Brake Fluid

[76okievette]

Quick Question, I put some DOT 4 brake fluid in my 76 before I realized it was not DOT 3, I only put in a small amount but now I am concerned about it. Should I purge the system and replace all the fluid?

 

[wishuwerehere82]

DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases.

If you haven't purged your system in a while, now may be a good time to do it.

 

[76okievette]

DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases.

If you haven't purged your system in a while, now may be a good time to do it.

Thanks Pete I will put it on the list of things to do. I appreciate the response.

 

[bmotojoe]

Standard brake fluid is very susceptible to having moisture introduced into it. Even a partially used bottle can have moisture buildup into it. I always use Valvoline Synthetic brake fluid in all my cars. The synthetic fluid actually resists moisture much better then the standard brake fluid. You will also feel a difference of the pedal if you’re out for a drive on a nice twisty downhill road. Also, when it comes time to flush your system out, it is a good time to change the brake reservoir cap and rubber seal.
Brian

 

[76okievette]

Also great advice I will consider it. I don't know much about synthetic brake fluid but for your post it sounds like a no brainer to use it.

 

[Gunther]

Hi

I had an issue with VBP O-ring calipers leaking.
Somebody told me that I should only use DOT3 fluid because the DOT4 has some additives that dry out the rubber seals.
I contacted VBP and they promised that their seals are compatible with all existing brake fluids.
DOT3 is interchangeable and intermixable with DOT4 and just adding a drop surely makes no harm to the system.
I was under the impression that all DOT3 , DOT4 and DOT5.1 are anyway syntetic oils ?
The other option is the silicon fluid that is not intermixable with any of the other DOT fluids. Everything even needs to be cleaned thoroughtly before changing to silicone fluid.
I presently changed back to DOT3 because of this leakage issue I had on both front calipers at the same time with only 6 years after rebuilt with the new seals. My car is only a street driver and I never had any issues yet with overheating temps. I guess that automatic cars do brake a lot more. My BB is a huge brake when I let the gas pedal go.
Günther

 

[Vettehead Mikey]

Also great advice I will consider it. I don't know much about synthetic brake fluid but for your post it sounds like a no brainer to use it.

It's far from being a no brainer and is not a simple conversion.

There's tons of debate over which fluid is better with no clear winner. If your brakes are working fine, leave well enough alone.

 

[wishuwerehere82]

That's right. Unless you completely drain, clean, and dry your complete system, switching to Silicone Dot 5.1 fluid will be a disaster. Mixing Dot 3,4, and 5.1 will result in a clumpy globby mess that will clog the brake lines and be impossible to remove from the calipers. Stick with the Dot 4, and don't use silicone.

 

[JohnZ]

ALL brake fluid is "synthetic"; DOT3 and DOT4 are compatible, and are glycol-based; DOT5 is silicone-based, and is NOT compatible with DOT3/DOT4.

 

[Twin_Turbo]

Dot 5.1 is NOT a silicone based fluid, it's a polyethylene glycol based one, just like 3 &4. These are all hygroscopic and will mess up your paint job. However there are issues w/ the silicone DOT5 fluid also. It's more compressible resulting in a spongier pedal and it can be hard to bleed. Also there are some fluids w/ sealing problems (due to swelling agent issues)

There's another problem and it's all about water, hygroscopic fluids absorb water, silicone ones do not and this means the water will puddle...and it'll do so at the lowest points, in the caliper. This is especially and issue with non ss sleeved calipers, the water puddle will quickly ruin the bore leading to leaking brakes. Rotor runout due to warping, loose bearings or simply improper installation will aggrevate the situation especially when using the lip seal which is notorious for pumping air (and moisture)

I'll take my Super DOT4 or 5.1 over any DOT5 any day

 

[76okievette]

New Brake Question

Which is the best type of "bleeder"? There are the hand pump used at each wheel, manual pump tank the fits over the resevior and also the type that uses compressed air which type does everyone recommend? I think I am going to flush out the DOT3 and Dot4 and go back with the orginal DOT3 fluid. Suggestions?

 

[Peer81]

Why go back to 3? When you flush everything just go with Dot4 I think

Groeten Peter.

 

[JohnZ]

Which is the best type of "bleeder"? There are the hand pump used at each wheel, manual pump tank the fits over the resevior and also the type that uses compressed air which type does everyone recommend? I think I am going to flush out the DOT3 and Dot4 and go back with the orginal DOT3 fluid. Suggestions?

As I posted above, DOT3 and DOT4 fluid are 100% compatible - there's no need to flush the system just because you have both types of fluid in it. If you still want to flush and fill/bleed with fresh fluid, the Motive Products power bleeder (www.motiveproducts.com) is the best sixty bucks you can spend for a tool; makes the notoriously-difficult bleeding of '65-'82 Corvette brakes a ten-minute job for one person - no other method even comes close.

 

[76okievette]

As I posted above, DOT3 and DOT4 fluid are 100% compatible - there's no need to flush the system just because you have both types of fluid in it. If you still want to flush and fill/bleed with fresh fluid, the Motive Products power bleeder (www.motiveproducts.com) is the best sixty bucks you can spend for a tool; makes the notoriously-difficult bleeding of '65-'82 Corvette brakes a ten-minute job for one person - no other method even comes close

Thanks John that power bleeder is what I was looking at Corvette Central sells it with an adapter for the C3's I think I will go with it. I appreciate it.
I am really flushing it because I have had the car for 3 years and have never done anything to the breaks they were completely rebuilt right before I got the car and still work but I would feel better flushing it out.

 

[Gunther]

Hi

It is surely recommended to flush the system once in a while to replace all old fluid.
Unfortunately, there will always be a leftover of old fluid in the calipers.
The accumulated water will stay on the bottom of the calipers , the bleeding point is at the top.
The only way to realy renew all fluid is to remove the calipers , dismantel them, reseal and reinstall, then fill with new fluid.

Good luck. Günther