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LOST REAR BRAKES - wrong fluid type?

SGT ROCK

SGT ROCK

Member
HELP!!!!!

I have a 1999 FLHTC. The front master cylinder cover says DOT 5 and the rear says DOT 4. The dealers (two of them) seemed confused and said to go with the manual. It says DOT 5. I did last spring when I changed the fluid for the first time at about 45K miles.

Lost rear brakes after a few hundred miles, so I re- flushed with DOT 5 and refilled with DOT 5. ( There were no bubbles but a lot of tiny black specks in the flushed fluid) I thought the specks were gunk loosened by the fluid flush/change. I ran 3 or 4 full resivoirs through the system before the final bleed. The brakes were OK until they failed completely again today.

I'll appreciate any suggestions. I'm not sure the dealers know the answer and there is no way to contact the factory with the VIN to ask about the different master cylinder covers.

Sgt. Rock
 
Last edited by a moderator:
I would think that your master cylinder is in need of a rebuild as all the main parts in your rear brake system are the same as my 92 softail i would assume that dot 5 would be the correct brake fluid
at 13 years old it would not be unusual for the brake master cylinder seals to have failed
I would suspect that at some time in the past the brake master cylinder reservoir cover has been replaced with a more modern one as the ABS braking systems need a glycol based brake fluid (dot 4) to operate correctly
dot 5 brake fluid is silicone based and can not be mixed with glycol based fluids
Rebuild kit for the rear master cylinder part number 42382-87C

Brian
 
Finally got a new cartridge assembly for the rebuild. When I took the master cylinder apart, I found a greasy / gel-like substance around the outside of the old cartridge and the same stuff inside when I pulled the guts out. I installed the new cartridge assembly, blew the old fluid out of the line and caliper with low pressure air. I refilled with DOT 5. All is working well....we'll see how long .
 
That greasy gel is what happens when you mix DOT3/4 Glycol with DOT5 Silicone brake fluids. Hopefully what you did was enough, however I am one to change out ALL the rubber parts that contacted the incorrect fluid. Glycol swells certain types of hoses and seals purposely, so rubber parts swell and seat, but on a DOT5 system, the parts swell and stick which is not good.:(
 
NEWHD74FAN said:
That greasy gel is what happens when you mix DOT3/4 Glycol with DOT5 Silicone brake fluids. Hopefully what you did was enough, however I am one to change out ALL the rubber parts that contacted the incorrect fluid. Glycol swells certain types of hoses and seals purposely, so rubber parts swell and seat, but on a DOT5 system, the parts swell and stick which is not good.:(
Click to expand...

Changing all the hydraulic parts would be the BEST way to go here, cross contamination is an on going problem in older systems flushing MAY not get all the old fluid out and the rubber parts may have already begun to swell or break down jMO
 
Looks like I should get some new seals and redo the caliper...at least it's less work than pulling the master cykinder was.
 
+1 on all the above. I also (every time I check my fluid) look at the condition of the Master Cylinder cover. The painted ones are painted inside also and that paint peels and flakes off into your fluid.

Additionally DOT4 over time will also corrode the aluminum itself on underside of the aluminum covers. It did on my rear one. I popped the gasket and peep hole out and wire brushed the cover good to get all the scale off it. Cleaned everything up good with denatured alcohol and reassembled.
 
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