Brakes won't hold back wheels

[davepl]

After adding trans fluid I lifted the truck off the ground a couple of inches, fired it up, and put it in drive. It didn't even stall (insert advertisement for Quadrajet and stock setup here).

However, I had to push on the brakes with all my might to stop the rear tires from turning. I'd like to claim its sheer torque but I imagine something's not right.

Note that because it was up in the air you wouldn't normally see this, as your fronts would hold you. I don't know if mine will, and I'm not crashing to find out!

The only different thing about my setup is I converted to '72 3/4 ton front discs. Kept the '70 rear drums. Booster, master, combo valve, everything else is from the '72.

In any event, the pedal feels fine. I'm wondering if it could be as simple as the star wheels not being set right.

When I turn the wheels by hand I think I can hear a light scuffing, so I thought the pads were engaged.

Or should I be turning them until the wheels WON'T turn and then backing off? Not sure how to get the proper adjustment. Dana 60 3/4 ton.

[69chevytrucker]

put it in reverse on stands pump the brakes a dozen time then try in drive should ratchet the brakes up for you

[69chevytrucker]

or turn the star a few more turns

[70SBC10BOB]

Jack up your truck.

Turn the rear wheel in one direction and adjust the star until it almost stops.

Turn the rear wheel in opposite direction and adjust until it stops.

Back off the adjust 6 to 8 clicks. The wheel should have a slight drag and your shoes will be centered in the drum.

Good luck,
Bob

[cdowns]

i'd take the brake drums off and look to see that you have good amt of brake shoes to try and stop your rear wheels with

[davepl]

Brand new shoes and freshly turned drums. Parking brake seems OK.

Do the adjusters work without the momentum of the vehicle I wonder? Can I do the "let the wheels go backwards and then hit the brakes" up on the lift?

If that doesn't do it I'll reset the star dial thing by hand.

[70SBC10BOB]

The only way to adjust drum brakes is by manually adjusting the star as described above. The automatic adjuster only works in reverse and will not get them centered properly. It is to maintain adjustment and really doesn't work that well.

Since you put new shoes on, was the short shoe to the front or back? The short shoe must be in the front for proper brake wrap. (Ever notice how a vehicle with drum brakes doesn't stop as well in reverse?? Or how parking brakes don't hold in reverse? Brake wrap.)
Bob

[Stocker]

^^ Good point about the short / long shoe placement.

Originally Posted by davepl

Do the adjusters work without the momentum of the vehicle I wonder?

Yes -- they simply move the bottom of the shoes farther apart, which moves the shoes closer to the drums, where they should be when properly adjusted.

[67 cst swb]

I would say if the front brakes are good... its time to do a burnout!

[davepl]

Originally Posted by 70SBC10BOB

Since you put new shoes on, was the short shoe to the front or back? The short shoe must be in the front for proper brake wrap. (Ever notice how a vehicle with drum brakes doesn't stop as well in reverse?? Or how parking brakes don't hold in reverse? Brake wrap.)
Bob

I had them done by Differentials Northwest, which is a specialty shop that hopefully put them in correctly.

Seems to be a lack of agreement here about the adjusters. If backing up spreads the bottoms of the pads out, what does manual adjustment do better?

If I'm reading correctly it's that it centers the pads, but doesn't that happen about the first time you use them anyway?

I'm asking because I don't know. Not trying to argue.

[jdw]

In this other post http://67-72chevytrucks.com/vboard/s...d.php?t=641176 you mention your stall is too low at 2500 rpm. Someone will correct me if I'm wrong, but if the stall is too low, the torque will over power the driveline by spinning the transmission.

[davepl]

Too low? 2500 is pretty loose. Stock is more like 1500. So the idea has merit but I think its backwards from how my setup actually is.

[jdw]

Oops. When you said "undersized" I take it you were talking about dimensions, hence the 12qt vs 10qt fluid. Not the stall. Duh.

[davepl]

I was, but smaller converters are usually higher stall, right? When I was a punk before higher stall converters were cheaply available people would use Vega converters, and they were much smaller in appearance.

[jdw]

If the stall is too high, I believe it won't go anywhere. I'm waiting to hear some more on this.

[70SBC10BOB]

Originally Posted by davepl

Seems to be a lack of agreement here about the adjusters. If backing up spreads the bottoms of the pads out, what does manual adjustment do better?

If I'm reading correctly it's that it centers the pads, but doesn't that happen about the first time you use them anyway?

I'm asking because I don't know. Not trying to argue.

Your brake shoes have to be centered in the drum with the top of the shoes against the anchor pin at the top. The wheel cylinder push out to apply the brakes. When you release the brakes, the springs force the shoes back to the rest position. Wheel cylinders can only be affective for certain amount of travel. That is why you need to adjust the star at the bottom of the shoes to minimize how far the wheel cylinders pistons must travel. Centering or adjusting the shoes as described above, will accomplish that goal.

Bob