Howdy

I think I got a handle on this but I dunno it’s always helpful to get another opinion. I haven’t gotten to the bottom of it and I already started throwing $ at the problem.

My bigblock 54 dodge pickup is sitting on a dakota front subframe. Brake wise everything is new from the banjo bolts up- hoses, lines, master. The donor truck had been sitting a year or so but was a runner and had decent looking pads loaded in with a lot of meat on them and the rotors/hubs had a little surface rust but freshly packed bearings with clean grease under the caps. So I didn’t have anything to lose by trying to run them.

Well now a year later I finally got the truck running and both front calipers are sticking applied after using them. I tried loosening the m/c from the booster to see if I had the booster pushrod adjusted out too far not letting the m/c piston return- no dice.

I went to a pepboys that said they had my calipers but when I got under the car I found they sold me two different wrong ones!

I threw new pads on the old calipers hoping that if the caliper pistons were worked in then out again they might free up. No luck there either but they did move in ok with not too much effort on a c clamp. I cracked a bleeder and it didn’t squirt like I would expect if it had a bunch of pressure trapped in there.

So I ordered a new set of calipers off rockauto but I have a nagging feeling it would have to be a bad master cylinder since both sides are doing it? It’s a corvette style master with a line for each front brake right off the master and an adjustable prop valve in the rear line so no factory prop valve to go bad. I don’t mind having new calipers to install but both calipers sticking is fishy.

Any ideas or comments?
Thanks!
Radar

Do the brakes stay locked up or is it just a matter of them dragging a little? All disk brakes drag a bit.

I mean the 512/2500 stall pushes them just fine but I could smell thrm after driving a mile and they’re pretty tight

having done all the typical isolating moves (loosening M/C, cracking bleeders) to verify it's not a hydraulic pressure issue I doubt it is the M/C.

Though I was never a fan of those generic fits all booster setups based on the vette M/C. They tend to be problematic but usually the problem is not enough brakes, not brakes all the time.

Did you clean and lube the rails the calipers ride on? Are there any worn spots in the guide ways that could be hanging them up? there was a thread on that the other day, with pics.

Found it

It could be rust in the bores of the calipers not letting the pistons come back any, I suppose you could look at that.

Is there a pushrod adjustment on the m/c side?

Ran into this once on a Magnum, switched out the booster and the pushrod was way longer than the original, but did cause my calipers to not drag at first, but got worse as I drove.

Something to consider?

I have seen a lot of sticking calipers on the Dakotas. Just changed a pair out last month. Because they are such a problem, I usually get them from a salvage yard after looking at them and determining they are not OE. Those things are expensive and RA shipping is outrageous and then you have the core charges and return shipping.

A quick check to see if it is the caliper or the hose or master is to crack the bleeder. If it is the caliper, it won't help. The brake will still be tight. But if it is the hose or master, then the brake should release. If it seems to be the hose or master, press the brake pedal a few times to get the brake to stick and then you can then go to the brake line off the master and do the same thing to determine if it is the hose or master.

I agree with Dave on sticking calipars.My 99 Durango had no problems.I did frt pads and rotors at work.Drove off all perfect.ASfter about 15 miles one locked and smoking.Back top work replace the left as right was fine.New pads and rotor on that side.Left again and after about the same mileage same thing.Cussed myself out as I should have replaced both like I always do but was short on time.After all new drove it for 2 years and my son ghad it for 4.Still going great as his friend bought it.Rocky

Yeah I ordered calipers already because they are the only thing new. The vette deal was for small diameter dual booster availability plus I don’t mind not hunting down mopar size fittings either. If the calipers dont fix it I’ll do a new mc

Solved my caliper problem. The rubber brake lines were collapsing. Under pressure when the brakes applied then collapsed when the peddle is released. The caliper stayed under pressure until the brake was applied again. I was told that some caliper pistons are made of a ceramic material.

He's already stated in the very first post that he both loosened the master cylinder from the booster to make sure it's not a push rod length issue and that he's done the crack the bleeder test to verify no hydraulic pressure remains.

This pretty much eliminates the hoses, the master cylinder, the pushrod, the booster, the lines, the combination valve, the hoses, etc.

Well I came this far a whole year of 15-20+ hrs on it a week. I can afford to throw $150 and a 1/2 day at it.

I’ll let yas know how it works out 👍

Thanks!

i may be full of sh.. , er, malarkey, [probably more the former than the latter] but i believe the GM masters use the front bowl for the front brakes, and the rear bowl for the rears. that is exactly opposite from the way ma mopar plumbs ours, so there "may" be one of those rubber things behind the tube seat in the rear port, allowing 10lbs or so residual pressure to remain, which wouldn't be much of a spurt cracking the bleeder.
i ran into this once before using a GM based kit, so ?? just something you may want to check out, i suppose.

stick a drill bit into the brass cones & if it has the RPV you will feel it as it is just a piece of neoprene and a spring then pull the brass cone (the hard part) to R&R it.

I believe I ordered a disc/disc master when I got the one that’s in there now. I made a bracket and run an aftermarket knob style proportioning valve. The MC has four outputs. The inboard side is plugged. The front port goes to the front of the prop valve block which splits it to my hard lines which go to the front hoses. The rear port goes to the valved section of the prop valve, then straight down the frame rail to the rear hose.

I do know that chevys don’t run the rear brakes off the front of the MC like our cars do. Good thinking to check for a drum residual valve in the port though- thanks!

I’m stuck home today waiting for AC mechanics to finish up. My email says the new dorman chevy style disc/disc 1.125” bore master should be coming on the brown truck today from summit along with some raybestos remanned calipers. I have new pads in the old calipers with about 1.5 miles on them to swap into the new calipers.

I am planning to bench bleed the MC of course. I will peek in the ports and see what’s in there first looking for drum residual valves but I don’t really know what I’m looking for. As far as I know the difference between a drum and a disc section is the valve in the port and also the increased volume in the reservoir for caliper piston displacement? The old MC had disc/disc reservoirs too.

I also plan to air check the splitter in the prop valve with a rubber tip air nozzle to make sure it is open and not restricted. Other than that I’m not usually into throwing a bunch of money and replacement parts at a problem but I’d rather buy calipers and a MC and only have to re-bleed all my brakes the one time than do it twice.

Fingers crossed!

I got a chance to replace the master and front calipers this morning. I gravity bled them some but didn’t get a good pedal yet.

My new working theory of the previous problem is contaminated fluid. I’m thinking if there was some water in there it could have been making steam pockets when hot? Although usually that would make a spongy pedal afterward right? Or possibly sucked some gunk up that was blocking something like a 1 way valve?

When I opened the old mc to suck out most of the fluid the front was brown and the rear was still clear/yellow. Seems like a clue. When I swapped the calipers I left the hoses open until they ran clear fluid.

I also made a rod with a concave end to go inside my new m/c which is hollow inside the back like a manual brake setup. It has a little too much play- maybe I’ll make a longer rod or extend the booster rod adjustment or both. It could be my pedal is already ok I just need the travel I’m missing to build pressure. Gotta get another jug of dot 3 and a couple hours to finish the job.