HarleyTechTalk

99' FatBoy - Want to change the front brake caliper from the single to a twin cam four piston caliper. 
My bike uses Dot 5. New Caliper uses Dot 4.
Using TC caliper and braided line so only MC will have the Dot 5 fluid.
If I flush the MC with alcohol will that clean the Dot 5 out of it?
Do I need to rebuild or is flushing adequate for the seals?
The TC caliper is from a 2000 softail.

You only need to switch away from DOT 5 if you're using anti lock brakes, I think, but see what others say.

No anti lock brakes. Bike is a 99'.
Have read where some say mixing the two fluids causes a reaction on the seals.
I thought a good flush would minimize the 5 and not much to mix with the 4.

If your caliper came from a 2000 model (as you stated) It would have come with dot 5 fluid so no need to flush. If it somehow now has dot 4 I would flush the caliper with alcohol and run dot 5. You are correct in not wanting to mix dot 4 and dot 5.

Is the caliper new or used? 

You mention that the "new caliper uses Dot 4",  not sure if that means it's a used caliper from a year that uses Dot 4,  or if it's new and for a year that uses Dot 4?

I would try to use Dot 5 if possible,  I believe 2006 was the first softail year that used Dot 4...not positive. 

If the caliper is new unused,  I would bolt it on and use Dot 5.

Harley normally offers 2 rebuild kits,  one that is just the rubber parts and the other has the same rubber pieces plus the pistons...neither are much money.

IMO the benefits in performance of Dot 4 are overrated and don't outweigh the fact that Dot 5 won't damage paint and being hydrophobic doesn't absorb moisture and doesn't need to be flushed/changed near as often as Dot 4.

Don't get me wrong,  I like a plenty strong front brake with a tall lever.  My Deuce (04/Dot 5) came with dual disc,  braided lines and semi-floating rotors.  I keep the caliper pistons clean to maintain a tall lever and run Lyndall Xtreme pads...I just don't see Dot 4 adding much at all.

Caliper is used from a 2000 FXR softail.
It is in good condition and I would only rebuild if there was an issue with the fluids.

I thought Harley changed to Dot 4 in and after 2000!
Maybe not this model though!

DOT4 only required for ABS.  I don't believe they changed till several years later.  DOT 5 is good.  Does not absorb moisture, is kind to paint and lasts a long time.  No way I would use anything else if I didn't have to.

Quote from: Grayrider on August 14, 2016, 04:01:11 PM
Caliper is used from a 2000 FXR softail.
It is in good condition and I would only rebuild if there was an issue with the fluids.

I thought Harley changed to Dot 4 in and after 2000!
Maybe not this model though!

Unless somebody used something other than Dot 5 in the caliper you should be good to go.

 

All 2006 Model Year models except XL models changed to Dot 4 brake fluid, the XL models changed in the 2007 Model Year.

DOT4 is required for ABS due to the microscopic bubbles that form in the DOT5.

DOT 4 appeared on the 2005 Police models because that was the first year that ABS was offered as an option on those models only

Dot 4 was used on 2005 model FL's - all models in 2006.

True

2000 FXR Softail??.......

Use Dot 5