PDA

View Full Version : Switching from DOT 5 to DOT 3 brake fluid



91 240
04-13-2006, 05:52 PM
I'm helping a friend out who just got a 98 240 from a hardcore road racer in VA. His brake system consists of Z32 calipers all around, Z32 m/c, stainless lines and DOT 5 fluid. This going to be his daily driver. He's noticed that the pedal is a little spongy, which I know is common with DOT 5.

I know DOT 3/4 and DOT 5 are of totally different composistions and are incompatable to mix. I know you can switch from a DOT 3/4 to DOT 5 if the entire system is bleed before adding the DOT 5.

Now, is it safe to switch from DOT 5 to back to DOT 3? I've heard that DOT 5 is very tough to completely remove from the system. I've also heard that switching the fluid types could possilby damage the rubber parts in the system (calipers, m/c) causing repairs or replacement.

Is there a good way to completely remove all the DOT 5 without having to worry about replacing anything? Or, would he be stuck rebuilding the calipers and master cylinder and replacing all the lines?

Hopefully someone will know. Thanks

Kookz
04-13-2006, 06:20 PM
Is it definitely DOT 5 and not 5.1?

240x2
04-13-2006, 06:42 PM
I'm helping a friend out who just got a 98 240 from a hardcore road racer in VA. His brake system consists of Z32 calipers all around, Z32 m/c, stainless lines and DOT 5 fluid. This going to be his daily driver. He's noticed that the pedal is a little spongy, which I know is common with DOT 5.

I know DOT 3/4 and DOT 5 are of totally different composistions and are incompatable to mix. I know you can switch from a DOT 3/4 to DOT 5 if the entire system is bleed before adding the DOT 5.

Now, is it safe to switch from DOT 5 to back to DOT 3? I've heard that DOT 5 is very tough to completely remove from the system. I've also heard that switching the fluid types could possilby damage the rubber parts in the system (calipers, m/c) causing repairs or replacement.

Is there a good way to completely remove all the DOT 5 without having to worry about replacing anything? Or, would he be stuck rebuilding the calipers and master cylinder and replacing all the lines?

Hopefully someone will know. Thanks




From what I heard it really su* balls to do this,u have totally drain the system,and bleed the system as bad as 3-5 times,some times change lines,dont take my word but good luck... http://forums.freshalloy.com/images/graemlins/ack2.gif

91 240
04-14-2006, 08:03 AM
The previous owner said that it is infact DOT 5.

Broaner
04-16-2006, 06:35 PM
Going back to DOT 3/4 is easier than the original switch. The problem with the 3/4 to 5 swap is that the 3/4 is much more corrosive and is actually a thicker fluid. So, the seals in the system get chewed away. But you don't notice that they're bad until the thinner DOT 5 is put into the system. The 5 is much less corrosive but it leaks through the seals that the 3/4 didn't. So, if they seals hold for the 5 they should be more than adequate for the 3/4.

Now about how they mix I can't speculate too much. I've heard that flushing with denatured alcohol works well.

rogoman
04-16-2006, 07:56 PM
Is there a good way to completely remove all the DOT 5 without having to worry about replacing anything? Or, would he be stuck rebuilding the calipers and master cylinder and replacing all the lines?


To completely remove DOT5, the calipers and the master cylinder must also be disassembled and washed out.