I'm on the slippery slope of while I'm doing (fill in the blank), I might as well (fill in the blank...usually multiple blanks and sometimes a full restore). I pulled my engine for rebuild and decided to do some cleanup. Mainly degreasing the engine bay but also cleaning all the gunk off the front axle while everything is nice and accessible. In the process I discovered that my axle vent was not threaded into the axle properly- it was just sitting there. The threads are almost all stripped off the vent piece, so that will need replaced. But the threads on the axle housing are a bit buggered too. From the few remaining threads on the old vent (haven't received the new one yet), it would appear that the threads are a 7/16"-20 fine thread. I can spin a die on the vent piece just fine, but there are only a couple threads left so it is nearly impossible to verify that this is actually the correct thread pitch. However, I cannot get a tap to start into the axle at all and I don't want to force it only to find out it is pipe threads or some weird thread pitch. I think it will probably end up pulling the cover and run the tap from the inside to make sure it I don't cross thread it. I have to pull the cover anyways to make sure no water or debris got in anyways.

Oh yeah, the important part- it is a 1975 F100 4x4 with a high pinion Dana 44, that I am not 100% sure is original to the truck. Can anyone verify what the correct size/ thread pitch is for the front axle vent?

 

I think you may have already messed it up if you've run 7/16x20 tap in there. It's NPT threads, not standard thread. I'm not sure, but I think it's 1/8 NPT. You've got to have a vent, so if you have to drill and tap it for a larger nipple, you should do it.

Yeah, you do need to look inside, and clean it out.

 

At least some of them are standard thread: https://www.wildhorses4x4.com/produc...co_Brake_Hoses
Probably due to them doing double-duty as a brake hose tie-down anchor bolt.

Paul

 

The front axle is NPT the rear axle is SAE. There is no front brake lines on the front axles like there is on the rear axle.

 

On what trucks? Two-wheel drives and 4wd 250's and 350's sure. But every Bronco and F150 that I've ever worked on had the single hose from the frame down to the axle (both front and back), the junction block that the breather bolt holds down, then the tubes out to where the rubber hoses join them.
That is unless I've just been spending too much time with the Broncos (very possible! and never noticed that the 100's and 150's followed the same routing as the heavier trucks?
If so shame on me and I have to go back to school!

Paul

 

Yep, as far as I remember, every Dana axle I've owned, front and rear, had NPT thread for vent nipple. Ford 9" is SAE, and holds down the rear brake Y block.

 

That's what the parts catalog pic shows.

C4TZ-4022-A .. Front Axle Vent - 1/8" -27 x 1 1/4" long / Obsolete

1964/91 F100/250 4WD // 1971/79 F600 4WD // 1979/91 F350 4WD

NOS ONLY in San Jose CA has 2 = 408-227-2353.

CARPENTER NOS PARTS in Concord NC has 4 = 800-476-9653.

GREEN SALES CO. in Cincinnati OH has 23 = 800-543-4959.

 

You likely can drill it out and put about anything you want in it. It does not have to be tapped either, press fit with lock tite would work fine, but threading would be the best way. The vent is not a critical part in general so use your imagination, but do it right for the next guy.

 

Where do you find the part description and application info? I do not see that in the parts catalog or I am missing something. That helped confirm what seemed to be the consensus that it was 1/8" NPT. I finally got a tap that size today and that was indeed correct. Got the threads cleaned up and waiting for the new vent to show up. The threads weren't that bad, just a bit buggered from where the PO had tried to force the stripped out vent back into place. I tried a straight 1/8" pipe nipple first and could not get it to start. Tapped it out and it's smooth as butter now.

And for what it's worth, the vent does not hold down the brake line junction. Well at least not on a 1975 F100 anyways.

 

Ahh, that's right. I'd forgotten that the trucks (or at least some years?) separated that function. I've seen that but forgot. On the Broncos the breather bolt holds the brake lines on both front and back.

Thanks for that clarification. Definitely helps.

Paul