brakes dragging

[weq92f]

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Welp it's now happening to me...Noticed a drag then chased it to the front discs. Both front calipers are dragging too much. The drag on each side is equal.

Here's the twist...it doesn't drag once everything cools off. It doesn't drag until everything gets up to temp. I can't duplicate on the "bench" with it idling and me randomly pushing on the brake pedal for a while then holding it for a while, etc. and so on.

I'm thinking this is caused by pressure not releasing rather than both calipers having an issue simultaneously. Note also this brake dragging is a new thing without having made any changes to the system. But...a while back one of the lines to the master came loose and I lost brakes. The repair to that consisted of only attaching the line and pouring more fluid in. Given this...I think it's probably the proportioning valve.

What do you all think? How do I go about diagnosing the valve?

Thanks,

-weq

[SkidmoreGarage]

I would think that the front residual pressure valve (inside the proportioning valve) would fail open and not closed. This would lead me to believe that you may have air in the lines, especially if you only added fluid and didn't bleed the lines.

Once the air gets hot, it expands and can push the calipers out. You would think that excess pressure would bleed off back into the MC through the residual pressure valve (but that may be a product of where the air is and how much), but a brake bleed should be an easy place to start.

[weq92f]

Originally Posted by SkidmoreGarage

I would think that the front residual pressure valve (inside the proportioning valve) would fail open and not closed. This would lead me to believe that you may have air in the lines, especially if you only added fluid and didn't bleed the lines.

Once the air gets hot, it expands and can push the calipers out. You would think that excess pressure would bleed off back into the MC through the residual pressure valve (but that may be a product of where the air is and how much), but a brake bleed should be an easy place to start.

So went back and found I can reproduce without driving. It’s likely what you mention. Takes just a few mins of not using the brakes for the drag to go away. About long enough for air to cool down.

Digging out my bleeder now....

-weq
Posted via Mobile Device

[SCOTI]

How old are the lines?

It's possible there is some internal swelling which adds to the issue (swelling slows return flow). If they have some age & your plan is to bleed things, swap some fresh hoses on since they're not crazy expensive.

[mikeshome]

Are you sure the fluid put in was brake fluid? Seen this happen when wrong fluid was put in. .Or bad master.

[weq92f]

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Since I was without helper I used my vacuum pump to bleed just the front. The negative pressure at the bleeder causes air to be introduced into the stream of fluid through the threads. As such I wasn't able to see the air but it must have been there because after bleeding enough fluid to basically flush the system, my drag is gone.

What's strange is the pedal now vs. before bleeding isn't really any different. It's not very firm. The fluid was dark and now is looking real fresh at least on the front...

I'll be bleeding the rears next.

Thank you gents.

-klb

[SkidmoreGarage]

Good to hear, you can seal the threads of the bleeder to speed up the vacuum bleed. There are strong opinions about it online, but you can always clean it off the threads after you clear the lines. Sometimes it's the only way to get the job done by yourself.

[Minkota]

What application is the Master Cyl for? If it is for Drum/Drum then it will have a residual valve in it and cause the brakes to drag.

[mr.mud1]

hi,i have had old brake hoses collapse internally,letting fluid through under pressure but not allowing it getting back by the collapsed section,having the effect of holding the brakes on.hoses will look perfect from the outside.just a thought.

[weq92f]

Originally Posted by Minkota

What application is the Master Cyl for? If it is for Drum/Drum then it will have a residual valve in it and cause the brakes to drag.

It's a disc/drum setup. All was working well until a fitting backed off up on the proportioning valve and introduced air. After "fixing" that, this dragging problem developed. I'm now convinced this was all just air in the lines.

-klb

[1971Stepside]

I had this issue on my system (hydro with Wilwood MC) and it was the pin length between the MC and booster. Once shortened the problem went away.