Front end problems

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Duster jud

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I have a problem with my 73 duster. I really hope someone can help me. I've only owned the car about two weeks when I drive the car about 5-10 minutes it feels like the front brakes come on buy them selves and it will start bouncing like I have a flat tire. The brakes don't completely lock up but there on, if I let off the gas it's enough to stop the car right away. The front brakes are disc and the pads look new. I'm stuck everything looks good but I can't figure it out. Has anyone else run into something like this or have an suggestions on what to do I would appreciate it. Thank you in advance
 
Try opening a bleeder and see if they let go.
If they do, then it's probably something to do with the master cyl (like to long of a rod or something keeping the master from returning all the way)
If they don't it could have to do with a distribution block or an internally collapsed hose.

Either way it will answer some questions.
 
If moisture got into the caliper's piston, rust will form and may prevent the piston from returning (releasing). If this is the problem, a rebuild or replacement is in order for the caliper.
 
Old fluid hoses do that also. Flow becomes sort of like a check valve in that higher pressure fluid will flow one way, free flow doesn't go the other way. That or anything else at a front side would effect straight line stopping. First be absolutely sure the fault is at front brakes. If I knew for sure your car is 100% OEM parts, my suspicion would be a bad master cylinder. Knowing how much aftermarket stuff has been installed, aftermarket adjustable proportion valve could be the fault.
 
It's the calipers for sure. Have them rebuilt or trade them in for a pair of rebuilt ones. I would also advise you to have the rotors turned and put on new pads no matter what the current ones look like. That way you will have a good new front brake job. Also remember to lube the slides with a tiny bit of white grease when putting it all back together.
 
If your calipers have phenolic pistons they need to go. They stick and cause what you describe. Get replacements with stainless steel pistons. Flex hoses collapsing internally can also cause a similar problem as mentioned.
 
Duster 73 said:
It's the calipers for sure. Have them rebuilt or trade them in for a pair of rebuilt ones. I would also advise you to have the rotors turned and put on new pads no matter what the current ones look like. That way you will have a good new front brake job. Also remember to lube the slides with a tiny bit of white grease when putting it all back together.
Click to expand...

mguner said:
If your calipers have phenolic pistons they need to go. They stick and cause what you describe. Get replacements with stainless steel pistons. Flex hoses collapsing internally can also cause a similar problem as mentioned.
Click to expand...

That's right, it could be that Phenolic garbage I forgot about that.
Phenolic is basically a plastic and does warp and get scored easily.

So if the OP loosens a bleeder and it doesn't let go it could also be the caliper pistons jamming.
I was under the impression it eventually let go on it's own, and then did it again after a short time of driving again.
I don't think stuck pistons do that. (but maybe)
 
I have a theory.
I think one(or possibly both) calipers is dragging on the disc, right from the get-go.The reason of this dragging could be from several different reasons. I think the compensating port is plugged or blocked. I think the overheating brake fluid is trapped, and expanding enough,or boiling, or moisture in it is boiling,to create enough pressure to lock up the wheels. That's what I think.
I think if you crack a bleeder as TB suggests,right when the event occurs, you will have a shower of extremely hot brake fluid and instant relief!Be vewey vewey kaawful!
 
Welcome to the club - the forum and front end problems. No mistake about it, you heve a mopar !
 
Check the easy stuff first. What color is the brake fluid in the master cylinder? If it's anything other than clear, it needs to be flushed out. You say the brake pads are new, what do the brake hoses look like? New? Or old and rotted looking? Is this a car with power brakes or manual?

With a "new to you" car, it's always best to start with the easy stuff. Brake fluid and hoses are cheap. If the problem persists after that, move to master cylinder and then the calipers. If it's a power brake car look at the booster too. The hoses go bad MUCH more frequently than the calipers do. In fact, in my experience anyway, the master cylinders fail more often than the calipers do. I have the stock and apparently original calipers on several of my cars. I have the original brake hoses and master cylinders on exactly none of them. The single piston 73+ calipers are pretty reliable, they're not nearly as prone to issues as the earlier Kelsey Hayes calipers. I've even used 73+ calipers straight out of the local wrecking yards, unknown history, unknown miles, crusty looking, the whole bit. Pistons moved freely in all of them. And if the brakes seem to work ok and then get worse as you drive, the calipers wouldn't be my first suspect.
 
Drive a bit until the wheels lock up. Then loosen the 4 bolts on the MC a few turns and check if the car will roll again.
If so, the MC pushrod is too long.

Very common and most likely issue, going by your description.
 
I opened a bleeder and it freed up the wheels. The brake pedal is very stiff I think I'm going to try and replace the booster. The fluid and hoses look good. Thanks for all the help I was stuck and I'm new to the forum and all this help is amazing. Where is the compensating port? I also read while the car is running hold the brakes shut the car off while still holding the brake pedal should stay when you let go,means your booster is good mine doesn't stay not sure if it's true but that is why I'm gonna try the booster that and that trailbeast bleeder idea worked. Once again thanks
 
Vacuum boosters aren't cheap. They don't make brakes either.
I think I would google "testing vacuum brake booster".
Factory service manuals are free downloads.
 
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