1990+ Proportioning Valves (according to FSM) Newer brakes are better

[Ondonti]

I went through Chris Grim's thread collecting any extra information to add to the minimopar table (split pressures and ratios) in an excel chart. Failed to be able to read any tag (??) on my 1992 P bodies proportioning valve.

Looked in my 1992 FSM and P bodies both Drum and disc only use a Yellow 400 psi split .43 ratio valve.

There is a chart and none of the high pressure valves exist on the newer cars. 500psi is the highest but .27 .43 and .59 are all used.
I will post it up when I get some functional batteries.

Still mulling over in my head how the valves compare to the type of body and rear brakes used.

I think I will just type it up

AA 14" disc-drum 400psi .43 Yellow
AA 14" disc-disc 400psi .27 White
AP 14" disc-drum 400psi .43 Yellow
AP 14" disc-disc 400psi .43 Yellow
AY 14" disc-drum 500psi .59 Black
AG 14" disc-drum 400psi .43 Yellow
AG 15" disc-disc 400psi .27 White
AJ 14" disc-drum 400psi .43 Yellow
AJ 15" disc-disc 400psi .43 Yellow
AJ 14" disc-disc 500psi .27 Grey


Now, my attempts at understanding based on other threads i have read. One issue in my mind is the claim by some that disc brakes need more pressure to the rear..Maybe the old disc brake setups were just piles of crap?
The willwood brakes I am adding are 4 pot calipers vs our 1 piston calipers in front. But i think since these are meant to replace drum brakes they will not be a huge problem. I still want to understand our stock Proportioning valves before being forced to redo my brake lines like Brian.
I have the feeling the convertible option on some cars was an important determining factor for prop valves, even if most of them didnt get the option! thanks a lot James! (effin vert P body):P

AA 14" disc-drum 400psi .43 Yellow (240mm drums?)
AA 14" disc-disc 400psi .27 White (goes against the idea that modern disc brakes need more pressure)
AP 14" disc-drum 400psi .43 Yellow (220mm drums?)
AP 14" disc-disc 400psi .43 Yellow (not sure why the lighter P body gets more rear disc bias? This makes no sense to me. maybe it is because of the rear heavy convertible versions?)
AY 14" disc-drum 500psi .59 Black (heaviest drum brake car with more body weight in the rear, i can understand the higher split pressure and ratio though Vigo with his "cant tow as well as your 3.0 AA AY 3.3" might disagree)
AG 14" disc-drum 400psi .43 Yellow
AG 15" disc-disc 400psi .27 White (less pressure in the rear used, like the AA body 14" disc)
AJ 14" disc-drum 400psi .43 Yellow
AJ 15" disc-disc 400psi .43 Yellow (this 15" car gets a higher ratio then the G body, maybe because of the rear heavy convertible versions?
AJ 14" disc-disc 500psi .27 Grey (higher pressure because the 14" discs are less likely to lock up but once they split you don't want too much pressure? why does this car not use the 400psi .43 yellow? Is this a weird convertible issue again?)


Seems that they are more worried about having too little rear brake bias then too much. Worried enough that they over brake biased J and P body cars even in 1992 so that the convertible versions would be able to brake properly.

This is just a hypothesis but any suggestions?


------------------------------------------------
(This is what I originally wrote before I looked into what prop valve I had. I originally wanted to ask about a front/rear brake setup, deleting the diagonal setup.)


After seeing someone use some nice copper brake line that can be bent by hand, I decided it would be nice to change brakes lines from diagonal to front/rear. This would allow a single adjustable proportioning valve to be used. Adjusting two valves sounds absolutely terrible.


Brians post here on the subject got me worried and also a bit confused.

http://www.turbo-mopar.com/forums/sh...7&postcount=58

i had this problem with the k car. i originally hooked it up so it was split from the master cyl front/rear rather than diagonal but the master bottomed/locked up when the rear brakes hit their limits first and the fronts did little, so i put a "H" pipe between the front and the rear. i have a wilwood valve only on the rear. lines.

all i needed was a few adapters, lines and some tees to install it.

Brian

The easiest fix would jut be a

[Ondonti]

I invite anyone to post and edit my guesstimation chart with their own ideas on Proportioning valve differences.

[thefitisgay]

subscribed

[Speedeuphoria]

No need fore copper you can bend most bends in steel line by hand

One issue in my mind is the claim by some that disc brakes need more pressure to the rear..

Never heard that before, just the opposite


On the "slope" doesnt this mean % going to the rear or is it a longer calculation?

these are all based on '92 year??

I know all of the daytonas and I thought Lebarons used 11" vented rear after '91

did the P body get 11" vented rears ever ? as I'm thinking not so that could be it??

I have always pondered on this myself as it seems like some info is missing. Like someone pulled a prop off a vert car and said that all of the xx bodies have this prop valve. Or they didnt look at any verts?

Does anyone have info about the weight distributions of these cars? Ah yes allpar which on one states "depends on engine size"
AA body 63/37
AP body 62/38(not from allpar maybe wrong?)
AG body 61/39
AJ body 63/37 also for Lancer

Also dont we need to consider the master cylinder used? Do all of these cars use the same?

[zin]

How much pressure your new calipers will require will depend on how much more or less square area they have compared to what they are replacing.

400psi applied to 10 square inches will have much more clamping force than 500psi applied to 5 square inches; 10 x 400= 4000psi (total force), vs 5 x 500 = 2500psi.

I also agree with you on changing to a front/back vs the diagonal, the front/back has much better potential performance, while the diagonal has better safety in the event of a failure...

If you want the lines to look good, invest in a tube bender, they aren't too expensive and will go a long way towards making the job look great and probably easier. Also, I'm not so sure I'd go with copper, if it's soft enough to easily bend by hand, 1500+PSI of hydraulic pressure might do a number on it too, better to use regular steel, or better still, stainless! No more rusty lines with that stuff! And you can use a slightly thinner wall so it's not as big a pain to bend, just make sure you get the annealed stuff!

There's my .02, don't spend it all in one place!

Mike

[Ondonti]

First, if you look at the 1980's prop valves, the disc brake cars have very very high pressure, high ratio prop valves. Much higher then the drum brakes. THen in the 90's the story is reversed. To me this means there is a big difference in the function of the disc brakes between those generations. That or Chrysler engineers in charge of brakes were idiots. Considering all the complaints I have seen of the 80's disc brake cars locking up the rears and having high pressure/ratio prop valves, I might wonder if Chrysler hired a few guys from ATT Tech who got things backwards.
Most of the brake upgrade suggestions on these sites always say "get the prop valve" but I would probably say "don't get the prop valve!" Especially since most people who need brake upgrades have removed weight from the rear of the car.
The people who understand a proper brake setup seem to not be the ones contributing too all these historical threads. They usually just say "buy an adjustable one" when there really is an easy answer for the average joe who doesn't want that complexity.

Never had a rusted brake line before.
The copper stuff only scares me if it got nicked by something. I always end up "off road" at some point, even in my race car so hmmm. Even a ditch into the gravel could spell disaster at a Road racing event.


Think of slope as a percentage. No prop valve = 100% or 1.0.
Split point is the brake pressure at which the prop valve starts to only allow a percentage of total brake pressure to go to the rear.

So a Yellow valve would start sending 43% of total brake pressure to rear for any pressure beyond 400.
So if front Brake pressure was 500 on the yellow, the rears would only see 443psi.

I think I will leave the adjustable front rear with 1 prop valve project for a day when I can afford to flat spot some tires on a road course.

[zin]

Baring installing the adjustable unit, which is only a good idea with a front/back set-up, I think your stuck with making a SWAG! Make your best guess at it, it seems you are on the right track, and see how that works, then try different prop valves to suit your taste.

You can kinda see why folks just say, "get the prop valve" when doing the conversion! It's difficult to call out the best choice for a given application, but the "stock" valve should work OK. One other thing to keep in mind, at least when converting from drum to disc is that the prop valve (which is really a combo valve as it does more than just biasing front/rear brake pressure) for drums will have a higher pressure residual valve, which could cause some problems on discs as the drum brakes use a higher pressure to hold the shoes close to the drum whereas the discs don't need one, or one with only a PSI or two...

I haven't been as lucky as you on the rusted brake line, though my experience wasn't with a TM, it's not one I'd care to reproduce!!

Mike

[Ondonti]

residual valve? No information in the fsm or forums about that. I thought drums just had to be mechanically adjusted for our cars?

From the charts it seems like the prop valves are the same disc to drum as far as construction goes. yellow drum = yellow disc

[Vigo]

Hmm... my thoughts on this.

For one thing, no 240mm drums on cars. Only 200 and 220 mm.

As far as how my dynasty tows: stock 3.3 604 is MUCH less powerful at the wheels than modded 3.0/543, and most of that is the trans. Other than that i see no difference in their towing potential.. unless i have better brakes? 11" all around. I anticipate the dynasty being a lot happier towing with a 3.8 and geared down 604. I still got it up to 85mph and got 17 mpg with a gcvw of almost 8000 lbs (2 cars, dolley, 3 people+ LOTS of gear/tires/tools) going to GRM. Every inch of both cars was packed to the brim. Because of emergency braking situations (seen a few on the ~3000 mile grm round trip) I dont feel safe towing more than 3000 lbs with my 3000 lb dynasty with no trailer brakes.



Also, ive done the rear disc swaps on 2 cars.

93 dynasty: Ive had both 89 10.5" discs and 91 11.25" discs on the back. Ive always had the stock prop valve and its always locked up the back first. Usually.... One thing that bugs me about this car is its a crapshoot which wheel will lock up first. Sometimes its the fronts, sometimes it the back, all in similar conditions. It really screws with me. OT a;lsp has 11" fronts.

89 Aries: 89 10.5" discs in back on stock valve, also locks up the back first.

So thats from both 'generations' if you could call it that, with basically the same result.


Id like to know how it all breaks down too as far as the factory valves.

[Speedeuphoria]

Mine locks up the rear 1st but I kept the stock drum prop valve and have stickier/wider tires on the front and not much weight transfer(the front doesnt move when I sit on the fender)

[turbovanman²]

I've done 2 rear disc swaps, both suffered from poor rear brakes, you could feel them not working, put in the correct prop valve and maxed out the adjustable rear doohicky on the van and bingo, rear brakes work. Drums don't need as much pressure to operate due to their small wheel cylinders-meaning bores.

[jory]

I kept the stock yellow prop valve on my spirit when I upgraded from disc/drum to 11" discs front and rear. The rears would never lock up before the fronts, in fact it felt like a perfect balance front to rear. One time stopping from 120mph the FR locked first. I used the same valve on a different car with a similar setup and the brakes were still well balanced. I will have to see what the stock 10" disc prop valve on my 89 daytona does with the 11" brakes. I'm pretty sure its the one with a black tag. The rear brakes are swapped I just have to do the fronts and the master cyl. I love the big brakes there is no comparison.

[Vigo]

Sounds like different people have had wildly different results.

[moparloper]

On any of the drum brake equipt vehicles I've worked on, the residual valve for the drums was located in the master cylinder. Because of the spring return on the shoes you have to reduce the pressure gradually. In any of the ones I've worked on it is a small "duck Bill" valve located behind the tubing seat. If changing from drums to discs it will feel like the rear wheels are dragging or locking up first, expecially if pumping the brakes. I have no disc/drum FWD mopars to verify this but in any of my trucks or older cars this was always the case. Disc/disc MC will not have it.

[Vigo]

Ive never been aware that there were any different master cylinders.. I cant recall being asked if a car had drums or discs when buying one.

Im probably going to buy a new master cylinder for my 93 dynasty soon, and that could come either way, and both ways had the same size 24mm mc, so i will see if they ask me anything or show more than one.

[Speedeuphoria]

I thought it was 21mm for drum and 24mm for disc on the master

[135sohc]

The difference in master cylinders is based upon a combination of things, some matter, some dont and the factory made changes along the run that also come into play.

All info below was pulled from the 1994 parts catalog.

using a P body for example.

21mm is used for front discs, rear drums. 90% of Shadows/sundances probably got that size.

7/8" is used for disc/disc (most callout ABS and not 4 wheel disc since ABS was only available with rear disc and not drums) read between the lines there.

24mm was never used.

A & J body.

7/8" was used from disc/drum as standard since they got the bigger 220mm rear drums as standard equipment. Also used from ABS (read rear/4 wheel disc) with the 14" wheels aka solid rear discs.

24mm was used from disc/disc with the bigger brakes with or without ABS.

[boost geek]

My m.c. is labelled 1", is that classified as 24mm?

[Vigo]

Its extremely close in conversion, probably the same part.

[boost geek]

So I should be able to use rear solid disk/front large disk on my S.C. with that m.c.