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Old 06-07-2024, 11:31 AM   #1
Diastole
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Default Rear Diff Plug HELP

I am new to Model As. I have a early '30 coupe.

I want to change the diff fluid. This car sat in a garage since 2015.
Owner recently passed, sadly. Rest his soul.

The fill-drain-plug has half of the lugs sheared off. I am looking for some help for a possible solution on how to remove it w/o damaging the housing.

See photos

I can try some vice-grips after heating the metal housing. Or, drill a hole, tap with left hand threads, and install a left hand thread bolt. Or weld a 3/8" square bar in what remains of the plug.

Being Model A's are new to me, and my interest to not reinvent the wheel, I am asking for any help or suggestions I can get.

I can do two of the three thoughts above, I do not have left hand tap and die set.

Thanks in advance

Diastole in the Smoky Mountains
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Old 06-07-2024, 11:46 AM   #2
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Default Re: Rear Diff Plug HELP

If it was mine I would weld a large nut to it , should come out easy, sometimes easy outs makes a easy job hard
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Old 06-07-2024, 11:51 AM   #3
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Default Re: Rear Diff Plug HELP

East out, or as Randall says.
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Old 06-07-2024, 11:54 AM   #4
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Default Re: Rear Diff Plug HELP

Vise-Grip might work, hopefully it isn't seized in the rear-end
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Old 06-07-2024, 12:48 PM   #5
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Default Re: Rear Diff Plug HELP

Try the vice grip first. I would avoid drilling the plug because of introducing chips into the housing. If the vice grips fail, I would grind off what is left and then weld a nut onto the plug, as Randall said. Do the weld in steps so as to not heat the housing too much. The heat from the welding should help with the removing the plug.

My plug on my differential has the square hole recessed in the plug and is a much stronger design. Buy a new plug from one of the usual vendors.
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Old 06-07-2024, 03:19 PM   #6
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Default Re: Rear Diff Plug HELP

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I vote no on easy outs, if they break, the job gets 10X worse. If you can weld, go that way. Chase the threads with grease in the flutes of the tap to keep chips out of the diff. I use Teflon tape on my plugs.
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Old 06-07-2024, 07:01 PM   #7
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Default Re: Rear Diff Plug HELP

Bruce, I will second the use of Teflon tape. Not only will it seal but it will prevent the plug from freezing in the housing.
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Old 06-07-2024, 07:04 PM   #8
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Default Re: Rear Diff Plug HELP

I like thread sealer and magnetic plugs.
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Old 06-07-2024, 08:20 PM   #9
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Default Re: Rear Diff Plug HELP

Wire brush, and penetrating oil sprayed liberally on it 3 x day for at least a week first. If you own a Model-A now you need patience!

And I do not mean WD-40!
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Old 06-07-2024, 10:16 PM   #10
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Default Re: Rear Diff Plug HELP

Is there enough sticking out to use a pipe wrench?

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Old 06-08-2024, 03:41 AM   #11
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Default Re: Rear Diff Plug HELP

Just weld a big nut to it and remove. An easy 5 minute job.
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Old 06-08-2024, 05:35 AM   #12
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Default Re: Rear Diff Plug HELP

I would take it to someone that knows how to weld and have them get it out someone like a professional welder or a body shop that has the tools to remove it or a Ford dealer would have the tools to remove the plug as there are places that work on just Model A's around have them get it out for you as you mass that up you will never get it out.
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Old 06-08-2024, 06:24 AM   #13
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Default Re: Rear Diff Plug HELP

If you chase the treads as Bruce suggested in Post #6, flush the case with a solvent like kerosene and, in any case, add a magnetic plug at the bottom as Blockhead recommended in Post #8.
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Old 06-08-2024, 06:25 AM   #14
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Default Re: Rear Diff Plug HELP

Heat the plug , Don’t heat the housing! After the vice grips don’t work, try a center punch tapping it in a circular motion in counter clockwise. For those suggesting welding a nut ? Don’t you first weld a washer and then a nut to the washer ?? When I worked in an airline tire and wheel shop sometimes to remove counter sunk screws we would have a welder tig weld 2 towering tits to the screw heads and then used vice grips.
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Old 06-08-2024, 08:15 AM   #15
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Default Re: Rear Diff Plug HELP

I always replace those female plugs with male ones. Easier to use a wrench to remove.
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Old 06-08-2024, 08:44 AM   #16
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Default Re: Rear Diff Plug HELP

Charlie, not enough sticking out for a pipe wrench.
Gene, started applying Kroll penetrating oil yesterday. Would you prefer PB Blaster?
Group, if I am going to weld a bolt, I do not want to screw up the two sides sitting proud. If I going to weld a nut, it does not matter. So vice-grips option is still pending. The nut likely has not been removed in 19 years in talking to the widow wife. Husband complained about that after they bought it 2005.

I like the welding idea yall propose. I'm a savy novice welder. I went to the mill and bought a piece of 1/2" square bar. It matches the 1/2" socket designed for the plug. I can weld that to the raised edges and use a 1/2" wrench. Once the penetrating oil soaks in.

I ordered 1/16" welding rods with flux since I am out of gas for the MIG welder. That should give me plenty of penetration. I do not have a TIG peddle.

Bob, thanks for the IM. I agree with your diagnosis. The problem is the damaged plug has a 1/2" recess for a socket wrench. That leaves very little metal of the plug to accept the torque. The new plugs have a 3/8" recess and that leaves more metal on the edge. See photos. I will replace the drain plug with a magnetic one and thicker walls, thanks, nkaminar.

Plan to try on Wednesday (four days hence). I will update you'all.

Thanks,

Diastole in the Smoky Mountains
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File Type: jpg drain plug.jpg (19.7 KB, 22 views)
File Type: jpg Drain plug square bar.jpg (38.2 KB, 45 views)
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Old 06-08-2024, 11:11 AM   #17
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Default Re: Rear Diff Plug HELP

Yeah, thats the plug I have. I bought a 3/8 breaker bar for it that just fits my plug.

Your idea of welding in a square shank is excellent.

Love, love, love the Smoky Mountains. You are so lucky to live there. How about sharing some photos of where you live.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 06-08-2024, 11:41 AM   #18
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Default Re: Rear Diff Plug HELP

I'm a gas welder myself. I braze cast iron like that so that the banjo casting doesn't crack. It would heat the plug in the bore well enough for it to come loose. Heating and welding cast iron can be tricky. Concentrate heat on the plug as best you can. Let it cool slowly.
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Old 06-08-2024, 05:27 PM   #19
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Default Re: Rear Diff Plug HELP

Kroil is great!

Don't chase those threads with a tap. Pipe threads are not that way, ask a machinist.

If you go the weld a nut on, turn the air on an impact gun down to 30lbs, and hit it a time or two with the trigger. Advance the air 5lbs each time. It will come out.

Wait ill you get a gas bottle refill...you will be glad you did.

Last edited by Gene F; 06-08-2024 at 05:43 PM.
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Old 06-09-2024, 05:15 AM   #20
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Default Re: Rear Diff Plug HELP

I think a gentle hand with a pipe tap would be okay to straighten out the threads, especially at the entrance. It is different from running a machine thread tap or chaser through a tapped hole.
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Old 06-13-2024, 10:08 PM   #21
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Default Re: Rear Diff Plug HELP

To All,
Welding square bar was quite easy and uneventful. The plug backed out with little force. The penetrating oil and heat combined with blasting air on the plug to "contract" it all contributed.

See Photos

The inspection hole appears non-tapered. The replacement plug (ordered from supplier) threads in but after about 3/16" to 1/4" I meet significant resistance.
When I compared it to the drain plug a noticed a stark difference.

The drain plug is tapered!


The old inspection plug does not appear tapered, but it is very short.

Please help?

Does anyone know if the housing is tapered for the drain or inspection plugs?
Could one be tapered and one be non-tapered?

I did not chase the threads. If they are tapered I can ruin the threads in the housing. None of the suppliers have tapered plugs. The are all non-tapered or cylindrical.

Should I just install teflon tape or orange Loctite and reinsert?

All the threads look good, both on the plugs and and housing.

A couple of posts said to wash the housing out with kerosene and refill. Is that necessary? The fluid was dirty but not congealed.

Please advise.

Diastole
Attached Images
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Old 06-13-2024, 10:17 PM   #22
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Default Re: Rear Diff Plug HELP

Yes, the plugs should be " pipe thread.
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Old 06-13-2024, 10:26 PM   #23
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Default Re: Rear Diff Plug HELP

Y-Blockhead,
Help me understand, pipe threads are tapered threads? Is that right?

I am new to all this.

The inspection plug I removed was non-tapered and ALL the suppliers sell only non-tapered plugs.

https://www.snydersantiqueauto.com/p...8061&cat=41823
https://www.brattons.com/DIFFERENTIA...ductinfo/5920/

In this "new car to me" and my first Model A, the drain plug I removed is tapered. See last photos, the plug tapers in the calipers.

So, what do I do?

The only replacements are non-tapered. Do I reuse the old drain plug because it is tapered.
And, since the old inspection plug is now welded onto a piece of square bar, I have to replace it. All the replacements are cylindrical, non-tapered.
But, it looks like the plug I removed was non-tapered, but it is so short, I cannot be certain.

Diastole
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Old 06-13-2024, 10:46 PM   #24
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Default Re: Rear Diff Plug HELP

Snyder's says 1/2" pipe thread. That would be tapered.
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Old 06-13-2024, 10:47 PM   #25
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Default Re: Rear Diff Plug HELP

The plug you link to from Snyder's states in the description "The original style. Can be used to fill and drain. This style of oil plug is 1/2" pipe thread."

Pipe thread is tapered thread.
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Old 06-13-2024, 10:48 PM   #26
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yes, pipe thread is tapered. if you do run a tap in there, only put in a little ways. only enough to chase the threads. not cut them any deeper.
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Old 06-13-2024, 10:59 PM   #27
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Default Re: Rear Diff Plug HELP

Wow, thanks for the help.

So, I can use the new plugs. Screw them in until snug. If they sit proud, with threads sticking out, above the level of the housing, that will be okay. Better than too deep

I appreciate yall
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Old 06-14-2024, 03:40 AM   #28
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Default Re: Rear Diff Plug HELP

As I think someone said earlier, use teflon tape, especially with so little thread engagement. Gentle turning of a pipe tap might straighten out some threads and give more engagement.

This might be useful: https://www.mcmaster.com/2616A18/
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Old 06-14-2024, 04:23 AM   #29
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Default Re: Rear Diff Plug HELP

* pedant mode on *


sorry for being a bit anal and, hopefully not, confusing the original poster...


Not all pipe threads are tapered, that is plainly wrong. For instance most (1) female pipe threads are parallel, that is the case in NPT, NPS, BSP, G and R. But you also have parallel male threads, like G or NPS. It depends on where you want to seal the thread, within the thread itself or on, for instance, a shoulder with a sealing o-ring.


Sorry for the rant but this is my pet topic...



(1) i say most, because there are also tapered female threads, like Rc.


* pedant mode off *

Last edited by TomInCologne; 06-14-2024 at 07:13 AM. Reason: Edit: added NPS as a parallel thread...
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Old 06-14-2024, 06:14 AM   #30
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Default Re: Rear Diff Plug HELP

The non tapered threads are used in Europe and the plugs have a flange and a gasket is used. All the pipe threads in the US are tapered. The threads can be cut too shallow or too deep, and that will determine how far in the plug will go in. The threads on the plugs can also vary, which will also determine how far in the plug will go in. You could try different plugs. If you have access to a pipe die you could recut the threads on the plug.

If you chase the treads in the housing, only do a little bit at a time and then test the plug. As I suggested earlier, use Teflon tape. You can use the white or yellow tape. The tape will act as a lubricant and a sealer. Make sure none of the tape extends to the end of the plug or beyond so that the tape does not end up in the differential.

If you chase the treads, make sure you get all the chips out of the housing. Use a solvent wash with the drain plug open. Inspect with a dental mirror or bore scope.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.

Last edited by nkaminar; 06-14-2024 at 08:47 AM.
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Old 06-14-2024, 08:07 AM   #31
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Default Re: Rear Diff Plug HELP

Careful you all ! Not all American pipe threads are tapered, some are parallel pipe threads, now you all have me wondering ? are the female holes in the differential straight or tapered pipe threads ? Just maybe that’s why hardware store pipe plugs don’t fit well in my differential and transmission ?
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Old 06-14-2024, 08:51 AM   #32
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Default Re: Rear Diff Plug HELP

B H, If the threads in the differential housing were straight, then the plugs would have a flange and a gasket would be used. Ford used a normal tapered pipe plug. The straight threads could also have a different TPI, depending on the size.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.

Last edited by nkaminar; 06-14-2024 at 09:05 AM.
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Old 06-14-2024, 08:55 AM   #33
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Default Re: Rear Diff Plug HELP

You can get one like this at Home Depot. Easy to remove with the male end.
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Old 06-14-2024, 09:29 AM   #34
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by Planojc View Post
You can get one like this at Home Depot. Easy to remove with the male end.
I wonder why Ford used different style on drain plugs on the transmission and differential? Innie on the diff, outie on the trans??
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Old 06-14-2024, 09:57 AM   #35
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by Y-Blockhead View Post
The plug you link to from Snyder's states in the description "The original style. Can be used to fill and drain. This style of oil plug is 1/2" pipe thread."

Pipe thread is tapered thread.
Not all pipe threads are tapered, NPT is tapered and NPS is straight. Typically, pipe threads are NPT (tapered), but one has to be careful.
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Old 06-14-2024, 10:29 AM   #36
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Default Re: Rear Diff Plug HELP

Make the one you took out look nice, cut it down and reuse it. Just a thought.
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Old 06-14-2024, 10:30 AM   #37
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Default Re: Rear Diff Plug HELP

There are straight pipe threads, think electrical rigid conduit.
NPSM free-fitting mechanical joints Thread

NPSM is a lesser-known pipe thread standard series defined in ASTM B1.20. This thread series creates a non-pressure tight connection. It is mainly used in mechanical joints and special applications with no internal pressure and, consequently, no sealing requirements. It is possible to achieve a seal with the aid of an O-ring.
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Old 06-14-2024, 10:33 AM   #38
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by 46HARLEY View Post
Make the one you took out look nice, cut it down and reuse it. Just a thought.
Ditto
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Old 06-14-2024, 11:13 AM   #39
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Default Re: Rear Diff Plug HELP

The taper for American National Pipe Thread is very slight and isn't measured in degrees, Its measured by length/diameter ratio. The two small sizes have 27 threads per inch so it doesn't match with normal standards for screw thread, The intermediate sizes are similar to screw threads at 18 and 14 TPI but they taper that little bit over the length/diameter ratio. At 1-inch they change to 11 1/2 TPI so they are odd.

There are so many different types of pipe that it was impossible to come up with a single thread type. I use a lot of AN type pipe thread for aircraft and most are straight but they use a 37 degree flair in the tube if using aluminum aircraft tube or aircraft hose fittings. There are AN fittings that are NPT on one end and AN on the other so that they can mate well with castings.

I've had to Heli-Coil buggered NPT threads in engine cylinder castings before and it requires a lot of care in drilling or reaming a bore for the tap to cut the Heli-Coil threads. There are tools to check for proper depth of cut and fit. A certain amount of clean up and dressing can be required to get a proper fit.

Last edited by rotorwrench; 06-14-2024 at 11:21 AM.
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Old 06-16-2024, 11:59 AM   #40
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by Diastole View Post
I am new to Model As. I have a early '30 coupe.

I want to change the diff fluid. This car sat in a garage since 2015.
Owner recently passed, sadly. Rest his soul.

The fill-drain-plug has half of the lugs sheared off. I am looking for some help for a possible solution on how to remove it w/o damaging the housing.

See photos

I can try some vice-grips after heating the metal housing. Or, drill a hole, tap with left hand threads, and install a left hand thread bolt. Or weld a 3/8" square bar in what remains of the plug.

Being Model A's are new to me, and my interest to not reinvent the wheel, I am asking for any help or suggestions I can get.

I can do two of the three thoughts above, I do not have left hand tap and die set.

Thanks in advance

Diastole in the Smoky Mountains
Any Results on removing Plug??
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Old 06-16-2024, 01:58 PM   #41
Bob C
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by Gary WA View Post
Any Results on removing Plug??

See post #21.
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Old 06-16-2024, 03:33 PM   #42
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Default Re: Rear Diff Plug HELP

Use the plug sold for that application. The housing is unlikely to have been modified.
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Old 06-16-2024, 03:59 PM   #43
Gene F
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Default Re: Rear Diff Plug HELP

Post #27 yes.

Are you a local model A chapter member?
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Old 06-16-2024, 05:15 PM   #44
Diastole
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Default Re: Rear Diff Plug HELP

Thanks for all the help.
Yes the plug removal process went smoothly, following y'all's advice. Attached are some final pics for those who have messaged and posted.

Yes I am in a club (a great one, with awesome resources), and I went to them first:
1) check with Ford Barn
2) email the MAFCA technical director
3) I am not sure
4) sounds like you got a great plan

I had a set of NPT taps. I ran them in and boom! no resistance and no chips. Threads were fine.
The Snyder's plug screwed right in with teflon tape.
No leaks after running her for about 10 miles.

Diastole in the Smokies
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Old 06-16-2024, 06:02 PM   #45
Gene F
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Default Re: Rear Diff Plug HELP

Quote:
Originally Posted by Diastole View Post
Thanks for all the help.
Yes the plug removal process went smoothly, following y'all's advice. Attached are some final pics for those who have messaged and posted.

Yes I am in a club (a great one, with awesome resources), and I went to them first:
1) check with Ford Barn
2) email the MAFCA technical director
3) I am not sure
4) sounds like you got a great plan

I had a set of NPT taps. I ran them in and boom! no resistance and no chips. Threads were fine.
The Snyder's plug screwed right in with teflon tape.
No leaks after running her for about 10 miles.

Diastole in the Smokies
Good for you. I am a but surprised that one or two of them did not offer to come over and take a look and give you their experiences....
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Old 06-17-2024, 09:35 AM   #46
Tom F OHIO
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Default Re: Rear Diff Plug HELP

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Are the plugs suppose to be painted black or not?
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Old 06-17-2024, 10:15 AM   #47
Bob C
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Default Re: Rear Diff Plug HELP

The Judging Standards say unfinished or raven.
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Old 06-17-2024, 10:38 AM   #48
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Default Re: Rear Diff Plug HELP

Mine was screwed in so hard that almost nothing worked until I filed two edges off and it fit a hex ratchet with two good surfaces to get it out. Then bought a replacement from one of the usuals. Worked a charm. No idea why anyone would screw it in so tight except that...of course they all leak a few drops a week.
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