68 Dart GTS brake problems

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markfh

markfh

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After sitting on jack stands for 25 years I replaced the entire drum power brake system front to back with the exception of the PB Booster and wheel drums. Everything is all stock. I used DOT 5 fluid and had a problem sealing it up. I wound up using copper gaskets on some most of the fittings which finally stopped the leaks. The brakes finally work but they're not right.

The brakes are a little mushy and when stopping the pedal goes pretty low to the floor. After applying them if I pump the pedal it comes up high and gets real hard but does not translate to more braking power and actually a little less.

I've tried standing on the brakes to see if I could lock them up but they won't.

Any ideas?

Thanks
 
The mushy is likely air in the lines,, and the low pedal is likely adjustment,,

So, first, adjust them up till they scrape on the drums,, then bleed them,, you should be good..

hope it helps.. cheers
 
Pump up the pedal until it's stiff, then try holding pressure on it. If it slowly sinks to the floor the master is no good.

I agree with air in the lines though.

Did you bench bleed the master before installing it?
 
Some other stuff to throw in besides already:

DRUM: Have the drums been replaced or turned? If they were turned how far oversize? The larger drums get, the worse the shoes fit. This causes poor braking and poor pedal, because the shoes are effectively too small inside the now too large drum

DISC: Same thing only different. If the discs are worn uneven, the pads don't seat over full surface area, causing poor braking. Discs MUST be trued

Lining type. Some types of lining just don't stop well, and or could be glazed.

People have reported rotten, expanding hoses. Generally a low mushy pedal is a combo of adjustment and bleeding.

If drums tighten the adjusters up tight until the wheels won't turn, see if that improves the pedal.

How are you bleeding? Exactly? If EG you are not closing the bleeder as the pedal comes down to the floor, you might be sucking air back in on the upstroke.

Read the posts above. Good advice there

READ the service manual. DOWNLOAD one if you don't have. Go to MyMopar.com There is no excuse for this. THERE IS NO EXCUSE. In extreme cases actually read the manual. There are test procedures, including hooking up pressure gauges (what a concept)

On a dual system, the distribution block (drums) or the proportioning / metering valve (disk) may be AFU
 
Thanks for all the information and suggestions.

Like I said I replaced everything in the braking system (all drum no disc) with the exception of the booster and wheel drums.

I did bench bleed several times but apparantly not sufficiently because I put it back on the bench tonight and pumped that sucker for an hour before it quit giving bubbles.

It's back on the car now and I'll adjust the brake shoes as suggested then bleed the rest of the system again.

One thing I noticed is that the new "as original" MC from Jim's has both reservoirs the same size. The one this replaced I took off the car 25 years ago has a larger reservoir in the back.

Wonder if that's going to be a problem and whether or not I have to replace it.

67Dart273 I have an original service manual and use it often.
 
Taking that long to bench bleed a master might be indicative of some problem with the master, IE say, sucking air into the rear of the cylinder, etc. Is this a new or rebuilt master?

Normally a master with "same size" reservoirs is a drum brake master. I do use my original drum master on my 67 with 4 wheel disk. The reason the drum / disk masters have larger for the disk is that as the pads wear, then "use" fluid. As long as you "watch" fluid level, that is not a concern.
 
This a new MC from Jim's that is supposed to be THE one for this car according to their listings. I'll keep an eye on the levels and if I feel this one isn't doing the job I'll rebuild on of the two others I have. Once I get them apart that is.

I'm thinking it took so long because of the plastic fittings that were difficult to seal that came with the bleeding kit. In respect I should have just gotten a pair of steel lines to work with. The time would have been worth the money.
 
Sometimes when I bench bleed, I just put my finger-tips over the ports . They seal really well. A half dozen or so strokes and its done. I know what youre gonna say. How can you tell its done if you dont have a visual? Just try it sometime.
EDIT; Yeah its messy, but its like 3 minutes or less, badaboom!
 
Okay, got the MC bench bled, gravity bled the right rear then the left rear. The front two don't gravity bleed worth squat. Is that indicative of a MC problem or is that normal. I know the right front has the line that goes up over the back of the engine on the firewall and I would think that would make gravity bleeding difficult but the left front should bleed fine.

Tomorrow I'll test the brakes to see if there's any improvement. Got work to do tonight.
 
Sounds like you removed the MC to "bench bleed". Many take that term too literally. I always install the MC on the car and bench bleed using the pedal. It may take 50 strokes to get all air bubbles out. I also don't like the plastic bleeder fittings since they can suck air past the threads, or the push-in type can pop off. I try to keep bent metal tubes for bleeding. If your existing MC was original, it suggests the car had factory front disk brakes.

Install the drums w/ shoes fairly loose, so they don't drag. When you first test drive, back up many times in a parking lot, jamming the brakes hard each time so the self-adjusters do their thing. The pedal should start taking less motion. I use DOT 5 in most my cars. I was afraid a wag would state the oft-claim "silicone is spongy". But, do carefully pour it in down the side of a funnel so it doesn't entrain air bubbles, since they take longer to settle out in silicone.
 
Yep. Put it on the bench. Since I've been working on it alone it was easier to see the tiny bubbles and make sure when they were gone.

It worked and with gravity bleeding the rear and finally getting my better half to help with bleeding the front I think all the air is out now and the pedal feels good.

When I can get back to it in the next couple days I'll back off the pads a little and drive it again.

Next project... carburetor.
 
Got it down and drove it a bit after adjusting the pads. The brakes work much better but I still get a high hard pedal when stopped and releasing just a little lets the car roll. At least they self adjust and I can stop now so I'll be driving the back roads for a while.
 
Sounds like the booster is not working. The pushrod may need adjusting.
Try this; With the car turned off, pump the brakes about 8 times to rid the reservoir of trapped vacuum. Then push the pedal about 50% down and start the engine. Almost immediately as the engine evacuates the booster, the pedal will fall down about 1 inch with no help from you. If yours does this, the booster should be fine. If it does not perform like this, then,the pushrod may require adjustment.

When you replaced the flex-lines, are they original rubber-type?
A high,hard pedal, that releases, and doesnt hit the floor, is usually a good thing.
 
AJ/FormS said:
Sounds like the booster is not working. The pushrod may need adjusting.
Try this; With the car turned off, pump the brakes about 8 times to rid the reservoir of trapped vacuum. Then push the pedal about 50% down and start the engine. Almost immediately as the engine evacuates the booster, the pedal will fall down about 1 inch with no help from you. If yours does this, the booster should be fine. If it does not perform like this, then,the pushrod may require adjustment.

When you replaced the flex-lines, are they original rubber-type?
A high,hard pedal, that releases, is usually a good thing.
Click to expand...

Okay, did that and the pedal does fall about an inch. FYI there's only about an inch or so from there to the pedal bottoming out.

The flex-lines are new but they are the original rubber type. I'm trying to keep the car exactly stock and as original as possible.
 
Well then the booster aint broke. EDIT; hooray!
The pedal parks high, gets hard, and has about an inch before bottoming out.Sounds pretty good so far.
I take it the biggest complaint is how much leg power it takes to stop the beast.Is that right?
 
You are using old drums? Did you have then turned? How much oversize are they? Even "lightly turned" drums with new shoes is likely to require some break-in as the drums as you turn / wear them become larger and larger, and the "circle" the shoes fit starts to touch only in the middle of the shoe surface.

"Used to be" you could have the shoes "arced" to fit the drum. This is a special grinding fixture which changes essentially the diameter of the shoes to fit the drum

Ammco_890_Brake_Shoe_Grinder_Stock_401_p1_w500.JPG
 
^^ doh, 67,you snuck in there! lol.Thats exactly right.
the "circle" the shoes fit starts to touch only in the middle of the shoe surface.

And before the self energizing feature kicks in(light application, or when stopped), the pedal can feel springy. Not spongy or mushy.But since you mention a high,hard pedal, im going in a different direction.
Going back to post#19, did you have the drums machined?
 
67Dart273 said:
You are using old drums? Did you have then turned? How much oversize are they? Even "lightly turned" drums with new shoes is likely to require some break-in as the drums as you turn / wear them become larger and larger, and the "circle" the shoes fit starts to touch only in the middle of the shoe surface.

"Used to be" you could have the shoes "arced" to fit the drum. This is a special grinding fixture which changes essentially the diameter of the shoes to fit the drum

Ammco_890_Brake_Shoe_Grinder_Stock_401_p1_w500.JPG
Click to expand...

Yes, I am using the original drums and they don't appear to have been turned but then I haven't measured them. What is the wall thickness for stock drums?
 
Drums are not measured that way. Drums are measured as to inside diameter, with a special tool.Then the measurement is compared to the maximum allowable dimension, that is stamped on the drum, or is available from a drum supplier, or of course, the FSM.

Now, getting back to post#19,
If your brandy new shoes are in fact just touching in the centers(common), and the drums are serviceable and round and not ridged around the inboard edges,nor badly grooved, then you need to expect to travel perhaps hundreds of miles, before they become "broken in", to the point of normal braking ability.That is with normal leg power. In the mean time, excessive leg-power will tend to glaze those two little spots/per drum making break-in take all the longer.
There is only one way around this; new stock diameter drums, to go with those new shoes. Those new shoes, are now used. They will/may require deglazing; a light skuffing with abrasive-paper or, I like a light touch with a sharp lathe-file.
These will also still require a break-in, but it can be all finished in a hundred miles.At that time, brake performance should be much improved, and easy on the leg.
If youre strapped for cash,perhaps leave the rears.
There is a second option,listed in post#19. But those grinders are getting hard to find, and oversize cut-to-fit shoes, even harder.
 
The replacement shoes we get these days are approx .030 over size, with the idea that they'll seat in,, so most replacement shoes never match when first installed anyway..

If it were mine,, I'd drive it a while,, re-adjust,, and re-bleed in a few hundred miles ..

jmo

hope it helps..
 
What AJ is trying to say is "it ain't gonna work"

To sum this up "easy" you need to

find new drums.

determine if you can even use the new shoes before they get worn unevenly because of the old drums

OR turn the old drums if they can be (.060" over is the old standby limit)

and then find the mentioned arcing machine. Town the size of Houston? Should be one there somewhere LOL Find the oldest mechanic in the oldest shop still in business you can find. Ask them if they can "turn drums" and "arc shoes"

This is an example of an old drum "mike". Simply put, you are measuring the inside diameter of the drum.

908500.jpg
 
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