2manycars

A friend of mine os restoring two C3s for two other friends - a 70 LT1 coupe and a 71 LT1/ZR1 coupe. We're running silicone brake fluid in the ZR1. It was a MAJOR PITA to get the brake system to bleed properly and get pressure, and also to get it to stop leaking! The car has an entirely new/rebuilt brake system on it. Is this the usual ordeal in using silicone brake fluid? The 70 is using the normal type, and that one didn't give us any problems. Any experience on the C3 board with this issue??

PatG

I put DOT5 in mine a bit over a year ago with no problems. I purchased a NEW master cylinder when I did mine and had just put o-ring pistons in my previously sleeved calipers. Where is the system leaking? Did you bench bleed the master cylinder before hand?

mrvette

Yes, Silicond DOT5 fluid is a bit of a problem to get working correctly, but once it settles in for a while, it's fine...it tends to hold air bubbles in the fluid suspension for some reason, apparently...so the pedal will never quite be as hard as it was,...but there should be still plenty of pedal and no problem locking them up if needed....


sometimes letting them sit for a week helps...as the air works it way to the top....found that too....


GENE

R1234

Yes, I'm using the silicone. It came with the VBP o ring caliper set.
I used a vacuum pump to bleed my system. I never did get all the air bubbles out but my car sat for along period of time before I was able to drive it. So, I guess the air bubbles settled out during that time. Everything in my brake system is new. The brakes feel good.

2manycars

Pat, the master was not bench bled, which turned out to be the first part of the problem. That part of the car has been assembled and sat dry for quite awhile. I thought bench bleeding would be best but we didn't want to disassemble it again. We ended up bench bleeding it in the car on the rear bowl only, since the front brakes were flowing fluid pretty much right away. It took a LONG time to get pressure to the rear, even using a powered vacuum pump on the bleeders. The leaks were coming from the line fittings - one on the frame, and several on the proportioning block. Took several retightenings to get them to stop leaking, and they felt tight, too. all lines and fittings are brand new, so dirt was not an issue. I'm betting that letting the car sit awhile, then possibly bleeding it again may help, too. We ruled out any ZR1 related stuff, since the front brakes were bleeding OK, and they are the only difference in the ZR1 system from standard Corvette.

I'm relieved to hear that slow bleeding seems to be typical with this fluid, and that the car itself should be OK. I don't think h my friend feels like pulling those brakes apart again. The car will be finished soon, and he's looking forward to that! It's regular driving days are ended, too, from what he tells me. The owner isn't going to drive it.


[Modified by 2manycars, 10:52 AM 3/3/2003]

PatG

Well if you had leaking from the fittings then you were probably sucking air into the system through the fittings as well. Since the leaks are fixed I would do some more bleeding, I always use the manual two man method, one on the brake and one turning the bleeder screws.

vettfixr

Here's something that I did when I converted over to Silicone fluid that may help. the problem with bleeding the system is that the silicone, being very thick, tends to keep air bubbles from rising to the top. Just filling the master cylinder can introduce air into the fluid and thus into the system if you bleed it immediately. I tried bleeding my car a half a dozen times to no avail. Finally what I did was fill the master cylinder and let it sit overnight. This allowed any bubles in the MC to rise to the top. I would then bleed one brake and then fill the MC and let it sit again overnight. It's a real PITA but it works. You may have to bleed one caliper for more than one filling depending on how much air is in the lines. The upside is that once I got everything bled correctly the system has been leak free. I do feel that the pedal is a little more spongy with silicone fluid than regular fluid but that's just might be me.

2manycars

Yep, the last step we did was manual bleeding. We went around the car that way two or three times. That's when the pedal finally came up. I think it should sit a couple of days and be bled again. :yesnod:
We're fairly certain we got rid of the leaks. He'll be checking the floor under the car, and the frame rails for evidence of leaks, and then he'll go around the fittings with a Q-Tip and see if there is any fluid present there. :yesnod:

Sigforty

I converted my car a while ago. It seems to perform alot better on the silicone fluid. I just rebuilt my master cylinder before I made the swap, and cleaned all my lines out with Denatured Alchol. No problems with the DOT 5 here.

Michaeljh2000

Yes, have Dot 5 in mine as well and it was a PITA!!! Best thing I can recommend is to let the system gravity bleed overnight if that what it takes to get all the air out. I switched to Dot 5 when I added a new master cylinder and stainless sleeved calipers. Now, it has worked great for years.

norvalwilhelm

I converted to silicon when I totally rebuilt my braking system. I did it only to save the paint. At least once a year I seem to do something to the braking system of just to remove the trailing arms.
I pressure bleed only. I have a vacuum bleeder system but never use it. I put a special cap on the master cylinder, turn the shop air to 10 psi and plug it into the cap. I then bleed one back wheel , then one front before refilling the master and doing the other wheels.
I have never had a problem bleeding my system. The problem with the vacuum bleeders is that they continually suck air around the bleeder screw so you can never tell when you are no longer getting air in the line.
While silicon doesn't mix with water it allows water to sit in the line or caliper as a puddle of water corroding where ever it sits.
If it wasn't for the paint I would use Ford brake fluid.
Yes fords are good for many things including the Tremec transmissions.
Just kidding I drive a ford :) :)

hunt4cleanair

Remember silicone has an affinity for air while Dot 3 has an affinity for moisture. When you use the typical pump method...you're introducing air into the system.

The recommended procedure for using silicone is gravity bleed. Do the recommended mechanical things suggested above like bench bleed the M/C but then do a gravity bleed. It allows the bubbles to rise to the top as pointed out but also does not introduce addiontal air by the use of mechanical brake bleeding procedures.

Gary79

i converted to silicone in april 99, when i purchased a "total" brake kit from Muskegon brake. I also flushed the existing lines with alcohol several times. i could not get my vacuum system to bleed the brakes, so we did the two man method, actually, my wife worked the pedal. it took awhile to get fluid to the calipers. when it did, the wife would pump the pedal and hold it down, i would close the bleeder screw, then open it up on when she pushed the pedal back down. we followed the bleeding sequence and then did it again the next day. haven't had any problems and have not added any fluid in almost 4 years. bench bleeding the master cylinder is a must.

Barry's70LT1

About 13 years ago I converted to DOT5 and SS calipers.
Rebuilt the MC and flushed the lines.

Bench bled the MC, and gravity bled all wheels.

I never experienced any problems. Had, and still have, a very firm pedal.

The only thing I did while gravity bleeding was to use a small rubber hammer and tapped the MC, lines and wheel cyls., to help release any trapped bubbles.

norvalwilhelm

I have never had a problem bleeding brakes either by the 2 man method or the pressure bleed. Getting a nice firm peddle has never been a problem. In my shop I have a very very expensive vacuum bleeder or the pressure bleed which I prefer.

2manycars

Thanks for all the input!! I'm passing it along to my friend... :cool: :cheers:

Robd

Can someone explain the correct way to gravity bleed the brake system. Thanks

Michaeljh2000

Answer: Fill up the master cylinder with brake fluid. Go to the caliper which is furthest away, the right rear. Loosen the outter bleeder screw and wait until fluid comes out without any indication of air. Once you are certain there is no air, proceed to the inner side of the caliper and let it bleed out as well. Continue to each caliper that is the next furthest away. You will have some fluid wasted and it may take a while, but this was the only I finally was able to bleed my system.