Sticking disc brakes on both sides (Cuda).

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petebryan
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Sticking disc brakes on both sides (Cuda).

Post by petebryan »

Hi all

Looking for some of your collecive wisdom please (you've been invaluable in the past!).

The disc brakes on the front of my 1970 Cuda are both sticking on, and have quickly (over 2 or 3 drives) got worse to a point where I only just got home in the heat yesterday after a short drive yesterday, with some smoke starting to come off the offside brake as I got home (again offside slightly worse of the two).

On the jack, I can turn both wheels by hand but only with quite a bit of effort. The pads are clearly right on the disc.
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I sensed a bit of stickiness last time out, though wasn't bad, but has got worse quickly. They've been well behaved for last 20 years albeit on low mileage. Curious that both discs have gone at the same time too - so the car doesn't pull one way, but just wants to stop entirely, and in a straight line.

The only other symptom is that the brake pedal feels very hard when I'm driving and braking, with very little push down movement available (though this releases when the car's been stopped a while and is restarted).

Any thoughts or tips before I scour youtube and start taking it all apart ?

Thanks in advance!
Pete
1970 Plymouth Cuda 383.
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Pete
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Re: Sticking disc brakes on both sides (Cuda).

Post by Pete »

When was the last time that you changed the Brake Fluid?
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Matt
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Re: Sticking disc brakes on both sides (Cuda).

Post by Matt »

Pushrod between master cylinder and servo may be adjusted too long, not allowing master cyl to retract fully. Either that, or the brake pedal is being prevented somehow from coming all the way back up, which will produce similar symptoms. These are the most likely causes , seeing as both wheels are affected.
Last edited by Matt on Thu Jul 14, 22 9:56 pm, edited 2 times in total.
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Matt
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Re: Sticking disc brakes on both sides (Cuda).

Post by Matt »

Flex hoses can collapse internally as well and cause calipers to drag. Either that , or both calipers’ pistons or sliders have started binding at the same time. Unlikely, but possible. Crack the lines open first before then after the flexibles and see if the calipers release. This will narrow the problem down to m/c, hose, or caliper. Normally the front wheels should spin freely by hand.
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Blue
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Re: Sticking disc brakes on both sides (Cuda).

Post by Blue »

What often happens especially with cars that sit around for long periods of time is you get corrosion around the exposed area of the caliper pistons. They can’t retract so what happens is when everything has heated up and expanded, the brakes bind and you get a hard “dead” feeling pedal. When everything has cooled down the binding goes away and the pedal feels more normal. If that’s your issue, the pistons need popping out and the corrosion polished off using something like a rotary wire wheel. In mild cases this will fix it, but heavy corrosion and pitting is likely to case the caliper to leak once the piston is retracted. In that instance, provided the seal is in the caliper rather than on the piston itself, you can replace pistons and seals, you can even get plastic pistons that won’t corrode. Check Matt’s suggestions first.
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petebryan
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Re: Sticking disc brakes on both sides (Cuda).

Post by petebryan »

Many thanks all, for fast and helpful input.

Pete - brake fluid changed a couple of years ago, so relatively recently (previous stuff in there a lot longer).

I'll work through those thoughts and ideas and let you know how it goes. Hoping to get to the Nats...

Cheers again
Pete
1970 Plymouth Cuda 383.
petebryan
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Re: Sticking disc brakes on both sides (Cuda).

Post by petebryan »

Right, I've taken the brake pads out (used a big screwdriver to lever the stuck capiper and pads up and off the disc) and all looks reasonable inside, just a fair bit of black brake pad dust. Pads look ok also - outer one is around 5mm, inner one around 7mm of remaining pad.

Before I start to cracking open the brake lines, I was wondering how far the piston should actually go back in? - it looks fairly well retracted as it is (see photo).

Thoughts?
thanks
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Pete
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Re: Sticking disc brakes on both sides (Cuda).

Post by Pete »

They should go in further than that - virtually flush with the body.

I have had a similar problem on another vehicle recently, and that proved to be sticking Pistons.. take out, polish up, clean the Caliper bore, lubricate with red grease and reassemble...sorted for now, but I will probably need new Calipers.

Also, the thicker the Brake pad material the lower the propensity for sticking.

I found this on the race car to the point that I have shims between the Piston and Pads to keep travel to a minimum.
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petebryan
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Re: Sticking disc brakes on both sides (Cuda).

Post by petebryan »

Starting with Matt's plan then, I got my G-clamp on the piston, and (unsurprisingly) couldn't move it in at all.

I then cracked the brake line above the flexible hose (so where it meets the metal brake line), and this immediately released pressure and allowed the piston to be pushed in with the G-clamp. If I've understood the logic right, this means that the caliper and flex hose are ok, and the problem is further up the system, eg master cylinder.

I'm not sure what to do next. I've been doing some googling around this and a lot is mentioned about the adjustment of the power booster rod. I'm wondering if the garage that did my brake fluid change may have tweaked that to make the brakes a bit sharper, and overdid it (they didn't mention it and I didn't ask them to do it, but the brakes were a lot sharper after the fluid had been replaced). Though that was a while back, I've not done many miles since because of covid etc and other factors, so maybe it's been there a while getting worse.

There are some complex ways (complex for me at least) to back off that adjustable power booster rod, and one or two easier ones that seem to be just taking off the M/C bolts to expose the rod and taking it back a quiarter of a turn at a time.

Does that sound like a reasonable next step? Or are there other ideas?!

thanks again in advance!
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Pete
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Re: Sticking disc brakes on both sides (Cuda).

Post by Pete »

Yes, I think you are on your way now, and there should be free play in the Pushrod, especially when brakes are hot.

My pal tried many years ago to make his Granada brakes sharper by adjusting the rod. 10 mile later the car was locked solid with the discs smoking....
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petebryan
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Re: Sticking disc brakes on both sides (Cuda).

Post by petebryan »

I've had a bit of a re-think on my approach to this, and have decided to take the calipers apart to make sure they (and the flexible hoses) are all ok, before I start looking at more difficult areas. I've got a couple more questions I hope you can help with:

(1) Having got the calipers on the bench, it's tricky to even get the pistons out of the calipers (maybe should have done that using the brakes whilst still in the car!) so I'm starting to look for piston pulling tools - does anybody have any recommendations please?

(2) Alternatively, if anyone knew of a decent company that specialisted in servicing calipers, I might look at that option also - again, any recommendations please?

(3) I can blow through my (cleaned up!) flexible hose, but not especially easily. I can't work out if that's because of the narrow bore of the hose or if it's a sign of some restriction. I appreciate this is difficult to describe but any thoughts on how easy it should be, or any other way to test it?

Thanks again for your continued helpful input!
Cheers, Pete
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Re: Sticking disc brakes on both sides (Cuda).

Post by andyrob »

ive had this a couple of time esp when cars been sitting, ended up changing master cylinder on my new yorker & on my ramcharger put 2 new calipers on it ( even though then wernt 100 percent siezed but just kept hanging on) the calipers were peanuts off rock auto.
As also said ive have the brake flexy semi blocked stopping fluid returning
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Pete
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Re: Sticking disc brakes on both sides (Cuda).

Post by Pete »

1) Compressed air - keep your fingers well away or put wooden blocks in to stop the Pistons shooting out...

2) Buy new.

3) Buy new. Or make the lines up on AN-3 Braided Hose.

None of this stuff is particularly expensive (or good quality).
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Matt
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Re: Sticking disc brakes on both sides (Cuda).

Post by Matt »

The problem is almost certainly further up the system, as you've proven by cracking the lines open , but by all means do the calipers and flexibles whilst you're there.

Even good flexibles will be tough to blow through because of the small bore. Replacing with new standard hoses is cheap and easy and is probably worth doing whilst apart.

Caliper servicing is straightforward. (or new ones are cheap)
Remove piston , remove rubber outer dust boot, remove rubber pressure seal. Remove bleed nipple.
clean main caliper bore with fine wet& dry - say 600-800 grit.
Clean out seat recess in bore for outer dust boot with a pick, as there will be rust in there.
Piston will either be chromed steel or moulded phenolic. Replace with new if any signs of corrosion, scoring, etc
Fit new rubber pressure seal in groove, lubricating with brake fluid . It may fit in either way round but check the profile in case it should only go one way. I can't remember.
Installing the new dust boot and piston is a little tricky and requires making a simple sleeve tool . I'll post the details later.
job done.


Checking booster pushrod length:
Undo master cylinder and move clear of booster.
Using vernier calipers, measure pushrod stickout from mating surface, and then depth of master cyl recess from mating surface. Clearance when assembled should be 30-60 thou. The end of the pushrod is adjustable as seen in the image.
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petebryan
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Re: Sticking disc brakes on both sides (Cuda).

Post by petebryan »

Thanks again Andy, Matt, Pete, much appreciated.

Hadn't realised that these things were relatively cheap, though looks like there may be supply issues on the remanufactured ones - will look further into this over next few days.

At the same time, will probably also look to refurb the ones I have, particularly if it takes a while to get the stuff from the US.

Again, many thanks.
1970 Plymouth Cuda 383.
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