[1869]

So I did a rear disc swap this fall on my model 20 rear (84 CJ7 power brakes). I bought the kit from stainless steel brakes corp. I believe the rear calipars are from a crown vic or something simalar, anyways they have combined parking brakes in them. I installed a corvette MC because I was getting no pedal with the stock one.
I havent driven it much since the swap but have not been happy with the brakes performance at all, the original setup with rear drums stopped much better. Now I drove in the snow and ice the other day and slammed on the brakes and the rear tires will not lock up at all. If I drive up a dirt hill and stop I will slide back down backwards because only the front brakes are working.
I have the original proportioning valve which I believe is the problem. How do I "gut" it like I have heard people talk about? Or do I need to get an adjustable valve and does it take place of the stock one or does it go inline somewhere else.
The last time I bled the brakes I started from the rear. I was getting a very good pedal but as soon as I started bleeding the fronts the pedal got softer and softer as I progressed. I believe this has something to do with the prop valve not working good with the 4 wheel discs.
Also the pedal feels much harder than I think It should. after a certain point it does not matter how hard you push the pedal you still stop just as fast. The brake booster is working cause it is even harder to push with the vaccum hose unplugged.
I have ruled out bleeding as a problem because I have gone thruough two bottles of fluid by now and no progress as a result. It is also much harder to stop the vehicle in low range because of all the added torque. Needless to say I will not be doing any wheeling with the brakes this way, especially after the 33" SSR's go on.

Help please??

 

[MTPockets]

I have seen 2 methods to "gut" the prop valve. Remove the nut on the front side of the valve and pull out a brass spindle thing with a rubber washer on one end of it. Some people remove the washer and put the spindle back in. Others leave the spindle and washer out and replace the nut. Try this link.

http://www.stu-offroad.com/brakeconv/bc-5.htm

Several people frown on this practice and would probably recommend just replacing the valve with one from a vehicle that already has 4 wheel disc, like a Grand Cherokee. All of the adjustable prop valves that I have seen, do not replace the original valve, they go inline to reduce pressure. They will not help if your original valve is bad. Good luck.

 

[LEVE]

1. I'd never gut a proporting valve,
2. But you may want to rethink the OEM one.
3. This is what you're bettin' you're life on,
4. May I suggest:

 

[MNT]

I have a similar proportioning valve, but mine is a Mopar. The think I do not like is that I have no low fluid warning. Hasn't been an issue, but I check the fluid level regularly. Anyone have any idea on how to get that warning back.

TIA

 

[CJ7Taz]

If you went to rear discs for better braking, you done bad.

For braking, drums are superior to discs. Discs cool better, don't fade when hot and shed water better than drums but they don't provide as much stopping force.

I converted to rear discs as well, still have the original proportioning valve and an adjustable after it. I don't have any problems other than with the parking brake holding. You don't need the Corvette master cylinder. You still need the original MC bore size to be compatible with the front brakes. You need to size the rear caliper bore size to match the system. You change the master cylinder to get more equal reservoirs so that you don't run out of brake fluid as the pads wear.

I don't know what you've done but something is wrong. My first guess is that you don't have the system bled. Having run two bottles of fluid through it is not an indicator that the system is bled. I could run 5 gallons through mine and not get the system bled unless I unbolt the rear calipers and get the bleed screw to the top of the rear pistons. It just ain't gonna bleed otherwise no matter what.

 

[1869]

When I got the corvette master cylinder I did some research to make sure I got the correct "style". It has the same bore and stroke as the stock CJ MC. When I bled the brakes I did have the calipars unbolted with a board between them so I dont think that is the problem. I am pretty certain it is the prop/ combination valve that is causing the problem. As far as disc not stopping as good as drum, maybe that is true, however my old drums were worn down to the rivets and probably were not adjusted and the still stopped better. But like I said I dont believe ther rears are woring at all. I have read that caddy elderado calipars depend on the e-brake to adjust the brakes. I think mine are from a newer lincoln but maybe they work the same way.

Prop/ combination valve from a grand cherokee? any idea what year to get one from?

 

[CJ7Taz]

In reply to:

I am pretty certain it is the prop/ combination valve that is causing the problem.

[/ QUOTE ]

Yep, that's it. The problem is always in the mystery pert. Just forget I bothered to take the time and tried to help.

 

[pbmcauliffe]

I recently had the "no pedal" problem in switching to 4 wheel discs and read lots of posts here and other boards and found a lot of different stories. Seems for every person that said keep "x" part in the system, other people had that part as their problem

Mine is a manual system, but here is what I found to work for me;
I originally had a 1" bore disc/disc master, 1/2ton Chevy caliper front & rear, removed factory disc/drum combination valve, adjustable prop. valve for rears and had bleed the system numerous ways (power, vacuum, pressure, gravity) and had extremely low pedal on the first stroke, after that the pedal was higher. The rig would stop, but didn't like the pedal going down 2/3 of the way before they worked each time. In troubleshooting I found the problem to be in the rear from the 'T' out to the calipers.
I removed the rear adj. valve and had same problems, added a 2 lb residual pressure valve and they were a bit better, swapped lines on master, no change.
The other night I thought maybe I wasn't getting enough fluid to the rears so I installed a cheap reman corvette 1 1/8" bore disc/disc master into the system and I have a lot better brakes than before, pedal is higher, firmer but not hard to push.

 

[1674]

Just wondering if you also bled the master cylinder after swapping it or if your just bleeding at the wheels?

 

[2344]

In reply to:

I am pretty certain it is the prop/ combination valve that is causing the problem.

Yep, that's it. The problem is always in the mystery pert. Just forget I bothered to take the time and tried to help.

[/ QUOTE ]

well.... seeing how he just said he already did what you suggested, I dont see how getting pissed at him for saying it didnt work acomplishes anything. he has the same bore and stroke as the origanal mc, unbolted the calipers etc...

and.... for someone who is constantly flaming other for spelling and paying attention to what people are saying in their posts I am surprised.

"pert"

Phil

 

[MNT]

I always thought that you only wanted one proportioning valve in line. That way the brake fluid would not be "proportioned" twice. Is this not true??

 

[CJ7Taz]

In reply to:

I always thought that you only wanted one proportioning valve in line. That way the brake fluid would not be "proportioned" twice. Is this not true??

[/ QUOTE ]

I only WANTED one but then I didn't WANT to take the original one apart nor bypass it. Someday, somebody will be parting out a Jeep and I'll ask for the proportioning valve for shipping. Then I can take it apart, defeat it's proportioning function, still keep the warning switch and replace mine if I'm successful. Until then, two in series is working fine.

Now expanding on your question, do I NEED two? NO. Does it work to have two? Seems to, been that way for years.

All the proportioning valve does is slow fluid to the rear brakes by restriction in the flow so they don't lock up too quick. (The rear of a Jeep is light and the weight transfers to the front when braking.)

So, in this particular case we hear that the rear brakes won't even lock up on ice. That means NO fluid would be getting through the valve. On the other hand we know that fluid DID get through when bleeding the brakes. Those two fact taken together make me believe it is something besides the proportioning valve.

 

[100]

In reply to:

Then I can take it apart, defeat it's proportioning function, still keep the warning switch and replace mine

[/ QUOTE ]

I'm glad I don't drive in the same areas as you,,,,,,,,,,,,,,,,,,,
You better hope the warning light can see into the future because if you gut the PV, your also combining the front and rear brake systems through the PV's bore after you remove the piston and spring. If the system leaks anywere, ALL the brakes fail, front and back. By the time the warning light goes on, your brakes are nonexistent. You have obviously never disassembled a PV and are only quessing at what MIGHT work.
Brakes are nothing to guess about !!!!! or to state advice based on your guessing. If you need a PV, buy an aftermarket one like the summit adjustable. It's only 39 bucks and it works, it's proven to work, it's been used before and works. Modified jeeps have different weight bias's then a stocker's PV will provide. And with some MC, the balance is already correct, without having to proportion it. I use a Caddy MC with Hydro Boost and don't even use the Summit PV that is install ( it's adjusted wide open). My brakes are perfectly biased without the PV but no rig is the same.

On My rigs, I run new hard lines fom the MC to the front soft lines(no PV), then run a short 6' long hard line from the MC to a Summit PV, then hard line from the PV to the rear. Very simple and clean,,,,,,,but most of all, very functional.

And who the hell told you that drums are better then disc?!?!?!? OHHHH, never mind, I forgot how you say dumb things for the propose of invoking reaction. (i won't use the web term)

(edited 3 times for spelling,,,,,,and I'm sure where's more but I give up

)

 

[CJ7Taz]

In reply to:

(edited 3 times for spelling,,,,,,and I'm sure where's more but I give up )

[/ QUOTE ]
Shouldn't that be ",,,,,,and I'm sure THERE'S more"?

Yep, never had one apart before that's why I want an extra to experiment with. Didn't you read? Or did you cut off the quote where you did for effect?

[/ QUOTE ] Then I can take it apart, defeat it's proportioning function, still keep the warning switch and replace mine if I'm successful.

[/ QUOTE ]
And I already have an adjustable.

 

[Neurosis]

In reply to:

If you went to rear discs for better braking, you done bad.

For braking, drums are superior to discs

[/ QUOTE ]

Taz, can you point me in the direction to information supporting that fact? Ive looked everywhere and everything ive read in fact says that disc brakes stop faster and more efficiently. Im not saying your wrong so dont lash me because I really dont know, but i'd just like to read something that backs that up.

 

[CJ7Taz]

I don't really know of a place to point you, it's been discussed here several times. Drums have an advantage because once you push the shoe into the drum, the rotation of the drum assists by pulling the shoe in. Look at the way the pivots are set up on dual cylinder front drums. This can also cause the brakes to lock up on you or worse yet, have only one lock up.

Now if you are backing up, they don't work as well but they generally don't need to. Some of the rears (maybe most) are set up to pull a shoe in either direction of rotation. For a Jeep, either discs or drums will do unless you get too big on the tires. Get 'em hot or wet and you'll appreciate the discs.

 

[100]

In reply to:

Didn't you read?

[/ QUOTE ]

Yes, I read that you think gutting a PV may be a good idea without even knowing how they fuction,,,,,,,,,,,,it's not a good idea. It's such a bad idea that someone could die.

In reply to:

And I already have an adjustable.

[/ QUOTE ]
You stacked an adjustable PV after the stock one?

,,,,,,,,,,,,the only thing that will do is restrict more line pressure to the rear system,,,,,,totally opposite from what needs to be done. With winchs, larger motors, lifts, cages, etc,,,,, braking traction in the front is increased and more line pressure is needed in the rear to balance the braking, not less.

As far as Disc to drum comparisons,,,,,,,,,,,,,,,,(the most extreme braking "stopping force" power comparison I could thing of would be loaded "Big Rigs", so that is what I used)
-quote-Jim Clark, Dana's chief brake engineer, says the typical tractor with drum brakes on all corners will stop in 270 to 280 ft from 100 km/h. However, he says that by increasing steer-axle brake torque (with disc brakes) to about the same level as drive-axle braking torque (still with drum brakes), you can bring that distance down to 200 ft or less. He's achieved 209 ft in tests with that arrangement, and says a disc brake with greater torque could break the 200-ft barrier. For a loaded tractor-trailer, he figures a 10% stopping-distance reduction is achievable with the use of disc brakes just on steer axles.
-/quote-

-quote-AlliedSignal says its Bendix air disc can drag a 97,000-lb rig down from 90 km/h in a 49-ft shorter distance (then drums). That's with discs just on the trailer, not the tractor. But put discs all around and add EBS (electronic braking system), and it says the gain is 75 ft.
-/quote-

But whatever,,,,,,,you seem to have all the bases covered here,,,,,,,,,,,

In reply to:

 

[OlllllllOCJ]

After reading this complete thread I have a few comments and wish to toss in my $0.02 worth.

I installed an SSB rear disc brake kit on my 1985 CJ7 a couple of years back. There is no comparison between the drum setup and the disc when it comes to the parking brake and off road performance, the disc brakes are vastly superior.

I also had some problems getting the pedal to feel normal and at some points didn't have any back brakes at all. During the installation I drained all of the brake lines to rid myself of the muddy looking old brake fluid. I accomplish this be simply opening up the lines at every point that I could including at the proportioning valve. I also installed a new "stock" master cylinder following the bench bleeding instructions that came with it.

The first shot at bleeding was a conventional process, having my son work the brake pedal while I crawled around under the Jeep and opened the bleeders one at a time. Needless to say we put a lot of brake fluid through the lines but didn't get out the air. The pedal was hard on the second pump but mushy when trying to stop.

The SSB kit has bleeders on the hose fittings and the calipers have the original bleeders on them. I guess SSB was trying to tell us something (it's mentioned in the SSB instructions too). I had a feeling that air was being trapped in the caliper so I looked for a way to bring the caliper and hose up higher than the lines across the axle. I found that if I turned the rotor around backwards and held it in place with a lug nut that the hoses had just enough length to allow the caliper to sit on top of the rotor. After several more bleeding sessions, using both the bleeders on each caliper, things were getting much better but still not quite right.

The final resolution to my problem (seemingly similar to yours) was to simply jack the back of the Jeep up about 18" higher than the front and bleed the rear calipers again as described above. There was still a substantial amount of air in the system hiding somewhere and it came out. The pedal feels normal, the Jeep stops great, the parking brake holds in either direction and I couldn't be happier with the results.

Aside from the SSB rear disc kit and some braided hoses on the front all of my components are stock Jeep or direct replacements. The proportioning valve is the original 1985 vintage that rolled off the assembly line with the Jeep.

I'm a long time follower of the KISS principle, Keep It Simple Stupid………

 

[RRich]

Did the kit say to continue using the proportional valve?

Proportioning valves are mainly to balance the braking between drum to discs. With all 4 as discs, you may not need it.

Then the balance front to rear braking is acconmplished by the caliper piston size and MC bore size.

One neat way (and fun) to tell if you have too much front or rear braking - flat hard dirt area - run fast and throw it sideways with the steering, then hit the brakes fairly hard. Your slide should stay flat, not loop you. That's exactly the same thing that will happen on ice, but this time you are in better control because you planned on it.

 

[CJ7Taz]

In reply to:

Yes, I read that you think gutting a PV may be a good idea without even knowing how they fuction,,,,,,,,,,,,it's not a good idea. It's such a bad idea that someone could die.

[/ QUOTE ]
SHOW ME! Show me where I said anything like that in this thread or any other.

From your previous post:

In reply to:

You better hope the warning light can see into the future because if you gut the PV, your also combining the front and rear brake systems through the PV's bore after you remove the piston and spring.

[/ QUOTE ]
Again - SHOW ME! Show me where I said that I was removing a piston OR a spring from a proportioning valve in this thread or any other. The only time I said anything about removing any spring was when Tom was having trouble passing inspection with his emergency brake on a Caddy rear disc swap. I told him, that if he hadn't already done so, to remove the spring from the end of the Jeep parking brake cable because there is already a spring on the Caddy calipers. You don't want both.

Now for your braking statistics, they were written for idiots by an idiot. The mixing of metric and empirical units is the first clue. Nobody that even had a clue as to what he was doing would give a stopping distance in feet while giving the speed in kilometer/hour. That aside, 100km/hr is 62mi/hr. The standard stopping distance for ANY vehicle at 60mi/hr is given in some drivers manuals as 188 ft and even to get that, they had to use a coefficient of friction with the tires locked and sliding. You can do much better than that if you don't slide the tires because the static coefficient of friction is higher (tires not sliding). So we know the 209 ft you quote is WAY too high and the 270 to 280 ft for 62 mph is absolutely ridiculous. What did he do to come up with that figure? Maybe locked up all the wheels on a loose gravel road.

In reply to:

But put discs all around and add EBS (electronic braking system), and it says the gain is 75 ft.

[/ QUOTE ]
Congratulations! You got one thing right, I knew that eventually you would. The problem is that you don't understand the significance of it. The EBS didn't add any force to the braking system, it reduced it. It pulses the brakes so you don't lock up the wheels. Remember, from above, that static coefficient of friction is the higher. If you lock up the wheels and slide the tires, your braking distance will increase.

The maximum braking effort comes just before you lock up the brakes. If your brake system will overcome that point and actually slide all the tires, you have enough braking force whether it is drums or discs. So, if I want to sell disc brakes and prove to you that they are better, I build a device to apply the brakes at a particular pressure so it's a fair and honest test and there is no cheating (you should be suspicious already of the last part of that statement). I set the device to produce enough pressure to just lock up the drum brakes and measure the stopping distance. I now, right in front of you, remove the drums and replace them with the discs which do not produce as much braking force. I run the same test and since I'm producing less braking force, the wheels don't lock up, the tires don't slide and the braking distance is less. At this point I ask you how many of your vehicles I can convert to discs for you. Then after you leave, I laugh at the dumba$$ I just sold snake oil to.

It's just simple, basic science. It can be how planes fly or how magic is performed. (And in case you're wondering, David Copperfield doesn't really cut the lady in half.) Learn a little science and you can prove about anything to the unenlightened. You believed it and you THINK you're intelligent.

In reply to:

You stacked an adjustable PV after the stock one? ,,,,,,,,,,,,the only thing that will do is restrict more line pressure to the rear system,,,,,,totally opposite from what needs to be done. With winchs, larger motors, lifts, cages, etc,,,,, braking traction in the front is increased and more line pressure is needed in the rear to balance the braking, not less.

[/ QUOTE ]
Sorry, wrong again. The added weight to the front and the weight transfer from the lift allow the use of more braking force on the front without locking up the front wheels. You want less pressure to the lighter rear to keep from locking up the rear wheels and sliding the rear tires early.

Now, I've wasted enough of my time teaching you basic science. Go to your local college and take a physics course (as many times as you have to in order to pass), come back and we'll talk more. Er, maybe an English class too so you won't be accusing me of saying things that I didn't.