BRAKE LINE PRESSURES?

[EDMO 1078]

I've been thru two hydraulic courses in my life, and didn't think I was one of the dumbest in the classes -

Sooo - Someone please explain to me why and how the Grove MC with 5/8 bore and short stroke makes their claimed 1000 psi, while the Matco MCs only give 600 psi with the same bore and stroke.

EDMO

[herman pahls 9]

Hi Ed

Seems suspicious to me also that 2 different 5/8's bore MC's would make such drastic different pressures with all else being equal.

If the the bores and pedal pressures are the same and the leverage ratio of the pedal to MC are the same, the pressures should be very similar.

So here is what I learned regarding this subject just last week.

I recently bought a model  4 Kitfox with 21" Nanco's with the original 1998 kit supplied Matco internal facing calipers with 5/8 bore Cleveland master cylinders.

Brake performance was adequate with the 21" Nanco's on 8" dia. wheels.

The only way I could install my 29" Airstreaks on the model 4 was to take the Matco Series E brakes off my model 2 which accommodate 6" dia. wheels.

These brakes with 29" tires on the model 2 performed very well.

These same brakes on the model 4 were terrible at best.

The model 4 weighs 70 pounds more than the 2.

The model 2 has 1/2 bore MC's which make all the difference versus the model 4's  5/8 bore MC with the same calipers, rotors and tire diameter.

Matco prefers to know pressures before they want to take the time to trouble shoot brake issues.

So I hooked up a 1000 psi gauge and found the 1/2 MC's put out 800 psi and the 5/8 only 450 at what felt like similar foot pressure.

The model 4 had another set of holes only a 1/4" closer to the fulcrum and the pressure went up to 600.

When I install 1/2 bore MC's on the model 4   I expect much improved brake performance.

Leverages and bore make a big difference in brake performance from my recent experience.

Herman

[saskavid 47]

Ed:

Matco probably only gives a 600 psi rating to their masters because that is the psi limit that their bottom end systems are engineered to work effectively to. There are so many wasy to configure mc's in a toe brakeing system and all the variables feed off each other.ultimately the weakest link is the make or break for how much line psi any system will develop. the weakest link typically is that most brakesystems for ac are bult to known set of compromises to control overall weight. Herman makes valid points about the 1/2 to 5/8 bore scenario, but in the typical avid system/setup, the smaller the bore the furthur the mc must stroke to move the same ammount of fluid for activation as it's larger counterpart and hence less mechanical leverage because of the extra movement. So basically gain leverage in one area lose it in another>

[EDMO 1078]

Herman and Mike,

      Thanks for the replies.   Herman, Matco makes an insert to change the bore from 5/8 to 1/2" - simple to install, and cheaper than new MCs.  Unfortunately, they may not work in your Cleveland MCs.

      I understand the differences in the advantage, and disadvantage, of the small bores - just cant understand the difference in psi claims for the 5/8 bores.   I haven't seen where Grove makes any pedals, so the lever attachment could be just about anywhere.

Fortunately, I now have both brands of MCs to use with my Grove calipers, so I may be able to compare results.

I think the MC-4? I have are 1/2" bore?

EDMO

Edited 13 May 2014 by Ed In Missouri

[herman pahls 9]

Ed

I ordered from Matco the 1/2 bore MC's.

Mike

You are correct about the the more pedal travel required when using smaller bore Master cylinders and in my case it is a non issue and the only way I can get the brake performance I need for 29" tall tires.

I could have stayed with the 5/8's bore MC and gone with the dual caliper system per side that Matco offers which many of the Just Highlanders use.

The dual caliper system would also increase the pedal travel

[EDMO 1078]

I may need to replace the ends of the MC rods with forked ends, but I have not found where Grove or Matco offers these separate.

EDMO

[herman pahls 9]

Hi Ed

I just installed the Matco 1/2" bore MC's and what a night and day difference in brake performance over the 5/8 bore with 29" tall tires.

Before the brakes would only hold 3000 rpm and now they hold  full throttle static (5400 rpm) with a 912S  (100 hp)

I am sure Matco will sell the forked ends (clevis) separate since I needed the longer ones to get my brake pedals forward of the rudder pedals.

Herman

[EDMO 1078]

Herman,

      I thought that all of the Matco MCs now were 5/8 bore - at least that is what Spruce says.   The original MC-1 had 1/2 inch bore and a reservoir - So, what MC did you get?  Did you buy the inserts?  I have several MC-4 sets, but I sold my MC-1s long ago.

BTW:  The Cleveland MCs are 9/16 bore from what I have read - half way inbetween the others.

EDMO

[EDMO 1078]

Herman,

      I cant find any Matco MCs with 1/2 inch bore - which ones did you order?

I also cant find the insert kit for the 5/8 bore to make it 1/2 inch.  Guess I'm just dumb?

EdMO

Edited 17 May 2014 by Ed In Missouri

[marksires 484]

Here is the link to the 'intensifier' kit for the MC5, they also have one for MC4.  I installed it on the MC5's that were originally in my Avid.  It helped, but not a lot.  I ended up building new pedals with MC4GH (shortest ones they had) to get the geometry right, and they work great.

 

http://www.matcomfg.com/MASTERCYLINDERINTENSIFIERKIT-idv-3282-46.html

Mark

Edited 17 May 2014 by mark

[dholly 718]

The model 2 has 1/2 bore MC's which make all the difference versus the model 4's  5/8 bore MC with the same calipers, rotors and tire diameter. So I hooked up a 1000 psi gauge and found the 1/2 MC's put out 800 psi and the 5/8 only 450 at what felt like similar foot pressure. The model 4 had another set of holes only a 1/4" closer to the fulcrum and the pressure went up to 600.

Herman-

My KF3 braking w/ MC-1's was waaaay better than my KF4 w/ MC-4A's (same wheels and calipers but larger tires now). Lotsa talk about improvements made to pedal geometry when the cylinder attach tabs are on the rudder torque tubes themselves (ala all Avids and KF1-3) but, as you know, the KF4 master cylinders are attached to the floor ahead of the rudder torque tube so I am trying to figure the best way to get the recommended 2.5:1 leverage with the MC-4A's.

With regard to using the top tab hole closest to the toe piece, didn't you experience interference of the clevis fork and pedal cross pivot tube? I seem to recall that was an issue with mine unless I angled the pedal uprights rearward by taking up a hole or two in the rudder cable adjustment straps. Also, I don't see where you mention which master cylinders you settled on, are you using MC-4A's or something different?

Thnx, Doug