84 Corvette Brake Warning Light

[Thomas F.]

My brake warning light is burning on my 84 Vette. It is not burning because the emergency brake is on or because of a problem in the ignition switch. I have already checked out these two possible causes. The only other source is the master cylinder switch that is only suppose to light the light when there is a failure in the brake system. I just installed a new master cylinder, but It did not come with a new switch so I had to use the switch from my old master clyinder which fits just fine.

Now I am not an electrical wizard and this switch really has me confused. There is only one wire that leads to the connector that plugs into the switch but the connector has two terminals which plug into two terminals on the switch itself. Hummm.....that is strange! This is the way it is shown on the wiring diagram also.

From my research, I think the circuit of this switch is normally open if everything is ok and closed if there is a problem. When this switch closes it completes a ground circuit and turns on the brake warning light located in the center cluster.

If anyone has any experience with this switch and/or understands how it functions please respond.

Knowledge is power.

[Thomas F.]

Re: 84 Corvette Brake Warning Light

After more research and wiring diagram study I have discovered the connector to this warning switch has two terminals of which only one is used. The switch itself also has two terminals either of which will work. Why it was designed this way I don't know but it doesn't matter which way the connector is plugged in to the switch it will work.

My problem is either with the master cylinder or the brake warning switch. Since the master cylinder is new I suspect the switch is bad although it worked ok with my old master cylinder. I have decided to return this master cylinder for an upgraded version which comes with a new switch also. I will post again and let everyone know it this solves my problem.

Another thing I discovered while dealing with this brake issue is that neither the Haynes Repair Manual or the GM Service Manual mentions bench bleeding a master cylinder. If I am mistaken on this please let me know.

[Thomas F.]

Re: 84 Corvette Brake Warning Light

Correction, today I did find a reference to Bench Bleeding the Master Cylinder in the Haynes Repair Manual. The GM Service Manual talks about pressure bleeding the brake system so I guess there would not be any need to Bench Bleed the Master Cylinder if you had this type of equipment as was probably used in the factory.

[John H.]

Re: 84 Corvette Brake Warning Light

Correction, today I did find a reference to Bench Bleeding the Master Cylinder in the Haynes Repair Manual. The GM Service Manual talks about pressure bleeding the brake system so I guess there would not be any need to Bench Bleed the Master Cylinder if you had this type of equipment as was probably used in the factory.

Tom -

The process(es) you see in the GM Service Manual and in the aftermarket (Haynes, etc.) service manuals are unique to the aftermarket service environment, as the bleeders were never touched at the factory. The plant used an "evacuate-and-fill" system which drew a very high vacuum through the tiny compensating port in the master cylinder, held it briefly to check for gross leaks, then injected degassed brake fluid at 60 psi through that port with the system at high vacuum; this process resulted in a complete system fill and bleed (followed by test) in less than a minute, without ever touching the caliper bleeders. This only worked with a brand-new "dry" system; once the system was "wet", conventional Service bleeding procedures were required. The same "evacuate-and-fill" process was used to fill power steering, engine cooling system, and the A/C refrigerant system.

[Mike E.]

Re: 84 Corvette Brake Warning Light

Tom -

The process(es) you see in the GM Service Manual and in the aftermarket (Haynes, etc.) service manuals are unique to the aftermarket service environment, as the bleeders were never touched at the factory. The plant used an "evacuate-and-fill" system which drew a very high vacuum through the tiny compensating port in the master cylinder, held it briefly to check for gross leaks, then injected degassed brake fluid at 60 psi through that port with the system at high vacuum; this process resulted in a complete system fill and bleed (followed by test) in less than a minute, without ever touching the caliper bleeders. This only worked with a brand-new "dry" system; once the system was "wet", conventional Service bleeding procedures were required. The same "evacuate-and-fill" process was used to fill power steering, engine cooling system, and the A/C refrigerant system.

John,
Do you remember if those systems back then were made by Dominion Tool and Die? During the late 90's I worked for Bosch and we worked together with them on production trials. It was kind of amazing what the vaccum would do to lip seals, it sure was the best way to fill a brake system though providing it was still dry. I actually wrote some software that monitored the vaccum pulled on all four corners that would attach to the bleeder for testing. The Brake guys didn't like to pull the system crazy low because of the damage it could cause to the seals.

Mike

[John H.]

Re: 84 Corvette Brake Warning Light

John,
Do you remember if those systems back then were made by Dominion Tool and Die? During the late 90's I worked for Bosch and we worked together with them on production trials. It was kind of amazing what the vaccum would do to lip seals, it sure was the best way to fill a brake system though providing it was still dry. I actually wrote some software that monitored the vaccum pulled on all four corners that would attach to the bleeder for testing. The Brake guys didn't like to pull the system crazy low because of the damage it could cause to the seals.

Mike

Mike -

I don't recall offhand if Dominion was one of the suppliers or not (45 years of CRS, you know)
. The brake application was still in development, and I do recall the limitation on vacuum to avoid rolling the seals over.

[Terry M.]

Re: 84 Corvette Brake Warning Light

Tom -

The process(es) you see in the GM Service Manual and in the aftermarket (Haynes, etc.) service manuals are unique to the aftermarket service environment, as the bleeders were never touched at the factory. The plant used an "evacuate-and-fill" system which drew a very high vacuum through the tiny compensating port in the master cylinder, held it briefly to check for gross leaks, then injected degassed brake fluid at 60 psi through that port with the system at high vacuum; this process resulted in a complete system fill and bleed (followed by test) in less than a minute, without ever touching the caliper bleeders. This only worked with a brand-new "dry" system; once the system was "wet", conventional Service bleeding procedures were required. The same "evacuate-and-fill" process was used to fill power steering, engine cooling system, and the A/C refrigerant system.

When I got the Buyer's Tour in 2008, Bowling Green used the "evacuate-and-fill" process as described above. I don't know the vacuum or pressure levels, but it must work pretty well after all these years. I seem to remember something like that at Connor Ave. too. Am I right John?
I wouldn't be surprised this is another one of those industry wide processes.

[Mike E.]

Re: 84 Corvette Brake Warning Light

When I got the Buyer's Tour in 2008, Bowling Green used the "evacuate-and-fill" process as described above. I don't know the vacuum or pressure levels, but it must work pretty well after all these years. I seem to remember something like that at Connor Ave. too. Am I right John?
I wouldn't be surprised this is another one of those industry wide processes.

It was that at least for Chrysler and Ford too because in my other life I went to several assembly plants that used master cylinders from Bosch or Bendix before Bosch bought them. C4 M/C were made by PBR (not Pabst Blue Ribbon ) so I never got to BG. That would been fun! I did go to the Rouge Assembly Plant for the Mustang, but I was never a Ford guy so it was like Meh.

If I remember correctly what would happen was the lip on the seal would get sucked into the comp port and damage the seal. We used Lexan models to see how the seals would react to the vacuum and that’s how we finally found it. Not all types’ master cylinders had the issue, just a few. Anything involving hydraulic brake failure will get an OEM’s attention quickly. Running the Lexan models became standard procedure on any new design before job one.

Some M/Cs do not have any type of pin retaining for the plastic reservoir, when the system went to fill mode we had a few reservoirs blow off from the pressure. When this would happen the customer was NOT pleased.

Mike

[John H.]

Re: 84 Corvette Brake Warning Light

When I got the Buyer's Tour in 2008, Bowling Green used the "evacuate-and-fill" process as described above. I don't know the vacuum or pressure levels, but it must work pretty well after all these years. I seem to remember something like that at Connor Ave. too. Am I right John?
I wouldn't be surprised this is another one of those industry wide processes.

Terry -

Yes, that's correct - "evacuate-and-fill" became pretty much a "generic" process for fluids across the industry many years ago.

I recall a conversation in the 70's when I was at Lordstown with a dealer from North Carolina whose technician was doing a brake job on a Caprice and couldn't bleed it because the bleeder hole wasn't drilled through into the piston bore. I explained to him that we didn't use the bleeders, and he wound up driving to the plant to see the process for himself.

Had a similar adventure with another dealer who got a car with no valve stem in a wheel (and no hole for one) and drove to the plant to see how we inflated the tire by blowing air in between the rim and the tire and never touched the valve stem. We subsequently added a light and photoelectric cell ahead of the "stemmer" machine so it would "kick out" a wheel if it had no valve stem hole.