1977 Mack RS600L breaking front wheel studs

[Art_H]

Just picked up a 1977 Mack dump truck. Well maintained, but it seems it has been breaking wheel studs on a regular basis. Both front left and right. Meritor brand studs and nuts. They only lasted around 12 months before one or a few would break off. Any ideas as to what is causing this???

Wheels?

Poor fiction contact on the wheel to the drum? causing wheel impacts on the studs when braking hard?

Any input would be great, thanks.

 

[mitch504]

Budd or Dayton wheels (10 studs and tapered nuts, or 5 or 6 studs and rim clamps)?

It sounds like you are talking about budd wheels, normally broken studs are caused by them being loose, or over tight. Most 1" impact wrenches are capable of 1200-2000 ft-lbs, but Budd wheel studs only call for about 450-600, depending on size.

I would replace all the studs and tighten them to the correct figure w/ a torque wrench and see if this fixes it. Make sure the new studs are properly seated.

Most trucks of this age have inboard mounted drums, so I wouldn't think it would be a moving drum causing this.

 

[grandpa]

Along with what Mitch said, your parts store should have a plastic spacer that goes between the wheel and drum on the stud's,,,, that has ended most of my problems.

 

[wilko]

Most 1" impact wrenches are capable of 1200-2000 ft-lbs, but Budd wheel studs only call for about 450-600, depending on size.

I've watched a lot of people run the nut down and hammer on it for three or four seconds. Ouch. I stop after less than a half second of hammering. Don't know what my torque reading is (wish i did), but they stay put and nothing breaks.

 

[Art_H]

I believe they are the daytons on the front, 10 stud with tapered nuts.
Budd on the rears. No issues there.

The prev owner changed them religiously at the Mack dealer. They have been done many time, I have the work records form the past 8 years. They apparently tried different methods of mounting the press in studs to ensure there was no issue with install. Torqued to spec. Meritor parts. He tried another manufacturer and they only lasted 6 months.

I'm liking the idea of the plastic spacer... Such an odd issue that it seems difficult in troubleshooting...Don't want to start changing the axle...

Thanks for the advice.

 

[Art_H]

Just a quick one...Wheels studs are likely grade 8?? 150'000PSI tensile, and 60% in shear. These studs are pretty big to be failing like that.

 

[Greg]

Can't be Daytons with 10 studs. Daytons are going to be either 5 or 6.

 

[d9gdon]

Does it have flotation tires on the front?

 

[Art_H]

It has 425s on the front. I'll grab a pic here and try to post

 

[Art_H]

Here it is.

 

[mitch504]

Yep, those are budds

 

[wilko]

I see those tires and I wonder how much weight has it been carrying on the front, over what kind of road and how fast has it been going? If they ran those tires so they could put 20,000-plus pounds on the front on rough pot holed roads with a rabid chimp behind the wheel, well, there's the problem.

 

[grandpa]

Almost looks like what they call a pilot hole wheel, and those wheels require special nuts.... they have shoulders on them.

http://ts4.mm.bing.net/th?id=H.4579415594960983&pid=15.1

 

[mitch504]

Granpa, I am afraid you may need to convert from bifocals to trifocals. Those sure look like tapered budd nuts that are seated deeply into the rim.

Looking at that picture makes me think a couple of thoughts:

Are the rim holes worn out, so that the nut is going into the tapered hole too far? I don't think that's it, but...

Usually when you see floater fronts they have less offset. I usually see the tire sitting out farther, so that the hub is closer to the center of the tire. Usually this causes bearing trouble due to putting too much off angle load on. I have converted a lot of trucks floats and everything I've read from rim, hub, and axle manufacturers, reccommends keeping the hub nearer the center of the rim, or using much heavier components than what is usually recommended for a given load.

 

[grandpa]

Trifocal's smyfocal's,,, I can see their bored out in the hole's.....lol My thoughts, right wheel wrong nuts,,,, but its a mute point now as it looks like they need to be recycled..... :cool2

 

[mitch504]

The threads are way different, and you can put a Budd rim on a hub piloted hub, but you can't put a hub piloted rim on a Budd hub.

Now that you mention it, having a Budd wheel on a hub piloted hub probably could cause broken studs. I know they won't stay tight, I once got a deal on a bunch of nearly new Budd rims because a local company bought a couple of used trailers and went out and bought new tires and rims to change them to the same size tires as their others. They took them to 2 or 3 tire dealers before my friend saw them and told them what was wrong.

If it was me, I'd get two new rims that have 3 or 4" more outset and try that.

Btw, what are the plastic spacers were you talking about? I don't think I've met them.

 

[grandpa]

I get them from Napa... about a sixteenth thick,,, http://pitstopusa.com/images/F21350576.jpg

 

[Art_H]

Trifocal's smyfocal's,,, I can see their bored out in the hole's.....lol My thoughts, right wheel wrong nuts,,,, but its a mute point now as it looks like they need to be recycled..... :cool2

LOL...I'll get a close up tomorrow.

 

[Art_H]

My first thought when I saw the wheels was that they were recessed a little, but there was still a flange to support etc.

I like the idea of the potential rim offset being suspect. Wouldn't a 1 ton dually truck have the same issue then with their extreme offsets??

 

[mitch504]

Not with bearing issues as the bearings are still in the center of the tire, and the studs are evidently heavy enough. Your studs are the same as the ones that run w/ 11R 22.5s.

It may not be the cause, I just don't normally see them setup like that, I'll try to remember to get a pic of one of mine tomorrow.