77-78 Rear Brakes - A couple years ago, one of my rear wheel brake cylinders started leaking so I bought a pair of rebuild kits (WAGNER F96618) from Rock Auto. Problem is that when I took my cylinders apart, I discovered that the rebuild kit would not work for my cylinders because the piston seal was a different design and would not fit.

Here's a pic showing one of my pistons, and the seals. Old (leaky) one on the left with the large hole, and new one from the rebuild kit that doesn't fit my piston because the hole is way to small:

 

At that time I gave up and just bought a new pair of wheel cylinders (AUTOSPECIALTY / KELSEY-HAYES W51104) and put them in. Problem is that one of those cylinders is now leaking, and I'm back to the same problem again. The rebuild kits don't fit the wheel cylinder. They could use different piston designs inside, but here's what my cylinders look like from the outside:

 

And there is this snippet from the 77 FSM. Seems it may have been a manufacturing source difference, but I don't know who won the contest:

So, anyone have any insights? I know I could just purchase yet another pair of wheel cylinders... I mean, they're cheap enough! But the ones on there are so new, there's nothing wrong with them except the seals are leaking. A rebuild kit would be perfect.

Problem is that all of the rebuild kits on Rockauto have pics of the seals with the small hole, and I've not found anything anywhere that looks like it has the large hole seal. Despite the fact that the new CYLINDERS you buy use the large hole style! At this point, I'm not even confident that I could purchase a pair of wheel cylinders and rebuild kits from the same manufacture at the same time and have them even be compatible!

Anyone ever seen a rebuild kit that has the large hole style piston seal??? Any other ideas?

I just pitched a pair , I might be able to find them and look. They said -made in USA- on them, didn’t give them a second look. New ones leaking that quickly -ugh

I received my rear wheel cylinders for the 77 280z from RockAuto yesterday, here is what they sent,

 

 

77 is a transition year?

I got the aluminium one a week ago.  Bolted right up, no problems so far.  Sucks you have to send one back to the border. 

Break the fluid line loose before you remove those two small bolts.  Learned that the only way I know, backwards.

Thanks for the input guys.

Site, You ordered a pair and that's the pair that arrived? Mismatched from each other? So is that darker one that says "made in USA"... That one is cast iron? One of the rebuild kits I have (I think it's a new Wagner) has the same markings and shape on the dust boots. And it looks like the dark one uses the small hole seal. Can't really tell about the other cylinder.

I think I'm going to force one of the small hole seals onto one of my pistons just to see what it looks like. I suspect it's going to bulge out so far there's no way it will fit into the bore.

And madkaw, if you do manage to pull yours from the can before they get picked up... If they use the small hole seal design, I'd love to have them. I've got a lifetime supply of rebuild kits but nothing to use them on. Seems it's a potluck crapshoot of potentially mismatched castings from Rockauto.

And forgot... My spring is different too. Mine is straight and not tapered. And it doesn't "clip" onto the back of either piston. The raised bumps in the middle of the opposing pistons kinda locates it, but doesn't retain. It just floats there between the two.

Well I managed to force a small hole seal from one of the rebuild kits onto one of my pistons, and NFW is that gonna work.

Here's the cylinder parts. Old original seal style on the bottom piston, and the newer small hole style on the top:

And here's a closeup of the seals. You can clearly see that the seal on the top piston sticks out way to far. I did try and couldn't even get it into the cylinder bore. I couldn't even get that seal up over the piston rear without tools. I had to stretch it so far I was worried about tearing it. With lube, I managed to get it on with the help of two screwdrivers, but it's clearly wrong:

This is killing me... I took the car down last Thursday with the expectation I would have it back together in a day. Slap some new seals in there, and put it back together. Done! Now it's one of the nicest weather weekends we've had all year, and I can't drive my Z because the stupid seals don't fit!!  

If I read the bigger picture right you have two old cylinders, one of which was leaking, and two newer cylinders, one of which is leaking.  So, hoping that moisture and storage hasn't damaged the older non-leaker, and that you still have it like a good hoarder should, you have an old non-leaker and a newer non-leaker.  Esthetically displeasing but should get you on the road while you work on the mismatched leakers.

Chris is the one that got the mismatched set.

I only bought one and it was the newer looking aluminium with a yellow plug and a black bleeder cap like in his post above

I meant mismatched as old versus new.  CO has/had four cylinders, two leak and two don't.  Or didn't.  

By the way I have a set of the early sliding cylinders, for 1976, if anyone needs some.  One old non-leaker and one new non-leaker.  And brake shoes.  I switched to the 78 style brakes.  A puzzle for the next owner.

7 hours ago, Captain Obvious said:

Site, You ordered a pair and that's the pair that arrived? Mismatched from each other? So is that darker one that says "made in USA"... That one is cast iron? One of the rebuild kits I have (I think it's a new Wagner) has the same markings and shape on the dust boots. And it looks like the dark one uses the small hole seal. Can't really tell about the other cylinder.

I think you are talking to me right? Yes they came in separate boxes from two different warehouses, the darker one is cast iron and the plastic bag that it came in had holes, wear spots, looked like it had been kick around on the floor for a few years. Hopefully they will both work just fine.