Brakes problem, Help!

[Kaegi]

I would check plunger depth at back of master cylinder and check that pushrod from pedal to booster isn't too tight.

[PwrWgnDrvr]

I would check plunger depth at back of master cylinder and check that pushrod from pedal to booster isn't too tight.

How is that going to cause the adjuster to rotate and lock the brakes?

[RAYMAN]

does anyone have a diagram of the brake shoe placement and springs for left and right?

[dodgeboykim]

does anyone have a diagram of the brake shoe placement and springs for left and right?

Do you have a Factory Service Manual

[RAYMAN]

I do not have a factory service manual. I wish i did.

[dodgeboykim]

I do not have a factory service manual. I wish i did.

Cant go wrong with the FSM Bible.

[RAYMAN]

were can i get a fsm?

[PwrWgnDrvr]

Reprints better than new:
http://www.autobooksbishko.com/repair-manual.html

New ones were $35 in 1978, so don't think these are too expensive in 2020 $.

[martincom]

To clarify, you just added in the vacuum booster and retained the existing master cylinder?

If so, the rod length protruding from the vacuum booster may be too long. Did the donor truck have the same type/model of master cylinder as the receiving truck?

If you replaced both the vacuum booster and master cylinder from the donor truck, were they both the same brake system type, drum or disc?

[Kaegi]

I would check plunger depth at back of master cylinder and check that pushrod from pedal to booster isn't too tight.

How is that going to cause the adjuster to rotate and lock the brakes?

it wont cause adjuster to rotate but will pump op the brakes as you drive till they start locking up.

[PwrWgnDrvr]

I would check plunger depth at back of master cylinder and check that pushrod from pedal to booster isn't too tight.

How is that going to cause the adjuster to rotate and lock the brakes?

it wont cause adjuster to rotate but will pump op the brakes as you drive till they start locking up.

I get that. But rayman keeps backing off the adjuster to free the brakes. Soon they will be fully retracted and that will no longer be possible. How many times has he done this, how far has the adjuster been moved, does it stay put or tighten back up? Impossible to diagnose this problem accurately with the significant lack of details provided. Plenty of "could be" and "try this" is about it for suggestions.

[JLeather]

There's a tool for doing the pushrod adjustment:

https://www.jegs.com/i/JEGS/555/631315/10002/-1

We'll worth the money. You want about .020" clearance, done with the tool and a feeler gauge.

Autozone claims to have Duralast rear brake drums available still. I think that's what I put on my truck but can't find the receipt.

I've had adjusters apply the rear brakes before by putting the wrong one in the wrong side. I believe they are opposite-threads. This was not in my Dodge, so may not apply here. It's unlikely for them to spontaneously start acting up. I'd focus on the pushrod adjustment first.

[martincom]

I'm gathering this problem came with the master cylinder/vacuum booster upgrade. So if nothing had changed at the wheels, it is highly unlikely that is where the problem is.

[digdoug]

I also think it is a problem with no free play between booster and master. If the cylinder can't come to rest, there will be too much residual pressure. To easily confirm this, pump the brakes, then go out and take the cap off the master. Loosen the two nuts holding the master to the booster. If it's adjusted too tight, the fluid will release into the master as you loosen the nuts. Eye protection is a good idea.

[Wildergarten]

If it's adjusted too tight, the fluid will release into the master as you loosen the nuts. Eye protection is a good idea.

Methinks this hath bin validated by ick-spur-meant. Yucky.

[RAYMAN]

I did keep the master cylinder that was in the truck and just added the booster all the brake components at the wheels are the same with new shoes and adjusters. im going to check the rod adjustment this week. Thank you all for the advise.

[Jim100]

I had bad contact between the "blade" of the adjuster and the star wheel. Had to bend and file to get good grip.
Im not usually right but it happened to me. New stuff.
jim

[Jim100]

Were you able to come up with a solution to your brake problem?
jim

[RAYMAN]

Jim100- I have not had time to look at it yet. The last time i did however it seems like as soon as there is vacum supplied to the brake booster the front rakes start to apply with foot off of the pedal. Im thinking the adjustment on the push rod in the booster is wrong.

[martincom]

I think you're on the right track. Now that you clarified you retained the original master cylinder and just added the booster, it sounds as if the booster pushrod is too long or there is foreign material in the pushrod socket of the master cylinder.

When your brake lock up, rather than adjusting them loose, open the bleeder on the wheel cylinder and see if they release (if there is pressure being held, the fluid will spray out). If there is, the piston isn't returning far enough in the master cylinder to clear the relief port.

A FSM will be the best investment you can make in your truck.