Proportioning Valve Problems, among other things

[thedadbodrod]

Alright folks, where do I buy a new/refurbished/used stock proportioning valve (or distribution block according to some, but I'm unsure)?  I've been trying to bleed my brakes for 2 days now but my front right will not bleed, albeit by gravity, vacuum, reverse bleeding, the works.  I've read in a number of places that the little "pin" in the proportioning valve has done it's thing where, when bleeding, it decides to cut off flow.  Trouble is, I can't get the "pin" to go back to resting position.  I tried manually pushing the pin after removing the brake light sensor gizmo on the prop valve, but that didn't work.  Tried bleeding in different orders, that didn't work.  Tried slamming the brakes with the engine running and not running.  ETC.  I tried everything but couldn't get that line to open up.  Where can i find a replacement?  If not replacement, what easy mod can I do to keep as much stock as possible?

Base model 88 short bed - 4.0L 4wd automatic 75k miles

-General notes: 

1. years of squishy brakes
2. premature locking of rear tires when stopping
3. general pull to one direction when braking
4. ^^^ new repairs include all plastic lines, calipers, pads and master cylinder are new
5. no mods
6. 29inch tires no lift
7. no pinches or clogs in rubber or solid line, from caliper to prop valve
8. desire to keep as much stock as possible but willing to lightly mod to have a running jeep that stops for once

Questions, recommendations, links to other posts, all are welcome.

Edited October 27, 2021 by thedadbodrod
additional notes

[Pete M]

I would pull the soft line of the caliper and see if fluid comes out at all.  could be a DOA caliper.   if still nothing, try pulling the hardline off the distribution block and see if fluid comes out there.  I'd hate for you to go through all this to find its a pinched line.

 

if you haven't seen it yet, the link in my signature has a thread about the factory bleeding procedure.  it won't help clear a front line, but will help get the air out of the second rear line (the emergency bypass line)  

[thedadbodrod]

7 minutes ago, Pete M said:

I would pull the soft line of the caliper and see if fluid comes out at all.  could be a DOA caliper.   if still nothing, try pulling the hardline off the distribution block and see if fluid comes out there.  I'd hate for you to go through all this to find its a pinched line.

 

if you haven't seen it yet, the link in my signature has a thread about the factory bleeding procedure.  it won't help clear a front line, but will help get the air out of the second rear line (the emergency bypass line)  

 Soft line and caliper have flow through them, and fluid was coming out of the front right when I had started bleeding, but cut off at some point and won't resume.  I think it's the prop valve because of that little "pin" inside not showing the indentation that prevents the brake light circuit from being completed, if you're aware of what I'm talking about.  

[Pete M]

I guess I'm confused by "pin".    can you circle what you're referring to?  in my head, if one side of the front works, the other should too.  it's possible that dirt got inside and is now plugging the end.

 

it looks like a prop valve, but it doesn't do any proportioning, just shuttles over to open up the emergency bypass for the rear.  so technically it's not a prop valve. (even though most everyone refers to is as such).  MJs have the prop valve (height sensing) in the rear of the truck.   

[thedadbodrod]

Circled in red is the 'pin,' I've read the word a dozen times today but can't remember what it is. Circled in white is that little recess of the pin that I cannot see when I remove the break light connector.  In the next few days I'll give that bleeding procedure a shot and see if that frees up the front right line.  If there's dirt in my lines then I got a score to settle.  With God.

[gogmorgo]

MJ bleed procedure is to start by bleeding the rear with one of the front bleeders open, then closing the front bleeder, bleeding the back again, then the front.

I'm with Pete, if it's an issue with the shuttle valve in the distribution block, it'll affect both front callipers, not just the one side, and I can't imagine an open, unobstructed bleed screw would be any different than an open brake line. Did you try pulling the bleed screw out entirely?

Most replacement callipers come with plugs in the port for the brake hose, and it could cause interesting issues if it was left in and possibly pushed into the calliper. I can't think of any non-catastrophic way a calliper could fail that would obstruct the bleed passage, short of it being plugged with something.

[thedadbodrod]

I tested both the caliper and the soft line and got flow through both.  Considering that it's just the one side that's obstructed, it seems like I should try to clean out that solid line and/or that port on the distribution block.  I'll give that a run as well 

[Eagle]

The shuttle valve does not impede flow to the front brakes, as far as I know. That would defeat the purpose.

 

This one happens to be an XJ proportioning valve, but the front circuit outlets are the same:

 

 

If it's the right front that's giving you problems, you need to check the lower/rear outlet on the distribution block.

 

[cruiser54]

This^^

[Whitaker717]

I have somewhat of a strange question regarding this system. Can you use the MJ distribution block with the back distribution valve gone or bypassed? I am not sure if that will work or not. Just curious. 

[cruiser54]

The best I've experienced is eliminating the distro valve completely and installing an adjustable one in the rear line. 

Better braking performance overall as the distro valve has passages that are smaller than the ZJ and the brake lines. 

 

 

[Whitaker717]

Can you use only that valve in the front without the adjustable one in the rear? Will it work properly? Just curious. 

[Eagle]

2 hours ago, Whitaker717 said:

I have somewhat of a strange question regarding this system. Can you use the MJ distribution block with the back distribution valve gone or bypassed? I am not sure if that will work or not. Just curious. 

 

Yes. How to do that has been discussed here multiple times. To eliminate the rear height sensing proportioning valve, you have to remove the second line to the rear. The one you remove is the one that comes off the front/bottom outlet on the distribution block. The line coming off the "nose" of the distribution block is then connected directly to the flex hose at the rear axle.

 

If you do this, you also need to be aware that you will then always have 100% available braking pressure/force to the rear wheels. Especially when the bed is empty, this will greatly increase the likelihood that in hard braking or a panic stop, the rear wheels will lock up prematurely, causing a spin-out. The cure for that is to install an after-market, adjustable proportioning valve in the line to the rear brakes.

[Whitaker717]

Thanks Eagle, just still trying to wrap my peanut brain around that darn brake system. 

[Eagle]

18 minutes ago, Whitaker717 said:

Can you use only that valve in the front without the adjustable one in the rear?

 

Yes.

 

Quote

Will it work properly? Just curious.

 

Not unless you consider premature rear wheel lockup to be proper operation. It's dangerous -- that's why the industry came out with proportioning valves.

[gogmorgo]

20 hours ago, thedadbodrod said:

I tested both the caliper and the soft line and got flow through both.  Considering that it's just the one side that's obstructed, it seems like I should try to clean out that solid line and/or that port on the distribution block.  I'll give that a run as well 

Thinking about this a little more, the valve shuttles when there’s less pressure in the front brake circuit than in the rear. This is why opening a front bleeder will shuttle it. So keeping that in mind, if you open a rear bleeder instead and stomp the brakes, the higher front pressure should force it back. This would happen as part of the normal bleeding process when you’re bleeding out the rear after bleeding the bypass.

 

When you say you tested the calliper and soft line for flow, how exactly did you do that? Because to me that means you pulled the line off the calliper and pushed the brakes and it squirted fluid, then you put it back on, opened the bleed screw, pushed the brakes, and got fluid out. Which is contradictory to the issue you’re having.

Usually when checking for a blocked line, I would start at where the line beaches off from the known unobstructed lines (I.e. lines to other brakes where you get fluid out of the bleeders) and carefully crack each connection down the line to see where I stop getting fluid pushing out, although in the case of the brakes, I would start at the calliper and work my way back up.

 

If you think the distribution valve is obstructed, remove it, disassemble it, and clean it out. It’s more than possible some junk that had collected at the bottom of the reservoir over time got pushed into the system while you were bleeding.

[thedadbodrod]

To test flow through the new soft line and caliper, I disconnected the soft line from the hard line, put a reverse bleeder onto the soft line, opened the bleeder valve and pumped fluid through the soft line and caliper with no problem.  Therefore the problem lies somewhere between the end of the FR hardline and MC.  Looks like the next step is taking it apart and cleaning 🤟

[cruiser54]

If the problem was in the distro valve. wouldn't both front brakes have a problem?

[thedadbodrod]

Seems like that's the consensus, therefore, it's not the distro valve.  Gonna tinker with it this weekend with all of the new info and I'll update you all.  

[ghetdjc320]

12 hours ago, Whitaker717 said:

Can you use only that valve in the front without the adjustable one in the rear? Will it work properly? Just curious. 

Basically you will get 100% pressure to all 4 brakes. Stock rear drums already lock up sooner than stock front disks if given the same input pressure. An empty bed makes this situation even worse as eagle points out. 
 

Here is some general info that may be helpful: 

 

[jeepmjga]

Just a thought because I did this, are the calipers on the correct side? If they are upside down they won't bleed correctly. I only ask because its easy to do. The bleeder and fitting should be on top. If you want to nix the whole stock MJ setup, Summit racing sells Wilwood prop valves.for about $100. I ended up using one and it works great, used existing brake lines, just had to find some adapter fittings to connect everything. I can take some pics if needed. 

[thedadbodrod]

That's a good observation, luckily I did a double take when starting this whole brake rebuild and made sure the calipers are where they should be.  It's looking like the wilwood prop valve is the best bet so I'll do some digging to find those posts and how-tos, depending on how the next few hours goes.  Pictures would be appreciated.

[thedadbodrod]

So, odd turn of events.  Before going any further with trying to figure out what was stopping flow to the FR lines, I decided to try and bleed it one more time.  Lo and behold, it worked.  I followed the MJ bleeding procedure with good results.  As per the usual with these stock brakes, it's still garbage, but it's better than before.  Doesn't pull to the left when I brake anymore either, so that's a relief.  Garbage with a new bag.    

I find absolutely no security knowing that the problem I had was and still is a mystery, seeing are brakes are pretty important in Southern CA.  BUT HEY it's back on the road after 4 months, various repairs, over 2 gallons of brake fluid, approximately 12 cans of brake cleaner, and 19 bug bites.

[cruiser54]

Have you adjusted up the rear shoes?