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Was ahout to top up the brake fluid on the truck when I realized that I'm not sure what is in there. I would assume its the "stock" silicone DOT 5 based fluid, but not really sure. So how you tell which the difference between a glycol and a silicone based brake fluid? Taste? Smell? Put it on a salad?

thanks
Jim Jefferson
www.knockabouttoys.com

Correct me if I'm wrong guys. When the truck was new it got Dot 3 type fluid. For those applications I use Dot 4 which is also OK for disc brakes. The Dot 5 Silicone came into use in the 80s if I recall. The Dot 5 advantage was that it wasn't hydroscopic (sp) and didn't absorb moisture like regular brake fluid. It was REAL pricey when it came out and the first gallon I purchased cost about $35. The down side is in a Hi-Po race car you didn't get the same performance as Dot 4. I ran a 280i TVR with it and after a hard run changed back to the Dot 4 as my braking suffered. Yet I left it in my hydraulic clutch and my slave cylinder lasted for years. Can't seem to remember how to tell the difference other than the original Dot 5 usually was purple.
A real test is put whats in the master on a painted surface, if the paint peels it's regular brake fluid. No damage it's Dot 5. That was another advantage of the 5

DOT 3 is correct for the stocker. DOT 5 is supposed to be less corrosive-the two are NOT interchangeable.
Gary

I thought about the paint peeling thing so I made up two test strips on the truck - one strip with the master cylinder contents and a second with two brands of usual DOT 3 stuff. Well in the end neither paint peeled.

The fire dept must have used some good paint.

So back to square one - how do you tell the difference?

The other thing I have noted is that the current fluid is a little more slippery when rubbed - perhaps the silicne based stuff.

JIM

I use prestone synthetic DOT 3 brake fluid in mine. No complaints so far. BTW - Synthetic will still peel paint, so be careful if you use it. I spilled some on my axle while bleeding brakes one time and the paint bubbled right up.

Just directed to this by Nobby Peers of Whitworth Marine.

http://www.whitworthmarine.com/

Following posted on the G503 forum regarding brake fliud ID

http://www.g503.com/forums/viewtopic.php?t=132537

JIM

Much like Pasteur and Darwin, and inspired by Kurt Lesser on the g503 forum I have started my own brake fluid experiment.

First however I must figure out how to post some photos – more to follow.

jjefferson wrote: I would assume its the "stock" silicone DOT 5 based fluid, but not really sure.

DOT 5 wasn't around yet when our trucks went into production, so it can't be "stock."

Yeah I think I put DOT 5 as a typo. Hate typing on my laptop, spend half the time fixing what I just typed. Case in point just had to retype that last sentence.

Well filled the M37 with DOT 3 and all is OK. Compared it with my 97 chevy pickup brake fluid - jsut for giggles. Turns out that the 97 fluid is green - new one on me. Perhaps because it is a green trucks, after all the M37 fluid was a nice rusty color and the truck is red.

Yet another mystery to solve.

Jim

Has it been decided whether or not the DOT 5 silicone is OK for our trucks? I have a gallon of the Mil Spec stuff ready to go in my system this weekend.

Am I making a mistake?

refit1701 wrote:Has it been decided whether or not the DOT 5 silicone is OK for our trucks? I have a gallon of the Mil Spec stuff ready to go in my system this weekend.

Am I making a mistake?

Unless the stock system is thoroughly cleaned, you are headed for major issues. I personally don't think any flushing method is this thorough. I'm talking take each component taken apart & cleaning so NO TRACE of the DOT 3 is left if you want to convert. Actually it's better to do it when the whole system is being rebuilt with all new components.

As for the paint stripping test being fool proof, it isn't. Regular enamel paint, yes it will curl like paint remover has been applied. On fully cured urethane paint like we use on our restorations, brake fluid has no effect at all. So if you are testing fluids with the paint removal test, you need to verify the type of paint you have or you can easily arrive at a false test result.

MSeriesRebuild wrote:
Unless the stock system is thoroughly cleaned, you are headed for major issues. I personally don't think any flushing method is this thorough. I'm talking take each component taken apart & cleaning so NO TRACE of the DOT 3 is left if you want to convert. Actually it's better to do it when the whole system is being rebuilt with all new components.

Ok then I don't have a problem as my entire brake system is all new components. Whew! Thanks, Charles.

john - if you are replacing everything - including the steel lines - like Charles said - no problem. I ended up keeping the steel lines but flushed the heck out of the system. Are you doing 100%? Keith

My lines were rusted badly and I was not willing to trust them so out they are going. I guess you could say I am keeping the tee fittings and the brass ones behind the cylinders but other than that, all new.

My truck might not end up being a perfect job but I am aiming for 100% on the brake system.