75 280Z - 5 speed swap from 81 280ZX - any catches I should be aware of?

[Dave WM]

I would just check for radial play with the drive shaft installed. a little heavy oil on it. if play is not excessive you should be ok.

[HusseinHolland]

Measuring the fill & drain plugs - it appears they are 1/2" NPT - 14tpi gauge fits better than metric 1.75 pitch. Comparing with 1/2" NPT copper pipe & cast iron plug

 

 

[Captain Obvious]

Word on the street is that the tapered pipe threads used (everywhere?) on the Z's was British standard... BPT.

So the 14 TPI would be correct, but the thread profile is a little different than NPT.

[HusseinHolland]

1 hour ago, Captain Obvious said:

Word on the street is that the tapered pipe threads used (everywhere?) on the Z's was British standard... BPT.

So the 14 TPI would be correct, but the thread profile is a little different than NPT.

That makes more sense - also  the OD of the NPT bung is oversize by about .010" - doesn't thread as far in by hand without more effort

[Captain Obvious]

The reason it doesn't thread in as far is probably because of the thread profile differences. NPT uses 60 degree threads, while BPT uses 55 degree "Whitworth" style threads. So while the pitch is the same, there are some minor differences in the shape of the peaks and valleys.

That said... If you are working on one of the sizes where the BPT and NPT thread pitches actually lines up the same (some of them do and some don't) and you aren't intending to hold back a lot of pressure, you can usually get away with using an NPT plug in an application where the correct part is actually BPT. Put an extra wrap of teflon tape on it and crank it in. Of course, the right thing to do would be to source a BPT plug.

Edited June 3, 2024 by Captain Obvious

[Zed Head]

McMaster-Carr has BSPT fittings.

https://www.mcmaster.com/products/pipe-fittings/thread-type~bspt/low-pressure-galvanized-iron-and-steel-threaded-pipe-fittings/

[HusseinHolland]

6 hours ago, Captain Obvious said:

The reason it doesn't thread in as far is probably because of the thread profile differences. NPT uses 60 degree threads, while BPT uses 55 degree "Whitworth" style threads. So while the pitch is the same, there are some minor differences in the shape of the peaks and valleys.

That said... If you are working on one of the sizes where the BPT and NPT thread pitches actually lines up the same (some of them do and some don't) and you aren't intending to hold back a lot of pressure, you can usually get away with using an NPT plug in an application where the correct part is actually BPT. Put an extra wrap of teflon tape on it and crank it in. Of course, the right thing to do would be to source a BPT plug.

Thank you for the detail - I don't need them, I have both my fill and drain plug, it was more just I couldn't find a direct answer & enquiring minds want to know, ya know 😁

Edited June 3, 2024 by HusseinHolland

[cgsheen1]

There is no pressure (other than weight of the fluid) in the transmission. Most people tighten both the fill and drain much tighter than they need to be. They only need to be as tight as not to leak. I used to recommend just using Teflon tape on the threads but now use Loctite 567 Thread Sealant and only tighten to snug or slightly past. (got pretty sick of having to use a 3 foot cheater bar to remove customers fill plugs and an impact on the drain...) 

(I'm a journeyman plumber and spent 35 years cutting and threading pipe. Just like flare fittings, there's science to threaded pipe fittings - which the fill and drain plugs are - just like there's science to the dissimilar metals involved. Tightening a threaded fitting too much is as bad or worse than not tightening enough. "Pipe dope", Teflon, cutting oil (lubricant) it used to control heat caused by friction. Too much friction (heat) causes micro fractures in the metal of the thread which means leak. So, the Teflon is actually more of a lube than a "seal"... Also the more torque you put on it, the more friction there is, more heat to damage the metal. - There, I've given my unsolicited plumbing advice for the day!)

[HusseinHolland]

3 hours ago, cgsheen1 said:

There is no pressure (other than weight of the fluid) in the transmission. Most people tighten both the fill and drain much tighter than they need to be. They only need to be as tight as not to leak. I used to recommend just using Teflon tape on the threads but now use Loctite 567 Thread Sealant and only tighten to snug or slightly past. (got pretty sick of having to use a 3 foot cheater bar to remove customers fill plugs and an impact on the drain...) 

(I'm a journeyman plumber and spent 35 years cutting and threading pipe. Just like flare fittings, there's science to threaded pipe fittings - which the fill and drain plugs are - just like there's science to the dissimilar metals involved. Tightening a threaded fitting too much is as bad or worse than not tightening enough. "Pipe dope", Teflon, cutting oil (lubricant) it used to control heat caused by friction. Too much friction (heat) causes micro fractures in the metal of the thread which means leak. So, the Teflon is actually more of a lube than a "seal"... Also the more torque you put on it, the more friction there is, more heat to damage the metal. - There, I've given my unsolicited plumbing advice for the day!)

Thank you - I also use Loctite thread sealant on pipe thread, and only snug the plugs. 15 years back when I was  modding the crankcase vent system on my 500AWHP Volvo wagon, I used a bunch of 3/4 copper pipe & 1/2" NPT fittings as part of the block vent (occupies much less space than AN fittings of similar ID) - I used to use teflon, but I found it didn't always work well with oil / vapor connections, so I switched to the Loctite 567 😁

Edited June 4, 2024 by HusseinHolland

[HusseinHolland]

Had to take another day off work today, the cold I had, I gave to the Mrs, and she gave it back. She just finished a round of antibiotics, so that's next for me. Hopefully tomorrow I'll feel up to working on the Z.

[HusseinHolland]

I was going to replace the T/O bearing carrier, however the replacement I got off RockAuto (listed & illustrated correctly on the site) - came as the wrong part

form factor & dimensions are all wrong. I just cleaned mine up & replaced the bearing. No evidence of wear in it, or on the input shaft sleeve

Edited June 4, 2024 by HusseinHolland

[Patcon]

14 hours ago, cgsheen1 said:

There is no pressure (other than weight of the fluid) in the transmission. Most people tighten both the fill and drain much tighter than they need to be. They only need to be as tight as not to leak. I used to recommend just using Teflon tape on the threads but now use Loctite 567 Thread Sealant and only tighten to snug or slightly past. (got pretty sick of having to use a 3 foot cheater bar to remove customers fill plugs and an impact on the drain...) 

(I'm a journeyman plumber and spent 35 years cutting and threading pipe. Just like flare fittings, there's science to threaded pipe fittings - which the fill and drain plugs are - just like there's science to the dissimilar metals involved. Tightening a threaded fitting too much is as bad or worse than not tightening enough. "Pipe dope", Teflon, cutting oil (lubricant) it used to control heat caused by friction. Too much friction (heat) causes micro fractures in the metal of the thread which means leak. So, the Teflon is actually more of a lube than a "seal"... Also the more torque you put on it, the more friction there is, more heat to damage the metal. - There, I've given my unsolicited plumbing advice for the day!)

Thanks for the tip. Just ordered some. It's amazing how expensive so many of these items have gotten