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 Page 1 of 2 12
Username Post: 1/4" brake lines        (Topic#348259)
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-17-17 07:20 PM - Post#2714813    

On my 53 3100 pickup I'm running Wilwood 12.88" disk brakes, 6 piston front and 4 piston rear. I haven't bought master cylinder yet. Wilwood tells me I have to run 3/16" brake lines and can't run 1/4" because of pressure? I have about 85 feet of 1/4" polished stainless tubing left from a factory I built. I don't understand why it matters. Same in, same out?



 




raycow 
Honored Member
Posts: 27072
raycow
Loc: San Francisco, CA
Reg: 11-26-02
11-17-17 11:54 PM - Post#2714824    
    In response to Mick53

Does Wilwood know what purpose was your tubing was sold or intended for? If it was made for some kind of low pressure application, then yes, you could possibly have a problem.

However, until Wilwood can give you an explanation of why replacing a 3/16" line with a 1/4" line of equivalent pressure rating would have "pressure" issues, I would think their concern is unwarranted.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-18-17 04:18 AM - Post#2714826    
    In response to raycow

Thanks Ray, They didn't say why when I spoke to their engineer. The tubing I have is for very high pressure use. My engineer says he uses it in his street rods. I also have some very nice compression fittings for it so I don't have to use flair fittings.



 
Shepherd 
Frequent Contributor
Posts: 1032

Loc: Lake George, NY
Reg: 11-11-15
11-18-17 05:06 AM - Post#2714829    
    In response to Mick53

From a hydraulics stand point, the smaller line would require somewhat less pressure to move a smaller column of fluid thru the lines, this would change the pedal feel, check this thread.http://www.pro-touring.com/archive/index.php/t-34180.html



 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-18-17 08:39 AM - Post#2714843    
    In response to Shepherd

Thanks. Not sure I understand it completely but my engineer says he has 60 feet of 3/16" he will give me if I want. It comes in 20' straight lengths. He also says to use their special compression fittings because it is too rigid to flair. He's going to fix me up with fittings. I love the way fellow gear heads help each other out.



 
Shepherd 
Frequent Contributor
Posts: 1032

Loc: Lake George, NY
Reg: 11-11-15
11-18-17 10:53 AM - Post#2714853    
    In response to Mick53

Do not use compression fittings in your brake lines, in NYS they are illegal. We double flare 3/16 lines routinely here.



 
raycow 
Honored Member
Posts: 27072
raycow
Loc: San Francisco, CA
Reg: 11-26-02
11-18-17 11:16 AM - Post#2714856    
    In response to Shepherd

I believe Mick may be intending to use special high pressure fittings rather than the conventional type of compression fittings you might be thinking of.
https://en.wikipedia.org/wiki/Cutting_ring_fit ting

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Shepherd 
Frequent Contributor
Posts: 1032

Loc: Lake George, NY
Reg: 11-11-15
11-18-17 11:45 AM - Post#2714860    
    In response to raycow

Yeh, hope so, regular compression fittings are not designed for brake systems.



 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-18-17 03:39 PM - Post#2714882    
    In response to raycow

Thanks Ray. I Don't know what they call them. I will have to look at the crate or ask. They are by no means a standard fitting. If you put one of these fittings on you have to cut it off. If you had to buy them they are quite expensive. I will look into it. We use them on giant ammonium compressors and the like. I'm building a dry ice manufacturing plant.



 
Ray P W 
Contributor
Posts: 341

Reg: 09-30-15
11-22-17 08:19 AM - Post#2715326    
    In response to Shepherd

Shepherd,

The link you attached contains this comment:

"The volume of fluid moved through a brake system is determined by the MC piston bore and the caliper piston bores. Assuming that the fluid is incompressible, then what goes in, must come out. If we ignore line size and push a volume of 10cc of brake fluid in one end of a brake line with the MC, 10cc will come out the other end, regardless of diameter, length, or pressure. The brake line could be .06" or 6" in diameter and that would still be true as long as we assume that the tubing doesn't expand.

I still don't believe or understand the assertion some are making that line size effects the "tunability" of a system, because in my experience and realm of knowledge, it does not."


His "What goes in must come out" statement appears to be the answer or am I missing something?

Ray W



 
Rick_L 
Honored Member
Posts: 27249
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-22-17 10:19 AM - Post#2715341    
    In response to Ray P W

The volume required to apply the brakes is small. The difference in line size does not make any difference at all.

As a general rule, use the size of tubing that your components are made for, avoiding adapters. It just keeps things simpler.

If you insist on compression fittings, you have to use some that are rated to 2000 psi or so. There are a couple of companies that make them, Swagelok is probably the best known. They are rather expensive compared to flare fittings. Personally I would used flare fittings, either 45 degree inverted flares which require double flares, or AN/JIC 37 degree flares which require single flares.

If the tube is hard or impossible to flare, it may be hard or impossible to bend it like you need. Inline Tube sells stainless tube that can be double flared with a decent tool, it bends well too. This is because it's the right alloy/heat treat and wall thickness for the job. Use a quality tubing bender too.



 
Shepherd 
Frequent Contributor
Posts: 1032

Loc: Lake George, NY
Reg: 11-11-15
11-22-17 02:11 PM - Post#2715360    
    In response to Ray P W

Check the 4th paragraph referring to pedal travel and feel. http://techtalk.mpbrakes.com/master-cylinder-2/mas ...



 
4dr 57 
Valued Contributor
Posts: 4492
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
11-23-17 08:02 AM - Post#2715458    
    In response to Mick53

  • Mick53 Said:
On my 53 3100 pickup I'm running Wilwood 12.88" disk brakes, 6 piston front and 4 piston rear. I haven't bought master cylinder yet. Wilwood tells me I have to run 3/16" brake lines and can't run 1/4" because of pressure? I have about 85 feet of 1/4" polished stainless tubing left from a factory I built. I don't understand why it matters. Same in, same out?




Are you planning on a P/B system?

Wilwood is possibly saying this possibly b/c their systems are usually manual brake systems.
Maybe 3/16" fittings with 1/4" line between them would make too much fluid pressure- it couldn't hurt to ask them.
SS brake lines for a non stock system will be tough enough. Good Luck.

It's all good. mostly




 
Ray P W 
Contributor
Posts: 341

Reg: 09-30-15
11-23-17 09:01 AM - Post#2715469    
    In response to Shepherd

"Check the 4th paragraph referring to pedal travel and feel. http://techtalk.mpbrakes.com/master-cylinder-2/mas ..."

Good morning Shepherd. Happy Thanksgiving!

I did read that and it was not news. There is no question that for a given piston travel distance more fluid will be displaced in a large cylinder than in a small one. However, the tubing simply transmits the displaced fluid. Fluid dynamics tells us that a larger pipe has less friction losses, however it seems unlikely that the short distances that brake fluid travels would be affected by that. A larger pipe has more surface area to be stretched by the fluid pressure but, again, would that be a factor in a car brake system? It's doubtful.

I recently encountered another hydraulic "rule of thumb" that makes no sense to me. I installed a roof rainwater harvesting system on my house. That system has very little pressure so a "booster pump" is required. A "rule of thumb" for water system booster pumps is that the "suction" (inlet) pressure is added to the pressure generated by the pump. But the pump electric motor is turned on and off by a pressure switch plumbed into the outlet side of the pump. That being the case, the pressure switch senses only the pressure exiting the pump.

Being a curious person I questioned that "rule of thumb". I asked an engineer at the pump manufacturing company, well drillers who install these pumps, plumbers who install these pumps and my own 2 sons who are both professional engineers (one mechanical and the other electrical). None could explain how a switch on the output side of the pump could sense suction pressure unless the suction pressure is so high that it spins the pump like a turbine and the suction pressure is always higher than the switch turn-on pressure.

It is in that same spirit of curiosity that I question the brake line diameter question. The answer may be simply that 3/16" line costs less than 1/4" line and less brake fluid is required to fill it, improving the car company's bottom line.

Ray W



 
Shepherd 
Frequent Contributor
Posts: 1032

Loc: Lake George, NY
Reg: 11-11-15
11-23-17 09:42 AM - Post#2715473    
    In response to Ray P W

For what it's worth, my 55 Chrysler had 1/4 all around, it also had 2 wheel cylinders per wheel in the front. My 51 Chev power disc/ drum, 1 1/8 master, has 3/16 all around, pedal feel has a little more travel than I would like, but stopping power is great, ton of variables here though. Had to fool around with pedal free play when first done, now about 1/4".



 
65_Impala 
Very Senior Member
Posts: 3918

Reg: 12-29-02
11-23-17 04:35 PM - Post#2715511    
    In response to Ray P W

The only reason the line would be a concern would be if it was small enough to create a restriction to the flow which would make it harder to press the pedal down enough to get the brakes to apply. But, 3/16" is smaller than 1/4" so for this case it can't be because the 1/4" line would cause a flow restriction.

I'd suspect it's simply because 3/16" is the size of the female flared ends on the brake hoses coming from the calipers.



  • Ray P W Said:
I recently encountered another hydraulic "rule of thumb" that makes no sense to me. I installed a roof rainwater harvesting system on my house. That system has very little pressure so a "booster pump" is required. A "rule of thumb" for water system booster pumps is that the "suction" (inlet) pressure is added to the pressure generated by the pump. But the pump electric motor is turned on and off by a pressure switch plumbed into the outlet side of the pump. That being the case, the pressure switch senses only the pressure exiting the pump.

Being a curious person I questioned that "rule of thumb". I asked an engineer at the pump manufacturing company, well drillers who install these pumps, plumbers who install these pumps and my own 2 sons who are both professional engineers (one mechanical and the other electrical). None could explain how a switch on the output side of the pump could sense suction pressure unless the suction pressure is so high that it spins the pump like a turbine and the suction pressure is always higher than the switch turn-on pressure.

Ray W




That makes sense. You can add the suction side pressure to the maximum pressure the pump can produce to get the maximum possible outlet pressure. For example, if the pump can produce up to 40psi and the suction side pressure is 5psi, then you can get a maximum of 45psi at the outlet side of the pump.

Why would the switch on the outlet be measuring the suction side pressure? When the pump turns off, a one way check valve closes which holds the water AND pressure on the outlet side by not letting the water flow backwards through the pump. The check valve is before the pressure switch.

That is similar to the same pump system installed in millions of rural homes. Nothing really special about it or how it functions. It's baffling how multiple engineers and professionals in that field couldn't explain it.

A similar pressure addition happens with multi-stage pumps. 7 stages of pump that can each produce 100psi are put in series in a common housing to create a pump that can produce 700psi at the outlet.





 
Don57 
"12th Year" Silver Supporting Member
Posts: 1363
Don57
Age: 67
Loc: Illinois
Reg: 04-28-00
11-24-17 06:12 AM - Post#2715554    
    In response to Ray P W

  • Ray P W Said:

A "rule of thumb" for water system booster pumps is that the "suction" (inlet) pressure is added to the pressure generated by the pump.




The inlet pressure is determined by the height of the column of water at the inlet side of the pump. As the pump runs and the height of that column decreases, the inlet pressure decreases. That, in turn, decreases the outlet pressure.

I'm guessing that the switch is on the discharge side only because it's a higher pressure and easier to monitor.

On the inlet side the pressure will only be 1 psi for a column height of about 28 inches. So you would need a 140" tall column of water to produce only 5 psi. I think you would need a pretty sensitive pressure switch for such a low pressure.


Mick - This has nothing to do with your brakes.


Don


 
Ray P W 
Contributor
Posts: 341

Reg: 09-30-15
11-24-17 04:45 PM - Post#2715599    
    In response to Don57

"That is similar to the same pump system installed in millions of rural homes. Nothing really special about it or how it functions. It's baffling how multiple engineers and professionals in that field couldn't explain it."

Impala,

Here's why they can't explain it. The rule of thumb makes no sense to me because the pressure switch is on the output side of the pump and I put the question this way:

"Let's assume hypothetically that the suction pressure is 80 psi and the on/off pressures on the pressure switch are set at 30 psi and 50 psi. It seems that under those conditions the suction pressure would be passed through the pump and is so high that the pump motor would never be switched on and, in fact, the suction pressure would spin the pump impeller like a turbine.

"But, the rule of thumb states that the output pressure would be in the range of 110 psi to 130 psi. Would it really be that high?"

That is what stops them in their tracks because an output pressure of 110-130 psi would not happen. In that case, the rule of thumb is not correct.

I want to be really clear here that I'm not looking for an argument. I'm just questioning a statement that makes no sense to me.

Ray W



 
Rick_L 
Honored Member
Posts: 27249
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-24-17 05:31 PM - Post#2715605    
    In response to Ray P W

If your inlet pressure was 80 psi, why would you even need a pump? You wouldn't unless the lines were very small and very far away from the point of use. In which case, sensing the pressure at the point of use makes more sense than at the pump outlet. This is because pressure drops in long lines relative to flow.

On the other hand, sensing the pump outlet pressure makes plenty of sense, and if the pressure is high enough the sensor shuts the pump off.

But this has nothing to do with how to plumb automotive brakes. The key thing to remember is that flow and the time it takes to flow is really small, and it's not continuous because the flow stops once the pad or shoe is in contact.




 
65_Impala 
Very Senior Member
Posts: 3918

Reg: 12-29-02
11-25-17 06:42 AM - Post#2715653    
    In response to Ray P W

Here's anther good rule of thumb then. There's never a sensible answer to questions that are complete nonsense.





 
Ray P W 
Contributor
Posts: 341

Reg: 09-30-15
11-25-17 07:32 AM - Post#2715662    
    In response to 65_Impala

'65 Impala,

This quote from raycow is another example of a curious person questioning the HOW/WHY of a "rule of thumb":

"However, until Wilwood can give you an explanation of why replacing a 3/16" line with a 1/4" line of equivalent pressure rating would have "pressure" issues, I would think their concern is unwarranted."

Some of us are content accepting what others tell us. It is easier and faster. But others of us are curious about how things actually work. In my work as a professional geologist I have encountered "facts" that don't hold up when questioned. Some of those things actually matter like how to properly size an onsite sewage disposal system or whether or not a particular slope will be stable.

Ray W



 
4dr 57 
Valued Contributor
Posts: 4492
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
11-25-17 10:57 AM - Post#2715686    
    In response to Ray P W

Reading the small print, Wilwood master cylinders impart fluid FLOW at a 2:1 ratio. The fluid Pressure may be the result of this and may not require a 1/4" line.

What is the pedal ratio of your truck?


No one commented on my reasoning as to why why Wilwood made the statement but I think possibly it is because of their master cylinders producing a 2:1 flow rate.





 
Rick_L 
Honored Member
Posts: 27249
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
11-25-17 03:21 PM - Post#2715707    
    In response to 4dr 57

What in the world are you talking about? What 2:1 ratio?



 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-25-17 03:24 PM - Post#2715709    
    In response to 4dr 57

I don't have anything installed yet. I finished my job last Tuesday. Now I can finally get started on my truck. Picked up my Frankland rear end a couple of weeks ago.I had the factory retube it and put a Gleason locker in it. Going to order axles next week. Should have my front axle in a couple of weeks. I'm having spindles made for the Wilwood 12.88" disks. Gaerte should have my engine done by the first of the year or so. Waiting on the bilit crank before they know what blower pulley to make. I have other 292's for mock up.Going to have to move the radiator forward and engine back into the cab a little. Had mid-shift kit put on the TKO600. Let the journey begin. I have waited 37 years for this.




 
4dr 57 
Valued Contributor
Posts: 4492
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
11-25-17 03:51 PM - Post#2715711    
    In response to Rick_L



Go to the Wilwood site Rick_ they have "what's it mean" answers, better yet, call them, that's what their there for.
I'm just saying what I read...although I would assume it means for every two inches of pedal push the Master Cylinder piston gets shoved 1" into the bore, but don't take my word for it, I'm an armature, ask Wilwo9od's Engineering Dept if you have to have a more informed, more specific answer. cheers
Stanley

Sunday morning- This morning I'm not so sure anymore. Couldn't find anything in the Wilwood master cylinder section except a Spec. that said the ratio was 1:1, or their pedal section pertaining to a 2:1 ration anything.All the pedal are 6:1 or more. gak!




Edited by 4dr 57 on 11-26-17 05:10 AM. Reason for edit: No reason given.

 
4dr 57 
Valued Contributor
Posts: 4492
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
11-25-17 03:53 PM - Post#2715714    
    In response to Mick53

Yep, Wilwood, although brake companys SalesStaff can be fussy about answering too many questions. They have products and know that they work. Their Engineers have details.



It's all good. mostly




 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-25-17 09:01 PM - Post#2715733    
    In response to 4dr 57

Wow folks thats a lot of info for a construction guy. I guess I will get with Erik at Wilwood when I get to the point of master cly and the like. He wasn't in when I called about the line size. Erik has helped me so far. I thought it was a simple question. Now at least I know how little I know. Thank you everyone.



 
4dr 57 
Valued Contributor
Posts: 4492
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
11-26-17 06:43 AM - Post#2715770    
    In response to Mick53



Note the 1/4" brake lines on this ride

https://scontent-dft4-2.xx.fbcdn.net/v/t31.0-8/241...



 
Mick53 
Platinum Supporting Member
Posts: 123
Mick53
Loc: Northern Indiana
Reg: 04-02-16
11-26-17 10:22 AM - Post#2715792    
    In response to 4dr 57

Nice.



 
65_Impala 
Very Senior Member
Posts: 3918

Reg: 12-29-02
11-26-17 06:26 PM - Post#2715846    
    In response to Ray P W

Ray W

Lecturing about how others are curious doesn't change the fact that your pump question you posed was complete nonsense. If your inlet pressure was 80psi and the pump shut off at 50psi then the pump would NEVER run and without it running it would NEVER boost the inlet pressure. If you forced the pump to run then it would still boost the 80psi and certainly would be capable of producing the higher pressure. But. it's still a nonsense question because it's asking about a system no-one with any common sense would ever build.

I already gave why 1/4" won't be an issue and why I suspect the 3/16" line size was given.



 




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