Proportioning valve sensor "stuck"

[Subourbon]

Hey folks, 82 suburban 6.2 diesel 700r4 4x4.

My rear brake reservoir was pretty much empty. Pedal had nothing then very very hard pedal about 1/3 of the way down.
And brake light was on.
Yay
So, I bought 2 wheel cylinder preemptively, and the proportioning valve centering tool, so that I can bleed without sliding the shuttle valve inside.

I think mines original to the vehicle coz it looks like it has seen some sh*t. The lines will likely just snap if I try removing them to work on the valve in a bench.

It's a 5/8 socket or wrench thats needed. And it will not budge. It's in that really accessible spot under the rad support. And i dont really have room to swing a ratchet

It feels like I'm slipping off of it, but a 15mm or 16mm won't go on either.

I'm here venting coz there's not much room in there and I'm pissed off. Also coz I'm wet coz it snowed today. Too early for this crap

I sprayed some jiga lube on it. I'll try in the morning I guess.

I absolutely need that centering tool to bleed the rear right?

Asking coz, what if I crack a bleeder on a front disc (either one) and stomp on the brakes a bit, which will then slide the valve over to the middle.

And then, gravity bleed the rear. As I (once I fix my leak of course) open A bleeder on the drum wheel cylinder and keep master cylinder topped up and let it bleed though bleeder screw by gravity, and tighten it up when there's a steady trickle of brake fluid.

Does that work? Or is there still air in the lines?
For a sensor, that sensor is really really stuck on there. What a pain.

Sorry for the rant, and appreciate any ideas or feedback.

And yes, I plan on redoing all the brakes lines at a certain point, and replacing & RELOCATING that goddamn valve is in the plans too

 

[83Stepper]

Usually, but not always once you've got the issue resolved, you can refill the reservoir and once the rears start building pressure again you should be ok. I wouldn't stomp on the pedal too hard, just smooth easy motions until she starts building pressure and the valve should recenter itself, or so it has been my experience so far. Can't say that I've had one that didn't go back to center after fixing the issue yet.

 

[Subourbon]

I've got the tool to center it, and I've heard a small pick can center the shuttle. But it's the goddamn sensor I can't get off. I might shorten the wrench tomorrow, maybe that will give me more range of motion. I've got the box end on the sensor, but the open end interferes with something underneath.
Once that sensors out, I'm golden.
I hope. Lol. I've got everything I need to complete the job

 

[83Stepper]

I've got the tool to center it, and I've heard a small pick can center the shuttle. But it's the goddamn sensor I can't get off. I might shorten the wrench tomorrow, maybe that will give me more range of motion. I've got the box end on the sensor, but the open end interferes with something underneath.
Once that sensors out, I'm golden.
I hope. Lol. I've got everything I need to complete the job

Yeah, it's a b*tch of a thing to get at in any of our trucks. Gotta love engineers from the mechanical aspect of things lol. Personally I'd try without resetting the shuttle inside the valve first just in case. Usually have to center the shuttle when she's been dry for a while and has almost seized in place. My 77 C10 was "farm fixed" with hard line from the master straight to the front calipers. Fixed the plumbing to go back to where it should've been in the first place and she reset without the tool which shocked me tbh. She was last on the road back in 1990 and probably sitting since 2000, so roughly 20ish years of sitting with no fluid on the front side of the valve.

Going to need somebody to assist to build pressure to bleed before doing the gravity bleed.

 

[Subourbon]

Oh I had some choice words for those engineers when I was under there for sure. I mean ots a good idea. But I saw a YouTube video but it right beside the master cylinder which let's be honest genius. Lol.
Thise took the time to put a Lil button in case the fronts get shut off. But the rear? Nope.

Try without resetting the shuttle? I'm confused by this, coz in theory, I'm nkt getting anything to the rear.
Just to be clear I haven't tried anything yet. My wheel cylinders and centering tool arrived today, and I just wanted to install the tool. I'm fairly certain it's rear passenger wheel cylinder coz I saw it was damp when I was underneath.

So,hypothetical if I replace wheel cylinder, theyre in, then I try normal 2 person bleeding.
3 to 5 pumps and hold, while I crack the bleeder? Coz if shuttle is slid over then, I won't get anything to the rear, right?

 

[Ricko1966]

Try having someone pump the brakes then hold firm pressure while you open a front bleeder. The shuttle should recenter,try a couple of times if you have to. The light should go out. Then you could vacuum bleed it. When the pressure balances is when the shuttle will quit moving. Never tried but in thoery if you could leave a front bleeder leaking( speed bleeder or one man bleeder) while you 2 man bleed the rear the shuttle would stay centered long enough to fill the rear wheel cylinders. Heck if you used a speedd bleeder or ome man bleeder on 1 front and 1 rear simultaneously the pressure would stay balanced.

 

[Subourbon]

Interesting theory with the 1 man bleeder x2 on opposite ends. Yeah, in theory you're right, it's a game of pressure. And the shuttle will slide where there isn't any... hmmm I'll head out in the morning and buy 2 and try it out.

Another thread said, even without the centering tool, a 1 man vacuum bleeder will work. When I did the brakes years ago I never figured out how to get it bled. I ended up taking it to a shop. Dunno how they did it.

 

[Ricko1966]

Interesting theory with the 1 man bleeder x2 on opposite ends. Yeah, in theory you're right, it's a game of pressure. And the shuttle will slide where there isn't any... hmmm I'll head out in the morning and buy 2 and try it out.

Another thread said, even without the centering tool, a 1 man vacuum bleeder will work. When I did the brakes years ago I never figured out how to get it bled. I ended up taking it to a shop. Dunno how they did it.

You'll have to get the shuttle centered 1st

 

[Subourbon]

Yeah I'll try a shortened wrench again tomorrow. If that fails, then I'll open up the bleeder on a caliper and river dance on the brake pedal, and hope i can slide it over to where the light goes off.

These answers have been helpful, ill get a couple vacuum bleeders a bottle of dot3.

 

[Ricko1966]

Yeah I'll try a shortened wrench again tomorrow. If that fails, then I'll open up the bleeder on a caliper and river dance on the brake pedal, and hope i can slide it over to where the light goes off.

These answers have been helpful, ill get a couple vacuum bleeders a bottle of dot3.

Try pumping the brakes putting pressure on hard and opening a front bleeder,that usually works.

 

[Subourbon]

The rubber button (for lack of a better term) is effectively a reset for the front system right?
Say if I step too hard or too long on the brakes and it goes from being centered to closing off the front, then press on that rubber button and it should bring shuttle over to the middle position

 

[Ricko1966]

The rubber button (for lack of a better term) is effectively a reset for the front system right?
Say if I step too hard or too long on the brakes and it goes from being centered to closing off the front, then press on that rubber button and it should bring shuttle over to the middle position

It's always gone back to center when I've done just what I said.

 

[Subourbon]

Roger that. I will give it a whirl then. Hopefully next time I post i will have brakes.
Cheers, appreciate the speedy helpful replies

 

[Subourbon]

So a wee update.

Had to shovel, put winter tires on the missus' truck, head to the hardware store. Get stuff.

Tried a shorter wrench, on the sensor that thing will not come off. I pulled on the valve to be able to get a socket on, i did manage to get it on. It pushes the socket up. Enough of that.

Put it all back together. And headed towards the rear wheels tonget ready to see what's what.

The hard line that connects tonthe rubber line that then goes to part that splits it to both wheels, (bolted on different cover) well, thats wet. So hopefully just a tightening job.
But,

Passenger side is wet a bit but wheel cylinder is fine, it smelt like diff.
Sh!t.
Nowtruck is jacked up at the rear, I take the fill plug out, ive got fat fingers so even with the pinky is hard to get in there but I couldn't feel anything. Touched a gear, but no fluid. Its also like 28 degrees out so... cold A.F

I filled up with a Lil oil can (capacity 180ml) id say it was close to 150ml before it leaked out of fill plug.

For context I changed the oil back in june 2023. Not sure what the "normal" oil consumption is on these diffs(if there is any!
But... I might be looking at a rear axles seal job....