drumking241

hey yall- having a problem with my C-4 (93 LT-1) brakes thats got me and my mechanic, ( a reputable Corvette Specialist) stumped, though id explain the situation and see if any of yall have experienced something similar or have any ideas- any comments would be appreciated, alright about 2 weeks ago, my brake pedal started going to the floor (off and on) and the brake warning light would come on, this was the first time it did this, called my Vette shop up and they said bring it up, they found no leaks, fluid was fine, he said my back brakes looked worn, but front where ok, and he took it up and down the street, and the brakes acted fine- so he said it didnt make sense to do it then stop, so let him know if it happened again, of course, on the way home it happened again, so i brought it up again the next day, ( it acted fine on the way there) he kept it a couple days, drove it alot, put it up on the rack and searched the brake system as thoroughly as possible, could not get it to do it, fluid was fine, and not a leak anywhere, he said my rear brakes where wore (badly) so he replaced them and turned the rotors, flushed and the replaced the brake fluid, and i picked it up. brakes acted perfect- problem solved- or so i thought, im disabled so i dont drive it to much, i drove it about 3 or 4 times in two weeks around town, brakes where fine and stopped on a dime), so i go on a 5hr trip to South GA to visit a relative who wants to see it, and two hours into it the brake pedal starts slowly getting down to the floor, in interstate heavy traffic they go down to the floor again, with no much stopping power, and the brake light again comes on, i had to turn around and pump it like crazy to get it home, i just took it into town and the brakes felt like when your brakes are worn a little, the pedal was going down further than normal and it took a little more pressure to stop , but it stopped pretty good with no light, why does this keep happening on and off? front brakes good, rear brakes new, full with new fluid, master cylinder appears to be working, no leaks to be found, -any suggestions? thanks for reading

antfarmer2

[QUOTE=drumking241;1589519018]hey yall- having a problem with my C-4 (93 LT-1) brakes thats got me and my mechanic, ( a reputable Corvette Specialist) stumped, though id explain the situation and see if any of yall have experienced something similar or have any ideas- any comments would be appreciated, alright about 2 weeks ago, my brake pedal started going to the floor (off and on) and the brake warning light would come on, this was the first time it did this, called my Vette shop up and they said bring it up, they found no leaks, fluid was fine, he said my back brakes looked worn, but front where ok, and he took it up and down the street, and the brakes acted fine- so he said it didnt make sense to do it then stop, so let him know if it happened again, of course, on the way home it happened again, so i brought it up again the next day, ( it acted fine on the way there) he kept it a couple days, drove it alot, put it up on the rack and searched the brake system as thoroughly as possible, could not get it to do it, fluid was fine, and not a leak anywhere, he said my rear brakes where wore (badly) so he replaced them and turned the rotors, flushed and the replaced the brake fluid, and i picked it up. brakes acted perfect- problem solved- or so i thought, im disabled so i dont drive it to much, i drove it about 3 or 4 times in two weeks around town, brakes where fine and stopped on a dime), so i go on a 5hr trip to South GA to visit a relative who wants to see it, and two hours into it the brake pedal starts slowly getting down to the floor, in interstate heavy traffic they go down to the floor again, with no much stopping power, and the brake light again comes on, i had to turn around and pump it like crazy to get it home, i just took it into town and the brakes felt like when your brakes are worn a little, the pedal was going down further than normal and it took a little more pressure to stop , but it stopped pretty good with no light, why does this keep happening on and off? front brakes good, rear brakes new, full with new fluid, master cylinder appears to be working, no leaks to be found, -any suggestions? thanks for readin[/QUOTE
Might be your proportion valve

antfarmer2

Might be your proportion valve...........not sure what happend to my last post sorry

John A. Marker

Sorry to tell you but your specialists is full of ****. Having your brake pedal go to the floor has NOTHING to do with rotors or the brake pads. You have an issue with FLUID. It is either leaking (which you have determined is not the case) or a seal in the master cylinder has gone bad and the fluid is bypassing the seal....therefore no fluid is going to the brake calipers. If is was a leak in the line, then if you pumped the brakes you would have fluid on the ground and the level in the reservoir would drop. Your pushing on the pedal and the fluid is going around the seals allowing the pedal to go to the floor instead of the seals holding and pushing the fluid thru the line and applying pressure to the brake pads.

Since you can not do the work yourself. I recommend taking the car away from your specialist and finding a good brake shop in your town that knows what they are doing.

enventr

Check the booster

Churchkey

See post 4&5.

If the situation occurs after long engine run time:
Check brake line proximity to exhaust components, boiling brake fluid = bad brakes.

RollaMo-LT4

A "Booster" issue will not cause the brake pedal to go to the floor.
You can get a very stiff (or hard to press) pedal since there is no vacuum assist, but even without a booster at all the hydraulic part of the system will still function.

As mentioned, if the pedal is going to the floor there is no fluid pressure in the line.

Hot Rod Roy

Time for a new master cylinder. The seals on the master cylinder piston are worn, and the fluid is bypassing the piston and returning to the reservoir. You can't see this fluid "leak".

I suppose it could be your ABS unit, but I doubt it.

drumking241

[QUOTE=antfarmer2;1589519147]thanks for the reply! ill mention it with the other responses!

drumking241

thanks so much for the reply! i have to stick up for my shop though, theyre not full of ****, theyve been arounnd since the late 70s and know more about my Vette than i could learn in 2 lifetimes, he never said that was the cause, thats just all he found, perhaps i made it sound like that in my post though, your answer was by far the most informative, and i will have the master cylinder checked out

drumking241

thanks!

drumking241

thanks for the answer! ill have that checked out as well

drumking241

[QUOTE=RollaMo-LT4;1589519565]



A "Booster" issue will not cause the brake pedal to go to the floor.
You can get a very stiff (or hard to press) pedal since there is no vacuum assist, but even without a booster at all the hydraulic part of the system will still function.

As mentioned, if the pedal is going to the floor there is no fluid pressure in the line.[/QUOT

makes sense, thank you!

drumking241

thanks for the reply! yes i was afraid that might the issue, its looking like it

aminnich

Let us know how it turns out.

drumking241

thanks guys for the answers theyve been a big help! ill let you know how it goes! God bless-

drumking241

will do! i see your a fellow Georgian!

C409

..... ..... ^^^^^ ... THIS !

bogus

old rule of thumb... no brake pedal = bad master; too much brake pedal = bad booster.

You have an aging master, for sure.

I do like the idea of checking the brake lines for heat related damage.

You don't mention mileage, but I would consider new brake lines to the calipers. The rubber ones can crack, leak a touch, then sorta self heal again... most annoying. You can get good ones from www.tirerack.com

Rock Auto has remanned master cylinders a pot load cheaper than anyone else.

Oh, and yes, worn pads can and will cause a soft pedal... if all pads are down, and you go for the brakes, especially on low fluid, you will bottom out the pedal.

As for fluid, use DOT 4 synthetic. Works great. Ford Motorsport is a great option, among others - ATE, Castrol, Motul, Valvoline...

I would be shocked if the ABS unit caused this. ABS is integrated in such a manner as to not cause a failure.

Ozzstar

I vote it's a failing master cylinder.