Disk brake problem!

The dana 30 is in and the brakes have been bled, the rear drums bled easy,the disk's up front seemed ok but when I was done (at least I think I'm done) they had no holding power.
I have the stock 71 master cylinder (dual reservoir) with the 2lb residual valve from Wilwood in line. I might have expected less than stellar performance but not no holding power, heck they just barely rub the disk good when the pedal is pushed and the wheel is off the ground. Any suggestions, don't just jump to conclusion about the master cylinder being to small as this is a NAPA replacent for the original, not the factory original type. Others have run it fine, are the disks that much harder to bleed, could there still be air in the system that I haven't gotten out, do I need to close the bleed screw while the pedal is still being slightly pushed, to in effect keep a small amount of load for adjustment on them, the cup is moving just not far enough. The lines are 3/16" all around, and new, all hoses are new also. The rear reservoir is however larger then the front by about 15% or so.

 

Sparky I was talking about the physical rear reservoir on my master cylinder, it has always been tied to my my back brakes and the front one was always hooked to the front brakes, a previous owner did this and I have just never paid it any attention until you posted what you said, I feel like an idiot now for not noticeing this, when I replaced the master cylinder about 8-9 years ago I just didn't notice and moved the lines over from the old to the new and never paid attention.

 

The calipers hold more fluid, so they need to be fed from the bigger reservoir. If you look at stock setups with unequal sizes you will see the bigger feeding the discs.

I take it they are the stock disc brakes. I'm sure you know that if you have a custom setup and the bleeder scres are not at the highest point you may never get all the air out. You may have to remove them, put a board between them and hold them so the bleeder screw is at top and bleed that way. Stock setup this should not be an issue.

Calipers have a very small movement. That is why the pads run so close to the disc. I assume you pumped them hard several times to "adjust" them to the disc. The first couple pumps after a pad change will get zero brake action until the pads seat against the rotor, then you should get good brakes.

If all else fails maybe try a slightly higher residual valve (5?) seems like I recall 2-5 being the "theory" recommended amount when I went to school a million years ago. I would especially recommend this route if the pads are retracting ANY noticeable amount away from the rotor after lifting the foot off the brake pedal. The tension of the O-ring seal in the caliper is what does the job of retracting springs on rear brakes, pulling the caliper and therefore the pads away from the rotor when releasing the brakes. This is the resistance the residual valve must overcome to keep the pads in contact with the rotor and ensure good brake response.

Keep us posted!

 

Mike, take a look and make sure you don't have the calipers on the wrong side.

I have the dana 30 with discs and the NAPA dual master cylinder. It works well. I had trouble bleading the brake calipers. Worked on it for a longgggggg time and finally had to get a friend over to help. After rebuilding the master cylinder, then replacing the master cylinder, then going through each brake line taking them apart at the joints etc. etc. my friend finally noticed that I have two left brake calipers. Air was trapped in the right side caliper. Took it off and held it in the correct position and the air came right out - no problem. If you do this put something in between the brake pads to keep them from going too far. Dang, I think I went through 3 quarts of brake fluid fooling around with this.

Having the little vacuum pump with the hose and cup helps a little. Can't remember the name of it but pretty cheap at NAPA.

 

Went and got them (for the disks), those things are the cats a$$$$
I have the brake lines hooked up right this time and they work great.
Thanks for mentioning that Sparky as I might have overlooked that if you hadn't mentioned it.

Impossible, I marked them when I took them off to rebuild the axle, besides I later found out they are cast L & R on the sides of the calipers.

 

Lynn when you buy the RPV's they are even marked on the package as to what they are for.

 

your master cylinder may not be displacing enough fluid for the new set up? If your back brakes are adjusted properly and your front pads are fully seated, no air in the system, sufficient stroke on the MC pushrod, etc then you may just not be displacing enough fluid. Just a thought.......Or, are you using a disc/drum MC? if so then never mind my post good luck

 

I finally got to drive my Jeep today, it was a good feeling, the steering is very light, haven't driven it over 35mph so we'll see later. My brakes stop decent but I can't lock them up either, I can start to make the tires squeal but thats about it. I have alot of pedal and I have to push the pedal pretty good, is this normal for the manual disk brakes. The brakes stop straight and even and they will rock the Jeep on the suspension pretty good, I guess part of this is not driving it in so long and having so many changes at once I might be, being a little over paranoid.

Your opinions please, I have the stock 71 dual reservoir M/C, its a NAPA replacement rather.

 

Mike, my disk/drum combo stops just fine. I'd say that I have about an 1-2" of pedal before it gets hard. Normally not much pressure is needed to start to slow down. If I jam on it hard then the rears lock up.

I think most of it is not driving it for so long...takes some getting used to for sure

 

Mike, without re-reading everything, were the rotors turned and new pads?
if so, they will have to "seat" in; the more you drive the better they should stop.
might even want to "ride " the brakes a little bit

 

Everything was new, I got the axle out of a friend of mines 77 cj5, and rebuilt the whole thing. It only had 43k on it to start with.