It has finally warmed up enough to fill my steering compartments with a citric acid solution and I cant figure out what type of plug to use on the bottom of the compartment. I thought it was a 1 1/2 inch pipe thread but it is a little bigger. Any ideas or should I just buy some expanding rubber plugs????    Grant.

look under the seat to see if the plugs are in the tool box??? i would think you could get the proper plug for cheaper the the ex panders will cost

Thread/plug size is a 2" x 12 tpi  straight thread.

Thank you OLD MAGNET. I have 3 D4s on the ranch and none had the plugs. I will see what I can find at the hardware store and get on with the acid bath before it gets too cold again. I hope it works to free them up. Thanks again. Grant.

Same plugs used for transmission and final drive fill. Maybe you could swap some around to get by.

You have saved the day again. One of my D4s is just a parts machine, so I will swipe a filler plug from it. Thank you again. Grant.

I could not get the filler plug loose on the D4, but found that D2 filler plugs are the same. The threads on my machine were pretty rusted and the plugs did not go far in. I put lots of teflon tape and got one not to leak. The other was worse so I used plain old plumbers putty. I had asked and been told that 10 gallons should fill the clutch compartment so I bought enough citric acid powder for 10 gallons. Well, 10 gallons did not even get it to the bottom of the clutch packs. I am ordering another 20 gallons worth of acid powder in the morning and start over again when it arrives. The saga continues! Grant.

one thing to remember is these old girls are all SAE threads so for those in countries using British based standards(which is just about everywhere outside the U.S) weirdly metric pipe is BSP except for conduit) you will pay more as you have to go to hydraulics suppliers as very few places stock NPT fittings that size.
BSP fittings will only screw in about 3 threads before binding and can damage the NPT threads also they wont seal properly.

Old wrote:

Thread/plug size is a 2" x 12 tpi  straight thread.
 

Hello OM
So just to clarify that would make it a 2" UNF thread not NPT, as 2" NPT is 11-1/2 TPI and TAPERED. No chart I could find lists a 2" UNF but every size over 7/8" has 12 TPI.

Regards

Phil
 

Old Magnet cleared this up for me. I went and swiped a couple of filler plugs from a D2 and they were the same as the D4 plugs. I am sure that the reason that they would not thread all of the way in is 70 years of rust on the steering compartment threads. I just ordered 20 lbs more of citric acid so if the weather does not get back to freezing by the time it arrives, I will get on with this project. Thanks to all. Grant.