Jeep XJ master cylinder pushrod?

[gtech636p]

I've finally gotten around to trying to work on the B1B again.  I have an XJ master cylinder bolted up and put the pedals in the floorboard last weekend.  I got around to trying to find the pushrod for the master cylinder but got distracted and didn't complete the task.  Unfortunately, the truck is ~ 7 hours away again.  The original pushrod is available, but I wanted to check what everyone else used before I put everything into the original pushrod.

 

Another slightly related question, to those who performed the swap before, did you cut some of the "guide" for the pushrod on the front of the XJ master cylinder or leave it in place?

 

Any help is appreciated.

 

 

[lostviking]

I used a Toyota master, because it has almost the exact same three bolt mount. You have to run a drill through to open the holes a bit. The stock rod in that case was about 1/5 inch too long. You should adjust yours to min length and install it, adjusting longer and see. If you can't get it in even with the min, then wack a bit off the end.

 

Dead give away, the brake lights are on. Too long.

[Jim Shepard]

I’m also trying to use the Toyota Corolla MC on my B2B. As you say, the bolt hole pattern is almost right on. However, the MC cylinder is about 1” too long and doesn’t clear the steering column. Did you have this issue and, if so, what was your fix?

[Los_Control]

@Jim Shepard Just curious what year MC did you use? Think I went with 91 or 92. I have about 1/2" clearance between mc and steering box.

Also I measured and it is 6" long. I measured from the outside of the base where the mounting bolts seat .... I butted the tap to it.

So add the thickness of the base mine is probably ~6.5"

[Jim Shepard]

Not sure but I think it was about a 2000. So, if I understand it, you measured from the end of the MC to the flat part of the flange where it bolt to the bell housing. Correct? 

[Los_Control]

You are correct, it was just easier to butt the tape to the mounting flange and 6" ..... It is mounted .

I just worked a little harder and measured total length and it is about 6.7/16" ... just under 6.5"

[Los_Control]

I just looked it up on my pc at rockauto and I can see my past choices highlighted it took me to 1992 Corolla

I looked for the basic mc without ABS etc.... There is a million to choose from, I chose middle of the road $52.

I know this MC will work for several years of Toyota, 2000might be to new and different.

.

 

 

https://www.rockauto.com/en/catalog/toyota,1992,corolla,1.6l+l4,1275409,brake+&+wheel+hub,master+cylinder,1836

[lostviking]

I used this one Duralast Brake Master Cylinder NM55022. Sorry Jim, I didn't see your question earlier, but my truck is a WD15, so next earlier design. I'm not sure if there was a big change in that specific area, but I have no clearance problems at all with mine.

Edited February 1 by lostviking

[Los_Control]

I really know very little about brakes and engineering a custom brake system ..... I can only copy what smarter people then me has done.

 

I've always heard it was the early 90's Toyota MC that works.

Besides the mounting bolt pattern, they also had rear drum brakes and the MC bore is 1" the same as our original MC.

 

I just did a quick search on a 2000 Corolla MC and         Master Cylinder Bore Diameter (IN)    0.812

 

So the piston bore is not the same size as the MC they are replacing.

I also think the newer cars all had 4 wheel disk brake, larger calipers, ABS and other trick options ..... just a total different animal then a 1992 Corolla.

 

Is the smaller bore bad? I have no clue, seems like it might give more pressure to accommodate the larger 4 wheel disk brakes.

It may be a longer, larger MC for the same reason.

 

I've just never heard of a clearance problem using the early 90's MC.

[Jim Shepard]

That Rock Auto MC sure looks like the one I took back to Napa today. If it isn’t too much trouble can you measure it from flange to nose?

[Jim Shepard]

BTW, I’ve asked Charles Akers, AKA, “Rusty Hope,” and maker of my kit, to get me a part number for the one he used. Hopefully we can get this pinned down and folks don’t have to keep reinventing the wheel…

[Los_Control]

Sorry just read up ..... I did give you the close to exact measurements .... While I love Rustyhope  .... sorry they are dragged into such a trivial problem.

 

It is just brakes, just get it done and make it safe. No sense in dragging the king of brakes into your issue.

 

I still say you have too new of a MC to work with your project ...... where did you hear a 2000 MC would work?

This was totally your choice.

[lostviking]

Yes, use a master from a car/truck that has disk/drum brakes. From what I've read, smaller bores change the firmness of the pedal. I can't remember which way. So long as the volume of fluid is enough to move the wheel cylinders and calipers enough to lock the brakes, that's the big difference. I'm sure there are numerous articles that explain the pedal travel changes, so I won't tax my memory and get it wrong.

 

As far as the flange, take a look at my thread on installing the Scarebird brakes in my truck. I literally just ran a larger drill through the holes and was able to install it.

[Merle Coggins]

On 2/2/2024 at 10:02 AM, lostviking said:

... From what I've read, smaller bores change the firmness of the pedal. I can't remember which way...

 

Today's physics lesson... Basic Hydraulics...

PSI = Pounds per Square Inch, or Pounds/Sq. In.

I'll use a 1 inch bore and a 3/4 inch bore as examples. So first we have to find the square inch surface area of the piston using the pie are square (π × r² ) formula. 

1" bore = 0.5" radius. 0.5 X 0.5 = 0.25 X 3.14 = 0.785 square inches of surface area. 

3/4" bore = 0.375" radius. 0.375 X 0.375 = 0.14 X 3.14 = 0.44 square inches of surface area. 

 

If I were to exert 50 pounds of force on the master cylinder piston with my foot how much pressure will be generated? 

50 lbs. / 0.785 sq. in. = 63.7 PSI with the 1 inch bore. (metric conversion; 22.7 kilos = 4.4 Bar)

50 lbs. / 0.44 sq. in. = 113.6 PSI with the 3/4 inch bore.  (metric conversion; 22.7 kilos = 7.8 Bar)

 

So, as you can see, the smaller bore will create more braking pressure with the same pedal force. Or, you could say it will take less leg force to generate the same braking force. However, as alluded to, the smaller bore will move less fluid so it will take a longer pedal stroke to apply the brakes. So it comes down to will a smaller bore master cylinder displace enough brake fluid before bottoming out to apply your brakes safely, yet apply more pressure at the same leg effort? Or do you need a larger bore to get the fluid displacement required, and need a little more leg effort to achieve the braking force needed.

 

Edited February 5 by Merle Coggins

[Veemoney]

3 hours ago, Merle Coggins said:

Today's physics lesson... Basic Hydraulics...

Nicely done Merle

[Jim Shepard]

How did you guys deal with push rod? The stock is too long (it could cut down) and “fat” (diameter too large).

[Los_Control]

I shortened mine .... at least 1" .... I did sneak up on it and cut 1/2" .... then a 1/4" until I got it to where I could insert it as needed.

I also made sure the rod was adjusted as short as I could get it.

 

Then on the bench grinder I rounded it down to a nice soft ball.

Now with the end rounded, it fit into the MC and now was about 1/4" too short .... and could easily adjust that with the rod adjustment.

It fit perfect  

 

Then I installed the toe boards for the first time, realized by asking here .... the toe board actually pushes the pedal down some more and the rod was too long .... so I got to do it all over again.

 

Just make sure you have the toe boards in place when making the modifications.

You do not want a sharp pointed edge on the rod, you need to round it off and soften it so you do not drill a hole in your MC.

But it doe need to be ground down to fit into the pocket.