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I’ve got a new (to me) 73 Z, and I’ve got leaks from the 3 devices mounted to the transmission. They all leak down the outside of the housing. I’ve found a drawing that calls them the speedo drive, reverse lamp switch, and the clutch slave cylinder. I’ve only been able to find a part number for the o-ring for the speedo, and not much info on how to get at them. Does anyone have the part numbers for the 3 o-rings or seals? Anybody done these before? I’m really hoping to change them without dropping the tranny. Thanks!

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All three can be accessed without dropping the transmission. You will need ramps or jack stands tall enough to get under the car, though. I haven't messed with the reverse switch in over 20 years, but I think you should be able to find a generic crush washer for the seal. The reverse switch at Rockauto.com shows a rubber gasket.

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The slave cylinder does not enter the transmission that has the gear oil. If there is a leak there, it may be the sign of a slave cylinder about to fail. (Photos are very helpful to show what you are seeing.)

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check the function of the reverse light if you use a washer. On mine it spaced it out enough to not work. IIRC I used some brush on thread sealant on that one.

Leaks can fool you, they often originate somewhere and then migrate to a low point. Lots of oil leaks can be traced back to failed seals in the trans striker rod. IF you pull the rubber boot up  and feel around where the trans shifter stabs in (you can do this from under the car with out having to remove the center console) you may find a pool of lube. This is NOT normal, its suppose to be sealed. Anyway if that is the origination point of oil leaks, the only way to stop is to pull the transmission, pull the rear housing and replace a seal and an o ring.

this is something that should be done next time you have the clutch  replaced, while the trans is out. Also you should replace the rear main at the same time, another source of sneeky oil leaks.

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The first thing I would do is degrease all the areas of concern and check regulary after each drive to determine where the leaks are coming from. Oil can spread and give the impression it's leaking from one spot, but accually coming from another.

Pay attention to where exactly the leak is.

1. Reverse switch: Is it leaking out the side between the transmission case and switch or out through the rubber boot where the wires are? Leaking through the side is s gasket. Leaking past the wires is a worn out switch.

2. Speedo: Leaking through the cable or leaking out between the speedo "adapter" and transmission casing? Leaking past the adapter is an o-ring seal. Leaking through the cable is a inner Lip-seal and is a little more difficult to change. If either one is leaking, I would replace both seals.

3. Slave cylinder: If it leaks replace it. If you buy a new one, strip it apart and clean it before installing it. The new units often have metal shavings left over from manufacture and that can destroy the new seals.

All the parts you mentioned are common leak areas and easy fixes with basic tools.

 

Edited by EuroDat
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I take it you cleaned the switch it to determine that. If you disconnect the switch wires and unsrew the switch, you will find an o-ring seal at the shoulder end of the thread. You can see it in SteveJ photo. It is an easy fix,. I have the size I used somewhere. Ill look it up.

The speedo is two seals. You should replace both. You can get them at most at most auto dealers. Here is a sreenshot from The Z Store.

Screenshot_20201021-221754.jpg

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@EuroDat, I recently replaced the seals on the tail shaft/shifter rod on my 71B transmission 83ZX. The o’ring was the only seal visible on the outside of the speedometer assembly. The seal that you are referring to above was not visible. Is the small seal part of the speedo assembly itself?

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Yes. It is the lip seal for the pinion shaft in the speedo adapter. You can't see it until you tap out the little roll pin and remove the pinion gear.

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14 minutes ago, Yarb said:

@EuroDat, I recently replaced the seals on the tail shaft/shifter rod on my 71B transmission 83ZX. The o’ring was the only seal visible on the outside of the speedometer assembly. The seal that you are referring to above was not visible. Is the small seal part of the speedo assembly itself?

It's deep down inside the housing. You'll need a pick type something to get it out and I'm pretty sure I used a 10mm deep socket to get the new one down inside.

DSC01492.JPG

DSC01494.JPG

Speedometer cable grommet (@ trans) - Open Discussions - The Classic Zcar  Club

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Here is a simple instruction for the FS5W71C in the 300ZX, but it works the same.

 

Screenshot_20201023-181214.jpg

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Hi,

So at this point for the tranny leak game, it’s me: 2, 73 Z: 1. The slave cylinder and reverse switch are replaced, not leaking, and working perfectly. Unfortunately, I can no longer tell how fast I’m going. I got the speedo pinion out, and it looks like it’s not the first time out of the car. Somebody had done some delicate work on it with a big set of vice grips. I went ahead and got a new one, and it looks exactly like the one in EuroDat’s procedure above. It was quite a bit different than the heavy steel one that I took out. It seemed to match up, so I stuck it back in. Good news, no leaks, bad news, no speed speed indicator. I checked the cable and it is not broken, and secure in the pinion. I ran out out time today and have not taken the pinion out again. 
 

Has anyone else swapped out this housing before?  I noticed the gear was slightly offset in the housing, but this seemed to be true in the old housing too. I’m pretty sure I got the housing in “right side up”, with the throttle shelf for the locking tab in the right direction. 
 

Any other thoughts?  Mm

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Sometimes the end of the cable will not seat in the speedo drive, even though the housing screws all the way down.  Best practice seems to be to pull the cable out of the sleeve and seat it firmly in its spot in the drive housing then push the cable back in to the sleeve while screwing down the locking ring.  If the car is up in the air it helps to spin the drive/propeller shaft with your hand while tightening down the locking ring, to get the slotted end in its spot in the speedo.  You might have to try that a few times until both ends of the cable get seated properly.  Not uncommon.

 

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So, in comparing the old and new housings, it looks like the offset in the shaft hole faces the opposite direction. In the pic, the locking shoulder in both is facing the same way. You can see the gear in the new housing over hangs to the right, but the hole in the old one is closer to the left. I’m going to see if I can put a shoulder on the opposite side of the new housing. 

0B9ACE6B-FA6F-4A5E-9A0A-B15BD9F9AEAD.jpeg

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You can swap the gear and shaft over easily.  Push out the small roll pin and the gear/shaft will side right out.  It takes some finagling to get the pin out and in but it's not too hard.

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Thatis because you have the later version. The version for the F4W71B and 280Z F5W71B is not what you see on most of the websites. I don't think it is still available. The later version 280ZX F5W71B and the F5W71C that had the non electronic speedo have the locating bolt under the speedo adatpor. You bought an adapter for those transmisions.

All the seals and pinion will fit your adapter, but I don't like your chances of getting the inner seal out without damaging it.

It is a simple fix. The groove for the locating tab and M6 bolt is on the wrong side so you can make a new groove or send it to a machine shop to make one.

You can make a groove yourself by carefully cutting a groove with a hacksaw and fine tuning it will a small metal working file. Buy a file that fits easilly in the original groove. Remove the outer o-ring seal and tape over the ends to prevent shaving entering the adapter. Don't go too deep or it will allow the adaper to turn and the gears will loose contact. You can test if it is deep enough by fitting it to the transmission (without o-ring or pinion gear) then fit the tab and bolt. Take little steps at a time. Too far and it is ruined.

Tip: To check that you are exactly opposite to the original groove. Use two too straight edges like a ruler or back of a hacksaw blade. Place one in each groove so they extend out the same direction. If they are parallel to each other, then your new groove is exactly opposite.

I wouldn't use your original adapter without replacing the inner seal.

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