My wife bought her a 62 Nova vert a couple weeks ago. I'm going over it to make it safe for her to drive. One of my concerns is the brakes. The pedal is hard and I don't think it would lock up on gravel using two feet. I have set up several street rods with the same basic front end and matching components with no problems at all. This car was set up with a Heidts Mustang II front end with 11” brakes. The power booster is a 7” single stage unit with the master cylinder probably coming with it but I do not know the bore size yet. The 85 TPI motor seems to have enough vacuum to activate the booster OK. With foot on brake during start-up the pedal will drop about 1/2” on vacuum. The proportioning valve looks to be a take off from something GM.(K317) The rear end is a stock 62 unit. The car will stop but you have to leave a bunch of distance ahead to do it safely. Any ideas where to start before replacing everything and not knowing which one worked?
As you can see in the photos, the lines were reversed to the porportioning valve. That was switched and still the same.
The 7" single diaphram booster is your first problem ,a 8 double would be much better. If the MC is a 1-1/8 bore dropping down to a 1" will work better with that booster. You need to look into it a bit further.
did the same swap , those mini boosters have very little boost and no extra capacity junkyard camaro booster from 82-92 or hydroboost have worked for me in the past
It is stock. I did see in the MBM site that if you are changing from manual to power, drill a hole 1" lower in the pedal to mount the clevis to. But wouldn't that put the rod out of alignment? I'm looking into a 9" unit and will be doing some bore measurements to see what I have and need. Did that on a 38 Chevy I had and got lucky with a used unit. I usually go for the new shit that cost an arm and leg.
My ride exhibits the same brake tendency as yours. In a way, not being able to lock up the brakes in a hot rod isn't an entirely bad thing. It's kind of like unintended anti-lock brakes. However, I think that I should have chosen a 7/8" master bore, rather than 1." I guess that's my project for this winter.
Might be as simple as a bad vacuum booster check valve. A few years back I bought a brake pressure test gauge kit from SSBC but I think you can get them from other brake companies. You mount it in place of the bleeder at each wheel one at a time and can determine what pressure you are getting. Saved me a ton of time determining that I had a bad adjustable prop valve. You can also connect it directly to a master with the correct adapter and see what the pressure is.
If the booster is bad, and you want a very difficult to find Mustg II vacuum booster.... my "special construction" car has pwr Mustg II rack and pinion steering from a 1978. The booster went bad and I was able to buy a Wagner remanufactured booster from Baxter Auto Parts ($108) no core required. They are in Portland, Oregon (503) 285-2548. Ask for Skip Baxter the manager.
What is the bore size of the M/C? Going down 1/16" in bore size will make a noticeable difference in pedal feel.
"It is stock. I did see in the MBM site that if you are changing from manual to power, drill a hole 1" lower in the pedal to mount the clevis to. But wouldn't that put the rod out of alignment?" I think stock ChevyIIs have a bracket that spaces the booster away from the firewall. If you drill the hole lower on the pedal to mount the clevis the bracket takes care of the misalignment. That would also change the pedal ratio making the pedal even harder to press! I think the master you have is a Corvette style which would be either 1" (used for non-power Corvette brakes) or 1-1/8" (for power Corvette brakes) 68-82. I'll bet your problem is with the booster as others have said. There have been a lot of problems with the aftermarket 7" boosters
Don't know until I pull it off. Booster seems to be working ok. The pedal drops about 1/2" at start up and then goes hard. Update: I put the Nova on a hoist today and looked it all over. The front lines are all 3/16 line to both front calipers. Coming out of the proportioning valve to the rear it is 1/4" for about 3-4 feet following the front cross member to the passenger side. At that point it is reduced to 3/16" with adapters running down the passenger side to a splitter at the rear end to the rear brakes. That all looks be be factory line. I did notice a kink in the 1/4" line just out of the proportioning valve to the rear but it don't look to be a problem. There is no 10# residual valve in the rear line. I'm not one to use used parts on a build as this one seems to have but then again I have seen new parts fail to. I ordered a new proportioning valve, #10 residual valve and will be upgrading the vacuum canister to a 9" soon and checking the master cylinder size at that time. I have a new MC setting on my shelf that is a replacement for a 68-74 Chevy Nova and it has a 1" bore that I can use.
yup.hard pedal is typically a booster.While the car is running,press the brake pedal .if the booster is bad it may create a vacuum leak and cause idle stumble.sometimes.or attach a handheld vacuum pump to the port and pump for a while to see if it holds.it may take a few minutes.Ive done this ,it works.
Now that you mention it the idle does seem to bounce around 800 to 1200 rpm. I have several things I need to check out and have done several of these myself but didn't build this one. I will be going over the complete system before it is done.
^^^^^^...What he said-hard pedal usually points to booster problem..give us an update when you get one.
A sure sign of a bad booster or possibly the check valve. From my experiences I've seen more bad check valves than bad boosters. Plus they're dirt cheap and easy to swap. Look over the entire hose for splits or a poor fit at the manifold fitting. Bob
I had some time this afternoon and pulled the MC. It checks out to be 1.023 bore, which I think would be a 1" bore. The vacuum at the booster is close to 18# and runs up to 22ish at 2500rpm with no load. I replaced the check valve with a new one I had and no change there. I try to do one thing at a time so I will know which one works.
Master cylinder too big... I put an F450 SD master cyl. (1 1/4) on an F350 with a (1") and observed your same dilemna. Just like the previous guy with the different leverage idea , you must exert more force to push more fluid to provide the necessary clamping pressure with the larger piston. Find an old oxygen or nitrogen tank pressure valve and plumb it in the line. Our old sprint car will scoot the tires and kill the engine at 1200 lbs.
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