Author Topic: 1991 Sportster Front Master Cylinder size  (Read 536 times)

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Offline g-wali

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1991 Sportster Front Master Cylinder size
« on: September 02, 2019, 12:37:38 PM »
Need to replace this part but there seems to be 3 sizes.  I have a single front brake.  I think its 9/16 but they offer 58 and 11/16.

Offline 14Frisco

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Re: 1991 Sportster Front Master Cylinder size
« Reply #1 on: September 02, 2019, 01:18:30 PM »
Per the parts catalog part number is 45019-85A.  Not 100%, but fairly certain it is 5/8".  If you have the stock one the size is stamped on it (if it is still on the handlebars, remove the switch housing and you'll see the stamp.)

BTW, same mc is/was used on the FXR, Softail and Dyna models.
« Last Edit: September 02, 2019, 01:26:51 PM by 14Frisco »

Offline g-wali

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Re: 1991 Sportster Front Master Cylinder size
« Reply #2 on: September 02, 2019, 04:14:59 PM »
Thanks!  I will take a look.

Offline FSG

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Re: 1991 Sportster Front Master Cylinder size
« Reply #3 on: September 02, 2019, 04:25:07 PM »
5/8"   :up:

Offline 14Frisco

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Re: 1991 Sportster Front Master Cylinder size
« Reply #4 on: September 02, 2019, 04:57:58 PM »
Why are you replacing it?

Offline g-wali

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Re: 1991 Sportster Front Master Cylinder size
« Reply #5 on: September 02, 2019, 06:31:05 PM »
I want to rebuild it since I am not getting any pressure building up.

Offline 14Frisco

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Re: 1991 Sportster Front Master Cylinder size
« Reply #6 on: September 02, 2019, 06:46:50 PM »
I want to rebuild it since I am not getting any pressure building up.

The reason I was asking was if you were changing your caliper you may want to consider another size master cylinder.

Instead of a new master cylinder, you may want to consider a rebuild kit i, e.g. 45072-87 "REPAIR KIT, master cylinder". Or an aftermarket rebuild kit (make sure it is for 5/8"), e.g. DS-195043.

Offline g-wali

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Re: 1991 Sportster Front Master Cylinder size
« Reply #7 on: September 02, 2019, 07:24:18 PM »
Yes not replacing. Just rebuilding.