Joined: Nov 05, 2009 Posts: 174 Location: Florianopolis, Brazil
Posted: Sat Dec 30, 2017 3:00 pm Post subject: Early M38/M38A1 x late M38A1 distributors
Hello guys, before 2017 ends, please let me know if there is any functional difference between the early M38A1 (or M38) x late M38A1 M170? Are there also different appropriate brands between them, I.e., Auto Lite x Prestolite? Thanks, happy 2018
There are four distributors used during M38/M38A1/M170 production.
1-Pilot model M38's (Pre-production) used the Auto-Lite IAU4001U which has no internal radio noise filter. Instead it has a remote firewall mounted filter. This arrangement was used only on the pilot models.
IAU4001U showing the routing of the filter harness conduit on production models in yellow.
2-Very early production M38 used IAU4004UT which has no internal radio noise filter. Instead it has a remote firewall mounted filter. This arrangement was used thru MC20599 May 1951.
IAU4004UT with external radio noise filter.
3-Remaining M38 production used the Auto-Lite IAU4006UT with internal radio noise filter. This distributor used a mechanical advance curve C2-P22 which was suited to the L134 engine.
IAU4006UT with internal radio noise filter
4-M38A1 production introduced the Auto-Lite IAU4006AUT with internal radio noise filter. This distributor used a mechanical advance curve 1046 which was suited to the F134 engine in the M38A1 & the M170.
Specs for the internal radio filter distributors.
Brands are easy. Until 1963 all were Auto-Lite. In 63 Prestolite took over Auto-Lite's distributors, generators, starters and other motors. So from a super correct factory restorer's point of view, not only will he need a distributor with a serial prefix that matches his jeeps date of delivery but he will also need to be sure it is an Auto-Lite before 1963 and a Prestolite after 1963.
Yes, you can force all four distributors to operate any of the M38's/M38A1's/M170's however your engine performance will be better with the correct one and for late jeeps if you decide on an early distributor then you will need to include a mounted firewall filter & special harness. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 05, 2009 Posts: 174 Location: Florianopolis, Brazil
Posted: Thu Jan 04, 2018 8:59 am Post subject:
Hello dear Wes! Thank you for your complete explanation. You killed a fly with a cannon shot!!! I still have two questions in respect to functionality of distributor spec IAU 4006 AUT and IAU 4006 UT. Both have same maximum advance angle and different advance curves. I am willing to use the IAU 4006 UT (appropriate to L head engines) in my 1967 M170 (so F head hurricane). So question: isn’t the advance curve a metter or adjusting the ignition point, I.e., setting the angle to attain the correct firing of each cylinder? Is the advance curve proportional to engine rotation? The second question goes the the radio filter. It seems that these two distributors are appropriate to my 67 M170, correct? Thanks again, all best in 2018!!!!
Joined: Nov 05, 2009 Posts: 174 Location: Florianopolis, Brazil
Posted: Thu Jan 04, 2018 9:34 am Post subject:
Hello Wes, still about the same two questions I’ve just made: Is there a way to change the advance curve from one kind of distributor to another? Which inner part of the distributor would be responsible for the advance? Please excuse my poor english!
The advance curve is regulated by the weight of the governor weights and the strength of the governor springs.
The weights Autolite PN IGC2168L, ORD# 7706790 are the same for both distributors.
The springs Autolite PN IGE24 or the set IGE24S, ORD# 7330828, NSN 2920-00-358-7800 are used in the IAU4006UT distributor & the two earlier remote radio filter distributors.
The springs Autolite PN IGB284 or the set IGB284S, ORD# 7376393, NSN 5340-00-350-2288 are used in the IAU4006AUT distributor.
The cam which has a stop plate welded to it controls the max governor advance with the two stop pin slots.
The cam with stop plates is XX (This is the same part in both distributors)
The weights are N
the Springs are P _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 05, 2009 Posts: 174 Location: Florianopolis, Brazil
Posted: Sat Jan 06, 2018 3:48 am Post subject:
Thank you Wes! I realize I have a wrong distributor in hands (4006UT) so need to replace springs and weight of distributor. Now I have to search correct a kit for my M170 (4006 AUT). Sure I will install it to feel how performance changes from one kind to another. If someone can report that, I will be gladly thankful. Best!
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