Thread: Brake troubles

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Originally Posted by Hotrod46

As I said earlier, I have the Explorer brake setup on my 46. Brakes work fine and the parking/emergency brake will hold the car in gear (NSRA Safety 23 test).

What master cly. are you using the Explorer one ? Thanks

Originally Posted by Navy7797

I removed the brake pad from piston side and moved the E-arm 3/8 to 7/16" dozens of times and no piston advancement, moved out but right back in when arm was released .

Navy, a little confusing here, you said no piston advancement but then it moved out and back in? Just trying to figure out if its "#2 - The sprag will seize on the inside of the piston and will never work again" or what. I still say swap a front & rear caliper which would check your master cylinder as well as valving, about 15-20 minutes should tell something then. Just really curious at this point.

Just curious, have you talked to the manufacturer?

Originally Posted by Navy7797

What master cly. are you using the Explorer one ? Thanks

I'm running the Corvette style 1" bore with a booster. A very common street rod part.

Originally Posted by Matthyj

Navy, a little confusing here, you said no piston advancement but then it moved out and back in? Just trying to figure out if its "#2 - The sprag will seize on the inside of the piston and will never work again" or what. I still say swap a front & rear caliper which would check your master cylinder as well as valving, about 15-20 minutes should tell something then. Just really curious at this point.

I thought that might be confusing. When the e-brake is applied it pushes the piston out but retracts without adjusting the brake when released. The sprag seems to only work with a full throw of the e-arm on the caliper, that can only happen when the caliper is off the rotor or a pad is removed.

Originally Posted by Hotrod46

I'm running the Corvette style 1" bore with a booster. A very common street rod part.

I'm running a Corvette MC with 1 1/8" bore. 8" dual diaphragm booster. So I guess I have that part right.

Originally Posted by 36 sedan

Just curious, have you talked to the manufacturer?

No I haven't, I have no idea who made them they came in a kit from Speedway. Haven't talked to Speedway either just short on time during the day.

navy------don't you have a quick change rear end in that car??? Those brakes are for c clip type axles only and your q change isn't that type rear- the clip axles can move in or out a little so calipers can squeese disc evenly-with your set up they can't do that

Originally Posted by jerry clayton

navy------don't you have a quick change rear end in that car??? Those brakes are for c clip type axles only and your q change isn't that type rear- the clip axles can move in or out a little so calipers can squeese disc evenly-with your set up they can't do that

That's a new one on me. I've never heard that there are calipers that require the rotor to "float" between the pads in order to work right. Can you explain and give examples?

Roger--those type calipers were designed for rear ends that happened to have "C Clip " axle retainers. Those axles could move in and out a slight amount. Brake calipers are critical to mounting and rotor thickness. It amounts to a stacking of the tolerances. If a floating caliper(only hydraulicly pushes from one side to squeese the rotor) isn't mounted on an rear end that has the correct axle flange to housing deminsion, designed spec thickness of rotor and/or pads, it will not function as designed. Add in an function like a parking brake that mechanically is applied vs the hydraulic function and is adjusted with a sprag ratcheting device that might not be installed correctly---like reversed sides of vehicle, upside down, backwards, etc-----

Remember that back in the 60s when self adjusting brakes came out that they were adjusted when brakes were applied while backing up. That line of engineering was applied to the early rear disk brake vehicles ( not necessarily the reverse thingie but the application of the parking brake EVERY time you parked was an element of the design/thinking.

I think Navy should replace the calipers to single purpose ones like most things use and add an electric hydraulic park valve to meet regulations. I'd suggest a disc on the pinion yoke but I think he has a quick change rear and the bottom shaft would not have enough ground clearance. A transmission output shaft brake would work best.

Oh and examples are the front wheel drive GM cars are what I think these calipers were designed for and then they got added to other rear wheel drive models for a while .Probably others also but I don't have time to cross referance all the part numbers

Navy, I don't disagree that you're not going to end up changing calipers, but I don't see it being tied to the fact that your axles are not c-clip. I believe that disc brake calipers are by design self-centering on the rotor, whether they are fixed (opposing piston) or sliding (one piston). You've got a lot of folks scratching their heads on this one, and I'd try Matt's caliper swap idea, just for grins.

Navy, I'm not convinced that you don't have a problem with the sprag assembly. Reading the instructions that Matt provided one thing that jumped out at me was their caution to never buy re-manufactured calipers, because the #1 failure of them is that the piston/sprag assembly was not used and froze up, rendering the caliper assembly/piston pretty much useless. Second is that you've said that when you pull the e-brake lever on the caliper the piston moves out, but the returns to the original position. Third is that you've said that your brake package came from Speedway, not from Master Power Brakes directly, and I'm wondering if Speedway may source their calipers from a re-builder rather than supplying brand new hardware.

It seems to me that the key to your problem is the sprag assembly in the rear caliper pistons. When you unhook the e-brake cable and pull the lever full travel it should ratchet out the sprag assembly and lock in a new position, ready for the next advance with the lever until it squeezes the rotor before grabbing the next tooth. To start I'd swap the front calipers to the back like Matt suggested, which should confirm MC operation. Assuming the MC checks out and the rear brakes work with the single purpose front calipers we would know that the problem is internal to the rear caliper. At that point I'd be confirming the operation of the sprag clutch assembly, or maybe buying a pair of new calipers from Master Power Brakes, but first I'd call MPB to see if they have any ideas. They seem to be pretty well versed in these "unique" GM rear calipers.

The other option is to buy a pair of single purpose calipers for the rear, and do something else for your e-brake function like someone else suggested earlier. Best luck chasing the gremlin, and thanks for your continued posting even when it's so frustrating.

I'll echo Mr.Spears, the sprag (I believe) should prevent the piston from returning to it's original position, when it does - you've lost any adjustment of "play".

a note for easy switching of front/rear calipers------just switch the lines at the master, you don't need to move the calipers-then see if the fronts react correctly!! saves a lot of time and effort.

Sprags-----if calipers are on wrong side of car????????

And----If during the assembly/rebuilding of the sprag cored calipers------if the sprag was installed backwards it won't work-----same deal if rollers are loaded with rust/crud

Oh the HORROR of it ! Well testing went on today with a change to a 1" bore Master Cyl. from the 1.125 cyl. that helped but did not stop the wheels. I attempted to swap calipers front to rear but there just wasn't enough fittings in the shop to make that happen. One thing did happen today was that the pads are staying right against the rotor after the e-brake is released, before they moved off .015 to .020". don't know what changed there. I bought a pressure gauge tonight on the way home and will see what kind of pressure is at the back end tomorrow .
I talked to Speedway Tech guy about the brakes and he had no idea if the calipers were new or rebuilt. He also had no idea of what the trouble was. He did tell I should have 900 to 1000 PSI at the caliper.
My axles don't move in or out at all. the bearing is pressed on to the axle and then retained via a plate and 4 3/8" bolts into the axle housing. Winters use's Ford Big Bearing style housing ends on this rear.
My calipers float on the pin/bolts with the bushings and the rubber o-rings. There's no issue with the calipers centering on the rotor.

Thanks for all the inputs, we'll figure this out soon er or later.