Are the 4006UT and 4006AUT distributors interchangable

[radtech]

Are the 4006UT and 4006AUT distributors interchengable?

[wesk]

Yes. The UT was for the M38 L134 so it's advance curve is slightly different then the AUT which entered service for the M38A1 F134. If you spend a little time in my photo album (the 2nd album) on the 1st page of Albums in my Ignition System Sub-album you'll find the Prestolite Charts. You'll note the 1st M38 distributor IAU4004UT is not on the sheets. It too can be used but must be used with the firewall mounted radio noise filter or you can modify the cable port on the distributor to use the later #8 lead terminal and ignore using a radio noise filter.

http://www.willysmjeeps.com/v2/modules. ... _album.php

[radtech]

Years ago my father who was a mechanic in the USAF from 1947-1988 told me not to use the AUT on my M38 as when the USAF had M38's they were told not to use the AUT on the M38's because of advance issues.My M38 still had the original 4004UT.

[RICKG]

Are the 4006UT and 4006AUT distributors interchengable?

I have a 4006UT and AUT and they both work equally well on my L134. If I recall it was you I sent my spare early 4004 base last year correct??

[mdainsd]

I bought a 4004 base off of someone here late last year, don't remember who.

At a meet last month I picked up a complete distributor with the special cable and the filter, all NOS for 5 bucks. Happy day!

[radtech]

Rick I used the housing I got from you on my spare that had a trashed housing.It looked like someone took a torch to it.

[wesk]

Radtech,

Was your question a rhetorical question to motivate a discussion or do you really wish to know if they are truly interchangeable?

The only real difference is as I posted the advance curves differ.

IAU4006UT uses curve C2-P22:
Adv / RPM 0/275, 1/385, 6/925, 10/1365, 11/1470

vs

IAU4006AUT uses curve 1046:
Adv / RPM 0/300, 1/425, 6/1050, 10/1575, 11/1700

The impact here is during acceleration until the max of 11 degrees is hit. Has no effect on cruising RPM and will not damage either jeep if the other's distributor is used.

Note also that USAF and Army both used the same technical pubs and parts list and the M38 parts list shows a linear supersedure starting with IAU4004UT supersedes to IAU4006UT and IAU 4006 UT supersedes to IAU4006AUT. The parts manual does show IAU4004UT & IAU4006UT using the same governor springs where as the IAU4006AUT uses a different pair of springs. If you have any concerns with the very slight difference in advance curves then just simply use the springs that are correct for the applicable engine. I was a USAF mechanic from 1966 thru 1989. If I had been confronted with this issue and the shop voiced a concern with the already approved by the Army and the tech data supersedure I would order the available supersedure unit IAU4006AUT and just installed the early springs in it.

[radtech]

A friend has a late 51 M38 with 6 volt CJ distributor and wanted an original.He has the choice of an AUT or UT and I told him what my father had warned be about the difference between the two.

[wesk]

Well I hope you explained to him the difference is nothing to worry about.

Using the A1 (AUT) distributor in an M38 (UT) L134 will snap up her acceleration of the engine between idle and 1700 RPM. No damage will result.

Just as using the M38 (UT) distributor in the M38A1 (AUT) F134 will very slightly reduce the snap of it's acceleration of the engine between idle of 1500 RPM. Again, No Damage will result.