Braking issue...fixed pics

[frotosride]

Progress was made today. I never posted this but I did replace the master cylinder some time in 2016. I didn't use an OEM JB5 but instead I put a different style on to see if I could mess them up even more...

Either way I now have a new JB5 master and me POL proportioning valve has been delivered. Already bench bled and mounted the master. I may have pushed over 1" when bench bleeding, wouldn't be the first time I've done that though.

Hopefully tomorrow I can finish the install and bleed everything. Unfortunately my youngest son, who usually pumps the brakes hurt his ankle and both feet riding his dirt bike and football practice. Guess I'll have to con another child into spending time with dear old dad.

[frotosride]

Got the proportioning valve in and everything tightened up.

Didn't have to con any of my children into helping. The youngest was eager to help as always. She lasted one round of bleeding and then it was time to switch out.

[frotosride]

Did a few stops in the driveway just to get a feel for progress after my oldest took over the pumping and holding efforts. Definitely still have air but the brakes feel so much different. Had to stop due to lack of DOT3.

As for the previous CPP advertised proportioning valve..well it leaked from day one. As soon as we started bleeding this rubber plug held in by a concave star washer popes out of the adapter for the rear output. Until today it has never stopped leaking. I even tried to peen over the small nipple under the plug with punch but to no avail. I will not tell you not to buy one but consider this a review for thought.


In the pic below you can see the rubber plug (lower left side) that I tried to pinch in the hole to stop the leak.

[frotosride]

Ok so the progress so far is brought to you by the tool of the day. I have used several air hammers over the years and have always been impressed by how simple they are and most of all how distructive they can be. This pair hammer has been the best so far. I just bought it for this project because all my others have broke.

 I managed to replace the rear hanger for the front leaf springs. They now have 2" do tubing and Kevlar reinforced poly bushings along with 9/16 greasable bolt!


I also replaced th front pads. They had ever wear but unfortunately it was indicative of both calipers hanging up. Only the putter pads were worn on both sides. The old air plow does handle a lot better. I adjusted toe to within a 16th of an inch and tightened the gear box just slightly after warming it up with a few spirited trips around some country roads.

[frotosride]

Ok I know there's still air in the lines and I will get it out hopefully today. Here are the current symptoms. The steering wheel still slightly turns left and the truck pulls right ever so slightly when braking hard. The drivers side rear tire is the only one that locks up.

When initially pressing the brake pedal, the first almost inch of travel does nothing and the pedal is firm. I can hear the diaphram venting in the cab. If I maintain the pedal in this position without applying anymore force the truck doesn't stop and I hear constant air hissing into the cab. Then after roughly an inch of pedal travel the pedal gets softer and the brakes apply fairly abruptly.
This leads me to assum that the 33 year old booster is bad. I do have a vacuum pump and gauges for refrigerant work, so I may use it to do a vacuum test on the booster.
Any educated ideas or assistance would be greatly appreciated.

      THIS IS THE TEST I INTEND TO PERFORM

Vacuum Brake Booster Testing and Diagnosis

Minimum engine vacuum required is 18”HG at idle in gear.

You will need a vacuum pump with a gauge to perform this procedure. Most “chain” parts stores will rent, loan or sell them.

1) Remove vacuum hose from check valve on booster. Place hose from vacuum pump onto check valve and draw booster to 20”Hg of vacuum.

2) Let booster sit with vacuum applied for 5 minutes. Vacuum should remain steady at 20”Hg. If vacuum does not stay steady at 20”Hg the booster it is faulty and will need to be replaced. If vacuum does hold steady at 20”Hg proceed to step 3.

3) With 20”Hg of vacuum in booster depress brake pedal once and release it. The booster should transfer SOME but not ALL of the vacuum. Depending on how hard the pedal is depressed it is normal to see a 5-10”Hg drop in vacuum. The most important thing is to ensure that the booster does transfer SOME vacuum but does NOT transfer all of the vacuum in its reserve. If vacuum remains at 20”Hg OR goes to zero the booster is faulty and will need to be replaced. If vacuum transfer is within the above range proceed to step 4.

4) Once again draw booster down to 20”Hg of vacuum. Depress brake pedal and hold down for 30 seconds. You should see the vacuum gauge drop slightly and then hold steady. Vacuum should stay steady as long as you are holding the pedal down. If vacuum drops while pedal is being held down the booster is faulty and will need to be replaced.

[bd]

Good assumption.  Replace the booster with a dual-diaphragm unit designed for JB5 brakes.

[frotosride]

I've been waiting for an excuse to put the hydro boost in. I've had it sitting for about 2 years. Looks like this may be the time!

[bd]

Nothing like adding more variables to the mix while attempting to diagnose an already elusive problem.   

[frotosride]

Yeah I know and I know better. My problem is I'm putting it on no matter what and I don't want to buy another booster. Maybe I'll check my other squares and see if one of them can donate.

[frotosride]

Ok so I went with my better judgement as recommended and went to the parts place.


Here's what I found...no power brakes on the R10 or whatever the GMC equivelant is.


Hydroboost on the blazer..kinda already knew that.

And the k20 is really crusty. Looks like I'm going to buy new and keep it long time!

[frotosride]

Picked up the new brake booster today. It was a reman unit and went in flawlessly. I did test the unit before installation and it performed great. Held 20" for over an hour which is when I got a chance to disconnect it. Cycled it multiple times, pausing at different points to ensure vacuum was used but not all of it. I repeated this 3 times before I was satisfied and got it ready for paint. Here's a pic of the set up I used. It's what I have on hand and worked great. Didn't get a single hand cramp from pumping it down.

[frotosride]

Took Old Blue out for a good shake down and I have never had the brakes work so well. The issue still remains. Push the brakes nice and slow like a normal planned stop and the truck will just gradually pull right, right into the ditch with no input to the steering wheel.
If a panic stop is rung up on the telegraph then get ready for some sketchy stuff. Steering wheel turns left, truck goes right and drivers rear will lock up. As soon as you release the brake pedal the steering wheel corrects itself slightly to the right. I am almost positive this is due to the calipers hanging up at different points throughout the travel of the pedal. I know that my pads showed obvious signs of both calipers hanging up.
I'm going to get out tomorrow and set up all the conditions with a panic stop from at least 50mph and take pics of how the truck lands.
Either way even in this current condition it is a huge improvement over any previous versions of braking... I'd even let someone drive it now.
I also picked up a pressure testing kit. I'll try and post a pic later. Haven't even opened the box yet.

[frotosride]

So this is the kit I purchased. I do a lot of hydraulic work so it will likely come in handy for more than just brakes. It seems to be rather all inclusive. It even has an attachment for abs style brakes. Not sure when I'm going to use it. Also I'm curious what pressure relationship I will see between a caliper that is hanging up and one that is sliding as it should. Any thoughts and or experience with that would help. When I think in hydrodynamic terms it would seem that the pressure will be the same given that the area of the applied force should be equal since the Pistons in the calipers are the same and there isn't any bias between the either side. There shouldn't be any intensifier effect given the area of applied force being equal on both sides even if one piston extends and accumulates more fluid volume...

Having said all that my brain started working. The side that doesn't extend will have a higher pressure due to volume. The accumulators I work with function on the same theory. They have a larger tail rod creating less fluid volume and operate at a higher pressure which allows us to establish a set of lead pumps that will effectively discharge faster and absorbe loads without other pumps starting.
Any one with experience on this topic would be great to hear from. I intent on doing my best to watch both sides at the same time to see if one spikes and maybe equalizes and so on. But positioning will be difficult.

[frotosride]

Try this link for the pictures that apparently haven't been loading.

https://photos.app.goo.gl/qrsDQDrvxT9EWYFR9

[frotosride]

Today I literally hod no issues with the brakes. They work break as long as you do not let the wheel go. I mean who really does that?

Fun story from bleeding. Since I put over 50oz of fluid through the brakes I pulled the 15 amp fuse for the brake lights. Well when all was done I reached in the door pocket grabbed the blue fuse put it back in and wouldn't ya know it, my dang bake lights don't work anymore...

After giving up on everything shy of smashing he switch with a hammer, I turned in for the night. Today I put a child in the seat and busted out the fluke. Pulled the fuse out, checked power and it was good. So I started investigating the fuse. I could have done a quick resistance check but instead I spent 10 minuets looking at it and I noticed it was blown. Very hard to see. Apparently there were two 15amp fuses in that pocket, the one I removed and a blown one... Love easy fixes!