Suspension bolts

[ajg617]

Scott'n'Wendy

Do you have an estimate of how many failures that you have seen posted?

Brian

I know of at least 5 more (all Momentums with 8K option) that we discovered when ours broke in August while on our way to Glacier at 16K miles. In fact, I gave 4 extra wet bolts to a Momentum owner that limped in to a neighboring campground with the identical problem - RR bolt completely missing with spring hanging loose and LR bolt sheared in half at the grease hole and wedged in to the spring eye and he only had 10K on it. GD mobile tech inspected all wet bolts that were left and all were well worn (as in gouged) at the bushing end and replaced but warned me not to drive more than a couple hundred miles before all springs, shackles, and wet bolts (again) were replaced. All but one broken half of a front spring bushing were gone completely. Close to 20K on the trailer and it is headed to Elkhart in April and if there is any wear/replacement, I will be going with IS. The response from LCI and Dexter to Don Clark's crew was no coverage due to road conditions.

[Country Campers]

After reading some of the other posts, across the web, it looks like most are in the heavy range, 7k and up axles. I wonder if the issue is with "over loading" the wet bolts, especially when it seems that "one size fits all" in this realm.

Brian

[ajg617]

After reading some of the other posts, across the web, it looks like most are in the heavy range, 7k and up axles. I wonder if the issue is with "over loading" the wet bolts, especially when it seems that "one size fits all" in this realm.

Brian

It's really hard to tell but the heavier axles put a lot of stress on the hangers and grade 5 bolts which the two mobile techs were surprised to see. I could think of four possibilities for me. 1) Poor quality wet bolts, 2) Hangers not tightened sufficiently (I know that was a Curt issue, but the marks on the axles where the old hangers were simply do not match where the new hangers are and they haven't moved), 3) No or inferior bushings installed at Dexter (I say this because when we pulled the springs there was only 1/4 of a piece of bushing in one eye - no evidence of any bushings or residue in all the grease on any other, including the one with the broken bolt still wedged in the eye), or 4) Hangers of insufficient strength for the heavier suspension (note the v-clip weld was not broken on the RR where the bolt was simply missing but was on the LR where the bolt was broken in half and wedged into the eye).

[TedS]

Don't Momentums have 3 axles to carry the load?

[ncitro]

Don't Momentums have 3 axles to carry the load?

There are a few with two.

[Scott'n'Wendy]

Cate&Rob
A fellow on another forum that seems to be of a like mind with you re:bushings

Actually, IMO, it's not too surprising that the bushings fail in these springs due to the fact that a brass bushing isn't really designed to withstand the forces in play on a loaded suspension. Bushings are mainly designed to allow a part to spin within the bushing, not absorb the pounding these spring eyes receive. Probably hardened steel would be a better choice than brass, maybe heavy duty roller bearings. IMO brass is a poor choice for this application.

[Country Campers]

I am trying to wrap my head around the fact that a single sized wet bolt, or even dry bolt as we had back in the day, is used for the same application from my #5200 axel up to a #8000 axel. There is surely a huge swing of load and impact difference between the 2. We have made countless pins for booms on excavators from the small type with 1-1/2" diameter pins to the large with 4" or even larger pins. Can you imagine a large excavator with 1-1/2" pins......

Also the same is the spring hanger itself. Yes some are longer or shorter but they are made from the same material and thickness.

As far as "heavy duty roller bearings" that would be a no, bearings do not like impact, even heavy duty ones.

Steel bushings, I like it and Rob may be on to something here and a report will be welcomed.

Brian

[TedS]

The designers may be deciding based on shear capacity. A 9/16 grade 5 bolt has a double-shear capacity of about 36,000 lbs. 4 bolts per axle would be 144,000 lbs. Impact could at least double the effective trailer load. A 15,000 lb trailer could present 30,000lb load at impact, or more. Still less than 5 times the bolt capacity. But the failed bolts are failing in bending fatigue. I don't think the designers are considering that.

A 3/4 inch bolt would step the shear capacity to 64,000 per bolt. 256,000 lbs per axle. Almost double.

[Jlawles2]

The designers may be deciding based on shear capacity. A 9/16 grade 5 bolt has a double-shear capacity of about 36,000 lbs. 4 bolts per axle would be 144,000 lbs. Impact could at least double the effective trailer load. A 15,000 lb trailer could present 30,000lb load at impact, or more. Still less than 5 times the bolt capacity. But the failed bolts are failing in bending fatigue. I don't think the designers are considering that.

A 3/4 inch bolt would step the shear capacity to 64,000 per bolt. 256,000 lbs per axle. Almost double.

As I work in a different industry than automotive, there is an extensive study on pins in bending with double shear. It's so well documented that ASME added it to the design guide for the equipment we use.

Roughly the bending is calculated as a uniform distributed load from the edge of the load bearing component to the opposing side. And gap in the load bearing area must also be accounted for. The supports are calculated using their center line not the inside edge.

Not the document we refer as this is structures, but by quick glance it appears similar: https://www.sciencedirect.com/scienc...43974X22006228

[TedS]

I'll ask for a little indulgence of the general public. I had to do some calculations. The bending stress in the 9/16 bolt is around 36,000psi. The fatigue stress for grade 5 is around 60,000psi. That's a factor of 1.7 for fatigue. Not great but OK, until you factor in the dynamics of our wonderful roads. Then 36,000 may become 72,000psi. Darn. Put in a crossdrilled hole, called a stress riser, for greasing and multiply that stress by 1.5 or 2.0. No wonder they break. That's also why we are told to install the bolt with the crossdrilled hole at 3o'clock or 9o'clock, a near zero stress position. At 12 or 6o'clock the bolt will break in fatigue, repeated bending.

Solution for wet bolt: larger crossdrilled hole, remove the hole's sharp edge, reduce the bolt diameter where the hole is drilled, install it as instructed and prevent it from rotating in service(that's what the knurling under the head is supposed to do).

On edit: By basis load per wheel is 2500lbs. Not that heavy.

Jlawles2 nice reference.

[Yoda]

The designers may be deciding based on shear capacity. A 9/16 grade 5 bolt has a double-shear capacity of about 36,000 lbs. 4 bolts per axle would be 144,000 lbs. Impact could at least double the effective trailer load. A 15,000 lb trailer could present 30,000lb load at impact, or more. Still less than 5 times the bolt capacity. But the failed bolts are failing in bending fatigue. I don't think the designers are considering that.

A 3/4 inch bolt would step the shear capacity to 64,000 per bolt. 256,000 lbs per axle. Almost double.

Ted and Brian Country Campers While the bolt may start out as grade 5 what happens to the meteorology during the machining process. I.E. the center drilling, taping for zerk and the outlet hole in the center. I know the process creates heat and stresses, but is it enough to change the overall hardness. While I cant find the picture of the broken bolt from a thread, there sure looked like heat discoloration at the fracture point.. . BTW in searching for replacement bolts I found some Chinese junk that was labeled as grade 3 especially for the solid ones. Also many brands don have any head markings. At lease MorRyde had the head stamp of the three marking for grade 5. Would grade 8 be better? I do know grade 8 does not like bending though if I remember my college classes on structural fasteners.

Keith

[Country Campers]

Yoda

The bolts would be machined followed by a heat treatment process.

Brian

[TedS]

Yoda drilling a grade should not be too tough. Grade 8 will get you more strength, sure. 180,000psi vs 120,000psi for grade 5, I believe.

on edit: 150,000 not 180,000

[ajg617]

Ted and Brian Country Campers While the bolt may start out as grade 5 what happens to the meteorology during the machining process. I.E. the center drilling, taping for zerk and the outlet hole in the center. I know the process creates heat and stresses, but is it enough to change the overall hardness. While I cant find the picture of the broken bolt from a thread, there sure looked like heat discoloration at the fracture point.. . BTW in searching for replacement bolts I found some Chinese junk that was labeled as grade 3 especially for the solid ones. Also many brands don have any head markings. At lease MorRyde had the head stamp of the three marking for grade 5. Would grade 8 be better? I do know grade 8 does not like bending though if I remember my college classes on structural fasteners.

Keith

Here are two pictures of the left rear broken bolt which remained wedged in the spring eye - RR totally missing. The fracture difference between the half with the grease hole and the the opposing side is pretty stark. I've also included a spring eye with a failed (not worn) bushing from the LF. With all the grease I would have expected to see brass flakes but none were found by the tech. The knurled portions were worn flat on the other remaining bolts so they were spinning.

EDIT I didn't think to measure how far the bored hole went beyond the grease hole.

[Jlawles2]

If properly machined, the heat treating can be done before or after.

The temper temperature for Grade 5 and Grade 8 is 800°F.

From what I remember about the bolt making process, bolts are heat treated after HEADING and THREAD FORMING (not cutting) as the lower strength materials are easier to form. https://www.youtube.com/watch?v=xEcg5wA5H_A about 3:47 note they form the thread by rolling the bolt against the plate that looks like a big file. There are some MFG that do CUT threads, but in general formed threads are stronger due to the crystal structure of the steel during forming.