M100 Leaf Spring U-Bolts

RonD2 · Post by **RonD2** » Tue Feb 21, 2017 12:28 pm

Kind of an odd-ball question, but can anybody give dimensions of leaf spring U-bolts for the left front M38 or MBT and M416 trailers?? Mine on the M100 are shot and need to be replaced. They measure 2-1/4 wide by 6 inches tall (inside dims), flat top, with 7/16-20NF threads for the long hex nuts. They sit on 10-leaf springs. I believe the whole set-up is original Dunbar-Kapple.

The M100 TM's don't give dimensions for the U-bolts, and neither does the M38 TM's so I can't really tell what's correct or not. The U-bolts on the LF of my M38 seems long to me, about 1-1/2 inches exposed below the nuts. The M100 part number is 7328295. Research leads me to believe they may be the same U-bolt as the left front on the M38 and possibly the same on the MBT and M416 trailers. But each has its own different part number (WO-A575, WO-642987) so I can't tell for certain.

Anyway, I thought I'd ask here for some guidance/advice before I call the suppliers and pester them with questions about various leaf spring U-bolt dimensions so I can get the correct size U-Bolts the 1st time. Nobody shows stock on the M100 part number 7328295. I'd rather not have to get them long and have to cut them shorter if I can help it.

Thanks!

Kendall · Post by **Kendall** » Tue Feb 21, 2017 5:52 pm

The U-bolts on the front of my M38 are flat-top and measure about 3 1/4 inches from top and 3 1/4 wide with about 1/4 inch of threads exposed.
The U-bolts on my M100 are round-top and measure about 3 1/2 from the top and about 3 1/4 wide and also have about 1/4 inch of threads exposed.

RonD2 · Post by **RonD2** » Tue Feb 21, 2017 10:18 pm

Hi Kendall, thanks for the measuring! It looks like your M38 and M100 U-bolts have about the same width (about 3-1/4 wide outside dim). With the U-bolt being 7/16, my stubby pencil says that's about 2-3/8 inside diameter. I measured my M100 axle at 2-1/4 diameter, and my M38 axle at 2-5/16.

You prompted me to see if my old wore out M100 U-bolts would slip over my M38 front axle tube and no, not without some serious forcing (didn't do that). Should've tried that sooner. I think I was wrong with my original post to say that I thought maybe the M38 front axle U-bolts were the same as the M100. I no longer believe they are.

Looks like I need a want ad for M100 U-bolts. Never seen any advertised or NOS. Does anybody make them?

Thanks again!

Post by **wesk** » Tue Feb 21, 2017 11:49 pm

Firts look up the parts number for the U bolt. If you go to the TM 9-2330-201-14 (M100 IPL) and round up the ORD part # 7328295 and the FSN 5306-732-8295 and google the ORD # the first hit is:
https://aerobasegroup.com/part-number/7 ... 0-732-8295

7328295
U Bolt; Fine Thread - 2A

7328295
Description: 2a Unf Thread: 7/16-20, Thread Length: 1-1/2"

Specifications
Distance From Inside Center Of Bend To Bolt End: 6.140 inches AAWV
Material: Steel comp 1335 or steel comp 1340 or steel comp 8630 or steel comp 8635 or steel comp 4130 MATT
Minimum Yield Strength: 140000 pounds per square inch CQHQ
Thread Diameter: 0.438 inches AHYM
Inside Distance Between Shanks: 2.281 inches AAWW
Style: Round bend STYL
Surface Treatment: Phosphate SFTT
Thread Class: 2a AAJD
Thread Direction: Right-hand AAJF
Thread Length: 1.500 inches minimum AASA
Thread Quantity Per Inch: 20 CMLP
Thread Series: Unf THSD
Federal Supply Class (FSC): Bolts
National Stock Number (NSN): 5306-00-732-8295

RonD2 · Post by **RonD2** » Wed Feb 22, 2017 8:54 am

Thanks Wes!

Awesome!

It never occurred to me that the part number is also the last 7 digits of the FSN. And then I looked up the part number 7328295 and forgot to pay attention that G747-7328295 is the complete part number, and G747 should've told me these U-bolts are unique to the M100 only or they might have had a G503, G529, or even a G740 prefix and part number. I'm learning.

I'll make some phone calls to see if I can get some made up.

Post by **wesk** » Wed Feb 22, 2017 10:37 am

It never occurred to me that the part number is also the last 7 digits of the FSN.

Don't always bank on that. You only see that normally on the very early FSN's that started being used in the early 50's.

RonD2 · Post by **RonD2** » Thu Feb 23, 2017 8:58 pm

Found an outfit in Ohio that makes custom U-bolts and has 2-1/4 x 6 threaded 7/16-20NF in stock. They come with the extra thick washers and long nuts. Ordered 2 pair, price was reasonable. Will report when I get them.

RonD2 · Post by **RonD2** » Mon Feb 27, 2017 10:08 am

DSUBAN.com! $9.88 each, delivered. Ordered Wednesday 2/22 and they were in my mailbox on Friday 2/24. Although the website allowed ordering 6-inch length, the way they make them came out at 7-inch, so I'll have to trim them an inch. The 2-1/4 inch width is right on.