purpose of left handed thread

32sbct · Post by **32sbct** » Sat Jul 23, 2011 9:54 am

Can someone explain the purpose of the left handed thread on the jeep wheel lug nuts? No other car that I know of has this but there must have been a reason. Also since I will be taking the hubs off for an axle service is there any reason, other than originality, not to change them over to right handed thread? Thanks

Post by **wesk** » Sat Jul 23, 2011 11:57 am

When the auto first came into our lives at the turn of the 19/20th century the wheel nuts for both axle and wheel lugs were not locking type nor did they employ the modern two different contact angles that wheel lugs started using in the 50's. So with no positive locking it was possible for a right hand nut if not torqued correctly to back off and unscrew itself from the rotating direction of the left wheels. Hence from 1900 to the mid 50's most cars and trucks used left hand nuts on the left side of the car/truck. We old timers whose first cars were 1950 models or older know better to check lugs closely for left or right on cars older than 1960.

The Willys wheel is designed for taper lug nuts and they use taper lug nuts so they do not really have to have left hand threads on the left side. So if you are rebuilding the brakes or axles it is a good time to make the switch.

32sbct · Post by **32sbct** » Sat Jul 23, 2011 6:46 pm

Thanks Wes! The odd thing with my M38 is that the left handed threads are on my front right and left rear..who knows how that happened.

GPA · Post by **GPA** » Sun Jul 24, 2011 12:59 am

It is used to keep the nuts from getting loose because of the gyroscopic effect. I've been working on Russian made trucks, made in the 70's and 80's and the wheel nuts still had left hand threads. Can not be totally useless and outdated idea, because even in 2011 it is still used in some single seater racing formulas, including F1. And it is original on jeeps.

12Bravo · Post by **12Bravo** » Sun Jul 24, 2011 8:26 am

I had a truck mounted machine shop (5 ton M944A1 chassis) made in late 80's-early 90's with left hand threads on lug nuts. I don't know about current 5 ton trucks but the M923 series still had left hand threads in the 90's

Post by **wesk** » Sun Jul 24, 2011 10:47 am

The heavy trucks retained the idea because it is very difficult to apply adequate torque in the field when changing tires without a 1" impact gun and a lot of air pressure. Also the dualies used a flat faced stud to retain the first (inner) wheel.

It's very common for Hubs to end up on the wrong side of the jeep when folks aren't familiar with the jeep.

12Bravo · Post by **12Bravo** » Sun Jul 24, 2011 10:11 pm

I'm sure it was a funny sight to see me and another guy standing on a mechanical 1 inch drive impact wrench (thing was 4 ft long) with a cheater bar on the end of it before 2 young privates figured out we were tightening the lug nuts instead of loosening them

Post by **wesk** » Sun Jul 24, 2011 10:33 pm

Been there and done that!

Cacti_Ken · Post by **Cacti_Ken** » Tue Jul 26, 2011 12:06 pm

I remember working on a Plymouth auto in the early 60's that had left hand threaded lugs. The Volkswagen did too.