9" rears dragging

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toomunsch

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72 Dart manual 9" drums ft and rr. I just replaced almost everything: master, lines, hoses, wheel cyls, shoes, hdw. After driving for a short distance the rears start to drag and get very hot. Next morning rear wheels turn freely. No binding of m/cyl pushrod. I suspect something with the new master. Parking brake cables are bad so struts are temporarily removed. Any ideas?
 
This is funny, as I just had the same issue with my 10" rears.

In my case I was missing one part and did not realize it. Also the shoes were constructed different than all the others I had for reference.
Green is like all others I had, red was new.
PXL_20230603_213848385~2.jpg


This guide plate was mia when I was reassembling the brakes yesterday.

The day before I went for a drive and the right rear was dragging when I got home

140deg vs 100 on the left

When i took the drum off the forward shoe was stuck behind the pad on the backing plate.

I'm guessing a combination of the shoe being different and the missing guide was the cause.

PXL_20230513_153557376~3.jpg
 
I'll definitely pull the drums and investigate that. Some of the parts I got were incorrect so I had to reuse some old hdw. The state of aftermarket brake parts is dismal
 
CHECK THAT THE MASTER CYLINDER IS FULLY RETURNING

In the bottom of the cylinder reservoir(s) are the return ports. You should be able to press down the pedal (have someone) and watch as it returns, you should get a spurt of fluid up through as it releases

Another way to check is to duplicate the problem, then crack the master line(s) and see if there is any remaining pressure, and if the brakes release
 
I'll look at that. Also the m/cyl piston was really hard to move when bench bleeding, much more than I remember, haven't done one in a while
 
In my opinion it is definitely in the master brake cylinder or wheel cylinders. Step on the brakes and the pressure is on and brakes won't release. Leave them alone for awhile and they slowly release on their own. Just like a slow draining sink.
I had the same problem with my wheel cylinders. They were filled with many years of old gunk. The gunk was plugging them up and they would lock up and then slowly release.
You have new brake cylinders so I would think the master cylinder is the culprit.
 
That's what I'm leaning toward too, especially considering how hard it was to push the piston in. Quality is not great these days
 
I have a new best brake mc on my shelf

The 4 mounting holes are drilled a few degrees off of horizontal
 
If it’s both rear brakes it’s most likely the master cylinder OR the rear brake hose. Just because the rear hose is new doesn’t mean it’s good, there have been issues with brand new rear hoses with inner linings that close up.

It’s also possible it’s the wheel cylinders, but, those are independent so it would be less likely that both are bad and yielding the exact same problem on both sides at the same time.
 
^^^^^This. Hoses can block up with sediment over the years.
 
the "green" shoes are less likley to hang-up on any ware on the back plate
the "Red" shoes are more likley to hang-up on any ware on the back plate, or indeed ware the back plate and hang up on the ware...

both styles are ok

check the back plate sections where the shoes ride and dress out any ridges wipe the areas with copper slip

without the strut in id guess the shoes can move to positions that they can't when the strut is there.... don't dicsount this as something causing your problem.

what type of shoe mounting do you use? early cone spring and square based hook style anchor or the later Pin spring and twist cap

the later version holds the shoes paralell with the back plate better than the cone spring hook things but you will need a bag of washers to stop the pins falling through the holes in a back plate designed for the square anchor things.

and if its all new you can more or less guarantee that the drum and shoes are not the same curvature so the middle or the ends of each shoe will drag when adjusted up as per the service manual...which expects perfect OEM parts

set it up so that the brakes are adjusted badly i.e where they would be by the time it needs a service. not dangerouse but in need of adjustment start there....

none of this "adjust until drum drags on shoe and back off a smidge"
adjust so it drags and back off lots of smidges.
Check peddle drop leave enough so it doesn't hit the floor but you want the rear shoes away from the drum when cold and hot to give them a chance to bed in nice without dragging.

drive it for a few weeks then adjust up propely by that time the shoes and the material on them will match the drum shape and you have a better chance of cool running rears.

if you want to delete the auto adjuster, you need the proper spring set. if you use the standard set, you may find 1 spring is just too short, and it pulls the shoes out of parralell with the back plate.

then the outer edges really drag and the drums get very hot.

old 9 inch stuff doesn't sell in the volumes that the 10 and 11 inch stuff does.
post 73 stuff kinda works better i.e the cup pin spring shoe mounting hardware

Dave
 
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Yes I think it's something back there as I just ran it, they got hot and heavily dragging. I cracked the line at the master and it made no change. I'll pull the drums tomorrow, too hot now.. thanks all, lot of good info
 
Update on these brakes. The drums had a lot of runout and I decided to take them to Oreilly for cutting, knowing those fools would probably not do a very good job. I used to run a brake lathe all day sometimes in the 80s. They came back all chatter marked up , but I tried them out. Ran better but still too hot, didn't feel right. I got 2 new drums and replaced the cooked shoes and it seems fine now. There ya go.
 
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