View Full Version : 84 FXR rear master cylinder rebuild question????

02-12-2014, 10:56 PM

New to posting on the forum, but not new to ChopCult and reading the forum. That being said, let me know if there are any problems with the post or location.

I am rebuilding the rear brake MC on my 1984 FXRT. I purchased rebuild kit and disassembled the original. When comparing them side by side they were significantly different...

Has anyone seen this before? Were the rebuild components upgraded from the OEM parts?

Any help/insight would be appreciated. Attached are some pics of what I'm working with. The left is the new rebuild kit and the right is OEM.


02-17-2014, 2:32 PM
I thought you might have received your answer and that's why I deleted what I had posted originally. Glad you got it via email, even though I had deleted it.

I'm putting the answer back up in case others run across the same issue. Like I said before, I'm glad you posted the question because one of the brake systems I have for the FXR I'm putting together uses this master cylinder and I would have most likely have had the same puzzled look on my face as you probably did when you got the repair kit.

The parts manual shows the original repair kit as the 42382-82A. Those are the parts on the right in your photographs. That part number, 42382-82A, is obsolete. The new rebuild kit are the parts on the left in your photograph. That part number is 42382-82B.

Attached is an image showing the part numbers and kits, as well as the notice about the change.

Since this is about finding part changes, here's another useful piece of info. A lot of people use Ronnie's Harley Davidson online parts lookup to find oem numbers and diagrams, but I've found that that one doesn't show the part number changes. However, St. Charles Harley Davidson online parts lookup does. Here's a link to St. Charles HD: http://www.stcharlesharleydavidson.com/oempartfinder.htm#

- Trig

02-17-2014, 3:44 PM
Thank you very much for the reply Trig. The info is very helpful as is that St. Charles HD link.

That o-ring seems like it may be too small to seal on the ID of the master cylinder if slid over the top of the piston. I'm guessing it should be stretched over the piston to be installed in that groove? I am a little hesitant to do this without knowing if it is correct or not. The attached cylinder internals schematic (#30 from Trig's attachment) seems to show two actual 'seals' whereas the rebuild kit comes with the seal and o-ring. Any insight? Otherwise, I will probably end up installing the o-ring over the piston groove and try it out...

Thanks again for the help!


02-17-2014, 6:13 PM
I took mine apart and low and behold, the parts were already swapped. I took some photos of how it's assembled. See attachments.

As you guessed, the o-ring is stretched over and goes in the groove about a third of the way down from the top of the plunger. The top of the plunger being the snap ring end...

- Trig

02-17-2014, 7:09 PM
You the man Trig!

Thank you very much for your help on this one.


02-18-2014, 10:46 AM
Glad I was able to help someone. That's one less turd I'll have to smoke in Purgatory.

- Trig

03-02-2014, 1:35 PM
Good info Im going to do mine too