44100-25500 not fitting

[tjp]

68 1600 vin 19XXX w engine 62XXX.

RL brake cylinder leaking at the back side so a new piston cup didn't help. It's a 3/4" cylinder so assumed that part number 44100-25500 (3/4 "all" from R-40001 according to the book) would be correct. Unfortunately the threads on the fitting will not screw into any of the NOS units with this part number or any of the 3/4" used ones on the shelf EXCEPT the one pictured here on the right which is a slightly different style. (can't rebuild the odd ball shown here as the bore is very pitted.

Soooo, thoughts please on why the part number above isn't fitting what appears to be an original rear cylinder.

thanks
tim

[Habitat.pat]

Where did you get the new cylinder? Might the threads be metric rather than the needed 3/8-24?

Peace,
Pat

[tjp]

aWhere did you get the new cylinder? Might the threads be metric rather than the needed 3/8-24?

New parts are in Nissan or Datsun boxes, (were) unopened, with the number 44100-25500. All the used ones, except the one I mentioned were all the same looking part as the NOS ones with 3/4 stamped on the side.

[DAC21]

Do the hard line fitting threads look buggered? 3/8 SAE will thread into 10mm threads, but probably only once as it will be damaged. Wondering if some other Datsun model 3/4" brake cylinder was used previously with mismatched threads, that would explain the different looking bodies.

[tjp]

Do the hard line fitting threads look buggered? 3/8 SAE will thread into 10mm threads, but probably only once as it will be damaged. Wondering if some other Datsun model 3/4" brake cylinder was used previously with mismatched threads, that would explain the different looking bodies.

Threads are clean and the hard line fitting does not leak.

[fj20spl311]

Maybe the hard line fitting has been changed to metric.
If the cylinder was metric, the line would thread in but might/will strip when you tighten.

[DAC21]

Maybe the hard line fitting has been changed to metric.
If the cylinder was metric, the line would thread in but might/will strip when you tighten.

Yep if the OP hasn't gotten it straightened out I'd go to Rockauto.com and buy the Centric Datsun 510 rear wheel cylinder. $13 delivered and see if that threads into the hardline fitting. That will confirm if the hard line fittings were changed out to metric. If that's the case then hopefully the OP made that same change on the other brake cylinder. $35 for two 510 cylinders is a win. Yes they are 13/16 vs 3/4 cylinders but I have yet seen any 311s Brake threads that thought it was the end of the world safety wise.