I didn't know the brake fluid was changed previously to Dot 5. One day I added Dot 3. Now I think 2 (or at least one) wheel is totally locked up. Have seen posts about fixing but solutions vary for some reason.

I know I have to flush the entire system, but do I also need to then push denatured alcohol thru? Or use the denatured alcohol to flush the system? If denatured alcohol, anyone know how much I need?

Do I need to replace the brake calipers? All or just that locked? Anything else that should be replaced?

Anything else need to change or do?

1971 Corvette
Thanks!

 

If you intend to use DOT 3 you need to flush with denatured alcohol.

 

I am in the process of rebuilding a '72 that had DOT 5 in the system. I removed all four calipers because I am restoring the chassis, and then opened up each caliper so I could thoroughly clean them out. They were already SS sleeved and I added an O-ring conversion kit to each one. I then blew out each hard line and hose with compressed air, followed by a generous shot of brake cleaner, then more air. I also disassembled the master cylinder and cleaned it out. I am confident that all the DOT 5 is gone. I doubt you will get it that clean unless you take everything apart.

 

I tried DOT 5 fluid in my C3 and was not a happy with the way the brakes felt while using the DOT 5 brake fluid so I switched back to the DOT 3. It is not that big a deal but I flushed my system with the denatured Alcohol. The DOT3 is the right material for our C3's. If I did it again I might flush the system twice instead of the one time I did it.

The brakes were first rebuilt with O-ring style pistons and then used for a short time before trying the DOT 5. The brake action with the DOT 5 was a bit too hard and I felt like I had better control and pedal feel using the original DOT 3 fluid. It almost seemed as though the DOT 5 brake fluid had to "warm up" to start to work better with the brakes. The DOT 3 does not do that on my C3 and my brakes are able to lock up all four wheels at once on the highway.

To actually CAUSE wheels to lock is new to me. Does the DOT 5 cause the rubber parts to expand or something? I never had any ill effects from my little experiment with DOT 5.

Pull the seized caliper and take a look at the seals in it. I like to split the two halves and clean and fix them that way as it is easier for me. If any of the rubber has expanded or been changed in some way I would replace it as well. If the wheel has damage to it you might have to rebuild them. Have you ever split a brake caliper like these? It is not that hard as I learned it by myself. You don't have to split them to rebuild them according to some. For me the splitting the caliper is a convenience to make it easier for me. A small brake hone attached to an electric drill can clean up the bores quickly and use lots of new fluid for lubrication and cleaning the brakes.

 

I have used DOT 5 for decades, even upgraded to O ring pistons. It has not caused caliper lock for me.

 

Are the rubber flexible brake lines causing the lock?

 

My buddy is running with a combo of Dot 5 and Dot 3 mixed together in his ratrod (he didn't know any better). Unbelievably with no ill effect other than fluid in his master cylinder looks like salad dressing.

 

To change from 5 to 3, I'd flush about 2-3 quarts of DNA through the entire system. The DOT 3 will completely mix with the DNA, so don't worry about any pockets of alcohol. I don't think your locked brakes issue is a result of combining DOT 5 and 3. They won't mix and end up separating like oil & vinegar but they have different characteristics so it's best to clean out the system.

I'd say your locked brakes are more likely due to degrading rubber flex hoses. As long as you are opening the system, flushing and bleeding, it's a good time to change out the rubber hoses.

 

Yes, it separates

 

Good point!

Sometimes the brake hoses deteriorate internally, where you can't see it, and the "broken off bits" clog the line, restricting back flow, when you release the pedal.

 

Well, after 20 years with the car and no problems the wheels didn't lock up until after I mixed the brake fluids.

 

Have you checked the hoses?

 

They looked fine.

 

You have X Ray eyes? They collapse internally and look fine on the outside.

 

I tried to explain the deteriorated on the inside brake line problem to a mechanical engineer I worked for in his machine shop. After long debate I proved it to him. The wheel was locked and guess what happens when I pull out my pocket knife and cut his brake line next to the fitting on the caliper. No more locked wheel. The didn't teach him that in college.

 

I first opened the bleeders on the locked wheels and they were still locked. Then I took the hoses off from the wheels that locked off, then flushed them which put them back. Nothing changed. Calipers still locked.

What else should I have done?

 

Been using dot 5 and now dot4 on Harley's for 50 plus years. Many, many times these fluids have been mixed. No, they do NOT lock your calipers.
And I have run DOT 5 in my C3 for about 30 years now. My brakes will throw you right threw the windshield if your not buckled up!

 

The brake calipers are locked, even with the bleeders open, and the hoses removed?

You know what to do now. Remove the calipers, and rebuild them. I like CSSB Inc. high-heat O-ring kits. YMMV.

Did you do anything else but add brake fluid? Is it possible that the caliper mounts are bent?

Don't forget to use new hoses, too, if you don't know how old the current ones are. They swell up on the inside.

 

^^^^^This^^^^^^^ Since you are going through the system, this is a good time to replace them.

If the calipers are still locked as you mentioned, my guess is you do not have stainless steel sleeves. When I first took my calipers apart years ago, there was a ton of rust and crud in there. You can send them out and have them sleeved. You could try honing them and rebuilding them. But making the bore oversized leads to issues too.

I have stainless steel sleeves and flush the system with fresh fluid every 2 to three years (more often if I track the car) and have not has issues since.

 

.
. What else you will need to do is replace all brake hoses. Replace or rebuild all calipers. Completely flush clean the entire system. ( I’d even put a new master cylinder on it for good measure )
If this never needed to have been done before in the last twenty years, , you have been blessed with good fortune. Do it now and keep smiling….