AL POLO

[ALAGENT99]

Hello all,

 I have a 1978 Avanti 11,  RQB 2802 and would like to know the correct type of brake fluid I should use.

 Thanks in advance for any help,

 AL 

[Dwight FitzSimons]

That depends on the type fluid in the brake system currently.  If it has DoT-3 or DoT-4, then put only DoT-3 or DoT-4 in it.  DoT-3 & DoT-4 are interchangeable.  I prefer DoT-4 because it is a bit less hygroscopic (absorbs less water).  If it has silicone fluid in it then add only that.  Someone else will have to tell us how one can tell which is which just from a sample.

If you want to change from one to the other then the entire brake system must be cleaned.  I have not done that, but others have and will probably chime in with that procedure.

--Dwight (2 1964 Avantis)

[Gunslinger]

If you don’t know low old the present fluid is…consider having the entire system flushed and fresh fluid added.

Also…if the age of the flexible hoses is unknown…you might have those replaced.  They can collapse on the inside with age even if they look good externally.  Brakes are too important to not take care of.

[Jim78]

My '78, RQB 2758, was factory filled with DOT5 silicone fluid.  There is a decal on the top of the brake booster warning to use only DOT5.  Yours was probably the same.  However, there is no guarantee that someone hasn't changed the system to a different fluid.  If you are unsure, the best bet is to take a small amount of fluid from the reservoir ans see if it mixes with a sample of DOT5 and not with DOT3 or $.

[Gunslinger]

If DOT 5 silicone fluid has been mixed with DOT 3 or 4 the fluid will usually look milky and cloudy…not a good mix and will cause problems.  If fluids have been mixed…a complete flushing is called for…preferably with new hoses and caliper seals and wheel cylinder seals to make sure all vestiges of the contaminated fluid are gone.

[ALAGENT99]

Thanks for all the good advice / answers, did not know it was going to be so involved.

AL POLO

[Dwight FitzSimons]

Your '78 Avanti is 55 years old, so the brakes cannot be in such great shape (unless they were just rebuilt properly).  One thing to start with, after determining which type the fluid is, would be to bleed the brakes (in order RR, LR, RF, LF) and see what comes out.  You will have to add fluid during this process.  If the fluid is dirty then further investigation will be needed. 

If the brake fluid is low in the master cylinder then there is a problem.  That fluid went somewhere.  You likely have a leaking wheel cylinder, but it could be from a hose or line, or the MC.

All of the advice from the other responders is good.

Brake systems seems simple, but maintaining good, safe brakes is not simple.

--Dwight

[Skip Lackie]

As noted above, your car was probably originally equipped with DOT 5, which many of us prefer for cars that are not driven regularly.  But anything could have been added over the past 50-60 years.  The easiest way to tell what's in the car now is to suck a little out of the master cylinder with a turkey baster and put in into a clear glass jar. Add a similar amount of DOT 3 (it's cheap and available everywhere) and shake it up.  If the car now has DOT 3 or 4 in it, the two fluids will mix completely.  If the car has DOT 5, the mixture will turn milky and eventually separate into two layers.  

If you want to change to a different type, you really should flush the system completely with a good solvent (alcohol or acetone) and replace all rubber components, like hoses and M/C and wheel cylinder cups.  Replacing hoses is always a good idea in any case.  Good luck..