Prop Valve 4 Whl Disc Brake Avanti/interim update

[DEEPNHOCK]

I like your incremental steps.
This way you know where it changed, and that makes it easier to change...
Oh, on the Yellow POS, my first 'heavy' brake application (that was over 50mph) was done at Osceola drag strip during South Bend '02.
Like yours..It stopped nice and straight[]
Nice work!
Jeff[8D]

The test drive was, thankfully, uneventful. I couldn't due a DEEPNHOCK 60 to 0 slam on the brakes and hold on test however hitting them hard but not locking them up from about 45 mph did not produce anything but a straight, nicely modulated stop. A tire screeching "holy crap" test will have to wait.
ErnieR

[bige]

I finally got to the brakes. I was sidetracked replacing the constant pressure valve body in my TCI 200 4R trans but now with the 'going' handled I got back to the stopping.

I removed the proportioning valve and did not install the metering valve so I'm out there 'naked' with full pressure to the rear brakes. I checked the brake pressure at the rear calipers and it's the same 1000 lbs that I have at the master cylinder. Everything I've read tells me I should have 1,000 lbs to the rear brakes for them to work properly so for now I'm not going to limit their pressure. I used my pressure bleeder with a special adapter for plastic reservoir master cylinders.







With the drums and the Chrysler dual master I could not power brake the car past 1300 rpm without the wheels spinning and the emergency brake didn't do anything going forward although it held a little in reverse. I didn't try power braking up until the wheels broke loose but it went past the rpm that it would normally break them loose.

The test drive was, thankfully, uneventful. I couldn't due a DEEPNHOCK 60 to 0 slam on the brakes and hold on test however hitting them hard but not locking them up from about 45 mph did not produce anything but a straight, nicely modulated stop. A tire screeching "holy crap" test will have to wait.

ErnieR


On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

[sbca96]

I know I got them to lock, but I dont recall which did first. I was
always under the impression that they rears should lock first, thats
what my Hawk did (as far as I remember). This paragraph explains the
reason the rears tend to lock first :

"Whether the car is equipped with front disc and rear drums, or has four-wheel discs, hydraulic pressure should be reduced to the rear brakes for several reasons. The single most important reason is because even under moderate braking, natural weight transfer reduces weight on the rear tires and moves the weight to the front. This unloads the rear tires, which makes it much easier to lock up the rear brakes in hard braking. Once the rear brakes are locked, the tires skid, which immediately causes loss of control."

Now I guess I need to get the Avanti out of the garage and see what
its doing now. I have changed it since that initial testing, it has
the 13" brakes up front now. My dad is visiting next week, so we had
planned on driving the Avanti around, he wants to try out the TKO. I
also want to get more video of it, maybe some of which lock first. I
know that the fronts are working, it nose dives quite well. I doubt
it would stink bug that much if the rears were doing all the work.

Jim, what did you find out with your Cobra setup?

Good info Jeff!!

Tom

[DEEPNHOCK]

Yes, you SHOULD run a proportioning valve.
For some enlightened reading, go to....
http://tinyurl.com/m7jujg

[bige]

I took the valve I bought apart just to see what's inside. If yours is like mine it's a simple deal that has a heavy spring inside pressuring a plunger of sorts. As you scew the knob in it increases pressure on the sping requiring more pressure to overcome the plunger and thus limiting the output pressure.

When the valve is screwed all the way out I doubt there is any pressure reduction going on. The spring in mine was loose enough to rattle around and 100 lbs of shop air just blew right through. So a guess on your system right now is that it's operating the same way it would without a valve.

I will update as I work through this.

quote:Originally posted by prager

Yes, is the prop valve a requirement bar none? I would just as soon not run one, but as soon as I leave it out i'll need it...Let us know on the test if you can..Thanks!!

Making resverations at the poor house parking lot for me and my 62 Lark..

On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

[prager]

Yes, is the prop valve a requirement bar none? I would just as soon not run one, but as soon as I leave it out i'll need it...Let us know on the test if you can..Thanks!!

Making resverations at the poor house parking lot for me and my 62 Lark..

[bige]

The question is...since no one has posted that they needed a proportioning valve are the rear brakes working as they should on any of these dual master conversions?

This was my concern from the beginning and the impetus for the disc brake swap. I'm wondering if the simple single to dual master swap is not so simple and results in reduced rear braking power. I'm going to do a pressure test with the commonly used replacement master cylinder just as an FYI.

ErnieR

quote:Originally posted by ChampTrucking

DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?

On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

[Laemmle]

Years back I purchased a hold off valve from Master Power.

Very simple.....when you hit the brake, there is an initial delay line.....in other words, the rear brakes become energized first, then the front disc's come on....works great and eliminated the front nose dive on Avantis when hard braking is employed.

[prager]

Many thanks Jeff and Champ..Good info..I think my mission is clear now..What were we talking about again???? I think I'll go with the 79 Trans Am disc/disc with power set up..1 1/8 bore..after your idea on the booster making up for it I'll give it a shot..Thanks again!

Making resverations at the poor house parking lot for me and my 62 Lark..

[DEEPNHOCK]

I would stick to the 1" bore master....
But....
If you are running a power booster, it will/should make up for the increased pedal foot pressure required.
I know of a lot of people who only run the Wilwood adjustable on the rear and it works ok. It is used as a tuning aid, and once you get it set where you like your brakes, it most likely will never get touched again.
One way to test your setup is to do a max effort panic stop.
If you can't lock 'em up (no anti-lock).... Then you probably could go with a smaller diameter master cylinder to raise the brake psi.
If, when you do lock 'em up, see if the fronts lock first, or last...
The fronts should lock up first.
The MP Brakes site has some good tuning info.
HTIH
Jeff[8D]

quote:Originally posted by ChampTrucking

DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?

[ChampTrucking]

DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?

[ChampTrucking]

Hey Jeff,Its Rich. RE: Vette master cylinder. We ( Prager and I ) are looking at a second generation Firebird master cylinder with disc-disc brakes,and a 1-1/8ths inch bore. It would appear to bolt onto the 64-66 power brake booster Wes installed on his 62. Whatta ya think??? Thanks for all the tech help too! Helps to review someone else's issues and fixes instead of reinventing the wheel!

[DEEPNHOCK]

You can get that 'Vette master as a rebuilt at your FLAPS.
I got mine from Discount Auto Parts for about $30
IIRC, you tell them it is a late 60's, early 70's 'non power' disc brake master cylinder.
Try this....
[urlhttp://tinyurl.com/mr7cve[/url]
HTIH
Jeff[8D]

quote:Originally posted by prager

Hey Jeff, (trying not to hijack the thread) How about a Lark with Turner Discs all around with a 64-66 pb booster. 2 stud master cyl mount. Would that Corvette master cyl fit this booster? Or is there a master just as good that can be off the shelf at my FLAPS? As it is now I have a 70 Chevelle Disc/drum m/c not yet installed..that I guess will not work..Any ideas? Thanks!!

[bige]

I do understand that. More pedal travel with the smaller bore also. I won't know until I take pressure at the front brakes but there is a visual difference between fluid forced out from the front and the back when bleeding. That sympton has existed through a couple of different size dual masters with factory brakes, Turner Front Discs/drum and now disc/disc.

I'll be able to take pressure readings next week and see for sure.

ErnieR

quote:Originally posted by DEEPNHOCK

Just remember....
The bigger the bore on the master cylinder, the less pressure you will develop in the lines (all other things being the same)..
You said you were running a 1&1/8" bore...
Most disc/disc setups (ie: Corvette) run a 1" bore on the master cylinder.
HTIH
Jeff[8D]

On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

[prager]

Hey Jeff, (trying not to hijack the thread) How about a Lark with Turner Discs all around with a 64-66 pb booster. 2 stud master cyl mount. Would that Corvette master cyl fit this booster? Or is there a master just as good that can be off the shelf at my FLAPS? As it is now I have a 70 Chevelle Disc/drum m/c not yet installed..that I guess will not work..Any ideas? Thanks!!

Making resverations at the poor house parking lot for me and my 62 Lark..