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08-19-2012, 10:04 PM
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#1 (permalink)
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Junior Member
Join Date: Aug 2012
Location: ohio
Posts: 3
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72 shovelhead brakes
OK so I introduced myself and told my story in the new people section. I'm in the process of getting the braking back in order. And I replaced the rear master cylinder with one from SamsPowersports on Ebay. When I got it the instructions say that I must run dot5. But back in 72 they only ran dot 3. So the new lines and new drum cylinder I have are dot 3 compatible not dot 5. The guy from Sam's says just run dot5 but I did and the brand new (not rebuilt) drum cylinder is leaking out the boot. So I have to assume its because I'm trying to run dot5 through a cylinder that is made for dot3. So I have new springs, cylinder bolt, shoes, the drum is in spec and a new master cylinder. But that master cylinder is calling for dot5 and everything else is calling for dot3. What are your thoughts?
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08-20-2012, 05:32 AM
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#2 (permalink)
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Greasy Member
Join Date: Jun 2008
Location: In my garage!!
Posts: 25,356
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DOT-5 can be run if there's NO natural rubber seals. I believe the seals in the slave in the rear drum are natural rubber.
I'd personally stick to DOT-3 or 4. You can get new cups for the rear brake slave at NAPA. Take the old ones out and the bore size should be printed on the cup, or take it with you and they'll match it up.
Make sure the bore isn't pitted too. If it can't be honed, then it's shot and needs repalcing.
__________________
__________________________________________
Football Season is over....
“When the going gets weird, the weird turn professional.” ~ Hunter S. Thompson~
Praise the Lowered!
11 year A.M.A. member.
4 year PA ABATE member.
RIP Rick Massey: AKA-Rubberdown. Godspeed, 02-02-12.
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08-20-2012, 08:54 AM
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#3 (permalink)
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EVO RULER
Join Date: Mar 2011
Location: terra dei Limberlost
Posts: 3,572
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Just did a 70 flh with a new master cyl it called for 5 but 3 causes no problems just rebuild your wheel cyl an use 3.
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*CONFORMITY IS JUST A SLOW FORM OF SUICIDE*
******SUPPORT YOUR LOCAL INVADERS*******
********RIP RUBBERDOWN RIDE FREE********
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08-20-2012, 10:26 AM
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#4 (permalink)
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Junior Member
Join Date: Aug 2012
Location: ohio
Posts: 3
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I just installed new:
Springs
Shoes
Master cylinder
Drum cylinder (brand new not rebuilt)
Ok I'm going to flush everything and clean it up and start over with Dot 3 then. Thanks everyone!
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08-20-2012, 12:46 PM
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#5 (permalink)
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Junior Member
Join Date: Dec 2008
Location: central Penna
Posts: 9
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My scooter all have rear shoes. I use DOT3. My understanding when you mix DOT5 in a cylinder that originally had DOT3 and wasn't theroughly cleaned, the mix of the two different brake fluids will deteriorate the seals.
__________________
1968 FLH assembled 6-21-1967
1969 FLH assembled 3-03-1969
1972 FX assembled 8-21-1971
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08-21-2012, 06:09 PM
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#6 (permalink)
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Senior Member
Join Date: Jun 2010
Location: Pennsylvania
Posts: 1,522
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I rebuilt my '68s brakes with a new master cylinder, Russel braided rear line and DOT 5 about 10yrs ago and it hasn't leaked a drop. Drag Specialities has a DOT 5 rated master cylinders , and maybe even a rebuild kit for each. I'm thinking I only rebuild the wheel cylinder.
But IIRC , it only has to be new rubber pistons. It can't be ones that had DOT 3 and were cleaned. And flush the hard line on the frame with plenty of brake clean.
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"Whatever doesn't kill you simply makes you , , , older! 
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12-07-2012, 07:52 PM
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#7 (permalink)
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Junior Member
Join Date: Oct 2012
Location: southern new jersey
Posts: 5
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72 shovelhead brakes
i used the 5.1 fluid that is compatible with 3 or 4 but takes more heat because that master cylinder is right next to the front pipe ,try it.
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12-08-2012, 05:08 AM
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#8 (permalink)
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Senior Member
Join Date: Jun 2012
Location: indiana
Posts: 220
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check out ATE super blue raceing fluids. syn. they may come in DOT 5 on-line.
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12-08-2012, 05:17 AM
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#9 (permalink)
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Greasy Member
Join Date: Jun 2008
Location: In my garage!!
Posts: 25,356
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Quote:
Originally Posted by hobo1948
i used the 5.1 fluid that is compatible with 3 or 4 but takes more heat because that master cylinder is right next to the front pipe ,try it.
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Agreed. 5.1 is compatible witn 3-4, and performs better as well.
__________________
__________________________________________
Football Season is over....
“When the going gets weird, the weird turn professional.” ~ Hunter S. Thompson~
Praise the Lowered!
11 year A.M.A. member.
4 year PA ABATE member.
RIP Rick Massey: AKA-Rubberdown. Godspeed, 02-02-12.
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12-08-2012, 06:41 AM
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#10 (permalink)
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Retired citizen
Join Date: Jun 2009
Location: Pt. Wash.,WI
Posts: 10,725
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Is 5.1 compatible with 5 ???
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Disclaimer : Don't believe anything I say unless you are absolutely sure that I know what I'm talking about .
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