I just bought a very nice Dodge M-880. I'm going through and cleaning up a few things. The brake fluid is nasty. I noticed it says synthic fluid only on the master cylinder, is this weird? Do i need to put dot 5 syn in it? Thanks

Most US military vehicles of the modern era were converted over to synthetic so yours probably will need it unless someone has already swapped it back to DOT3.

Are you suspose to use dot 3 in a syn brake system? I know on motorcycles your not suspose to change them because the seals are different. The truck only has 62,000 orginal miles and I'm the 3 rd owner. The Reserve base sold it to my local police station and they sold to me. It's pretty black. I may just drain it all and put the syn back in it and see what happens. I now you get better pedal feel with dot 3 because it is minerqal based. I don'r want to screw anthing up.

Are you suspose to use dot 3 in a syn brake system? I know on motorcycles your not suspose to change them because the seals are different. The truck only has 62,000 orginal miles and I'm the 3 rd owner. The Reserve base sold it to my local police station and they sold to me. It's pretty black. I may just drain it all and put the syn back in it and see what happens. I now you get better pedal feel with dot 3 because it is mineral based. I don'r want to screw anthing up.

I was under the impression that the DOT 5 specification was originally designed for the military. However, I haven't ever owned a military vehicle yet so I can't tell you for certain that this is true.

I can tell you that there should be no issues with running DOT 5 in your system. I know of guys doing this on the Mopar stuff without problems.

must use synthetic fluid! cannot change over unless you replace every rubber component in the system, hoses, master cyl, wheel cyls, calipers! Dot 5 should work without a problem! The nasty you see is a fungus that grows in the silicone fluid the military used, it will clog ports in the system, so it's gotta be flushed. I spent alot of years working on M882 1 1/4 ton trucks for the PA Guard, good truck, but you still need good luck!

Does the cap say dot 3,4,or5 all of these could be synthetic? I'm assuming it says dot 5 which is a silicone based fluid instead of 3&4's glycol based chemistry. I thought dot 5 was a newer invention than the m880 but I could be wrong. Anyway it's is an absolute no on mixing of the dots, except. There is a dot5.1 that is not silicone but glycol, so it can be mixed with 3&4,but not dot 5. As far as changing from dot 3&4 to dot 5 or vice versa don't bother, run whats in it and keep the system maintained. It's far simpler. However if the simple path does not interest you have at it. But don't flush the system with any thing but brake fluid, all petroleum products will atack the seals in a brake system. Which leads to the seal failure comments. I believe the reason the military wanted dot 5 is because it has no problems flowing at extremely low tempertures. However others will say its because it doesn't absorb water, there is a problem though with this "ability". The water that does get into the system "pools up" in the low spots, like the caliper, and can lower the local boiling at the caliper. Or cause localized corrosion or even support a fungus. On the other hand dot3&4 are hygroscopic fluids and absorb water readily, however better 3&4's have inhibitors that slow this process, such as synthetic 3&4's. In humid climates it would be best to change the fluid more often from a fresh can of fluid. The plastic bottle you've had for years just won't cut it. Oh yeah dot 5 has one more problem it has a tendency to absorb air or bubble easily which can lead to a "spongy" pedal feel till it degasses it self, if ever. As far as motorcycles Hardly-Capables are the only ones that specify dot5 probably because its not as harsh to painted surfaces. I've also been told if you mix 3&4 with 5 you get a gelatin like substance which i tried to do on the bench in a cup and could not duplicate. However a fellow mechanic in a shop that I worked at had to disasemble a entire brake system on a motorcycle cause the customer had switched his. I've later discovered via the enternet that the dot5 only reacts this way with a brake fluid byproduct? Well I hope I've added to your confusion:flipoff2: Sorry about rambling on it's late and I'm not correcting my grammer tonight.