It is time to do a major upgrade to the brakes on the turbo slant. The current brakes are all Mopar, but are a mix and match, and apparently not matched well. The rears are standard 8 1/4" big bolt rear with 10" by 2 1/4" drums. The front are disks off a 73 Sebring which was a B body car with pin type calipers. The proportioning valve is a off a 73 disk/drum dart. The problem is that when I hit the brakes hard and fast, at least one rear wheel locks up, and the car goes into a serious spin. I almost lost it two nights ago when a herd of dear leaped across the road in front of me. I didn't come close to the dear, but I was afraid I was going off the road and into a tree.

The rear linings are almost new. The master cyliner is an aluminum one from Mopar, off a volare. The front calipers are recently replaced, as well as the pads and rotors. There are new seals in the axles. The oldest component is the combination valve. The emergency brake was disconnected to make way for other more important hardware in the turbo and computer application, and I don;t want to replace the e-brake until I settle on a better brake configuration. I would like to put disk brakes on the rear. Is there any set up for Mopar 8 1/4" rears? Also, I will replace the combination valve and put an adjustable proportioning valve in the rear line. I purchased a new combo valve, and new master cylinder from Stainless several years ago, and never put them in the system. I was always waiting for a time when I had the brake system open for something else. Any comments or suggestions? This will be a winter project, more than likely, if I don;t kill myself in the mean time.

On any mix-n-match brake system, you absolutely need an adjustable prop valve in the rear line, IMHO. They are only $40 from Summit and will change your life.

I would suggest leaving your combo valve in there and adding the adj prop valve in the rear line - pretty easy and big gains.

Rear discs I've had good luck with - www.tsmmfg.com. They say they have kits for 8.25" axle. OEM parts based, so you can easily get replacements.

When we put the brake system on Project V, we had the proportioning way off (too much rear), and it felt like crap - couldn't stop it worth anything. That is with 13" Wilwood/Cobra brakes on the front! After 10 min of adjusting the prop valve, it felt like a Porsche...

We are using the stock '66 Valiant single-pot drums combo valve with the rear line blocked off (parts store line plug), and the rear line goes straight from the MC, through the adj prop valve, and directly to the rear axle. Road race tested and approved...

Lou

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Home of Slant6-powered fun machines since 1988

Check the hard lines in the rear. I have found some on the axle that were rusted shut.

What is the combination valve supposed to do, and why can you just by- pass it without problems? This has always been a mystery to me. Do all cars have them? All the lines on this brake system are fairly new. Hard, and soft. I have dot 5 in the system, which does not attract moisture, and thus avoids much of the pitting, corrosion and rust of Dot 3- and 4. I will check out the web site.

Dang that Lou...I saw that setup for the 8.25" and now have to budget up for that conversion....



Thanks Lou!!!!!


-D.Idiot

I think that the Mopar combo valves of the late 60s were nothing more than TEEs with a brake light warning switch and maybe a shuttle valve to block front or rear circuit if one loses pressure. I don't believe they do anything as far as proportioning or residual pressure. Correct bias was accomplished by matching the wheel cylinder diameters and disc caliper piston diameters.

On any mix/match system, these piston sizes will not be matched and you will be off balance. Unless you want to swap out disc calipers or wheel cylinders a few times to get the right match, you can just get the adj prop valve and be done with it.

Lou

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Home of Slant6-powered fun machines since 1988

Lou,

Sounds like you have the Wilwood on 13 inch rotors up and running now with some miles on it?

One comment on the use of the prop valve as a crutch is that you don't want to rely too much on the prop valve since it will make the brake feel soggy (blows off volume to drop the pressure) if you crank on it too much. So if you have to use the prop valve to really drop the pressure to the rear then you might be better off by going down one size on the rear wheel cylinders and then resetting the prop valve.

Andy,

I should have posted on the 13" brakes before, and I will do so in my Valiant writuep soon. They performed flawlessly on the 1.1mi VIR-Patriot course 2 weeks ago. I ran approximately 120 laps over 2 days in 20 min segments. No fade, very predictable. They will get a bigger test on the CMP track next month, which is supposed to be very hard on brakes.

I agree on not using the adj valve as a crutch with excessively mismatched components. However, in all of my mixed brakes setups (5 different combinations), I have dialed out the rear brakes by varying amounts with the valve and never noticed a soggy feeling. I think you need to be pretty far off for the valve not to work well.

Lou

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Home of Slant6-powered fun machines since 1988

Your kidding me,,, nobody's going to comment on the heard of "dear" ?

Sure that your shoes aren't contaminated wtih brake fluid or axle grease?
(leaky axle seal or wheel cylinder) Could be a screw up at the rebuilder, 3 shoes from one assembly line 1 from the other... Ive seen this and it drove me NUTS figuring it out! As far as the combo valves, the ones that look like just a tee usually are, common on 4 wheel drum cars especially pre 67 when there was only 1 chamber in the master. Back then proportioning was accomplished by wheel cylinder size, also by playing with drum diameter and width. How many A body cars have you seen with either 10" shoes in front and 9s in back, or they may be all the same size, but the fronts are wider?? Remember the cylinder diameters last time you rebuilt them?? fronts were bigger, right?? They did this with the bigger bodied cars a lot, too. 11 inch drums up front, 10s out back, or else the rears were like 2" wide and the fronts were 2-1/2 or 3" wide if diameters were all the same at all 4 corners. A binding condition in your pedal linkage, or just a plain old defective combo valve can cause what you have. Had that on my 85 Diplomat ex squad.

I ordered the rear disk set up yesterday. I got the parts for no hand brake. I hope I didnt; make a mistake there. He said if you have the handbrake and do not use it all the time, they go out of adjustment, and you WILL have problems with them.

Did I use the wrong term in refering to the dear? What is the right term for a group of dear running across the road in front of your car. I think it is a four letter word for sure.

Thanks for all the advice. It is about time I get better brakes on this car. To change out the drums for disks you have to either cut the backing plate off, or remove the axles, which requires opening the rear and pulling the "c" clips. Are these backing plates anything special. Anyone out there feel offended if I just cut them off? In other words, are they worth the trouble it would take to save them? They were sand blasted and painted about five years ago.

Vader,

I assume you got the TSMMFG kit? I have never really seen the need for parking brakes, and only have them for NC inspection. I was amazed at the difference between the TSM rear discs and 10" drums, even with the bias adjusted perfectly on both setups.

BTW, If you don't put an adjustable prop valve on that thing, I can't be your friend any more. I'm going to harp on this until you install one...

Lou

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Home of Slant6-powered fun machines since 1988

Ok, I'll comment...

"dear" is what your wife calls you when she needs something done.

"deer" are tasty furry 4 legged animals.

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My truck is a Frankenstein creation
Built from the dead carcasses of others
And brought BACK TO LIFE!

I have herds of deer run in front of me or on the side of the road fairly frequently where I live (at least groups of 2-5 are common). Haven't hit any yet (cross fingers).

Lou

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Home of Slant6-powered fun machines since 1988

I lost my beloved '84 Dodge Shelby Charger one morning when a doe committed suicide on the fender ... on the hood ... on the roof ...