Technical Need advice about calipers that don't release well, please

Hey guys,
When I bought my '48 Cadillac project someone had already replaced the front drums with Willwood calipers. I have just replaced the dead original master cylinder with reproduction copy from Kanter and I've been bleeding the brakes with a pneumatic tool. I think I've got all of the old fluid out because clean fluid is pulling through the lines now, and I'm beginning to get some pressure at the brake pedal. My problem is this: when I get a little pressure at the pedal and then release it, the Willwood calipers are still grabbing the discs making the rotors almost impossible to turn by hand. However, when I come back an hour later, they spin more freely but not perfect. My first thought is to disassemble the calipers and give every appropriate piece a coat of moly lube, but to me that doesn't explain why the discs spin more freely after an hour of sitting. Any ideas fellas?

 

PS: I did upgrade those puny jack stands since the first photo.

 

How do your brake lines look? No kinks or old rubber lines left.

 

Might want to check your rubber brake lines. If they are old they will tend to collapse. This will cause the caliper to retain fluid pressure. It sounds like that’s what I’d happenin.

 

Have you got free play between the pedal and the master cylinder? If you don’t the brakes won’t release.

 

Does the Kanter MC have residual pressure valve in it?

Caliper pistons only have square seals to aid in returning to at rest state. No return springs like drums.

 

From what I can tell the rubber lines to the calipers were replaced when the Willwoods were installed. They appear to have braided steel sheathing, with a clear plastic coating. Thanks for the suggestion.

 

That's a really good idea. It seems like the pedal has lots of free play but that could be only because I don't have enough pressure to make it firm. But it is possible that enough pressure is being sent to the caliper pistons to create this scenario. I imagine the Willwoods are pretty intense. Thanks, I'll try that.

 

Good point. I doubt the reproduction original style MC has any kind of residual pressure valve. Hopefully I can get the Willwoods to cooperate with this setup.

 

If it is a reproduction master cylinder of a stock one, it should have a residual valve built into it. It looks like a round piece of metal with holes in it with a rubber flap which can be taken out of the master cylinder. I imagine it's keeping pressure on the brakes that aren't drumming anymore.

 

Do you have any idea why the calipers seem to loosen up their grip after an hour of sitting? Would this possibly happen with the scenario you described? Thank you for your advice.

 

Look like 4pot calipers, 8 pistons total. Each piston seal will try to roll back and return the pistons. If there is a residual valve the seals eventually overcome the valve and self release.

 

After you've pumped them up , crack open the line @the caliper , if it releases , it's most likely not the caliper , next try opening the line at the m/c , if it releases it's the line , if not it's the m/c .Cave man diagnostics .

 

If the Kanter MC does have a residual valve, that will need to be removed, but a residual valve for the rear brakes may need to be installed at the rear line for correct operation.

 

This ^^^

 

This is very common. If the master cyl doesn't retract completely the fluid return hole will remain blocked and the brakes won't release until the pressurized fluid seeps back.

 

Thank you sir. Would you suggest that this rubber flap be removed to see if that takes care of the problem? Was it designed to be taken out if needed to function with a differing setup?

 

Great to know, thanks! You guys are the best.

 

Here’s a generic video, OT car, and some ad bs first, but only a couple minutes. To remove residual valve.

 

For the love of god DO NOT put moly lube anywhere near those calipers

 

Does the car have a power brake booster?

 

I had a problem with my Wilwood calipers when I came to replace the pads after about 20 years and 60k miles including a trip on the Boneville salt. I couldn't get the pistons to retract. Of the 8 in total at least 4 were seized solid. Had a devil of a job getting them out but succeeded without damaging anything, using hydraulic pressure and a variety of wood blocks and g clamps, so I could do one at a time. The stuck ones were really dirty with something. They're only formed stainless sheetmetal. Ran them in the lathe and cleaned with fine scotchbrite. Reinstalled with rubber brake grease. All worked perfectly thereafter, with a phenomenal improvement in braking that had simply slipped away over time. Root of the problem is the racing calipers not having dust seals / bellows. Racers presumably disassemble in the closed season. Great news was the stainless piston, unlike the usual rusty chromed finish! I replaced the seals for good measure ( I think I did!). I note Wilwood offer calipers with seals these days!

Can't say they were hanging up but so few pistons were operative I perhaps couldn't have noticed! Can't do any harm to strip them and check.

Chris

 

Ok, thanks. I was only going to put it on any pins that the pads slide on, or other such parts. I'd be sure to keep it well away from pad surfaces. I thought it was common practice to put some kind of anti-seize on parts like that.

 

It does not.

 

Good idea, thank you.

 

How long has the system been installed, and how long has it been sitting with brake fluid in it?

 

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Here is a basic picture of a rebuild kit. It is the littl e hexagon piece with the holes in it. And it has a rubber flap that keeps 10PSI on the drum brakes. If you take it out, I'm sure the brakes will be fine but you may need a residual valve for the rear.

 

Some calipers that travel on rails (70's ford products) it was common practice to lubricate the ways . Pin type mounts generally have rubber "o rings" in the caliper ears so theirs no need for lubrication.

 

It was installed about 2-3 years ago I estimate from the seller, then it sat for over a year when the brakes failed on him one day. The original-type reproduction master cylinder is brand new installed this week, and fresh fluid has been pulled through the lines.