Ok, now that Its starting ok, here's the next thing.

When I first got the truck, I thought that there were brake problems. The rotors needed to be replaced, and so I did that, and my dad said I should change out the Master cylinder too.(I did the MS first). As soon as I put the Master Cylinder on, the brakes started to grab all the time, like they were out of adjustment, and even on some occasions, start smoking just from normal driving. I put a spacer between the MS and the hydroboost.

Well I think that is unacceptable, and now the brakes are starting to grab again, and even lock up the wheel.(I mean, this happened the second I got it running again with a new starter. Not kidding at all).

Since this is a new MS(and the old one was ok it ended up, traded it in for the core), could the MS be defective?

As Always, your help would be appreciated. Thanks alot Gents.

Guipo

Brakes aren't really my expertise, but I know I have had some problems with replacement parts, mainly those that aren't the correct parts for my truck. I know the diesel equipped vehicles have different equipment than the gassers did. For example, most of the diesel 1/2 ton (the CUCV blazer included, it has 3/4 springs) had either a JD3 or JD5 brake system. I can't count the times that I've been asked which system I have by the parts guy, I used to not know, until I got a GM manual. Before, they just sold me the HD version for that model gasser, because they didn't know nor did they know how to find out. Thats been the majority my my brake problems.

Verify that you got the correct master cylinder, I seem to remember a somewhat larger MS on the CUCV's, and a notice to use silicone brake fluid, someone here will probably elaborate or correct me here hopefully.

If you didnt use DOT 5 brake fluid, you could be having all sorts of trouble!! Seems to me a check on the military vehcile list at www.mil-veh.org might be in order on this one.

Brakes binding could be from several problems. First, which brakes are not releasing, front or rear? If it is the fronts, caliper pistons could be seized. Remove caliper and compress piston with a c-clamp, it should move fairly easily. If it is rear, check the wheel cylinders. What was the problem that caused you to replace the master cylinder to begin with, this may help with the diagnosis.:eek:

front brakes.

I replaced the MS because when you pushed it all the way to the floor, it made noise and acted all funny. pulsating. Well I guess that normal, and so I didnt need to replace it, cause the new one does the same thing. The brakes themselves work very very well when working normal.

I replaced the Calipers and Pads as well, because the pision rubber seal was torn and damaged on both sides. So the piston was all the way pushed back.

also, I used regular old dot 3 liquid. I didnt know that I am supposed to use dot 5 silicone based fluids. I've asked at Steelsoldiers.com, and hopefully they will shine some light on that. its a m1009, so I dont know if that matters.

Not sure on the dot 5, but the key is don't mix. If you flush your system you can use dot 3. Now that you have mixed the two you had better flush the system anyway. You say you replaced both front calipers, how about the hardware? There are o rings that need to be lubed with silicone grease and the bushings need to be able to slide also through another set of o rings. Start with this stuff.:grd:

my problem is with that, is that it was doing this before I changed out the calipers. it started when I changed out the MS. Nothing else.

When I got the calipers from autozone, it came with all the hardware nessisary. I put some anti squeel on it, just like any other brakes I've done.

Bring the master cylinder back to them and tell them you want another one due to what you have said.:eek:

ok, and I'll take the oppertunity to bleed all the brake lines with DOT3. I'll update when I'm done. (should be friday):cool2:

Has the spring fallen off your brake pedal so that you have constant pressure on the master cylinder piston? There is a spring that keeps the pedal rod off the piston. If the spring is out or out of position then the weight of the pedal will be pushing on the master cylinder piston (kinda like riding your brakes).

Some GM autos have a split master cylinder braking system, i.e., one half operates the right front and left rear and the other half operates the other. If one rear brake adjustment is off then sometimes it will cause the opposite front to lock up. I haven't seen a pickup with that system so your problem baffles me if the pedal spring is still in place. :lol:

I dont belive there is a pedal spring. But the petal returns from the spring in the MS. I just found a brake line leak however, and am going to pinpoint it. I'm thinking that'll fix it. The breaks dont feel spongy at all. So I'm not sure how a leak works out.

also, when the brakes stick, they release as soon as I accellerate. No smoke this time. I hope it has something to do with that leak.

If both brakes are locking then I can't see a leaking brake line causing the problem. If only one side is locking then it could be possible since the side that has the leak would not be getting full pressure to the caliper piston. The vehicle should tend to pull to the side that is locking up.

Any case, you must fix the leak. If you replaced the hose to the caliper then it is probably the end by the frame. The hose attachment to the caliper must have new copper washers on each side. I never re-use the washers as they usually want to leak.

its leaking near the comination valve. I'm going to find it today. Hopefully it'll just need to be reseated.

I replaced the copper washers when I got new calipers too. We'll see. I think its only one wheel locking. Like I said it goes away when I accellerate, and when I brake its like a gradual thing, getting tighter and tighter until I stop.

Check the pushrod socket in the end of the M/C to see if the depth of the seat is the same as the one you took off. There are different M/C pistons for the same cylinder body. Some are deep and others are shallow. If you got one that was too shallow, it would have the effect of making the pedal pushrod too long, holding the piston in and keeping pressure on the brake system, causing them to drag.

I'd measure them with a depth mic if in doubt. I've seen this problem several times, you change a M/C and the brakes won't release. Pontiac had a recall on this problem in 1972 on certain Grand Prix's. They released some with the wrong M/C piston and it caused brake drag.

I hope it is not cross threaded (and that is easy to do). I don't tighten the master cylinder mounting nuts so I can wiggle the thing around when I am trying to get the brake line nuts rethreaded. I usually wire brush the threads to get the corrosion off and put a drop of Liquid Wrench on the nut threads if they are corroded. Brake fluid has an affinity for water that helps things corrode.

If the line that is leaking goes to the side that doesn't lockup then maybe you have solved the problem. I hope so. Brakes and exhausts are not my favorite things to repair.

You know this was my problem. I had to put a space in it. It seemed to be fixed. I'd like to get the right one to be honest, btu I dont know what to ask for at Autozone.

I no longer have the origional M/C since I traded it in for the Core.

But thats exactly the problem.(origianally, now I think I have a leak to fix.) Any idea's what I need to ask for at autozone?

Check the pushrod socket in the end of the M/C to see if the depth of the seat is the same as the one you took off. There are different M/C pistons for the same cylinder body. Some are deep and others are shallow. If you got one that was too shallow, it would have the effect of making the pedal pushrod too long, holding the piston in and keeping pressure on the brake system, causing them to drag.

I'd measure them with a depth mic if in doubt. I've seen this problem several times, you change a M/C and the brakes won't release. Pontiac had a recall on this problem in 1972 on certain Grand Prix's. They released some with the wrong M/C piston and it caused brake drag.

Just make sure you get a MC from a diesel. 1/2 ton or blazer are the same, 3/4 tons are different bore size. I have swapped MC from 1/2, 3/4, and 1tons that were all originally diesels and never had an issue. Simply tell them that the one they sold you is WRONG and you need another. Sometimes cores get mixed up. Good luck.:cool:

Wouldnt it make the most sense to see what brake system the VIN on a CUCV Blazer, and see what brake system it has before decideing if its the same as a 3/4 ton or not. You know how the gov is...

I have never found a lot of difference in master cylinders on vehicles that use the hydro boost. They are quite a bit different from vaccuum booster models, though. I currently run a one ton master cylinder on a 1/2 ton hydroboost system with one ton axles. Only difference is the bore size on the MC.

Wouldnt the wrong bore size potentially cause trouble? I was just assuming that the bore size on the mil blazer with 6.2 might be bigger than the civvy version due to the Mil's 3/4 ton rating... (could also be their odd way of rating things too) Just would want to make sure he gets the proper one is all.

well, good news is that I'm pretty sure that I have the wrong. Better news is that I dont have a brake leak. Ended up that the radiator is leaking on the combination valve. Best news is that my brake problem went away.

Now, I'm still changing out the M/C. And when I'm doing that I'm bleeding the stuff out of the lines. I think I probadly mixed the dot3 with whatever what was in there and I probadly have a solid particle somewhere. I just hope a good bleeding works it out.

about the bore size, the only difference I noticed between the new one and the core, is that the core had a additional hole that was in the middle of the concave on the piston. I didnt look that hard for any more difference, so Its absolutly possible the pistion sat more forward.