[daledaniel]

I have a 2005 Rubicon, last year had to flush the brake system due to some kind of mucky crap in it and refilled with DOT4 fluid, bled the brakes and went on now all of a sudden the thing is drinking a pint of fluid a week. I cant see any visiual signs of leakage could there be a real reason to only use DOT 3, I thought the other stuff was like an upgraded version of brake fluids. Help me get my baby back on the wagon!!!

[madduc]

Dot3 or Dot4 is fine and not causing ANY problem. If you can't see any place where the fluid is going it may be the master cylinder leaking. Remove the master from the booster(leave all lines connected) and look at the seal on the rear of the master.

[daledaniel]

OK I figured it out, the DOT 3 is thicker than the DOT 4. Last night I took the Jeep to the gas station to fill up the gas tank and realized that the brake reservoir was empty as well so I filled it up with the remaining DOT 4 I had inside then took off, the brakes worked better but they still would go all the way to the floor but they worked. The next morning took off to take wife to work and no brake fluid or brakes so I stopped off at the local Advanced Auto, they were having a special buy1 get1 on DOT 3 so I figured its gonna drink it anyway and bought 2 bottles. Filled up the reservoir again and after pulling out I noticed a harder pedal I mean almost like stock feel so I went to a professional brake shop and let them check it out and told them what all I had done and they confirmed the differences between the fluids and that the thinner DOT4 was bypassing into the brake booster and then into the engine where it was burned off. After gravity bleeding the brakes I am back to new. I guess that means I am a brake expert now

THERE! Now we learned something new today; stay away from DOT4, at least for me!

[FLATFENDER54]

Any one else can confirm this too??? ( I "thought" they were interchangeable and the D.O.T. rating was to do with boiling points and the amount of moisture that can get into the brake fluid) I think it was a coincidence your brakes felt better and you prolly still have a problem. Someone else will answer you better than I - I dont know a lot about brake fluids

[bluehdmc]

Originally Posted by daledaniel

OK I figured it out, the DOT 3 is thicker than the DOT 4. Last night I took the Jeep to the gas station to fill up the gas tank and realized that the brake reservoir was empty as well so I filled it up with the remaining DOT 4 I had inside then took off, the brakes worked better but they still would go all the way to the floor but they worked. The next morning took off to take wife to work and no brake fluid or brakes so I stopped off at the local Advanced Auto, they were having a special buy1 get1 on DOT 3 so I figured its gonna drink it anyway and bought 2 bottles. Filled up the reservoir again and after pulling out I noticed a harder pedal I mean almost like stock feel so I went to a professional brake shop and let them check it out and told them what all I had done and they confirmed the differences between the fluids and that the thinner DOT4 was bypassing into the brake booster and then into the engine where it was burned off. After gravity bleeding the brakes I am back to new. I guess that means I am a brake expert now

THERE! Now we learned something new today; stay away from DOT4, at least for me!

These guys don't sound very "professional" to me. If the DOT3 fluid is leaking into the booster you need a new master cylinder. You should not have ANY leaks in a brake system. I would remove the master cylinder and check behind it for a leak. there's a diaphram in a brake booster so the fluid shouldn't be able to "bypass into the engine and then be burned off".
You bled the brakes and changed to DOT4 fluid a year ago and all of a sudden you're having a problem now? Think about it.

[tjthorson]

Originally Posted by bluehdmc

These guys don't sound very "professional" to me. If the DOT3 fluid is leaking into the booster you need a new master cylinder. You should not have ANY leaks in a brake system. I would remove the master cylinder and check behind it for a leak. there's a diaphram in a brake booster so the fluid shouldn't be able to "bypass into the engine and then be burned off".
You bled the brakes and changed to DOT4 fluid a year ago and all of a sudden you're having a problem now? Think about it.

I would agree here. Brakes are not something to mess with - you really should know what you are doing.

DOT 3 or 4 is fine.... Sounds to me like you have air in the system from the "flush". If it went a year OK after the flush - next scenario is - it really wasnt full from the flush - and as the brake pads wore down, it starved the master cylinder and introduced air into the system.....

[06slvrrubi]

DOT 3 and DOT 4 ARE interchangeable. DOT 5 is a synthetic fluid and is NOT interchangeable with 3 and 4.
The only way brake fluid could be getting "burned off" by your engine by way of the booster, would be if the seals at the back of the master cylinder, where the pushrod goes thru from the pedal and the booster, are leaking and allowing fluid to enter the booster. Pull the vacuum line out of the booster and look for fluid residue in or around the vacuum line.
Also, have you looked very closely for any stains or residue at all four calipers?


I'm betting your master cylinder is shot, although it would be odd to have fluid leaking into the booster, I can't say that I've ever seen one leak that way before.