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Brake Pipe Sizing


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#1 ferruccio

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Posted 15 December 2011 - 10:10

I am trying to figure out why some manufacturers use 4 different pipe diameters from the ABS body to the four calipers. Most systems use identical sizes while some use two different sizes for front and bake pipes.

What is the rationale for using 4 different sizes? System is in a sedan road car, front engined, rear drive with brembo 4 piston calipers all round. Are the different sizes just a precaution to avoid mixing the pipes or is there a performance reason for it? Anyone remember their fluid mechanics courses? I slept through them :drunk:

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#2 Engineguy

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Posted 15 December 2011 - 20:05

Under static condition (i.e. brakes applied, or brakes not applied), it doesn't matter, in theory. My guess is the ABS would like to see the same system "flaws" at all four ports under active ABS operation... pipe swelling, flow resistance, tire wear, etc. Again, I'm just guessing/fishing.
Question: Does the caliper nearest the ABS get the smallest diameter pipe (i.e. to equalize flow resistance) or the largest diameter pipe (i.e. to equalize volume)?

#3 MatsNorway

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Posted 15 December 2011 - 20:27

Question: Does the caliper nearest the ABS get the smallest diameter pipe (i.e. to equalize flow resistance) or the largest diameter pipe (i.e. to equalize volume)?


Great question. What car are we speaking of btw?

#4 Greg Locock

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Posted 15 December 2011 - 21:43

Lots of reasons I can think of, but I don't know which if any is right.

1)Brake system compliance
2)because they can, it doesn't cost any extra, it might even be cheaper
3)weight saving
4)balance the resistance of each line
5) Poka yoke

It is a very good idea, I'll go and suggest it to the brake people.

#5 Lee Nicolle

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Posted 15 December 2011 - 22:40

I have never struck this myself, though on occasion different size nuts and threads on the same size pipes. And on one car one nut was a 12mm spanner and the other 3/8 spanner. That is a big WHY?

#6 Magoo

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Posted 16 December 2011 - 00:12

Are the lines actually different or merely the fittings?

#7 ferruccio

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Posted 16 December 2011 - 01:06

Are the lines actually different or merely the fittings?


Both fittings and lines. Car is a right hand drive Chrysler 300c SRT8. It's arranged like this:

FL - Large
FR - Small
RL - Small
RR - Large

Sorry I could not remember which large is larger and which small is smaller. Trying to understand the logic. My only conclusion right now is that its a safety precaution to void mixing up the pipes. The non SRT8 V8 variant of this car does not have 4 different sizes and has non-brembo calipers. ABS pump in both cars are made by ATE and they look identical.


#8 DaveW

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Posted 16 December 2011 - 05:26

My guess would be that it is a cheap way of making sure that the control system is talking to the correct corners.



#9 ferruccio

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Posted 16 December 2011 - 11:44

My guess would be that it is a cheap way of making sure that the control system is talking to the correct corners.


Thats what I suspect. Hoping someone with authority on the subject can give a definitive answer.


#10 bigleagueslider

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Posted 16 December 2011 - 23:43

.......Hoping someone with authority on the subject can give a definitive answer.


Sorry, I'm not an authority on the subject, but I'll risk venturing a guess anyway. :|

My guess would be that the lines are different diameters for reasons of frequency. If you've ever used an ABS at its limit, you would have felt the hydraulic pressure pulsations feeding back thru the brake pedal. It seems logical that you would not want any natural frequencies in the hydrostatic brake circuit coupling with the operating frequency of the ABS valving. Such conditions would adversely affect the ability of the ABS to accurately meter the brake fluid discharge.

Just my uninformed speculation. So take it for what it's worth.

slider


#11 ferruccio

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Posted 17 December 2011 - 01:55

Sorry, I'm not an authority on the subject, but I'll risk venturing a guess anyway. :|

My guess would be that the lines are different diameters for reasons of frequency. If you've ever used an ABS at its limit, you would have felt the hydraulic pressure pulsations feeding back thru the brake pedal. It seems logical that you would not want any natural frequencies in the hydrostatic brake circuit coupling with the operating frequency of the ABS valving. Such conditions would adversely affect the ability of the ABS to accurately meter the brake fluid discharge.

Just my uninformed speculation. So take it for what it's worth.

slider


Thanks I considered something along the same lines but on the lower cc 5.7L V8 variant of this model (no brembo calipers) the pipes are not in 4 different sizes. So.. Hmm..

#12 cheapracer

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Posted 17 December 2011 - 06:06

It's obviously something to do with stability or failsafe as the 2 diameters are diagonally opposed.

Maybe the different diameters pulse at different rates avoiding 2 opposite wheels at each end acting exactly the same at exactly the same time...

Edited by cheapracer, 17 December 2011 - 06:08.


#13 Lee Nicolle

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Posted 17 December 2011 - 06:53

I can understand bigger pipes for 4 spots but diametrically opposed makes no real sense to me.

#14 mariner

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Posted 17 December 2011 - 09:46

As a simple question does any know if the normal LHD 300 also has different sized brake pipes or is this some oddity for RHD?

#15 cheapracer

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Posted 17 December 2011 - 20:09

A lot depends on the volume of fluid you need to move to get the brakes to work. If you have 4 pot calipers at the front and 2 pot at the back,


I'm going to take a wild stab at this and say the 300C doesn't have 4 pot caliper on the left front and 2 pot caliper on the right front ... could be wrong though, I was once before on January 15th, 1981 at 3.42pm, hard to forget such a moment (but I had banged my head earlier that day).