creative brake system.

[IOPort51]

does anybody have any experience with putting a power booster on a manual brake master cylinder?? I would like to have a MC with the same size cylinder , front and back, and power boost. So the drum drum MC used in 1977 mounted on the power boost used that same year. Problem being the drum drum did not have the power option, as far an I can tell.

I know the flange is shaped differently but I think I could overcome that as long as the master cylinder was not going to blow a seal or the discs were not going to lock up with the slightest touch.

I may start by trying the drum drum, with the residuals removed, and see if that gives a positive result.:dunno:

 

[tinhorn]

Are you sure you want to do this? If I'm not mistaken, power brakes are necessary for disc brakes because of the smaller contact area, and the increased pedal pressure required. (The smaller swept area is also what keeps them from overheating as drums are prone to do.)

Power boosting a drum/drum system seems to be inviting lockup. But if I'm missing something I'm never too old to learn something new!

 

[mtnwhlr]

My '68 Charger had drum brakes that were power from the factory so I don't see it being a problem.

 

[BC CJ]

My 75 has drum-drum with power brakes. I am not 100 percent sure if it's factory... but they work pretty well.

In the Standard Catalog of Jeep they list power brakes as an option for 75 and disc brakes weren't on offer yet. So Drum-drum with power should be fine. Only question is weather your MC is compatable with a power system. I think it will be fine; internal functioning of the MC is the same just some added push... not much different than someone with beefy legs pushing the peddle

 

[Tinman22]

We have two 7s with manual disc front brakes hmmmm.

 

[IOPort51]

What I think I have learned:

power master cylinders, generally, have a larger piston than manual master cylinders.
they also have a shallow hole at the end of the piston where the manual has a deeper hole to hold the rod coming from the peddle.

The manual master cylinder is quite capable of being put on a brake booster, it won't explode from the increase pressure or anything like that. you will have to do something to adapt to the deeper hole in the end of the piston. I think this could give you a serious increase in braking force at the caliper/drum over the power master cylinder.

Disk brake caliper pistons require a lot more fluid to be pumped that drums do. the caliper cylinder pistons are as large as 2" diameter where drum cylinders are half that, give or take a bit. In order to deal with the larger disk pistons the master cylinder reservoir is larger. Things do get a bit confusing at this point when dealing with drum/disk systems as I don't know if the disks get more fluid because the proportioning valve is doing something. I don't think the average disk/drum master has two different size pistons and the stroke is the same. every answer leads to another question.

As for me, the problem is getting the full use of four wheel disks. with the disk/drum master I have now I don't think I am getting all the stopping I should have. A disk/disk master would be the answer, I think. The possibilities are a bit Limited but the 70s Corvette looks promising. I am going to start with a manual master cylinder and see if it will fit, I think it will, and if getting equal fluid to all four wheels will make things the way I think they should be.

The only dark cloud I see on the horizon is the increased stroke of the disk/disk master and if the CJ has enough peddle travel to deal with it.


this is just hours and hours of entertainment.

 

[mtnwhlr]

 

[Old Dog]

Jeeps mods so much fun

 

[Old Dog]

As a side note see this link to get really confused. There really is lots of good info here. Pirate4x4.Com - The largest off roading and 4x4 website in the world.

 

[IOPort51]

Dog, you made my day!! That should keep me in the state of confusion for three or four days. thanks!:rock:

 

[IOPort51]

can anyone tell me what the CJs peddle ratio is? I am thinking between 7 and 8 to one but it is a bit difficult to measure up under the dash.

 

[IOPort51]

thanks again Old Dog, that pirate site was well worth reading. The manual Corvette MC would have had the pressure I wanted but not the volume I think I should have. but the power MC will make the volume I want but I will have to use the booster to tie the whole thing together. The CJ has a pretty big caliper cylinder in the front, 3.1 inches. That takes a lot of brake fluid to make it move. The front of the 85 Cadillac Eldorado I took the rear calipers from were just 2.4", that was a pretty big car.

If my initial calculations are correct, and I think they are at least pretty close, it takes 4 or 5ooo foot pounds of torgue to stop a CJ. This is at the center of the pad radius, keep this in mind when choosing rear caliper brackets.

 

[tarry99]

thanks again Old Dog, that pirate site was well worth reading. The manual Corvette MC would have had the pressure I wanted but not the volume I think I should have. but the power MC will make the volume I want but I will have to use the booster to tie the whole thing together. The CJ has a pretty big caliper cylinder in the front, 3.1 inches. That takes a lot of brake fluid to make it move. The front of the 85 Cadillac Eldorado I took the rear calipers from were just 2.4", that was a pretty big car.

If my initial calculations are correct, and I think they are at least pretty close, it takes 4 or 5ooo foot pounds of torgue to stop a CJ. This is at the center of the pad radius, keep this in mind when choosing rear caliper brackets.

IO,

Your standard swing pedals in your Jeep have a 16.5" length from the fulcrum point to the foot touch pad. The normal offset for Manual brakes from the fulcrum to the push rod attachment point is 2.5" which equals 6.6:1 ratio and on the Power that same point is 1" lower which lessons the ratio to 4.7:1 ratio
(normal text book ratios are 6:1 and 4:1)

Normally you need a larger volume and longer stroke MC for Disc/Disc applications.

The Master that I use is a MC1321H which is a basic GM style just like the Corvette version..........has a 1" bore and can go either power or manual with an adapter that normally ships with it. It has ports on both sides which are 9/16"&1/2............this master normally ships without any residual pressure valve. The correct Proportioning valve will take care of that.

Use a dual 8" in booster.........there good for tire sizes up to 36" and in high altitude they recover more quickly than a single diaphragm.

The trick will be if you now have manual brakes or not when adding the booster the offset to the rod to change the ratio will be 1" off meaning the location of the mounting holes has to change at the firewall..............or sometimes the use of an offset adapter which I know you have seen these which are basically a linkage looking adapter which moves the unit 3" or so farther away from the firewall and at the same time reduces the ratio........sounds confusing but it really is not.............the only problem with using the adapter is that it pushes out the master & booster farther into the engine compartment and makes it heavy on that weak CJ firewall..........I normally re-drill the firewall and not use it unless it can not be helped then I add a brace to support the weight of the MC & Booster. PM if you have any questions and I'll try and help!

 

[IOPort51]

thanks Terry

I figured it to be between 6 and 7. Not bad for measuring in braille.

do you have a part number for the booster? I have the Jeep power adapter but the Corvette booster will require some creative engineering to adapt the input end to the lever on the adapter. the jeep is an eye and the Chevy is threaded, I think a bit longer as well.The Corvette is also a 8 3/4" diaphragm.

the new length is a PITA but the only interference is the air cleaner as far as I can tell.

 

[tarry99]

thanks Terry

I figured it to be between 6 and 7. Not bad for measuring in braille.

do you have a part number for the booster? I have the Jeep power adapter but the Corvette booster will require some creative engineering to adapt the input end to the lever on the adapter. the jeep is an eye and the Chevy is threaded, I think a bit longer as well.The Corvette is also a 8 3/4" diaphragm.

the new length is a PITA but the only interference is the air cleaner as far as I can tell.

IO,

The 8" booster is a PB8531 and measures 7.75" diameter , These brake guys sell all sorts of adapters to get you where you need to go...........not to say as some may get creative and need to build there own as would be the case in much of the Early CJ's conversions with the short wheelbase. Most laws state that you must use a factory push rod and cannot be welded together.
The adapter length is 5"inches and may work in your longer WB CJ......look at the picture and you will see that the linkage is offset which changes the ratio.
You may be lucky as your year Jeep may have enough room under the hood at its current mounting location to make the change to power.........honestly though every time I did one and thought it would be a easy change over it seem to always be a PITA..........The process is purely mechanical in nature ,
and the stuff just needs to get in the right position......
Last but not least I can't say the part numbers I gave you are totally correct for your application........they may work , but the correct way to build the system is knowing the piston sizes of each caliper the line size's along with the length to allow a total calculation of the total volume or needs of the system........that them gets matched to the Master Cylinder.

 

[tarry99]

IO

Sorry, here is a picture of the linkage and the offset that did not make it in the previous post.

 

[Old Dog]

IO sorry to highjack here but... what's the difference between a 8" & 9" booster? other than dia. of course.
Also I notice that in looking at them I sometimes see the single as listed for auto Transmission . and double listed for man. Transmission . any idea why?

 

[IOPort51]

Dog: this thread is to collect information about brake systems, as long a you don't ask if this will increase the clearance of the rear wheel wells, I welcome your .02.

Now back to the subject.

Terry, do you think it would be a mistake to go with the 1.125" piston on the MC? The Jeep original MC was 1.0625".

Is there an advantage to using the pb8531 over the stock corvette 9" booster, other than fit? I think I have the room for the larger booster and would like to be able to buy a replacement in BFE Okyhoma if the need were to arise. It would look as if it will not be any more of a problem to adapt to the Jeep adapter whichever way I go.

Your opinion is very much appreciated.

:ty:

 

[tarry99]

Dog: this thread is to collect information about brake systems, as long a you don't ask if this will increase the clearance of the rear wheel wells, I welcome your .02.

Now back to the subject.

Terry, do you think it would be a mistake to go with the 1.125" piston on the MC? The Jeep original MC was 1.0625".

Is there an advantage to using the pb8531 over the stock corvette 9" booster, other than fit? I think I have the room for the larger booster and would like to be able to buy a replacement in BFE Okyhoma if the need were to arise. It would look as if it will not be any more of a problem to adapt to the Jeep adapter whichever way I go.

Your opinion is very much appreciated.

Dog, The larger the booster the more volume........and less clearance under the hood which on these CJ's can go away quickly!

IO, 1.125" I believe it is too big.......larger bore = more volume ,less travel and less pressure so your pedal pressure to get the work done would be greater at a given pedal ratio.......
Notwithstanding having the booster which will obviously help the pressure..........but as you know optimum vacuum is about 21 inches and that may be hard to maintain all the time while off road and especially at altitude so hence a little smaller bore I think is more than capable just in case your down on vacuum at some point.

THe PB8531 in most circles is a real common booster all the street rod guys use them and they are direct replacements for a lot of common sizes........ you can find them anywhere.

Like I said fitting it in there is one of those trial and error installs, once you see where all the parts have to go just make a few adjustments so that it fits your needs............Your good at that , its just a common since install ,you'll be fine.

Check out PB Power Brakes on line.......if you call them, make sure you have all the caliper and line sizes and lengths available........they have a good site and like I said check out what they recommend..........I can just tell you what I have used in the past.
I have an Excell program here that I can run those numbers if you like.

 

[IOPort51]

I still have to bleed the system but here is the mounted and plumbed power brake system.

Turns out I did not have room for the 9" Corvette booster and have just enough room for that pathetic little 7" K&N.

I used an adapter to mate the booster to the offset and had just enough room to use a 3/8" heim end bearing on the end of the booster shaft with out cutting any of it off.

The adapter did make things 1 1/2" longer but I think that bracing the master cylinder mount bolts down to the fender will keep vibration and being dropped a lot from breaking things off the firewall.

I think the plumbing looks pretty good.
I like the tube in a roll over the straight sticks, it is a lot easier to bend and flair.

I would like to try working with stainless steel but I have read it is a PITA to flair with out some $500 machine. I paid quite a bit for the flair set I have.