Help with '75 brake diagnosis

[rpounds]

The VBP's seem to be the way to go. I will be checking into that. Thanks!!

Ron

 

[JohnZ]

The VBP O-ring seal kits have an outstanding track record for eliminating the "air-pumping" problem on the rears (which is caused by a combination of lateral rotor runout and/or excess end play in the spindle bearing pack, as the caliper is fixed). Unless you're going to set up a dial indicator and check both rotor runout and bearing end play, you're wasting your time - those have to be right, or you'll be working on it again eventually. The spec for bearing pack end play is .001"-.008", and for rotor runout it's .005" TIR, maximum. If either one exceeds those numbers, you're going to have a problem. Corvette rotors MUST be machined on the spindles (most quality brake shops and good dealerships have equipment to turn them on the car) to get the lowest possible runout numbers.

The Corvette rotors are excellent, and have more than enough mass and ventilation to stand up to just about anything - what kills them is hot-rod-Harry "race" pads, which "eat" them; with OEM pads, the rotors will last almost forever.

The parking brake system is VERY marginal, and even when all the parts are new, it isn't very effective; it works much better keeping the car from moving backwards than forward. Just the nature of the beast.

 

[rpounds]

Thanks John. I'll be setting up a dial indicator on this thing this weekend. While I'm at it, I want to check all four corners. End play is also of concern, so checking that while I'm at it will be worth while. I would like to buy a little bit of time until I'm ready to tear the whole rear end out of the thing for rebuilding the trailing arms, etc.

While I'm here, let me ask a question. How difficult is it to rebuild the trailing arms? I have access to a hydraulic press, etc. And, are there any tricks, tips, cautions that I should be aware of? Again, for future reference. I'm not planning on tearing it apart for a year or so.

Ron

 

[Vette/Berlina-coupe]

-Many genuine thankx to JohnZ and GaryWhite and Roy and Others for some really great advisories as to what is needed to bring the'ole C3's braking up to speed so to speak! Gary has already given the website for HydraTech, a really excellent device which gets rid of the vague-feeling pneumatic-boost(eng.vac.powered) system in favor of tapping Pos.-pressure from your C3's(most) power-steering Hyd.-pump, --but here's the website for the first thing that has to be set in order, VBP-Inc's(Vette Brake & products co.) patented rear/Caliper-seals-- http://www.vettebrakes.com/about.htm (but be sure to also turn the Rotor's with their respective axles as has been advised; and, install braided-steel flexhoses at all four wheels to virtually eliminate natural hose-expansion sloppy-feeling). From an engineering standpoint, what I perceive here from suggestions by all, -is for a C3-owner to first get their basic brake-system functioning better than new via the hitech components now available to us, then if'in you really want to make the system haul you down from the century-mark like never before, --check-out the terrific 300%/power-boost and even more solid-feeling pedal-action demonstrated (see their movie) by HydraTech! Wow, I am really stoked over learning of these great innovations to improve the C3-breed. [a word of caution here though: --remember, the rubber-band (belt) on your power-steering which is rather a life-line, as well as the engine-vacuum! I know of a fine local Doctor & Wife who were simply navigating a freeway/on-ramp not far from my office here in Pt.Loma SanDiego, --well, their engine suddenly died and he simply didn't have the where-with-all to unexpectantly command manual-control of the big Cadillac, --they both tragicly perished (GMC quietly paid-big to hush-up this "inherent-defect" we are all subject to, in our dependence upon power-assists to aid our control of a heavy vehicle). I am still drying-out the seat from my virtual loss of braking-control the other day (the big 122"-wb '80/Berlina-vette with bumpers like battering-rams, indeed narrowly missed wiping-out a half-dozen rice-burners).... -B.B

:dance

 

[sscam69]

Kinda freaky, how vulnerable you can be.


Up to this point I have not had any problems with my brakes BUT I don't drive my car all that often either. I must say that when I first drove the car the braking system impressed me. This thing could stop on a dime! Up to that point I had never driven anything with 4-wheel disk breaks. That Hydra-boost system looks like a fun item to try

This is an issue I will definitely address once I rebuild the suspension on the car.

 

[JohnZ]

The Corvette production disc brake system is an outstanding piece of work, and doesn't need "upgrades" to improve it, unless you're into professional road-racing, or doing repetitive high-G stops from 100mph all day long. There's plenty of swept area, and the rotors have plenty of mass and ventilation for heat dissipation. The unique design characteristic is the fixed calipers and constant-contact pads, which make rotor lateral runout critical to avoid "air-pumping" when the bearing pack loosens up beyond specs or the rotors get warped, or are removed and re-installed without being indexed to their original orientation - the rotors were originally machined while riveted to the hubs and spindles just for this reason, but most converted gas-station discount brake shops don't understand this, as they don't read Shop Manuals and 99% of the modern cars they work on have floating calipers and pads that aren't in constant contact.

The only reason for a Hydroboost system is in a case where the cam is so wild that the engine doesn't produce enough vacuum to operate the power brake booster; that's why GM put Hydroboost systems (or electric vacuum pumps, depending on the model) on the early 80's diesel cars (diesels are unthrottled, so produce very little vacuum).

Ultimate non-ABS braking performance (for a single stop) is determined by the tires, not the brakes - any car's brakes can lock up the wheels, but it's the tire contact patch that determines whether the car will stop in time or not.

About 500 million cars have been built with vacuum power brake boosters, and they're about as reliable as a component can be made; nobody ever intended them to be 100% reliable after 20-30 years of use; people tend to ignore maintenance until something breaks, and how many 30-year-old cars do you see driving around besides Corvettes? Not many. Even precision aircraft components (which cost 10X the price of similar automotive components) are hours-of-operation limited, and have very stringent rebuild/replace requirements based on hours of use, or the airplane isn't allowed to fly. Cars have pretty good reliability statistics for complex mass-produced machines that pretty much get continuous abuse and zero maintenance.

 

[sscam69]

Wow John

YOU are one knowledgeable fellow. You never cease to amaze me as to how much you know!

Where did you learn all this stuff!?

Ya know I think you kinda like an encyclopedia, just full of information!

Frank

p.s. I have A REALLY GOOD QUESTION. Since you were the Viper plant manager I am hoping you might have some insight as to how decisions are made up at the top.

Do you think the F-bods are going to make a come back?

I mean it really comes down to money, and I don't think GM will let the mustang take over that piece of the car market. So I think they will but................

 

[JohnZ]

37 years in engineering and manufacturing with GM and Chrysler didn't hurt any - I've been involved with design and manufacturing of cars and their components all my life for a living, and I've built and restored race cars, engines, and Corvettes all my life as my hobby; also have 7700 hours as a pilot. With all that going on for all those years, you learn a little as you go along

Whether we see the "F"-bodies come back or not depends on whether there's a good business case for them; they died because of poor sales - simple as that. They only sold about 70,000 of them (Camaro/Firebird combined) for the last two years, and that was less than half of the plant's capacity; even with the plant only on one shift, they still had 10-20 down weeks each of those last two years, and the astronomical fixed costs of operating an assembly plant make it impossible to make any money (or just break even) with the plant running at 35-40% of capacity on one shift.

 

[rpounds]

I hate to say it, but I'm not surprised that they couldn't sell the F bodies. My oldest son bought one 2 years ago, drove it for about 8 months and couldn't wait to get rid of it. Of course he took a beating, selling it so soon. But, as much pizzazz as the Camaro had, it was the most uncomfortable thing I think I've ever driven. Beautiful car . . . and I wouldn't mind having one as a toy. But, I'd hate to have to drive it everyday.

I really, really hope that they will redesign the thing and bring another one around. I hate to lose an american icon like the Camaro.

As a side note, my son now has a Mustang. It's about two or three months old and he loves it.

 

[sscam69]

With that sales record its no suprise they scrapped it. I hope they rethink things and put something that EVERYBODY will be excited about.


whats not to love about something that looks like this. Actually this is what I am hoping to buy not to far down the road as a daily driver. The yellow will be red but this is what I had envisioned. He just beat me to it :L