Kung Fu Brakes needed E350 swap

[ChEwBaCcA]

So I guess the question becomes.....what dual diaphram unit will bolt to the E350 and share the same rod style as found on the XJ.......anyone , anyone,

Chewy

 

[ScottRoz]

That 95 or 96 that people are using should work.
It is dual diaphram and is the old pre-97 style.
I can't remember which year right now, but I'm thinking 96.
Check on MADXJ.com
The article should have an addendum of what year works without modifications for older XJs.

Scott

 

[Carpenter]

Any late model ('95-'00) XJ booster would require a spacer to make the E-350 MC work. The '95-up master cylinders have a ~1" long extension coming out of the back of them that the pre-'95 MCs don't have. I'm curious to see how your swap turns out. I tried the E-350 swap and it made things worse for me. I conversed through e-mail with the guy in the above referenced POR thread and it baffled me how it made such a difference for him and made things so much worse for me. When I did the swap my pedal was much stiffer and with me standing on the pedal I could barely get the Jeep stopped. I bench bled the MC twice and bled the system countless times and nothing improved. I finally swapped in a '95 MC and booster and my problems were solved. I can now stop on a dime with 34" tires, braking is better than in my bone-stock '00 Chenvy Sliverado.

 

[Ed A. Stevens]

I did the "Kung Fu" E350 setup on my 88 XJ.
It wasn't magic for me. There is more pressure required to move the pedal
<snip>
The E350 cylinder is supposed to be 1 1/8" compared to the stock '88s 1".

Scott

The hydraulic ratio from this change (from 1.0" to 1.125") in the master cylinder is going the wrong way, to requiring more pedal effort (due to lower line pressure for the same foot force). This is why the braking demands more pedal pressure for the same force on the pads and shoes.

The size of brake hose lines have no impact on the line pressure (unless the old lines are kinked flat and block flow).

Anyone find a 7/8" bore master cylinder?

 

[Beezil]

carpenter stole my photchop!

whata jerk!

 

[ScottRoz]

Ed, you say that going larger is the "wrong way", but shouldn't a larger bore help, if the problem is the pedal going to the floor and not that you have to push hard on the pedal?

Scott

 

[Ed A. Stevens]

Ed, you say that going larger is the "wrong way", but shouldn't a larger bore help, if the problem is the pedal going to the floor and not that you have to push hard on the pedal?

Scott

The two issues are separate symptons.

1. Pedal to the floor (Lack of adequate fluid volume in the pedal stroke):

Failed vacuum booster? (excessive pedal rod travel with minimal brake rod travel)

Air in the lines? (compressibility in the systems)

Poorly adjusted shoes? (demanding volume to snug the wheel cylinders).

Failing (balooned) brake lines? (new lines, braided steel lines)

Basic components in good condition are a great starting point, before swapping out pieces.

Calculate the fluid volume of two 1" bore wheel cylinders (four pistons, what I run in my D44) moving the shoes 1/16"? Not much. The disc caliper pistons move only a few thousandths (again, very little fluid volume). Compare this to the volume in the two master cylinder circuits.


2. Pedal effort (lack of stopping power):

Brake swept area? (fixed with the XJ other than 9x2.5 shoes, 10x1.75 shoes, and 10x2.5 shoes. There is a slight change in pad size between 84-90 front pads and the longer/thinner 91-02 pads. Maybe SJ truck 11x2.5 shoes and WJ knuckles/rotors/pads or rear discs?)

Pad material? (lots of options)

Poor pedal leverage ratio? (fixed in the XJ)

Poor vacuum assist ratio? (single or dual diaphragm XJ, small XJ or large SJ diameter, or hydroboost)

Poor hydraulic ratio in the master cylinder bore? (stock 1" compared to: 1 1/8" with less line pressure for foot*lb force, or 7/8" with more line pressure for foot*lb force).

Poor hydraulic ratio of the master cylinder bore to the caliper and wheel cylinder bores. (front calipers are fixed design XJ, maybe a WJ swap increases the caliper bore area, and larger rear wheel cylinder options have been explored from the factory 7/8" and 15/16" sizes).

Calculate the brake line pressure and compare percent increases (or decreases) at the end shoe or pad with each change. Changing parts, with no basis to achieve the goal in mind, may not net the result you want.

I know one common fear is running out of fluid volume in the MC. This is combined with many stories of poor pedal feel. I agree the factory pedal is not the best feeling brake, and the system has an affinity to retain moisture and trap air (possibly due to bubbling in the MC during offroad travel). The factory flex lines are also not immune from balooning (steel braid lines are an option). Repair and upgrades, and good maintenance, should counter these problems.

I run a single circuit 7/8" MC on one of my old drum brake cars, with 1 3/8" front (10x2.5) and 7/8' (10x1.75) rear wheel cylinders. The pedal effort is very good without a booster. The clearance volume consumed by the four wheel cylinders is much greater than that demanded by an XJ disc/drum system. If someone has a part number for the 7/8 XJ master cylinder, I'll be more than willing to test it out.

 

[REDXJ4FUN]

OK if your saying we neeed to go smaller we can try an AMC MC since they proble are all very clse in build and since they are cars they may have smaller bores. For instance an 84 eagle wagon has an 15/16 bore. but when i grew up on a farm i know that when we used a biger cylinder on the loader it lifted a heck of alot more justa little slower. but then again we don't need to move more fluid just more preasure so smaller would be better:confused1

 

[Ed A. Stevens]

OK if your saying we neeed to go smaller we can try an AMC MC since they proble are all very clse in build and since they are cars they may have smaller bores. For instance an 84 eagle wagon has an 15/16 bore.

You are not confused, the bore size has an impact of the leverage ratio on the application end (the master cylinder) and the receiver end (the wheel cylinders).

A smaller bore for the application piston provides more line pressure for the same effort from the mechanical device driving the piston (your leg).

A smaller bore on the receiver piston provides less effort on the mechanical device being driven by the line pressure (the brake pad or shoe).

Can anyone confirm the Eagle wagon master cylinder bore?

Are these disc/drum Eagles?

 

[vintagespeed]

Ok Ed, I've got a simple question. Having driven an E350, I have to say that those are some sweet brakes. The question for me is, what is the magic part of this equation? The booster? Why can't the E350 booster be made to fit the XJ?

 

[REDXJ4FUN]

Ok acording to the advanced auto web site the eagle is a 15/16 . Un fountunatly all of my amc books are stored away but may be Eagle might know of one that might be even smaller. and yes the eagle was disk/drum. i knoow at some point some one said something about a 78 firebird MC that worked but who knows.

 

[AJsArmor]

Just thought I'd throw my .02 into it. Before I swapped the 8.8 w/discs in I had completely gone through my braking system (rotors, drums, shoes, cyl...also new master). Was better but still just was pretty weak just running 33's. After I installed the 8.8, not a big improvement until I removed the o-ring in the prop valve. That was a the biggest improvement so far but still wasn't happy so I read about the E350 swap and that was by far a HUGE difference! Now it will lock up the fronts, not quite the rears which is perfect for me. Jeep doesn't do a huge nose dive under hard braking and to me is twice the braking performance than it was when it was stock with smaller tires.

Here's a rough pic showing the difference in bore diameter of the two, E350 is on the right.

 

[Ed A. Stevens]

Ok Ed, I've got a simple question. Having driven an E350, I have to say that those are some sweet brakes. The question for me is, what is the magic part of this equation? The booster? Why can't the E350 booster be made to fit the XJ?

I understand the E350 booster can be made to fit with slight ovaling of the mounting holes. I have no doubt it can be made to fit. I question if it will provide the implied result, better braking force through greater brake line pressure?

What the larger MC diameter changes, is the volume of brake fluid pumped per unit length of stroke (more fluid per inch of stroke). The pedal is harder because the hydraulic leverage ratio decreases, it demands a heavier foot for the same force on the pads. It provides less line pressure in the brake system for the same foot pressure.

The observation that it works better (than the stock smaller bore MC) indicates the XJ brake system is not adjusted well, or has excessive slack volume (a drive rod that is too short, flex lines that balloon or piston/spring volume in wheel cylinders that consume fluid volume (pedal stroke), or the combo valve leaking fluid past the two circuits, or ?).

The E350 bore MC also works better with larger brake wheel cylinders and pistons on the wheels, the factory one-ton van application, because the leverage ratio is increased at the wheel end of the hydraulic line (1 1/8 wheel cylinders and larger diameter caliper pistons).

Any help?