brake rant

Yeah, I been resisting a lot of things for a great many years. 20 years ago one of the "Jeep Guys" in the town I was living in told me to give up on my 47 cj2a that I had just bought and part it out even after I bought parts from him. I just smiled and fixed it all and then drove it to his shop. I have a great deal of strength in my legs, Thats not the issue. The real problem is that this master cylinder is new and will not hold pressure over night or during braking. It should provide adequate pressure and certainly keep pressure overnight. My remedy suggested by Daryl is to use a MANUAL 4 wheel DISK brake master cylinder from a 1968 corvette. If that does not work for me I will either go hydroboost or vacuum.

 

I see you wired in a switch that does not rely on brake pressure. The offset pedal you made, do they deflect a lot under hard braking? your solution may be mine as well. Thank you for the pics.

 

I am having some issues and have been having my daughter help me with bleeding. I noticed the entire unit moves a bit under braking pressure. I may need to make a thicker mounting plate eventually but so far it has been working well.

 

Chris.............Swing Pedals.........

Probably don't need a thicker plate.........just a brace in the right place

 

Tarry, you're probably right. I should have put in swinging pedals to begin with. I could have easily just installed a vacuum assist brake system. I just honestly don't really want to do it all right now. I just want to drive it around for a while before I tear into it again.

 

I have the same issue. I have had my 11 year old son bleed brakes almost a dozen times. I got speed bleeders and put them in all 4 corners. Still make him help me.

my herm copy i made moves a bit too. not much though.

 

While I agree swinging pedals are a great upgrade, the through floor pedals can work fine. "a little movement" of the brake m/c bracket is too much. Fix that first then move on to the next issue.

 

A little movement is 1/8 inch at the end of the master. When I get my new vette master I am sure I will need to do some fabricating and maybe I will make a new stronger much better engineered bracket to bolt the master to the frame and brake pedal/clutch tube assembly. The outlets will face the frame. Whatever, as long as it works right.

 

I don't know if you are heading in the right direction in trying to cure your brake problem. The new master cylinder that you are intending to use has a larger bore than the one you presently have in the jeep. Although if your master cylinder has an internal leak the new one will probably cure that problem, with the larger bore it is going to create a problem in the mechanical ratio between master cylinder and wheel cylinders (review tarry99's comments).

If I were you, before I would proceed any further, I would review billaVista.com tech article The Brake Bible. I believe it is a good read which will help you overcome the problems that you are now experiencing.

http://www.billavista.com/tech/Articles/Brake_Bible/index.html

 

There are 2 different part numbers for 1968 corvette master cylinders. one for power and one for manual. the manual one has a 1"bore, the power one is 1 1/8. I bought the manual one and that has the same ID bore as the 1970 cj5 master I am presently struggling with. So just to be clear, I am NOT going with a larger ID bore master. Both of those corvette part numbers are used with 4 wheel disk brakes and are the master cylinders that I commonly see being used in aftermarket brake upgrade kits such as what "The jeep Guy"offers. I am going with Daryls advice. I am pretty sure he has done this a couple times, you may know him..... Ask him why he would steer me the wrong way.

My present master and the previous one are both 1970 replacement masters with the 1" bore, both new from 2 different suppliers. neither would hold pressure over night and neither would give satisfactory braking performance. They both would stop my jeep just fine, I just want it to work properly.

 

I am glad you are using the m/c with the 1" bore. The one I looked up was shown as 1.125". I still believe it would be a few minutes well spent to review the article I mentioned. There is a lot of good data there.

 

i will do that right this very moment

 

so, I either have flex in the brake lever, caliper mounting plate, ballooning flex lines, internal leak in master, bad residual valve, too small of M/C piston diameter or pedal ratio too high. could be other stuff too.

one thing we can disregard is the mounting brackets, disk size and calipers. they are from blazers and pickups that weigh twice the weight of a jeep. The brake lines are all new.

The residual valves are made mostly of garbage, the mounting bracket for the M/C could be made from 1/4 plate instead of 3/16 and I might be able to do something with the pedal ratio. I have been looking at the vanco hydroboost setup, but 650 bucks s to much money for me and it also is a complex mess of stuff that i really don't want to have to get into when i can just go cherokee vacuum brakes for a faction of the work and money. In theory...

I am going to install this vette master, rework the mounting bracket and see what i can do about pedal ratio. when that fails, and it probably will, i will just install cherokee vacuum assist and when that fails, crash into a tree and burn the remains.

 

Chris..............The facts are this:..................good braking systems are not just haphazardly put together.............The components are sized and once put together they produce a system that does it's job.................all of the Items that have been discussed all need to complement each other in order to get a decent brake package. That article from Pirate is spot on in it's approach...........but that's really old news and nothing new, just more clearly explained. I learned all of that years ago from techs in the brake business that clearly understood there products and how to trouble shoot them.

The most common problem with peoples junk yard Jeep swap systems can be traced to pedal ratio and then master cylinder sizing...........The ratio is easy.......about 4-5:1 for power and about 6:1 for Manual..............but that all still depends on many other things like, how much fluid volume your pushing.........which begs to ask the question how big are the pistons in total volume in the front and rear calipers? How heavy is the vehicle? , How big are the tires? How much Brake torque is required to stop this vehicle? Once a few basics are clearly understood then and only then can you size the system correctly.

As I mentioned before you need increased mechanical or power advantage , about 1200 psi to get a disc system to stop.......sure you can get lucky and have smaller volume calipers and a better ratio at the pedal along with the correct sized MC and 31" tires and it will work just fine................but we all know that no two jeeps are the same in components.

Your bleed back in your system is probably from the fact that your Master Cylinder is lower than your Calipers.....not knowing how its plumbed it could be your residual valves, could be your proportioning valve or even the Master............Some new Proportioning valves already have residual valves pre-installed as will as modern Master cylinders may also have them internal.

I know you have a 1" MC and that should be fine........if you want to supply me with the piston sizes in your Calipers along with the pedal ratio...........I'll run that through the Excel program and see if your generating enough force..............

 

I think you are on the right path. My buddies '69 CJ5 has been a BATTLE with brakes. My 40's and 50's stuff is easy to work on and works the first time. The complicated dual chamber setup (relatively speaking as I have no issues with my 60's and 70's GM vehicles which use pretty much the same parts.) seems to have a RIDICULOUSLY high failure rate with brand new master cylinders. I think his is on the 4th?! And it's acting up again. Exactly like yours. Bleeds great, no air. But you've got to pump it. And it bleeds down overnight. Everything suggests the master is bad.

So I follow along interested in your outcome.

 

:lurk:

 

My new corvette 1968 manual 4 wheel disk master cylinder has a 3/4 stoke and a 1" bore. This is the same as my 1970 cj5 master cylinder that has given me trouble. The physical size is much different though.


When taking out the cj5 master I noticed that the push rod was not perfectly aligned to the master. It DID allow full travel though. I also noticed that the whole pedal / tube thing is pretty wore out. I do not use the tang on the tube for the clutch, I use a cable, so i don't need a woodruff key cut into the new solid shaft I am making out of a hard chromed hydraulic ram. I am also going to make a new mount for the new master out of 3/8 plate. I am trying get all the flex and play out that i can without going insane. If i get too anal about it I will just go to swinging pedals and vacuum assist. This will take me a day or so I think. New design does not need the shaft to turn at all, just pedal arms to rotate around the shaft. Still will be some play, but I will try and minimize it. I like the retro through the floor look. I'm going to try and keep it.

 

I needed to bore a 1 1/2 hole for the master to fit through. I have owned a tool for 3 years that I have never used other than to check operation. Its a 75 or so year old camel back drill with functional power down feed. Its the only thing I have that will turn the morse taper drills that i have. Belt driven with a transmission to go below 15 RPM.


I set the down feed and kept the oil on it. Slow turning drill, big metal chips all curled up... so cool to use a really old tool.

 

I tacked up the new master mount. The old one I made a couple years ago is far more crude than the new one. The new one is made of 3/8 plate with 3/16 gussets. It will have another gusset at the top.

The .997 hydraulic shaft that i found new in a pile of scrap has grooves I machined in on both ends for snap rings. It fits the stock mount and goes through the new support attached to the master mount. The round section was welded to the ram, I cut it off, milled a flat and tacked it to the support arm.


Gonna finish weld the mount in a bit.

 

not pro quality but its Ok for me.