Question on 71 chevelle brakes: disc/disc valves - Chevelle Tech
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Brakes, Suspension & Steering Conversion questions & more.

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  #1  
Old Jan 18th, 13, 10:49 AM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Question on 71 chevelle brakes: disc/disc valves

Note: this is not a recent or short term issue, but one that I've been living with for years, there should even be old threads similar to this on here

I am looking seriously at buying a brand new combo valve made for a disc/disc car. Past that I have exhausted every thing I know to get this car to stop better. Is there any hope that this valve could be the cure or am I just blowing another $60 plus fluid and likely some hardline splicing for nothing?

My 71 Chevelle has never really stopped worth a crap. It was originally a drum/drum car. I used a 70 model donor car and transplanted the disc setup including the fluid valves for the front line and the one above the rear axle. The front line valve was giving me issues with bleeding so I just removed it and braking showed no change but I was able to bleed the fronts better and get a better pedal feel.

I used a brand new disc booster, and have since replaced that one yet again due to a leak. I have a brand new master cylinder for a 1970 with disc brakes. I also put on the pedal limiter from the disc car. The master cylinder and booster pin is the correct length.

I recently switched the rear drums for LS1 fbody discs with stock type pads and rotors. Front calipers were replaced, rear calipers are new

Front pads are Hawks HPS but in the past I have used everything from cheap metallics to ceramics, the Hawks just don't fade when I'm driving the car harder for longer periods.

Fluid is fresh Super Blue ultra high temp DOT3, front lines are fresh rubber, rear lines are fresh rubber

Car weighs 3650lbs with me in it.


When applying the brakes they almost seem to "creep in" rather than applying force instantly. From a low speed roll you can hit the pedal hard and it will slow then finally once the car is almost still catch and stop. They get better and have more instant bite when the pads get some heat in them, but still never anything like even the old 79-80 Chevy trucks I've driven and certainly nothing like even a stock new car.

Unless you are going high speed or on poor pavement, even the most forceful brake application will not get so much as a squeak from the 235/60 up front or the 295/50 hard as a rock crap tires out back.

My dad's 69 Chevelle with stock brakes will damn near break your nose by the time you press the pedal an inch. Mine will travel about half the total pedal travel, it is firm but gets very stiff about half way.


Feel like I'm beating a dead horse here, but I really can't believe this car with every brake upgrade shy of huge rotors and dual piston calipers or stainless braided lines should be this hard to stop.
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #2  
Old Jan 18th, 13, 11:40 AM
Philip Philip is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

I have the same rear disc as you on the Nova with 12" rotors on the front. The master is a disc/disc unit from an 82 Corvette. The combination valve used is from a 1982 Cadillac Eldorado with 4 wheel disc. I am using all braided stainless brake lines, but the rubber should be fine too. The car weighs 3556 without me in it. My brakes are very responsive, easily controlled to prevent lock up and stop the car well. On a closed course the brakes were tested at various speeds from 45 - 130 mph with no issues or fade.
The valve is still available new, AC Delco 25504613 Valve Assembly. I purchased one last year for the 72 wagon brake upgrade. It will get the LS f body brakes from a 2000 Camaro front and rear.

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  #3  
Old Jan 18th, 13, 12:40 PM
thunderstruck507 thunderstruck507 is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Thank you, didn't even occur I should probably swap master cylinders too. I will give mine to my dad to replace his leaking one and buy the one you mentioned.

The valve I was looking at is on ebay. It's brass and looks just like the one you posted.
__________________
1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #4  
Old Jan 18th, 13, 2:23 PM
72ragtop 72ragtop is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

I run a quick take up master cyl and combo valve from an 87 Camaro Z28 4 wheel disc, works excellent.
HTH, Jim
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  #5  
Old Jan 18th, 13, 4:05 PM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Rockauto had a Wagner master cylinder on closeout for $11 no core. So for $22 shipped I have that coming.

Now I guess since I will have to bleed and refill fluid I will get a block anyway, can't hurt at this point.
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #6  
Old Jan 18th, 13, 6:16 PM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Looking at details for that combo valve, it has a single in and double out for front brakes.

My car being a stock drum/drum car has a single out from the master to a distribution block mounted down by the headers which splits the front.

I am having trouble finding a place I could buy hardlines for a 1971 disc brake car. Or could I use compression fittings or something like that to extend these lines from where they met that frame block up to the new valve?
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #7  
Old Jan 19th, 13, 12:41 PM
72ragtop 72ragtop is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Compression fittings are a no-no on brake lines. Regular flare unions could be used to extend the lines and eliminate the tee.
Jim
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  #8  
Old Jan 19th, 13, 1:41 PM
Philip Philip is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

The single line out to the front brakes has to tee somewhere. It will work to run a single line out of the combination valve, just block the other port with a flare nut plug.
I did that to be able to run a line lock. The line lock acts as the tee with a single line feeding it from the valve.

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  #9  
Old Jan 19th, 13, 2:06 PM
Philip Philip is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

edit> Sorry reread your original post and see that lines from a 70 were used to plumb in the disc valves. So you are looking for the lines from the master cylinder to the combination valve that mounts on the frame? I am assuming you did not save your old lines or the distribution block. If you do have them before spending the money on the brass valve try installing the distribution block and original lines with the disc/disc master. end edit<

Here is a photo of the drum brake valve on my 71. It has 2 in and 3 out. The hard lines are the same for drum and disc set ups, the flex lines at the calipers will need to be changed. The size of the fittings on the aftermarket valve should be the same for the front lines, the rear will need an adapter.
In the photo above all the factory hard lines were used with the conversion to 4 wheel discs.

drum brake distribution block

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  #10  
Old Jan 21st, 13, 10:29 AM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

No the car is up and running and everything. But the stock master cylinder has 1 out front and 1 out rear. The front line goes to a block like the one you posted which splits the front line into 2 lines.

Sounds like as long as that block does nothing to limit fluid for disc/drum reasons I can do like you mentioned and run one line out of the new block and plug the second hole.

Thanks for the help guys!
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #11  
Old Jan 23rd, 13, 11:49 AM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Hey Phillip,

What size and flare is that plug? Do you recall where you bought it?

Kevin
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #12  
Old Jan 23rd, 13, 10:49 PM
Philip Philip is offline
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Default Re: Question on 71 chevelle brakes: disc/disc valves

3/16" flare nut plug, bought it at NAPA.
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  #13  
Old Jan 24th, 13, 10:20 AM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

Awesome I have one local so I won't have to order it.

Thanks again!
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #14  
Old Jan 30th, 13, 12:33 PM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

This is the valve I got:




So reading the description I found on their site (posted below), this block replaces the frame block I have and you simply do away with any other valves or blocks. It takes 1 front in, 1 rear in. It then splits it left and right front and one big line to the rear axle where it factory Ts off to left and right.

So I guess I don't have to do any plugging or running new lines, just use a flare joint above the rear axle to remove that proportioning valve. The front line already has one where the front disc "hold off" valve used to be.

Link to valve I bought:

http://www.inlinetube.com/Prop%20Valves/PR-101.htm
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1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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  #15  
Old Nov 4th, 13, 12:01 PM
thunderstruck507 thunderstruck507 is offline
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Kevin
 
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Default Re: Question on 71 chevelle brakes: disc/disc valves

UPDATE: Finally got around to installing the new valve and master cylinder. Had to change the flare fittings on 2 of the lines from stock (actually had to swap them between each other and re-flare).

Pedal feel is very firm but based on using a temp gun I think there is still a little air left in front left and rear left to be bled out.

The brakes are noticeably better than they have ever been (the nose of the car actually comes down some during hard stops now) but still not impressive in the least and aside from on damp pavement I haven't been able to force a full lock up of a wheel.
__________________
1971 Chevelle SS clone
head/cam ls1, 4l60e, 3.42 12 bolt
11.67@115mph, 1.71 60ft
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