One of the rear wheel cylinders on my 77 280 was leaking a little so I bought rebuild kits for both sides. I've got kits from both Wagner and Tru-Torque, and the basic P/N is 96618.

Pulled the pistons out of my wheel cylinder and pried off the old seals. Then I noticed that the hole in the center of the old seal is much larger than the hole in the new one and it would be an enormous stretch to fit one of the new ones onto the piston. Also, the new seal is thicker and doesn't fit the groove in the piston. I've got a set of old cylinders from a parts car and the pistons and seals in them are the same as what's in my car. In other words, I have the correct cylinders and pistons on my car.

I didn't try real hard to stretch that new seal onto my piston, but I don't think it's going to work. Did they change the piston design somewhere along the line and I missed the memo? Did I somehow get the wrong rebuild kit, and if so, what's the correct one?

Here's a pic showing the old and new

Hard to tell in this pic, but the new seal is thicker than the old one:

Here's one of the packages and you can see the other part numbers it's compatible with:

What the heck???

Rock Auto Shows

Dorman 96618 and Bendix 6672 as a fit for the following:

NISSAN 280Z (1977 - 1978)

For early 280z's it gives:

Doorman 96855 & Bendix 66673

NISSAN 240Z (1972 - 1973)

NISSAN 260Z (1974 - 1975)

NISSAN 280Z (1975 - 1976)

Looks like different parts after 76 and you seem to have an early cylinder. What month is your 77?

Edited September 21, 201212 yr by Blue

btw my 77 has two movable pistons in each cylinder. Earlier Z's only have one:

http://www.blackdragonauto.com/pdfcatalogs/pdf/ZR/0053.pdf

Blue, Thanks for the help. I'm familiar with both styles of cylinders and what I'm working on are the 77-78 style with the two opposed pistons. I had the earlier single piston floating cylinder style in my 74. In the pic, you can only see one of the pistons, but I assure you... I've got two pistons and two seals per corner.

The rebuilds I bought were Wagner 96618. I also got a box of parts from my previous owner that included some NOS brake parts, and in there were another set of Wagner kits (looked older than the ones I bought), and the Tru-Torque kits. I think I've got at least five rebuild kits, some unopened NOS still in sealed packaging and they are all the same... And none of them are correct for my cylinders.

And like I mentioned above, I dismantled and stored a set of 77-78 cylinders from a parts car a while ago, and when things started getting confusing, I pulled that box off the shelf to see if it could add any info. The result is that the pair of cylinders in that box were identical to the ones on my car, including the pistons and seals with the larger hole in the center.

Looking at the pics at Rock Auto, all the rebuilds they have appear to be the small hole style.

Something seemingly this simple, and it's just not making sense?

I certainly don't recall those diagonal groves when I rebuilt mine years ago... but my memory ain't so good.

Edited September 21, 201212 yr by Blue

Nobody? I'm the only one who has ever had such problem???

On a related note... I've got aluminum wheel cylinders. Does everyone else have the same, or are they steel?