Oil Pressure gauge fitting

[Volksnut]

So it's not a 1/8" npt, been reading it could be a brake line thread...what did you use.

[Wildergarten]

So it's not a 1/8" npt, been reading it could be a brake line thread...what did you use.

Are you talking about the fitting on mechanical gauges or the thread into the engine block (which is 1/8"NPT)? My '69 had an electrical gauge with a sender common to passenger cars, which is what I'll be using on my '68. So there's that possibility too.

[Volksnut]

So it's not a 1/8" npt, been reading it could be a brake line thread...what did you use.

Are you talking about the fitting on mechanical gauges or the thread into the engine block (which is 1/8"NPT)? My '69 had an electrical gauge with a sender common to passenger cars, which is what I'll be using on my '68. So there's that possibility too.

The fitting at the back of a mechanical gauge, the cluster is from a '68 if that matters....it looks like 1/8" npt but its not.

[Wildergarten]

The fitting at the back of a mechanical gauge, the cluster is from a '68 if that matters....it looks like 1/8" npt but its not.

Well that was a TRIP.

I looked at it and thought it was 3/8-28 UNF. So I dug out a 3/8 fine bolt and it only went in with fingers for at most a couple of turns. WTF? Got out the "universal" plastic plate to put against the fitting and couldn't make sense of it. So I got desperate and dug out my THREAD GAUGE that had sat in a toolbox drawer so long it had rusted. That test left no doubt: it's 3/8-27; The picture isn't perfect becauseI can't get the light such that you can both see the fit, read the gauge, and hold the camera but I can assure you it is light tight!!! Weirdest choice of threads I've ever seen. I'm guessing it was done to keep line workers from installing the hose backwards putting the compression fitting into the block.

Just as strange, the tube from the fitting rotates in the hose. In fact, it appears to be soldered to the ferrule, which is just weird. The fitting looks like it only goes in a few turns anyway, so you MIGHT be able to get away with 3/8-28. I'm really sorry, but the hose is no good or I'd sell it for a pittance. I'm going electric with the OEM sender with an aftermarket spare.
.

[Volksnut]

The fitting at the back of a mechanical gauge, the cluster is from a '68 if that matters....it looks like
1/8" npt but its not.

Well that was a TRIP.

I looked at it and thought it was 3/8-28 UNF. So I dug out a 3/8 fine bolt and it only went in with fingers for at most a couple of turns. WTF? Got out the "universal" plastic plate to put against the fitting and couldn't make sense of it. So I got desperate and dug out my THREAD GAUGE that had sat in a toolbox drawer so long it had rusted. That test left no doubt: it's 3/8-27; The picture isn't perfect becauseI can't get the light such that you can both see the fit, read the gauge, and hold the camera but I can assure you it is light tight!!! Weirdest choice of threads I've ever seen. I'm guessing it was done to keep line workers from installing the hose backwards putting the compression fitting into the block.

Just as strange, the tube from the fitting rotates in the hose. In fact, it appears to be soldered to the ferrule, which is just weird. The fitting looks like it only goes in a few turns anyway, so you MIGHT be able to get away with 3/8-28. I'm really sorry, but the hose is no good or I'd sell it for a pittance. I'm going electric with the OEM sender with an aftermarket spare.
.

Thanks for checking, I dont know why anything can't be easy.

[PwrWgnDrvr]

Cut the crimp part off, remove the rubber hose and hose clamp on a new piece of rubber hose. Or spend the $$ and have a hydraulic shop crimp on a new hose. Whatever, that end part of the hose, that fits into the gauge, is worth gold, eh?

[Txas2step]

Cut the crimp part off, remove the rubber hose and hose clamp on a new piece of rubber hose. Or spend the $$ and have a hydraulic shop crimp on a new hose. Whatever, that end part of the hose, that fits into the gauge, is worth gold, eh?

Terry, that's what I did on 3 sets set of Heavy Duty gauges with mechanical oil gauges. No leakage after 4 years.

[dodgeboykim]

Has anyone tried this hose



https://www.google.com/url?sa=i&url=htt ... AdAAAAABAK

[powerwagon54]

Has anyone tried this hose



https://www.google.com/url?sa=i&url=htt ... AdAAAAABAK

yes I have. It has the wrong fitting on it. The correct fitting is 3/8 x 28 which I verified thru a local hydraulic shop. It is no longer made. I use compression fittings to attach new hoses to the original fitting and have had zero problems for over 10 years now. That hose is 3/8 x 24 and will not thread into the gauge.

[Wildergarten]

The correct fitting is 3/8 x 28 which I verified thru a local hydraulic shop.

Having spent an hour looking at this, including under a microscope, I have to disagree. I tried threading a 3/8-28 UNF bolt into one of the two Dodge oil pressure gauges I have in the shop. The bolt didn't go in even two full turns, nor did the bolt thread fit against the compression nut on the hose end perfectly. So I got suspicious and dug out the trusy Screw Pitch Gage.

The OEM compression nut DID NOT fit up tightly against my 28tpi Screw Pitch Gage.
The OEM compression nut DOES fit my 27tpi Screw Pitch Gage, light tight.

To see the two in succession with the gage under the scope, there is no question about it. As I said above, this is the strangest part I've ever seen, a thread pitch in a manufactured product that makes no sense to me. As to the oil pressure gauge itself, that is much harder to inspect with the gage without some very special LED or fiber optic lighting to get in there well enough to see the fit. I'd probably have to disassemble the gage to remove obstructions. But I could put the OEM compression nut with the gages under our low power boom microscope and try the camera I've never used to see if I can get it to work on one of our old laptops. High time I did that anyway. The Screw Pitch Gage did get a cleanup out of this question.

This particular OEM compression nut only threads into the gauge I tested about 3-4 turns before the ferrule seats. One could probably force a 28tpi nut that far into it and make it work, but it would very likely strain the threads in the gauge. I am not surprised a hydraulics guy used to working on big equipment in steel wouldn't notice it in such a small brass part. Hence, I'm not confident in using a 28tpi hose fitting and were I in Volksnut's position would prefer to have a hose made up onto the OEM fitting per Terry's suggestion.

[powerwagon54]

every 3/8 unf (fine) thread bolt that I have seen is 24 tpi, not 28.

[Wildergarten]

every 3/8 unf (fine) thread bolt that I have seen is 24 tpi, not 28.

I checked, and you are right. It's been 30 years since I've been a machinist and memory failed.

It's not a 28tpi thread; it's 27tpi. If you want photos, I can do that.

[powerwagon54]

I dont need anything. As I said before, I have been fixing these for at least 10 years with no issues. You can believe what you want.

[Wildergarten]

[PwrWgnDrvr]

I think the thread pitch gauge should be believed

[Conductorblg]

I just went through this grief last week. My luck with hose clamping rubber line onto tubing has always been dismal and I thought about having a local shop just crimp on a new hose, but in the end had them (Oil Filter Service) cut the tube connecting the hose to the gauge fitting and braze on an AN fitting (although it looks more like he silver soldered it). This allowed connecting it up to braided stainless brake line. A stock fitting to convert to pipe thread screwed into the block at the other end.
Overkill perhaps when the original lasted 54 years and a little spendy, but hopefully the END of the problem of oil oozing out the ferrule and down the hose and dripping on everything under it, including my foot.

[Red383]

I was tired of oil dripping on my boot because the line was leaking at the factory crimp behind the gauge. I wanted it to be shorter, but I couldn't fine a female barb fitting. Oh well, there is plenty of clearence behind the gauge.

This is what I did, so far it is working good.

Aaron

[Wildergarten]

This is what I did, so far it is working good.

So far. It may not stay that way. If it were mine, I would find a way to support the weight of the hose bouncing up and down against the fitting into the gauge. A loose fairly wide ziptie would do.