Info needed: Transfer case vent

[Grant Bowker]

Based only on the part being designed/made in Canada my assumption is that it would be NPT (North American specification). This needs confirmation.


Some of my manufacture was done using reclaimed pipe and flat sheet and others were done using off the shelf NPT pipe nipples. Comparison would provide the answer but it will be a week before I have a chance to do the comparison or measurement so if others can do this sooner it would be helpful.

[Lynn Eades]

Grant, I dunno, but the influence of "mudda" England on the truck it's self was high, so I wouldn't write off BSP. As you say it needs confirmation.
I searched transmission breather (in images) There is a flat one under Midwest transmission breather at $6.00. There are options at bigger money. Back in the day, they may have been supplied by AC (GM) as in radiator caps, thermostats etc.

[Jacques Reed]

Originally Posted by Grant Bowker

Based only on the part being designed/made in Canada my assumption is that it would be NPT (North American specification). This needs confirmation.

I am with NPT also but haven't got those thread gauges to compare on my fittings. There are a few British threads on CMP vehicle so you cannot completely write off BSP- Wheel studs at 7/8" BSF are a good example.

NPT thread taper is 1:16, ¾” per foot- from Machinery’s handbook
BSPT is 1°47’ per side equals Sin 0.0311 = 1/ Sin1°47’= 1/32 each side = 1/16 (same as NPT!)

1/8 NPT 27 TPI 1/8 BSP 28 TPI
¼ NPT 18 TPI ¼ BSP 19 TPI
½ NPT 14 TPI ½ BSP 14 TPI

1/2" NPT vs 1/2" BSP: Both have 14 threads per inch, so they match up quite well. The primary difference is angle of the thread which is 60 degrees NPT to 55 degrees BSP. In low pressure applications they are ok to swap. Add PTFE tape as a bit of insurance if you feel it needs it.

In Australia NPT fittings are very hard to find. I was looking for a short 1/2" NPT nipple for the same location to swap different types of breather caps. Could get a s/s one from Canada from a home brewing company but the cost was excessive so left things as is. Shown is one available. No hexagonal area in the middle and very short like the original nipple on the transfer case.

Cheers,

[Paul Edwards]

Thank you guys for all your assistance, in the end I took the path with lest resistance.

Giving my transfer case is the early type with the vertical nipple and cap breather and whilst accepting the modification bulletin to fit the air cleaner type, it is clear why my squashed cap had been butchered to fit the tight space available. Latter breather housings were to have a new casing exiting at 45 degrees to overcome this issue.

So with the original pipe nipple and my plumbing skills I made a cap from 22mm copper pipe and a feed end cap, once painted no one will Know.

Cheers,


Paul

[rob love]

You'll just have to remember that if you drive into water that is above that level you will need to change the oil in the transfer case. Mind you, I guess the other cap doesn't prevent water from coming in either. So the only minor negative is that the normal breathing of the transfer case as it heats and cools will allow unfiltered air into the gearbox. So if you go driving through the desert,, or long gravel roads, you will want to change the transfer case oil more often.

In the real world of a restored cmp, I would say there is no negative to the modification you have done.

[Jacques Reed]

Originally Posted by Jacques Reed

I am with NPT also but haven't got those thread gauges to compare on my fittings. There are a few British threads on CMP vehicle so you cannot completely write off BSP- Wheel studs at 7/8" BSF are a good example.

NPT thread taper is 1:16, ¾” per foot- from Machinery’s handbook
BSPT is 1°47’ per side equals Sin 0.0311 = 1/ Sin1°47’= 1/32 each side = 1/16 (same as NPT!)

1/8 NPT 27 TPI 1/8 BSP 28 TPI
¼ NPT 18 TPI ¼ BSP 19 TPI
½ NPT 14 TPI ½ BSP 14 TPI

1/2" NPT vs 1/2" BSP: Both have 14 threads per inch, so they match up quite well. The primary difference is angle of the thread which is 60 degrees NPT to 55 degrees BSP. In low pressure applications they are ok to swap. Add PTFE tape as a bit of insurance if you feel it needs it.

In Australia NPT fittings are very hard to find. I was looking for a short 1/2" NPT nipple for the same location to swap different types of breather caps. Could get a s/s one from Canada from a home brewing company but the cost was excessive so left things as is. Shown is one available. No hexagonal area in the middle and very short like the original nipple on the transfer case.

Cheers,

Good Day,

Today I thought I would gamble $3.00 on a 1/2 BSP short nipple for my transfer case vent. A local home brewing supplier had these nipples. Although they told me on the phone that they had the straight ones without the hex in the middle when I got there that type was out of stock and they were not reordering them. Not an uncommon thing when chasing up parts.

I prefer the large breather cap to the smaller one so this will do in the interim. I can wait until I get the original style nipple- most likely from China on EPay. I still think the threads on the transfer case are NPT and if so, this proves that 1/2 BSP will do the job if 1/2 NPT isn't available, at least in low pressure applications.

Cheers,

[Paul Edwards]

Thanks Jacques,

The real issue becomes more apparent with the early tranny cases where the breather exits at 90 degrees (as opposed to 45 degrees), so harder to avoid hitting the chassis cross member with the replacement breather vent.

Cheers,


Paul