Brakes locking up

[1stchevy]

Like the title says my brakes lock up, all 4 wheels, after driving the truck for maybe 5 minutes. The truck is a '69 C10 with the ECE 4"-6" drop kit, ECE 5 lug conversion, ECE front disc conversion and a McGaughy's master cylinder/booster combo.

Any help is greatly appreciated
Chris

[NEWBIEC10]

My guess would be that the Master Cylinder is not working correctly.

[ssxty8]

Make sure you have enough freeplay on the brake pedal assy. If the brake pedal's rod to master/or booster is touching when the brake fluid is cold, it will grab when hot. You want some freeplay there, don't remember how much on trucks tho. Been there done that.
Good luck.

[lolife99]

1/8"-1/4" freeplay should be enough.
Any pics of your master cylinder assembly installed?

[1stchevy]

I'll check that when I can get back to it. And no pics right now but I'll try to get some. The truck is in storage and about 20 minutes away from my house.

If I remember correctly I think I've got it setup without any free play so that def could be it.

[Hart_Rod]

You have too much tension on the brake rod. I fixed one with the exact same problem last weekend. Shorten the rod and you should be good to go.

[1stchevy]

Thanks Rob, that's going to be the first thing I check when I get back around to it.

[1stchevy]

I shortened the rod then started to drive the truck and now the pedal stays just about on the floor. I'm lost guys!

[ssxty8]

You should need just a little freeplay, not enough to change from locked brakes to pedal bottoming. Maybe now you have too much?

[1stchevy]

This has really got me stumped to the point I'm thinking about pulling the mcgaughys unit and going with the wilwood tandem and no booster.

[chevy_mike]

Where are you measuring your free play at? You don't want the rod to have a 1/4" of play, you want the end of the pedal (where your foot hits) to have a 1/4" of play.

[1stchevy]

That's what we were trying to get yesterday and then when I started the truck and pushes the pedal down it stayed down.

[chevy_mike]

I thought the pedal has a spring that will pull it back to the up position. I don't recall 100% but I know my wagon had one as I had to get it lined up in the right hole. If you are supposed to have a return spring and don't, that could be your problem. The weight of the pedal will push on the booster and allow it to drop and will not return it back up.

Can someone confirm a return spring for the brake pedal?

[1stchevy]

Yes there is a return spring on the pedal.

[chevy_mike]

So what I am reading is, you have a return spring on the pedal but if you push the pedal down, it does not return, is that correct?

[1stchevy]

Originally Posted by chevy_mike

So what I am reading is, you have a return spring on the pedal but if you push the pedal down, it does not return, is that correct?

Yes, that is correct but the pedal only stays down when the truck is running.

[SCOTI]

Originally Posted by 1stchevy

Yes, that is correct but the pedal only stays down when the truck is running.

"Down" as in 'to the floor' down or as in the 'free-play' before the plunger actually starts pushing fluid out of the master cylinder?

[1stchevy]

Originally Posted by SCOTI

"Down" as in 'to the floor' down or as in the 'free-play' before the plunger actually starts pushing fluid out of the master cylinder?

When I started the truck I checked to see if I had any pedal feel and I pumped them a couple times then it stayed down just about to the floor.

[SCOTI]

Originally Posted by 1stchevy

When I started the truck I checked to see if I had any pedal feel and I pumped them a couple times then it stayed down just about to the floor.

That sounds like a master cylinder issue. I would check for leaks throughout the length of the lines. No leaks, re-bleed the master 1st then all the lines.

[chevy_mike]

If it goes to the floor when the truck is running but is fine with the truck is off, you have a booster problem, likely an internal leak that is allowing the vacuum on the wrong side of the diaphragm or bad check valve not allowing air back in.

Easy was to determine is to remove the vacuum line from the engine and plug the engine side. Test the brakes and see if they work like normal (only harder to push) or if they still work down to the floor and stay there.

[1stchevy]

Thanks guys I'll go back and take a look at this thing. This is the last thing keeping me from driving my truck and I'm getting aggravated.

[1stchevy]

Finally broke down and call Mchaughy's and talked with tech, going to try a few things they recommended and go from there.

[swissarmychainsaw]

Let us know what you find...