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759NRNG (Forum Partidario)
759NRNG (Forum Partidario) UberDork
1/31/21 7:28 p.m.

In reply to TheV8Kid :

Hmmmm....

wheels777
wheels777 UltraDork
2/11/21 10:43 a.m.

Between snow removal, delayed part deliveries and other projects .... we are trying to crowbar into the schedule a couple Challenge car builds.  Today's effort is to build out the brake pedal inside the revised foot well.

I can put a 13.5" petal into the box and sweep the push pad 5".  Current ratio holes are 6.35:1 and 3.48:1.  I want to get 1000 psi to the drum brake cylinders.  The 6.35 would need a 1-1/8" bore MC if I apply 150+# of force to the pedal.  The 3.48 would need a 13/16" bore MC.  

I have a 7/8" MC that has a total piston stroke of 1.125".  If I install the pedal with a 4.5 ratio and apply 150# of foot pad input I get 1,125 psi.  Also, the MC piston does not "bottom" out at the target 1000 psi hydraulic pressure.  So the 5" pad displacement and 1.125" MC piston displacement fall into a comparable compatible pedal ratio for the force to pressure relationships wanted.  

Now the question: will the guesstimated 0.88" (up to 1")  piston travel of the 7/8" MC supply enough volume for 4 drum wheel cylinders?  The 13.5" pedal length and the 5" pad sweep are defined.  

I guess I need to do a volume calc for the varying MC bores and corresponding ratios to see what the pad sweep would be, but thought I would ask here first.

Ultimately the goal is to avoid bottoming out the MC piston.

fusion66
fusion66 Reader
2/11/21 11:03 a.m.

In reply to wheels777 :

Do you have the drum wheel cylinder diameters handy? What assumption are you making for stroke required at each wheel cylinder for a properly adjusted brake? It seems like your answer will be highly dependent on those two factors. 

I tried to find wheel cylinder diameter online and struck out so far. 

Edit - looks like front wheel cylinders are 1 1/8" and rear are 7/8". 

wheels777
wheels777 UltraDork
2/11/21 11:14 a.m.

In reply to fusion66 :

Fronts are 69 Nova and rears are 69 Mustang.

And feel free to assume we adjusted them correctly.  

fusion66
fusion66 Reader
2/11/21 11:32 a.m.

Got it - it looks like the 69 Nova front/69 Mustang rear cylinder bores are  1.125"  front and .875" rear.

Not accounting for hose expansion or any deflection in the brake shoe itself, you should be able to get about .187" total travel at each cylinder for 1" of 7/8" MC travel which seems like it would be adequate for properly adjusted drum brakes. 

wheels777
wheels777 UltraDork
2/11/21 12:54 p.m.

Thank you.

 

I should have asked the question differently.   

To obtain 1000 psi to 150# foot pad force equivalent (AND ASSUMING AN EQUAL VOLUME IS PUSHED INTO THE SYSTEM TO CREATE THE 1000>150 BALANCE) a 7/8" MC at a 4:1 ratio.   A 1" MC would require a 5.26:1. A 1-1/8" MC would require 6.6:1.  Assuming the 7/8" strokes 1", the comparable 1" MC would stroke .759" and the 1-1/8" MC would stroke .606".

My available range for pedal ratio is between 4.5 and 5.  Otherwise I would have to go to the original hole at 6.35:1 with a 1-1/8" MC and the 150# input would be 962 psi line pressure.  

So rewording the question... is it acceptable to use 78-79% of the MC piston stroke range for the 7/8" MC we currently own?  Or should I go to the higher ratio pedal and obtain a bigger bore MC so that it operates in a lower range for the total piston stroke travel length?

It probably goes without saying that using what I have is my preference.  Also, (and this is an assumption) the 1000 psi I am targeting is for launching the car and the A-x use probably won't need as much line pressure <<< this is an assumption!!!

fusion66
fusion66 Reader
2/11/21 2:46 p.m.

I apologize that I am not quite able to follow along and I don't want to misguide you with bad information. 

When talking about pressure you have everything correct and I am following that part of your part selection. When you move over ot the amount of stroke that will be consumed for a given MC and pedal ratio I also follow along and agree with your assessment. 

Where I am getting lost is when we talk about the amount of stroke that will be used at the MC. This is very dependent on the amount of "volume" used by the system and is certainly impacted by MC bore, wheel cylinder bore, brake actuation travel (one of the biggest factors I think) and smaller contributors such as hose expansion under pressure. I think based on your design targets you are being careful to avoid "bottoming" (100% travel) of the MC and I agree that is good from a design perspective. Having a pedal ratio and MC stroke that is limited to 80% of the maximum available MC travel does not raise any flags to me from a design perspective but I typically deal with Master/Slave cylinders on clutch systems so I might not have a clear view of any issues that this could cause.

Hopefully someone with brake system knowledge can chime in and give a more direct answer.

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) MegaDork
2/11/21 9:05 p.m.

Yes, it is acceptable on a drag and autocross car. 20% is less than the reserve I would design in for a dedicated street car that could see some fade, but fade isn't likely on a challenge car.

wheels777
wheels777 UltraDork
2/11/21 10:16 p.m.
AngryCorvair (Forum Supporter) said:

Yes, it is acceptable on a drag and autocross car. 20% is less than the reserve I would design in for a dedicated street car that could see some fade, but fade isn't likely on a challenge car.

Thank you

wheels777
wheels777 UltraDork
2/12/21 8:30 a.m.

Calvin made new solid bushings to replace the 59 year old rubber pieces.

wheels777
wheels777 UltraDork
2/12/21 8:32 a.m.

Big engines need more room.  Moved the frame section outboard.

wheels777
wheels777 UltraDork
2/12/21 8:38 a.m.

Alan need more roomcheeky....okay everyone needed more room.  And since the V8 is now gone and the entire left side exhaust is gone.... how about 8-1/4" more foot well.

TheV8Kid
TheV8Kid Dork
2/16/21 7:21 p.m.

Wiring wiring wiring....

I even bench tested it, and it looks like it will work!

wheels777
wheels777 UltraDork
2/22/21 6:03 a.m.

Foot well is close to completion.  

wheels777
wheels777 UltraDork
2/22/21 6:04 p.m.

Slugging forward.

wheels777
wheels777 UltraDork
2/25/21 9:08 a.m.

Check out the latest video.

https://youtu.be/mNuYIf6W7CE

wheels777
wheels777 UltraDork
3/12/21 9:00 a.m.

Junk yard fresh bullet has entered the dungeon. 

wheels777
wheels777 UltraDork
3/21/21 4:26 p.m.

Bump steer corrected.

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) UltraDork
4/5/21 9:14 a.m.

This is awesome! I haven't been on GRM as much recently, so I'm glad I saw it when I did.

wheels777
wheels777 UltraDork
4/5/21 11:06 a.m.
AWSX1686 (Forum Supporter) said:

This is awesome! I haven't been on GRM as much recently, so I'm glad I saw it when I did.

Thank you.  Should be getting the engine soon.  Next video for this one will be the start up.  Probably mid to end of May.  

wheels777
wheels777 UltraDork
5/30/21 2:44 p.m.

Progress is being made by Calvin.

wheels777
wheels777 UltraDork
6/5/21 4:13 p.m.

One week marothon with an crazy sprint to the end and we made the NSRA East event this weekend.

wheels777
wheels777 UltraDork
6/6/21 11:53 a.m.
759NRNG
759NRNG UberDork
6/10/21 9:30 p.m.
wheels777 said:

Junk yard fresh bullet has entered the dungeon. 

What are the mileages on these Atlas motors y'all keep pulling? 

wheels777
wheels777 UltraDork
6/11/21 8:02 a.m.
759NRNG said:
wheels777 said:

Junk yard fresh bullet has entered the dungeon. 

What are the mileages on these Atlas motors y'all keep pulling? 

60K to 200K

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