Master Cylinder & Push Rods

[jimbo01]

I've been working on my linkage for the brake peddle and master cylinders. The question That I have is what is an acceptable amount of push rod being forced into the master cylinder? I've read that 3/4 is good. Also one more question since I'm at it lol. Is there amount of push rod that can move forward before preload sets in? Thanks for the feed back.

 

[2old2fast]

As soon as the piston in the M/C moves it is displacing fluid , so no , you don't want any "preload" , in fact , I like a little [maybe an 1/8"] of freeplay before contacting the piston . Also I would want to be able to fully depress the piston in the cylinder. My $.02 .
dave

Make sure you put a return spring on the pedal assy. !

 

[RPM]

When we set them up here we leave about .020" clearance in the push rod, no preload. We use a 3/8-24 thread push rod. 1/2 of a turn is about .020".

 

[jimbo01]

This is the brake peddle that I have. I have 3 inches of travel at the top and am only getting the 3/4 at the master cylinder. I could always move the peddle to the center of the floor to get more leverage but that idea doesn't seem to fly with me. If I were to reverse the peddle direction and got the same 3 inches at the top I would get around 1 3/8 at the masters. I guess I'm not sure how this would work for someone with the master cylinder under their feet let a lone under their seat.

http://shop.wintecfabrication.com/product.sc?productId=133&categoryId=7

 

[jimbo01]

I guess I should learn to spell pedal the correct way before going any further lol.

 

[RPM]

I guess I should learn to spell pedal the correct way before going any further lol.

No spelling police on this forum. Thank goodness.

 

[jimbo01]

Does anyone see a problem if I make a new pedal with the bottom reversed from the link shown above?

 

[2old2fast]

I'm confused about why you want to reverse the pedal , can you post a pic of what you're trying to do ?
dave

 

[jimbo01]

The way that the pedal was made and the current set up, the area below the pivot only gives me 3/4 of an inch at the master cylinders.

If I were to re fab a new pedal and reversed the area below the pivot point, and point it in the opposite direction I would then get 1 3/8 inch at the master cylinder.

 

[2old2fast]

I still can't follow how moving the lower part of the pedal closer to the M/C will give you more travel ??
dave

 

[jimbo01]

This is the best way I can try to explain myself. Sorry for the early CAD edition.

The black shows the relaxed stock pedal.
The green shows the depressed stock pedal against the firewall.
The pink shows the pedal while depressed against the firewall after new pedal is made.

After seeing it on paper I now follow what your saying. Back to the drawing board for me. Thanks for the help.

 

[2old2fast]

If it would help , I could measure from the firewall to the pivot point on my brake pedal ??
dave

 

[RPM]

Here is a chart on this page that might help. http://www.piratejack.net/index.php?option=com_content&view=article&id=14&Itemid=21

 

[jimbo01]

If it would help , I could measure from the firewall to the pivot point on my brake pedal ??
dave

Dave,
That would help and give me an idea of where I should be looking. I've got a few different things going on with my brake set up. I'm working with duel masters with a balance bar. The first thing that I'm working on is another pivot point for the master cylinders. The reason for this is because the balance bar wants to twist as pressure is applied due to the span of the linkage and the balance bar being at the masters.. While working on that I started looking at the amount of travel I had at the masters and come up with a measurement of 3/4 inch. I'm only showing an 3 inches of travel at the top of the pedal but at this time it looks as if the pedal is going to have to get bent to clear the steering support and I'll get another inch. I think what is going to have to happen is, move the pedal towards the inside of the car to get more leverage.

 

[jimbo01]

Here is a chart on this page that might help. http://www.piratejack.net/index.php?option=com_content&view=article&id=14&Itemid=21

Thanks Buddy!!

 

[2old2fast]

Jimbo , from the inside of the firewall to where the pedal pivots is approx. 7" - from the inside of the firewall to the pedal pad is 10"- normal stroke is about 4". hope this helps.
dave

 

[jimbo01]

Jimbo , from the inside of the firewall to where the pedal pivots is approx. 7" - from the inside of the firewall to the pedal pad is 10"- normal stroke is about 4". hope this helps.
dave

Dave,
Are we using the same style pedal?

 

[2old2fast]

Yep , pretty much.
dave

 

[jimbo01]

Dave,
My measurement from pivot point to firewall is only about or around 4 inches. Looks like I'll be moving that tomorrow. Where is your pivot point mounted on the frame rail? Top, center or bottom. I had mine mounted on the bottom and I think this might be the time to move that up as well. I spent the day working out my balance bar bracket and pivot and am pretty comfortable with where that is at this point. If I get the master cylinder push rod movement that I'm hoping to get, I'll have to do a little more fine tuning in that area.

If your pedal pad is 10 inches from the firewall, does that mean that your pedal is leaning towards the rear of the car? Thank you again for the help.
Jim

 

[2old2fast]

Pivot point is center of frame rail [maybe a little above center, been awhile since I was under there] , main pedal "arm" is pretty much vertical . BTW , I'm running a manual trans so the brake/clutch share a common shaft.
dave