55.2-59 Help with Power Brake Booster

[cab4word67]

We have a 57 C3100 with a 383 stroker and 700R trans. The truck has a 7" PB Booster mounted on the frame w/2lb inline vales ft and rr. . We have GM 194 calipers in ft and Corvette C3 s in the rear. All is new but it drives like it has manual brakes. Any Ideas? I have room for a 9" PB Booster but dont know if that will help?

[dsraven]

maybe do a few checks first, like vacuum available at the booster compared to what the booster needs. ensure the linkage is adjusted properly and not binding, the pedal height has a stopper so the pedal has a dedicated stop point so the freeplay at the booster is always the same. look at an inline vacuum check valve close to the engine to keep that line charged with vacuum no matter what the engine is doing, a vacuum reservoir to keep a more constant available supply or possibly a vacuum pump if the vac is lower than advised by the manufacturer of the booster. otherwise, in my opinion, cut your losses and install a hydroboost. if the brakes operate like normal except for the pedal pressure and all the linkage is like it should be and the master cyl bore size is specc'd for the system then it would seem that the small booster is simply undersized. pretty common really. just my opinion. not a fan of small boosters for this reason.

[jwhotrod]

I had a discussion with Ralph Seats who owns ECI a guy who i respect alot about brakes in my 55 chevy build. I plan on a LS3 with C4 suspension and brakes. His opinion is that there is no way i was going to build enough line pressure for the corvette brakes with a vacuum booster. he suggested i talk to the following http://www.hydratechbraking.com/ about hydraboost. which runs off of powersteering hydraulic pressure. The corvette brakes require high line pressure. the cool thing is it will fit in your brake mount directly t=replacing your vacuum booster.

[NeoJuice]

My two bits.

If you are unsure of your engines vacuum output a basic vacuum gauge is the perfect tool to confirm your engines vacuum. Depending on how modified your 383 stroker is it might not be producing enough vacuum. I think you need at least 20in/hg of vacuum in order to run a 7" booster.

In my scenario I have a modified 350 with a pretty aggressive cam and the motor does not produce enough vacuum. I have a 7" under floor booster and I added a Leed brake vacuum pump and that solved my power braking problems. I would also suggest to check all the other stuff DSRaven said as well.

[cab4word67]

Thanks guys, I checked everything down to the line and check valve. All good motor is making 10-14 hg of vacuum. Even checked the booster and it is also working. Ran a line over from my ZZ4 in my 67 just to make sure and with its somewhat higher vac it helped. We decided last night to go with the Leed bandit series pump. Will report back after install.
Thanks again everyone.
Chris

[NeoJuice]

On my truck I might add a vacuum canister this year for extra vacuum storage. I find that after driving for a while and not using the brakes or using the brakes to much you can loose vacuum pretty quickly because the vacuum pump is off and it has to switch back on. Compared to it being hooked up to engine vacuum when you have full vacuum all the time to the booster.

Right now what I do is I make sure to apply the brakes way ahead of my stop to make sure the pump is on and going and I have good vacuum assist to come to a complete stop.

If that makes any sense.

[dsraven]

diesel engines run vac pumps, some are belt driven, possibly one of those could be adapted and would run all the time. some are driven off the back end of the alternator, some are a stand alone belt driven affair. not sure on their output as a lot of diesels also run hydroboost. for anyone who hasnt dedicated funds for a small vacuum booster possibly tghose funds could be redirected to the purchase of a hydroboost set up. they are smaller and mount in the same place as the vac booster but work better in my opinion. always good brakes and lots of them in the wrecking yards for decent pricing. not that tough to hook up either.

[Rickysnickers]

Since we are talking about hydroboost, how would they work with a Ford rack and a GM pump? This is what I am using and have had to install a pressure resisting valve in the back of the pump. I think it reduces pressure to around 850psi. Doesn't the hydroboost require more than that?

[dsraven]

sorry guys, I just wrote up some stuff here, twice, and it didn't let me post for some reason. the page didn't load. anyway, long story short, I googled the topic and came up with this motor trend how to article which explains some stuff that may be of interest to anyone thinking of a hydroboost system or somebody having trouble with poor vacuum boosted brakes.

https://www.motortrend.com/how-to/hy...%20psi%20range.

[dsraven]

hmmm, it let me post that one.
dunno what the deal is. anybody else having trouble today?

[dsraven]

hydroboost requires 1300-1600 psi
mustangII rack requires about 850-950 I think. of course how the front end is set up also affects the ease of steering and some installs done without the thought of ensuring correct front end geometry have resulted in poor steering no matter what. when the IFS cross member is installed the truck frame needs to be levelled side to side and sitting at the intended rake angle, otherwise the geometry may not be able to be set correctly when done and it ends up being "as close as I could get it" from the front end alignment guy. that alone can make for twitchy steering and then when the over pressured steering rack is factored in things can get super hard to control and scary when driving in winds or on highways that are grooved out from traffic etc.

[cab4word67]

When you added the vac canister what improvement did you see in the brakes behavior. I just installed the new Leed pump and I get 1 great push to stop then the next one right away is so so. If I go to 3 its like manual again.

[dsraven]

sounds like you could benefit from a vac reservoir. the normal safety standard is 2 normal applications after the engine quiits I think.

[NeoJuice]

Ill be adding a vac reservoir this year.

[dsraven]

a cav reservoir can't hurt anything even if your brakes are working fine. it is just gonna be holding a sustained vacuum that should be there anyway whether from the engine or a vacuum pump. it isn't going to steal away engine performance if connected to the engine only as it will only top up to the best vacuum available due to a check valve between the res and the engine. if the truck is not driven for awhile it will draw a vacuum from the engine when it first starts up until the engine makes it's peak vacuum, which would likely be just after a rev up and then the throttle closed. they are small cannisters so it's not like they gulp huge breaths of vacuum at once. not really much different than running a full sized vacuum brake booster, nobody pays attention to the draw from them when the engine starts because it is minimal as long as the check valve is working properly. older vehicles with vacuum operated heaters and air conditioners used vacuum canisters and nobody paid attention except to wonder what was up with the old tomatoe juice can under the hood, lol.

[dsraven]

you could fab a vac cannister from a short length of abs plumbing pipe with end caps on each end and use a check valve and rubber bushing from a brake booster tapped into the end cap as the supply for it then another brake booster fitting-gutted so it is not a check valve anymore and will free flow-as the outlet or possibly a bulkhead fitting or something similar as a the outlet. then it could be attached to the truck somewhere out of site using a couple of large clamps like a lot of us use to hold our wiring to the frame, they are wrapped in rubber so they would grip the pipe well. if you fab one just to see if it works you may even like it enough to simply leave it as is. all done for a few dollars and a trip to the hardware store, if you don't have any plumbing scraps laying around or don't know a plumber who would likely give you the supplies all glued together. I suggest to drill the end cap first before assembly and use a step drill so the hole is actually round. otherwise drill chips will end up inside the canister.

[cab4word67]

I thought about making one, but found a steel one on Amazon for 29 bucks. I will update after the install, thanks again everyone.
Chris

[dsraven]

if you install a vac cannister and still have the issue with poor boost after the first pedal application you may want to run a temporary vac gauge on the system side of the check valve just to see what the vacuum drop is when the pedal is pushed. maybe the booster is using more than it should and the vac in reserve is gulped up with the first application. also, check to ensure the push rod from the booster to the master cyl is adjusted correctly as well as the pushrod from the pedal.are you running disc front drum rear brakes? if so, are the drum brakes adjusted correctly so pedal travel is like it should be? is the booster diaphragm possibly travelling further than spec for a normal brake application and so it uses more vac supply than normal after a single brake application to "refill" the vac chamber? what sort of pedal travel do you have once the free play is taken up?

[dsraven]

just spit balling.

[dsraven]

sorry, forgot the part about your turck having 4 wheel disc set up. I have heard, though, that the covette brakes seem to like a little more pressure to stop.
have you done a check on the bore size of the master cyl compared to recommended size for the caliper displacements? smaller bore size means the pedal is easier to push to get to a given required pressure but the pedal travel may be more to dispace the required amount of fluid to get the brake pads out against the rotors. larger bore size means less pedal travel because it displaces more fluid per inch of pedal stroke but more pedal effort required to generate the same pressure as the smaller bore master cylinder. that is assuming the pedal goemetry etc is the same for each one. like you tried one set up then swapped just the master cylinder to the larger one and tried the same tests again.
here is a little article that is a good start on what I am trying to explain.

https://techtalk.mpbrakes.com/booste...conversion-kit

[cab4word67]

OK here is the update, I got the Leed electric Bandet pump and it worked with one good push then got hard. now with the extra vacuum tank inline we have 3 good then #4 gets hard. This should be fine. Now we just need to wait for the pads to all seat.
pic shows both pump and tank under cab.

[cab4word67]

Hey Dsravon, to answer all your questions we have a 1" bore corvette MC and everything was checked out before we went to the electric pump. I questioned the one push too but it seems with a 7" booster there isn't much reserve. Now with the tank its not bad. If it was my truck I would still squeezy in the 9" booster. But right now I think he mite be taped out for awhile with all we have done. BUT it now works.

[dsraven]

good to hear it's working. nice lttle res unit too.
when you say wait for the pads to seat, do you mean you need to burnish the pads? there is a method for that which will possibly really help the brake booster do it's job and make the brakes work as designed. google how to burnish brakes for your manufacturer's info. a lot of guys simply install the rotors and pads and then just drive it but that doesn't actually burnish the pads as the manufacturer designed them and sometimes simply glazes the pads so they require more pedal effort to stop te vehicle and no way would they ever actually cause a skid. burnishing smooths the rotor surfaces and deposits a layer of the pad material onto the rotor surface. it helps eliminate brake noise etc as well. usually the manufacturer of the pads has a description on how they recommend to burnish and that may differ from one to the next or possibly for the different friction material being used. when burnishing I try to do it on a road where there is less traffic and also no stop signs or traffic lights. this is so, after burnishing, I can drive the vehicle for a few minutes to allow the vrake parts to cool down before I need to stop anywhere. stopping with really hot brakes can cause the rotors to warp and nobody is happy after that.

[cab4word67]

I have been doing that very thing. I have done about 15 slows from 30 so far. I was waiting until I got the tank and had good weather. Thin I will take it out on the back road where I can get up to 50 and slow down then cool then repeat, maybe this week.