Wilwood Disc on a 73 Challenger

[Steinman]

Just purchased a 73 challenger, love it but it will not lock up the 4 disc in a panic.
I have a 20# electric vacuum pump and a new booster. Brakes work good around town with normal stopping. Petal becomes very hard in a panic and feels like wet drums.
Wilwood tells me hyd is the only option but I am having a hard time swallowing this.

Any ideas?

 

[AUSTA]

What vacuum are you getting to the booster.
I did experience a similar problem with a large cam & went to the Hydraboost system in short excellent
I am running standard 70 disc front large finned rear brakes the proportioning valve also made a big difference to braking balance.
Tried the Wilwood Dynalite on the front but found the original Dodge discs were quieter & had better stopping
but generate more heat due to lack of cooling

 

[Steinman]

20 Lbs. of vacuum and a 1.125 bore Wilwood master cylinder.

 

[70Hardtop]

pedal, not "petal" (unless you are putting your foot on a rose)

 

[rbbruno3]

I don't have power brakes but do have 4 wheel Willwood disc with 7/8 bore Willwood MS and Willwood PV. Bill atRMS did tell me about a hard pedal with a larger bore. I assumed bigger is better. Not sure if this has anything to do with the power brake setup

 

[Wanda73]

Your situation sounds similar to mine when I "upgraded" to SN95 mustang discs, basically a home brewed 13" system similar to what Dr. Diff sells, serious props to him by the way, he tried to help me sort my junk even though I didn't buy it from him! Anyhow, my pedal felt fine in normal braking, but as soon as you really smashed it it felt like it was bottoming out even though it wasn't, and it wouldn't lock the front or rear brakes. A diesel tech loaned me a hydraulic pressure gauge and I found my line pressure was way low (4-500psi) with a 1 1/8 bore. Swapped to a 1 inch and it got better, but still felt like it hit a hard stop (like it was binding or bottoming out, but it wasn't) under max effort and wouldn't lock the wheels. I've heard of a small bore 7/8 or 15/16 (don't remember which)master, thus increasing pressure, but I couldn't find one. I did have low vacuum, and didn't want to run a booster, so I swapped to hydroboost off a cobra mustang. Best $114 ebay purchase ever for a used master and booster, and now she has the best brakes I've ever felt. I never figured out what caused the hard stop pedal feel, just know I could "bounce" the pedal on that stop, but if I cracked a front or rear bleeder it would drop to the floor. These are some pics of it going in, I changed it up a little from these pics, but it will give you an idea of how it fits.

 

[Steinman]

Thank you for the information.

After a lot of research and a 20# vacuum pump I have elected to go with the hydroboost.

Know anyone that needs a good vacuum booster and a 20# pump?

 

[Hemi Steve]

Your situation sounds similar to mine when I "upgraded" to SN95 mustang discs, basically a home brewed 13" system similar to what Dr. Diff sells, serious props to him by the way, he tried to help me sort my junk even though I didn't buy it from him! Anyhow, my pedal felt fine in normal braking, but as soon as you really smashed it it felt like it was bottoming out even though it wasn't, and it wouldn't lock the front or rear brakes. A diesel tech loaned me a hydraulic pressure gauge and I found my line pressure was way low (4-500psi) with a 1 1/8 bore. Swapped to a 1 inch and it got better, but still felt like it hit a hard stop (like it was binding or bottoming out, but it wasn't) under max effort and wouldn't lock the wheels. I've heard of a small bore 7/8 or 15/16 (don't remember which)master, thus increasing pressure, but I couldn't find one. I did have low vacuum, and didn't want to run a booster, so I swapped to hydroboost off a cobra mustang. Best $114 ebay purchase ever for a used master and booster, and now she has the best brakes I've ever felt. I never figured out what caused the hard stop pedal feel, just know I could "bounce" the pedal on that stop, but if I cracked a front or rear bleeder it would drop to the floor. These are some pics of it going in, I changed it up a little from these pics, but it will give you an idea of how it fits.
Your situation sounds just like mine. Brakes seem ok around town but in panic stop it feels like the master cylinder is bottoming...the pedal gets very hard and cannot lock the brakes. My setup is as follows GM single pot rear calipers, GM master cylinder and dual diaphragm booster and proportioning valve, and original Chrysler single pot front calipers. Have a line lock in the front circuit. All of this in a "73 Barracuda with a full roller 528 hemi. Cam is fairly mild and allows 14 to 15 inches of vacuum at idle. took the car to a brake shop who went through everything and bled the brakes twice. No improvement. Their opinion was that the 14-15 inch vacuum is the problem, Booster seems to be behaving correctly....on engine start the pedal drops a bit, after shut down can make about three brake applications before pedal gets hard. I pulled the master cylinder away from the booster thinking maybe the pushrod needs to be adjusted and found the pushrod is not adjustable. Master cylinder is a shallow piston type. I did not measure the bore at that time. I also have not measured the actual pressure at the calipers. I don't have the gauge to do that but I can buy one and get delivery in 4 or 5 days if necessary.

So, is my current setup a lost cause? Will the hydroboost setup you used salvage this in your opinion?

Steve
View attachment 47014

View attachment 47015

 

[Hemi Steve]

Your situation sounds just like mine. Brakes seem ok around town but in panic stop it feels like the master cylinder is bottoming...the pedal gets very hard and cannot lock the brakes. My setup is as follows: GM single pot rear calipers, GM master cylinder and dual diaphragm booster and proportioning valve, and original Chrysler single pot front calipers. Have a line lock in the front circuit. All of this in a "73 Barracuda with a full roller 528 hemi. Cam is fairly mild and allows 14 to 15 inches of vacuum at idle. took the car to a brake shop who went through everything and bled the brakes twice. No improvement. Their opinion was that the 14-15 inch vacuum is the problem, Booster seems to be behaving correctly....on engine start the pedal drops a bit, after shut down can make about three brake applications before pedal gets hard. I pulled the master cylinder away from the booster thinking maybe the pushrod needs to be adjusted and found the pushrod is not adjustable. Master cylinder is a shallow piston type. I did not measure the bore at that time. I also have not measured the actual pressure at the calipers. I don't have the gauge to do that but I can buy one and get delivery in 4 or 5 days if necessary.

So, is my current setup a lost cause? Will the hydroboost setup you used salvage this in your opinion?

Steve

 

[moparleo]

Hydro-boost is usually the Magic Touch.

 

[Steinman]

Hydro-boost is usually the Magic Touch.

Agree, go with the Hydro and forget the rest. Toughest part of the job is getting the upper bolts to the master cylinder under the dash out. Use a deep socket with a swivel joint and long extension.

 

[Hemi Steve]

moparleo
Thanks for the reply. Do you have a hydroboost in an E body? If so what calipers and master cylinder are you running? what was the source of the hydroboost unit? Wanda73 says he used a Mustang Cobra unit from EBAY. I read that there are many cars that used them and of course there are commercial sites that sell them. Unlikely that they all have the same specs so am looking foe some experience from those who have actually installed one. I looked into these for a 70 Hemi Challenger I used to habe before the Cuda I have now. I seem to recall that at least one of the commercial sellers provides an adapter plate to match the hydroboost to the vacuum booster holes in the firewall. It looks like Wanda73 has some sort of a mounting adapter. What I'd be looking for is a plug and play setup where I don't need to invent or fabricate a bunch of pieces for mounting or pedal pushrods etc. Any guidance on this?
Steve

 

[Steinman]

I got my set up from Matt Sweeting, Spezd Mfg. Mattpowerbrake@yahoo.com 714-330-5286.
A cheaper setup or supplier maybe found but I wanted something I could rely on and someone to call and speak to should I encounter problems. My only recommendation is be careful with the cut to fit hoses. I wound up having to get a special hose fabricated. Not a complicated install, just be patient. Google Hydro Boost for your specific car and you should get a lot of hits to look at. UTube also has some videos to review.
Good Luck

 

[Steve340]

14 inches of vacuum should be plenty to operate any vacuum booster.
When the pedal gets hard are the brakes actually locked on? or will the car still roll if you give a little push?

 

[Hemi Steve]

Steve340
When the pedal gets hard the car is definitely stopping but at that point the brakes will not lock up so there is more braking available at the tire patch that the brake system cannot provide. Before it gets to the hard feel I have a "power brake" feel to the pedal. The travel seems a bit too much by the time I get to the "hard feel" but the pedal is not touching the floor and I don't see any interference point in the pedal to booster linkage. The pedal responds properly while depressed during start up and after shut down I can apply the brakes maybe 3 or 4 times before the pedal gets hard. My brake people say I need at least 18" of vacuum.

Steve

 

[Hemi Steve]

Also, there seems to be more pedal travel before there is noticeable braking than I'm used to. Even so, I am not bottoming out the pedal against anything I can see. I've ordered a brake pressure gauge to see what I'm actually getting at the calipers. there is a "thing" in the front circuit that I cannot identify. it is between the line lock and the front calipers. Here is a photo...not a great one. It is a blue anodized piece maybe 3" long visible at the edge of the valve cover in the picture.
Steve

 

[Steve340]

That is a residual line pressure vale that would be used in a drum brake rear. It is a Wilwood. If you have disc rear you can remove it. It is not part of the front brake system at all. Until you get the brakes sorted it may pay to bypass that line lock. It could be a problem.
It is designed to restrict the fluid flow.
That brake shop are wrong in my opinion I have had cars run at 10 inches no problem at all.
However tiny diameter boosters do suffer if you have low vacuum but you do not from your supplied info.
If you have a lot of pedal travel and the standard e body under dash bell crank system this can go over centre and you lose push in layman's terms.
It sounds to me you might have a binding or master cylinder clearance problem.

 

[Hemi Steve]

Steve340
I've included a picture of the under dash brake linkage. Very busy space so you need to look closely to figure out what you are looking at. I thought that might be a residual pressure valve but couldn't understand why it was there in a disc disc system. I'll see what I can do to get that out of the circuit and also see what I can do to get the line lock out. Thanks for the feedback. Also, I'll check again to see if the residual valve is in the front circuit or more properly in the rear. with the line lock and proportioning valve plumbing in the same area it's easy to loose track of which line is which.

Steve

 

[Hemi Steve]

Oops, forgot to upload the picture. Senior moment. Here it is.

 

[Steve340]

Go back to basics and take your time is the best.
A disc brake system does not need that residual valve only required for drums.
I can see something but got to go out. Will reply later.