Fr. Master cylinder. Rebuild
 

Got rebuild kit, drag specialties no lube, can light touch of Vaseline be ok, thanks

Brake fluid itself has always worked for me.

WP

:icon_that:


But.... I just rebuilt the rear caliper for my 2001 Springer. I noticed in the instructions it said not to use DOT 5 for lubrication....? Since they supplied a seal lube in the kit, I used the seal lube this time.

I pieced the instructions with the part about not using DOT 5 for lube, just to share... I'm not sure I follow what they claim could happen...?

Just sharing for the heck of it.. maybe someone will know what they mean..

https://cimg6.ibsrv.net/gimg/www.hdf...d34c4b81c0.jpg

There was a time :) when only brake fluid was to be used.
Yes there are lubes nowadays that are recommended and makes things go together a bit more easy.

Back in the day there was a bit of finesse needed when assembling calipers , wheel cyl, or master cyl's.
The lube helps minimize the chance of damaging a seal during assembly.

If ya got lube use it if not brake fluid will work.

WP

Thanks WP50 for the info...

I had never heard (or maybe just never noticed) a lube for brake seals before this rebuild.... I was always told to use brake fluid... admittedly, my last caliper rebuild was about 15 years ago for a friend's softail.

I must admit, with the lube, the parts did seem to go together pretty easy....

The part I don't get is the second half of their warning, "Use of DOT 5 brake fluid causes increased lever travel." Not sure I see how or why using brake fluid as a lubricant will/can cause that.. :icon_denk:

I'd guess they have some reason to say that but I have no clue.
Only time I had increased pedal/lever travel was when I screwed up.
The screw ups did happen but gladly not often.

WP

I suspect the warning HD included about DOT 5 brake fluid as a lube is related to their recommendation to not use DOT 5 fluid at all. Or perhaps the risk of mixing DOT 5 with existing DOT 4 if the end use doesn't know better as most HD's likely used DOT 4 from the factory.

DOT 5 is more viscus and has been known to require more lever pressure to stop. And it's not compatible with ABS systems. Some complain about spongy brakes after a change to DOT 5 (from DOT 4), but I haven't noticed it on my older bikes that have been changed to DOT 5.

For assemble lube on brake cylinders and calipers, I use the same brake fluid I plan to run in the system. Never been a problem (so far). I wonder if the lube provided is compatible with all brake fluids? ie: DOT 5

Paul

I think you hit the nail on the head there, pgreer; Incompatibility between DOT5 and DOT4. That rebuild kit services many different years worth of master cylinders. Some bikes were DOT5 (like my '00 Deuce), some were DOT4. In order to prevent "contaminating" the system, HD states to use their lube. The seals will be fine with either brake fluid, to be clear.

But the reality is that using the fluid (that matches what the system takes) as an assembly lube is fine in practice. That's just how it's done traditionally, and how I've done it for decades.

Thanks everyone for your input just used brake the dot 4 brake fluid, that's what is called for, did have a hard time with the outer seal but found a pvc tubing that fit perfectly over it, that went great, attaching the handle the teeny tiny snap ring went zing, it's somewhere in our galaxy, so got c-rings instead, will carry x-tra but I think it will hold fine

I found one in the top of my tool box just a bit ago ???

Glad ya got it done WP