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Brake pedal pushes back??????

To be honest, I have never used a block to run the pistons out, although that is a good test.
But that many pumps is probably normal. Remember discs are a pressure not a volume system.
So when you press the pedal, there is only supposed to be a tiny amount of movement, but that tiny amount is supposed to be immensely strong.

Think about a 50 ton bottle jack.
Did not see the rubber problem, is the boot torn?. They are replaceable, but under normal use they are not worth doing so, because by the time they go bad, its just better to replace the whole thing.
Due to wear of the piston seals and the possibility of dirt getting in.

In this case, if they are new, and have just pulled out or got torn during checks, they might be worth reseating or replacing.

As far as a scary ride, as long as its not too high up, I'm fine. I have a problem with heights, but I have driven and ridden more miles in vehicles with no brakes than you would believe.

Also, did the piston leave a mark on the board? I would expect it to.
 
K85 Octane said:
I forgot to check pedal creep before I pulled the pads off and put a 2x4 in. I'll have to remember that.

The master has a much larger reservoir in the rear, which is my 1/2" port leading to the fronts. The rear is the forward 9/16" port and smaller rezzy.

I noticed last time the calipers were pulled. How can I fix the rubber? Also, it took close to 15-20 pumps to get the piston out this far. Does that sound right?



Click to expand...

That's not abnormal. Theres alot of volume in there.

Now bleed a few times and then push the pistons back in. Do each corner the same and see what happens. If you can watch the master at the same time you might see air come out.(I'm hoping you do)

Be careful doing this with the block of wood, I don't want you to push the piston out of the caliper and ruin the caliper.

FYI Fordum my old TBI motor with a "stock" replacement torque converter would overpower the brakes at idle with no lugging when on a hill. When ever I was on an obstacle with those brakes I had to shift to Neutral so that I could stop it. If it was steep enough I couldn't stop. It's very possible but my brake system was also very non stock too.
 
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Did the fronts and seemed fine, might have gotten a small bubble. Had to wrap some Teflon tape several time around the bleeder threads. It leaks pretty good but after the tape, zero leaks while bleeding.

Started to do the backs and the rear pistons retract with the brake pedal. They extend out and hardly push the block of wood, then release the wood completely as the pedal is lifted. It's odd though, the caliper WAS tight on the rotor and a little tough getting off.

I only have a 2lb check valve on the fronts currently. I have another one but due to the adapters I have on hand I'll need to put my adjustable prop valve back in. Lines won't connect otherwise. Here goes nothin......
 
Well, just broke the adapter. Snapped in half, plus the other one's flare looks old/used/or just really over tightened. So, if it takes a check valve, I'm SOL until Tuesday morning and only if they have the adapters :(
 
OK, the pistons retracting would cause a lot of the problems we have been seeing. You see how much it took to extend the fronts, so those pistons cannot retract much, or you get mushy pedal, too much pedal travel, lots of the things you have been seeing.

I have a suspicion you are zeroing in on the problem.

Mini, that is strange. Every standard shift I ever saw would stall an idling engine when you hit the brakes.
An auto gives you torque multiplication and is not a solid connection, so it would be more likely than a manual, but it still should stop if the brakes are good I would think.
 
Know if I need a check valve or is it something wrong? Not sure how a disc/drum master works, if this movement is normal or not.
 
If the piston is retracting a lot a check valve like you have in the front might be a good solution.
 
Yep, I'm betting you will need some kind of pressure holding valve for the rear. A lot of the time the main difference between masters built for drum and disc is the amount of pressure holding they give.
 
I'm having the same problem with my brakes after changing pads. I have 4 inches of dead travel. Then the pedal firms up and the car stops. Bled perfectly, but it just seems that the calipers are retracting more than they should be. I'm gonna try and new porportioning valve first for the disc/disc application. Then get some 2psi pressure valves and see if I can't reduce this dead travel.
 
K85 Octane said:
Know if I need a check valve or is it something wrong? Not sure how a disc/drum master works, if this movement is normal or not.
Click to expand...

To the best of my knowledge there isn't a difference between masters for disc or drums.

Residual pressure valves usually are needed in applications where the calipers are near the same height as the master. Think roadster stuff with the master below the floor.

That being said we run 2lb residual valves in the race car because the brakeman calipers have a lot of retract built into them. If that helps the issue then there isn't a real issue with using them.
 
There are differences between the two, the single most obvious, is the amount of fluid in the reservoir.
Since discs use more fluid when they wear, they need more. But, if you kept a close eye on the fluid levels, that would not be an issue since the pads wear slowly.

But the basic internal design is different between the two when it comes to disc vs drum.
Here is a link or two concerning that.

http://www.mbmbrakeboosters.com/ind...linder&catid=6:which-part-is-for-me&Itemid=14

http://www.motor.com/article.asp?article_ID=1969

But here is a part of one of the links that is pretty much to the point.
----------------------------------------------------------------------------------------------
<<A disc/drum master cylinder requires more fluid volume for the disc brake circuit, so the disc reservoir will be larger. An original disc/drum master cylinder may feature a built-in residual valve for the drum brake circuit. If a replacement disc/drum master cylinder is selected, an external residual valve may need to be added.
A disc/disc master cylinder (four-wheel-disc) features sufficient volume and stroke to provide required fluid volume to all four calipers. If a disc/drum master cylinder is used on a disc/disc system, the master cylinder will run out of stroke while trying to push fluid to the rear brakes, resulting in a long pedal travel and a spongy pedal feel. >>>

---------------------------------------------------------------------------------------------


Sound familiar?
 
Ok, so this is done. I'm not touching anything till BlazerBash. I "think" the fronts are working better but I have not had it out on the road. The pedal still feels like :poo:. Which I guess is what's going to happen according to Fordum's link.


Standing up, with about 5-6' between my eyes and the rear calipers, I can see the piston withdrawing each time the pedal is lifted up. The driver side a little more than the passenger side, but both did it. My eye sight ain't the best either. :doah:I put the valve in with an adapter from something I had laying around. It wasn't shaped the same on the inside but seems to be working. I might try picking something up on the way out of town. I also seem to have lost the 9/16" plug for the rear lines, I've looked everywhere. :doah:So I'll pick up one of those, too.

As for the style of MC, I'm sure the one I'm using isn't the best option. However, the 2003 Tahoe MC with it's factory prop valve and 4wdb set up didn't help either. Damn pedal was horrible too. So I'm flabbergasted :dunno:

The truck currently has my rollers mounted up, but still on jack stands. I'm checking over all the driveline bolts tomorrow. The storage is pretty much done for the truck. Need to get personal stuff together and I think I'm ready to roll. Only thing still in the air is the rental truck, hitch height, and trailer. :waytogo:
 
Wish I could go if for no other reason than to work on that truck. Who knows, I may make one before I die.
Not on my bucket list, because I have no intention of dieing anytime soon. Despite what I have been told.......

Be sure to post up what fixed it. NOTE: I did not say if it gets fixed. If that bunch out there can't fix it...........
Well, I will just have to scrape up the money for a flight to LA after all.

Despite all the talk about BB, I have no idea when it is. I know its real soon, but what are the dates?
 
"Starts" on Friday
I'm getting there early Wednesday morning

Take a flight to the closest airport to Moab, I'll pick ya up. Crash at the cabin :D
 
We are already here at BB14. Jason and Brent looked it over said to just eliminate everything between the master and the calipers. Bleed the crap outta the fronts and there you go.

Not goonna even mess with the rears tonight. Wade took it for a drive and locked the front 38's from 35 mph. When he got back said he was satisfied enough with just the fronts to drive it as is. Tomorrow Brent will pick up a fitting and will eliminate everything from the rear lines and we think this will end this issue.

California he front brakes work good enough now, so that you can't over power them in high range anymore.
 
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