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She’s running! Brake fluid type?

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This is rich Hartung with the 39 Desoto. Great to see your 40 Dodge moving and running on its own power.


First, can you contact the prior owner to contact them to see if they had added any brake fluid to the master cylinder which is under the floor pans?


Since the car seems to be a fresh barn find I would assume, and assuming that the prior owner used off the self brake fluid, and that would have been Dot3.


Do not install, again do not install DOT 5, that is silicone brake fluid and IT DOES NOT MIX.


If you are going to install DOT 5 then you need to bleed the entire brake system with denatured alcohol, Install all new rubber brakes hoses, rebuild each brake cylinder with new rubber cups, also rebuild the master cylinder with all new rubber components.


DOT5 can be a purple color and or even a yellow color.  Dot five will not remove paint from metal but DOT3 or DOT4 will remove paint when spilled on a fender or other painted surface. 


I have lots of cross reference catalog for this car such as the autolite electrical components and other info.


Rich Hartung


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I use Dot 4  in both drum & disc systems..........good to see your up & running..........andyd 

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I got my 51 with DOT 5 silicone fluid.

Most others are Alcohol based.

As said before, they cannot mix and some rubber cups are not compatible.

You can let your brake fluid test to have it identified, and I suggest to continue with the existing.

Silicone DOT 5 has a couple of advantages:

it does not absorb water - thus does not age and is nearly maintenance - free, it does not promote rusting, it is self- lubricating,

it is not heat sensitive as alcohlic varieties (very high boiling point), our military uses silicone DOT 5  in stored tanks, trucks, ships to have them immediately ready for use.


not mixable with others, system must be cleaned perfectly when cahnageing to it -as said before.

Purpur code colour is not durable and not good for safe idnetification after some years.

And be careful: DOT 5.1 is NOT mixable beeing alcoholic type.

best practice:

if ever  possible, stay with what You have!

Greetings from Düsseldorf

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To be blunt, these cars were engineered to use DOT 3 brake fluid.  Other fluids, such as DOT 5 silicone based fluid will work but you will notice a difference.  I don't know the mechanics of it, but DOT 5 in a system engineered for DOT 3 will seem spongy, almost like there is a bit of air in the system.  DOT 5 is good for show cars that don't hit the street very much, as it does not attract moisture, and doesn't ruin paint.  I put DOT 5 in our D24 several years ago when I rebuilt the braking system because we weren't using the car much and were in a relatively humid environment.  It has held up very well, but I don't like how the brakes work now that we have been using the car more...the aforementioned "spongy" braking, even though the system was thoroughly flushed.  (As noted, the DOTs don't play well together.)  If you intend to use Dotty as a regular, or even occasional, driver, then I'd recommend the tried and true DOT 3, and just adhere to regular maintenance on the brake system.

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