Hello fellas,

Looking for some direction here!!!
My 1978 corvette just recently had a power brake flush done on it by "Corvett Specialists"!!!!

You see the problem started with the right rear spindle breaking in half.
I replaced it, and since then my emergency brakes arent that strong and my brakes need to be continuously bled.

I know about the requirment now about replacing spindes, so I had these guys do it right... making sure the bearings had the proper clearance, etc...

Well, they said they checked everything, adjusted my brakes, adjusted my emergency break and I shelled out close to $400 for it.

The brakes were holding fine, until I drove it about 100MPH and applied teh brakes... thats when the pedal sunk a bit and the red warning light lit up the dash.

I was very pissed! To make matters worse, when I returned to the corvette place to remedy this situation... the emergency brake was not holding the car!! I mean what the hell!!!! Someone once said on this board that some people should not work on their own cars... I feel I could of done a better job if I had the equipment to do it!



So... what I noticed about my brake problem when I applied the pedal was that it is spongy. And if pumped several times the pedal returns to normal and light goes away.

Checked reservoir and no leaks!!!! NO LEAKS around calipers!!!!

The reason why I ask if this may be a vacume leak... is that I noticed the TACHOMETER going crazy when the brake was applied, or when I accelerated with the red warning light was on, the tach needle would jiggle up and down feverously! The corvette "specialista" said I may need to replace the brake booster!!!!!!!!!!!!!!!!

Someone know why Im having so much trouble with brakes on a 1978 corvette!

I gravity bled till pressure held. I power bled by Corvette guys till pressure held. Each time when driven... pressure gets lost!!!!!!

Just on long fast trips... seems to mess up when brake is applied!

Emergency brake... I have no idea why they cant adjust till it holds firmly!

 

Sounds more like a "runout" problem, if the rotor and spindle are not "true" the calipers will bring air into the system and give you a spongy pedal. After you bleed the brakes they work fine for awhile untill more air gets in. Ask your specialists if the have a dial guage, if not get a new repair shop.
The emergency brake is really just a parking brake, but if adjusted properly it will work. PG.

 

I'm stumped. At least, on the part about the tach being involved. Could it be that the tach "thing" is just a coincidence? The brake problem just sounds like there is still some air in the system...possibly stuck in the proportioning valve area.

 

The tach is electrical, don't see how vacuum could affect that. It's driven by pulses from the distributor. The parking brake is cable driven and uses shoes behind the rotor, so I don't see how that's connected to the spongy pedal either. Sounds like you have more than one issue.

 

Tach issue is probably connected to the brakes through the brake light switch could be a poor ground issue.Check to see if the capacitor is across the switch term.

 

soft brakes could be a run-out problem as already mentioned causing air to get into the system or could be from a leaky seal in the master cylinder. A seal in the MC can cause air pressure to bleed off causing the pedal to slowly sink to the floor while holding it but not actually leak fluid.

Parking brakes are a separate issue and not related to the main braking system issue of a spongy pedal. For what it's worth, the parking brakes on all of these cars notoriosly suck. The one on my '78 works "ok" but not what I'd call great even after a complete rebuild of it. On my '65 which is basically the same system it's absolutely useless no matter how many times it's been worked on. It will kinda hold the first few times after adjusting it but than goes back to being worthless again.

The jumpy tach issue can't be related to the brake issue as it's electronic ALTHOUGH it could be possible under certain conditions to have it be jumpy based on a vacuum issue such as if the vacuum advance can is not the correct one for the motor's vacuum level or it's not working correctly since it may be seeing a condition of vacuum that is just at the edge of the vac adv can coming in or cutting out. If that happens the timing will change as the VAC cuts in and out causing the rpm's to flucuate and that you would see on your tach.

sounds like you have multiple issues to work on on your car.

 

Thanks to all!!!

Question, how would one go about correcting the runout on the rotor and spindle???

I will return the car back to the specialists, I just want to know for my own sake... because I dont need to get ripped off or distracted with double-talk on this issue with the service manager.

Thanks again....

BTW: TACH only flipped out when brake warning light was on... first time I saw that ever.
Parking brake... I will go back to them to fix it!

 

Here's some info in brakes http://www.idavette.net/hib/vette_bbfh.htm scroll down to 12 & 13. PG.

 

Thanks thats a lot of good info!

One more question fellas, the caliper on the right rear... I remember when I changed out the spindle... the right rear pistons on the calipers didnt seem to difficult to push back. Is this any concern?

 

Stan
here is a very good article on brake rotor run-out and the best way to repair it:
http://www.lbfun.com/warehouse/tech_...unout_Dial.pdf

If you are interested, you can also find lots of other articles on your brake system including the parking brake on my website's Tech Articles page here:
http://lbfun.com/Corvette/Tech/vettetech.html
click on the second header title called BRAKES.

 

Here's a couple threads on shimming rotor. There are tons of threads on the subject. The 'search' function is your friend on this forum.

http://forums.corvetteforum.com/show...ght=rotor+shim

http://forums.corvetteforum.com/show...ght=rotor+shim

 

I had the same problem on my '70 a long long time ago and the problem turned out to be as stated above. The rotors were "pumping" air into the system due to excessive runout. After fixing that I went ahead and did the stainless steel calipers, new brake lines, new master cylinder, proportioning valve, synthetic brake fluid thing and no longer had any brake problems. Is there any such thing as a C3 that has a working parking brake?

 

I have one!!! {Ooops. I need to find some wood to knock on...quick!}