I am rebuilding my brake system in ny 67 electra glide & my new master cylinder says to put DOT 5 only so I cleared out my system of DOT 4 & replaced it with DOT 5. I now need to replace the rear wheel cylinder for the brake system & it says DOT 4 only. What do I do? Can I use DOT 5 with the new rear wheel brake cylinder or do I have to go back to DOT 4 & get a new master cylinder?

 

I just asked the dealer the difference on the Dot 4 and the Dot 5. Was told the Dot 5 was for the new ABS brake systems. Dot 4 is still mostly 100% mineral oil.
Just my 2 cents
(I stand corrected on this info stated earlier) Wouldn't want anyone to read that and think it was right, so disregard it totally.The Harley parts guy didn't know the correct information obviously .Below posts have better info on the subject of Brake fluid adaptations and mixing.and chemistry, hopefully no harm taken.

 

Thanks Hammer!

 

And when you mention you "cleaned out the system", assume you know you have to take apart all brake related parts and thoroughly clean them so there is no mixing of fluids

 

Yes. The whole system must be thoroughly taken apart & meticulosly cleaned. But the new master cylinder stated to use DOT 5 only for the hydrolic system but the new wheel cylinder states to use DOT 4 only. ??????

 

i have an 74 flh with new master on rear and front with still old banana brakes and i use brake fluid no 5 i also put in new o rings and seals and it works great

 

The difference is just in the make up of the fluids. The material of the o-rings is the same for both systems. You just don't want to mix them. I run a Wagner-Lockheed master with the banana clip rear and use DOT 5. Denatured alcohol is a good source to clean brake system fluid FYI.

 

Thanks all of you for the great advice! I will be running DOT 5 throughout.

 

hey 48 pan thats a heck of a good looking machine

 

I agree, that's a sweet one, I'm drooling just looking at it.