard pedal..swapped out the lines..only pressure flowed the lines without bleeding and had instant brake pedal..again..you do the math..the solution and only thing changed were the rear lines..

Not trying to start an argument. And I am sure your experience is valid. It just tells me there is something going on there that I don't understand.

[flathead]

I run 1/4" lines on my Camaro street stock race car, as do most everyone in my class, so it did not seem strange to me when I found them on my old truck when I started the brake project.

Thanks to everyone for your advice. The lines I can change, but I still need the 7/16"-20 fittings. Otherwise, I'm outta luck for this weekend.

[Plymouthy Adams]

Not to doubt you (too much) but I don't understand the physics you are describing. As long as the lines are not ballooning out under pressure it doesn't seem like it should matter what the diameter is as long as it is enough to carry the volume of fluid needed to extend the wheel cylinder pistons without too much back pressure.

I can imagine that smaller diameter lines would be easier to bleed. But once properly bled I don't see why there should be a difference.

Tod..plenty to read on this on the internet...and again you can call some of the brake folks if you wish..now on to another school of thought and probable cause for the problem as in my set up..in the above statement I left one item out...the proportioning valve..I am using one from the donor this system was borrowed...it is most folks ovservation that when going to 1/4 line instead of the 3/16 this throuws this valving all out of whack...GM does not use porporting valves in the their early disc drum non power units..instead they DID use the 1/4 line to the rear and it has been surmized this is to give the slow reaction to the pedal and as ofter feel to their brakes pedal..

I bought this car as a project in the works from another person..I really hate to say this but I have had to rework every aspect of the build so far..the brakes and the steering were issues that broke the camels back as they say..I quit on this car for almost three years...yes that aggrivating..lst night I think I put the last fix to the modification he made by correcting the way the rear axle was hung in the car..lots of cutting and welding to fix this..still don't have the same fever I had earlier on this car but after so many set backs something has to give..I was alomost to the point of burning the thing to the ground..this is the last car I will ever bought that someone else has worked on..

If anyone doubts what I have already researched and written, well the information is out there and in volumes..weed through it..I only posted what I did to hopefully keep someone from going through what I have been through...other than that ..you on your own and free to believe whatever you chose..

[Plymouthy Adams]

Not trying to start an argument. And I am sure your experience is valid. It just tells me there is something going on there that I don't understand.

I agreed with you that in the beginning I did not consider the tubing a problem..but after zero pedal and all things checked, no leaks etc was scratching my butt for answers....I went researching line size and found all the information out there that confirmed the problem..again I apologize for not mentioning the proporting valve as those in the know say it tries to compensate for the line and cannot..that may well be the single main arguement with the line size..see my post just above..GM and 1/4 line is their no cost solution to porporting in the beginning it is surmised..they use it extensivbely..also their master bores are a bit larger also..see early Camaro and Malibu/Nova setup and phyusical requirements..

rodding and changing stuff always throws a twist to things and you follow the master plan as best you can and go for a balance..but it is still not all etched in stone what one item works with the other..I often have more time in reading and research than in the assembly of a subsystem..

besides..this one was already plumbed by the PO in 1/4 line when I got the car..did not even suspect it to be a prob..

Edited September 7, 2012 by Tim Adams

[Jeff Balazs]

Tim;

Very interesting thread. And so true about the early GM system.......pretty basic. So basic it could easily be overlooked.

I wonder if a adjustable proportioning valve would have made any difference in the set up you had before you went to the smaller line size?

I am about to plumb up a 4 wheel disc conversion on my 52 PH. After giving it a lot of thought I decided to go with a Grand Cherokee M/C (match to my new rear axle) and a Wilwood combi proportioning valve. I know a lot of folks have used the PV out of a Cherokee but I think it would make it hard to get these brakes properly dialed in. The fabricators I spoke with said they were always able to get the right balance using the Wilwood unit. And this was on a wide variety of cars and trucks. So hopefully I will be able to report on it's effectiveness.

Jeff

[Plymouthy Adams]

I did not have an adjustable on hand to play with..if this system does not have a good balance then I will probably move in that direction..but gonna give this unit a chance to prove its merit first..

[flathead]

Don't know about your later truck, but on my older Plymouth there is a banjo fitting that is bolted to the rear cylinders and the brake line goes into that. Maybe your truck is that way too.

My one tons have a banjo fitting on the cylinder and the line attaches to the fitting.

I checked my cylinders, I was incorrect; while they are 7/16-20 threads, it is not an inverted flare fitting, so I'm thinking it may have had the banjo fittings. But then tonight on the way home from work, I spotted a '52, looked under it, and it looked the same as what I have for a brake set-up, but it did not have banjo fittings.

I'm so confused, I just want to drive my truck, it's the only thing keeping me from doing so...

[Jeff Balazs]

Flathead;

The original system on my 52 3/4 ton did not have any banjo fittings. The rear brake lines went directly into the upper wheel cylinders.

Hope this helps.

Jeff

[flathead]

Flathead;

The original system on my 52 3/4 ton did not have any banjo fittings. The rear brake lines went directly into the upper wheel cylinders.

Hope this helps.

Jeff

Jeff, do you know what fittings are used? Is it 7/16-20?

[Jeff Balazs]

Jeff, do you know what fittings are used? Is it 7/16-20?

It sure looks like that is it.....I don't have any of the old one I can measure as I am switching over to disc's and pitched the old corroded lines.

Jeff

[flathead]

Hot dog, I finally figured it all out, boys and girls. What I need was a simple 1/4" female inverted flare to 7/16"-20 adapter, available at your friendly local auto parts store, $5 each. Thanks all for your input, I appreciate it much!

[Jeff Balazs]

Great to hear you got it worked out.

Jeff

[flathead]

Now I am finished with everything, but need the flexible rear brake line - Where on this earth can I find one? What a pain this has been...

[MBF]

I bought mine at NAPA. Roberts also sells a 3 pc kit including the 2 front flex lines. Mike