Wheel cylinder bore size?

[0.C.]

So my rear wheel cylinder went bad this weekend.

I took out the drum and shoes and proceed to removed the cylinder to inspect it.

On the cylinder it says 11/16 so I called up about 5 different stores asking for a repair kit. They either had 3/4 and 13/16 and told me that there was no such a thing as 11/16 on their system.

It also drove me nuts cuase the repair kits where special order. and the wheel cylinders where $35 plus.If I would order it, with the holidays it would get here 5 days after.

So I ended up buying a wheel cylinder for $15 but it was 13/16 bore, at this point I wasn't sure sure if it would fit, but also I was running out of time.

So i went home and installed it and fit perfectly.

So my question is.

Did someone just swapped that 11/16 cylinder in there before, or 521's come with those 2 different sizes?

[patrowan]

I'm pretty sure the wheel cylinder is off a newer (try 76) 620. Someone probably changed them in an attempt to stop rear first lock up. Anyway both sides should be the same size or the braking problem gets even more interesting (oh no!).

[banzai510(hainz)]

Mine went out(521). I bought one but didnt know the size. It was the wront bore size but still worked.

 

best to get new FORGET those rebuild kits.

 

try ROCKAUTO.COM but I think I got mine from NAPA

 

I believe I installed the 3/4 3/4 =12/16 not a huge difference over 13/16

[DanielC]

I found the same thing with mine, only worse. I had four wheel cylinders I started to try to rebuild. I took all four apart. Two were marked 3/4, two were marked 13/16. The 13/16 looked too bad to use, after all, a stock 521 only has a single master cylinder, not a dual one. So I started to work on the 3/4 ones. I went and got two wheel cylinder kits, and when I tried to put them together, one wheel cylinder marked 3/4 was actually 13/16.

I ended up getting two new wheel cylinders, 3/4 size.

I got the wheel cylinders home, and one would not fit onto the brake back plate, it was machined bad, the center boss was off center. The nuts I had on my old wheel cylinders did not fit, and I had to get new nuts, no big deal since I was already at the auto parts store, exchanging the wheel cylinder that was machined bad.

The nuts I needed for the new wheel cylinders were a M8x1.25, my old wheel cylinders had 5/16x28 nuts.

I think that when you buy 521 wheel cylinders, you really get 620 wheel cylinders.

I know you can get 13/16 and 3/4 rear wheel cylinders, and apparently 11/16 are available. if this is true, it is nice to know, if you need to reduce rear wheel lockup in panic stops. Smaller rear wheel cylinder, less braking power at rear wheels.

[0.C.]

Well, I'm still not sure what size of bore I have on the other size since I didn't have enough time to remove the other drum.

I know for sure that on the front I have 3/4 and on the rear I have a new 13/16 cylinder but on the other side still unknown.

Now I don't have to pump my pedal to brake.

I also noticed today that my front left wheel locks when I hit the brake too hard.

I guess it's time to replace all 3 cylinders left.

[DanielC]

Bigger wheel cylinders, means more braking power at that wheel. The front brakes on a PL-521 are set up so that the forward motion of the brake drum tends to apply the brakes even more. The brake shoe mount, that holds the adjuster has to slide for this to happen. Make sure that it moves with a little force. It should move about equally on both sides.

Brake shoes do funny things when they get grease on them, clean your hands if they are greasy before you touch the brake shoes, or brake drums.

[650savag]

I just rebuilt the left rear wheel cylinder on my 78, 620 because it was leaking very bad. The repair manual says to remove the shoes first, but I was able to spread the shoes out at the top, and the slotted tension bar will hold them apart enough to remove the wheel cylinder. I did not check the right rear wheel cylinder, but the one that I rebuilt was a 5/8 bore. Does that sound right? The only thing in the kit was the two rubber lips that fit on the two pistons, and the two boots that go on each end of the cylinder. O'Reilly wanted $9.84 for one kit but I found the same kit at Advance Auto Parts for 4.79 and O'Reilly did a price match for me. They are in town.

[datzenmike]

620 front and rear or just rear... 3/4" (Haynes)

[glorydime]

I've been having problems with my front wheel cylinders. I have tried both 3/4 and 13/16 both won't fit in my y pipe.