GDaina

Can't bottom out the pedal to save my soul...It just ain't happenin'

mrvette

RONG, you have that input pin/shaft, that goes to a SPRING that in turn goes to the output shaft/pin to m/cyl.....I tore apart my old booster wondering WTF was rong, it's same essential design as was in another car some decades ago.....it's that spring in there that has something to do with the operation of the unit, all I know is when doing a DIRECT A-B changeover, one of my goals was to PROVE the point about my actual brakes being good from the m/cyl input piston to the rotors, and so I pulled the m/cyl off the booster, stuck on the HB, bled it through, and remounted the m/cyl to the HB unit....started the engine, went forward a inch, stopped, back a inch stopped, backed down the drive, noticing about less than 1/2 the brake pedal travel to stop the car, then drove down the street, and hit it per habit....planted my nose into the steering wheel....

NOW, show me how in hell that is not a definitive proof test....

CASE CLOSED.....and I found NO defects in my vacuum assist booster when taking it apart...it held vac fine until i popped that check valve outta the grommet, and it was completely intact internally, nothing seemed outta place or worn...

so, it's been that way since I put the HB on there....

I did have a front hose collapse on my, so 2 new hoses and a caliper O ring set, just as before...and 2 new rotors....

but that had nothing to do with the HB setup....

mrvette

see my above note, bet I could, easy....you all must have small feet.....size 14XXX here....and I can assure you they hurt with arthritis, so hate using much pressure on them, hurts to walk even....

HamadUP

Well, let me summarize it that way : I lost any hope with my brakes, (new 4 calipers, new m/c, new 4 braided lines .. still far from good stopping performance), but after having the HB, its much more than day/night difference! .. It is the BEST brakes I've ever experienced! ..

Note that I'm not talking about stopping distance alone, I mean the pedal feel, sensitive-ness of the pedal, and the stopping power, all are PERFECT!

GDaina

You don't read very well Gene, I have manual brakes, manual, not vacuum, no booster..size 11 shoes here...

Bet you can't bottom out my pedal...only way your shoes will touch the floorboard if yo tilt them downward and then yo itty bitty toe will barely touch...so case closed...Iz have spoken...

mrvette

mrvette

Exactly my experiences, and with more than just a shark too, actually the shark was the worst of the bunch, but it took someone like Norval to finally convince me to try HB, and damn if he wasn't right, which is when I tore into my old vac booster, wondering if in fact it was defective, in spite of it being like all other vac assisted cars...and sure enough, it was intact, like I said...so I just wrote it off as poor design for a 4wd disc car, but once in production starting in '65....well for something toss out to the engineering staff in say '63, not so awful evil...but gotta consider that '63 has been a while ago...

wcsinx

What spring? Are you talking about the diaphragm spring? That doesn't connect the input and ouput shaft. AFAIK both shafts seat in the diaphragm itself. I haven't torn apart my C3's, but I've had it out before. There was no play whatsoever between my input and output shafts. It felt like they were butting up right against each other. I wonder if maybe you had the wrong booster in your car? You should not be able to bottom out the pedal period.

Pull down the brakes on a brand new car, and there ain't much different. 1 piece floating calipers is just about the only major change since then.

Taijutsu

I just got off the phone w/brake tech. He said my unit was working just fine.
He explained that there is no nitrogen charge, there is an accumulator that gets charged from the unit.
When the PS pump fails, I get 1 or 2 presses on the pedal that work, after that you have nothing. The accumulator is not designed to get you home, it gets you off the road. That's it ,I will pick it up later and report anything interesting.
I don't know if this info will help anyone, now I know.

Ricisan

SHAKERATTLEROLL

A few members here in this thread said the same thing. That you will get 1 to 3 stops before it dies. A few people on this forum do know what they are talking about now and then lol.

HamadUP

No, it will not die, it will just be as hard as a manual brakes, so you still can drive your car safely, just you need to depress the brake pedal harder to stop the car.

Binnie77

EXACTLY, well put

SHAKERATTLEROLL

Yes just the easy part goes away. You just have to push Harder lol. Sorry as I did not see a need to say the same thing that has been said many times in this one single thread. Whewwwwww

Taijutsu

After the accumulator ran out, I had nothing! I could come to a stop using the trans and brake drag, but I did not have manual brakes.
I couldn't think about driving it home.
When the tech asked me how many times I pumped the pedal, I honestly couldn't remember. During a no brake crisis, I wasn't counting how many times I pumped the pedal. I come from the old school where you just keep pumping hoping to build up some pressure.
I don't know if this helped anyone or not. I need to retrain my brain to keep my foot into the pedal and not pump the brakes in the event this happens again. I know I have the belt tighter than it was.

Ricisan

Taijutsu

Now that I think about it, I doubt that I put my foot to the floor?
I'm sure I kept pumping when I didn't feel any pedal building up.
If there was some manual brake at the bottom of the stroke, I didn't find it.
I put on the $ PS belt and used my new craftsman pry bar to get it nice and tight. Hopefully this will not come up again.

Ricisan

Binnie77

Rick, now that you have the car moving again, take it for a test run, shut the engine down and see what the brake response is. That way, you will be prepared for the next time which is hopefully never Mine feels much like manual brakes after the accumulator loses pressure.

mrvette

That spring I referr to is about a inch+ long, and about inch in diameter, it was situated right around the diaphragm, but it was obviously situated on center with the input and output shafts, and the output looked like a long stem lawnmower valve....about a inch in diameter....I forget about the input shaft....anyway, that spring is wound out of about the same as a valve spring material....1/8 inch thick, and so it is not something you can compress easily, it will take all the leverage of your brake pedal assy to compress it...take apart the next shark power booster you see, like mine one that was all painted and corroded on the surface, making it almost worthless for a rebuilding core....but I never replaced it with one, so there was NO dud value to anyone, hense I tore it apart to see what I could....I was kind of surprised that spring was in there....as I saw no need of it....all I do know is that with relative ease my pedal saw the floor, and always did, with NO air in the lines, as proven by my A-B direct swap with HB unit...

all I can comment is about my battles/experiences with this '72 over some 15 years.....and it took a bit of convincing before I finally spend money to prove the case...but it WAS Norval that finally turned the case for me on this....maybe TT also....I forget...some 4-5 years ago now....

I should date reference when I do things...never have....



EDIT....thought of that old overhaul manual I have from '72,....and in there under brakes, is the section 5-22 showing the cross section of Bendix dual diaphram booster, and in there in the middle of it all is that spring I refer to above....they call it a Valve Return Spring....it has a cup in it, with the ball end of the input shaft seated there...and it presses on the diaphram with the output 'valve' shaped rod on the other side....sure enough...me not crazy....

68/70Vette

One thing that I think really didn't come out in all these posts is that (1) if you have a Big Block, (2) if you have a tall valve cover for roller rockers and a stud girdle, and (3) you want power brakes, then a Hydroboost is your only option. The stock vacuum can will most likely hit the valve covers.

My 68 has manual brakes and I wish I had installed power brakes. After driving all my cars with power brakes, the extra brake force required by the 68 catches me by surprise the first few times I have to apply the brakes.

wcsinx

Nah man, you're definitely crazy. But I don't doubt your findings on the booster.

I still contend that isn't why your pedal was bottoming out though.

gyopp

Sounds like a good idea but be carefull, a member here that I will not name smacked his 69 up pretty good when he turned his off and locked the columm.