Replacing rivets with bolts

[bbcmudtruck]

I have removed most of the factory cross members and replaced them with aftermarket pieces. I have drilled all holes out to 7/16 and installed grade 8 hardware. Bolt, washer, frame, washer, lock washer, nut in that order. My concern is the possibility of having nuts vibrate loose. I intended on using Loctite as well as the lock washers, but I've heard of cases where the nuts still backed off. Does anyone have any experience with "top lock" nuts? I've been told that you can reuse them as opposed to nylon. I'm leaning in this direction unless there is a better alternative. Should I opt with or without flange? Thanks for the help!

Here is an example of the top lock nuts:

Grade G/8
http://www.fastenal.com/web/products...endingMachine=

Grade G/8 with flange:
http://www.fastenal.com/web/products...endingMachine=

[jocko]

I think you're fine with a lock washer between the flat washer and nut, and Loctite. But if you really want to go crazy with it, you can drill the bolt and do safety wire. Probably way beyond what you were wanting to do, and I don't blame you. Have no experience with the lock nuts you linked - but I suppose you could use one of those in lieu of the regular old nut, but personally - I'd go with the grade 8 h/w you have, then go back after a week of driving and check em - then a month, then 6 months, and then never again. Just for your peace of mind - but I think you're just fine with the lock washers and grade 8 nuts/bolts and Loctite.

[Orange Crate]

"but I've heard of cases where the nuts still backed off"

The nut may not have actually "backed off" A riveted joint is an interference fit which helps greatly when trying to minimize the shear movement of two plates. A common bolted joint does not have this same shear prevention property. A bolted joint can easily match a riveted joint in tensile strength, but most common bolted joints are not installed as interference fit joints. But they can be, by drilling and reaming the hole to a size that is actually smaller than your bolt diameter by a few thousands and then cooling the bolt with dry ice and installing it cold. Anyway....a nut "backing off" is more likely due to the plates moving in shear allowing the bolt to also move and deform (stretch). When you have two different types of joining styles (rivets & bolts) in one system the weaker style will show up as a failure of some form (stretch in tensile or shear load). The style of lock nuts you linked to are used in aviation in high temerature aplications all the time and obviously work very well.

[bbcmudtruck]

Thanks for the guidance fellas. I'm going to play it safe and order up 80 top lock nuts and use them as well as the lock washers and loctite. The hardware that came with my ece cross member and shock relocation brackets were grade 8, but they sent nylon lock nuts. I'm just not a big fan of those and don't want a catastrophic failure due to one or more of the nuts backing off.

[RodnRudy]

The front cross member on our trucks is held on with 7/16 hex bolts lock washers and hex nuts. That cross member has stayed tight for a lot of years. The lock washer grips both the frame and the nut, and when torqued to specs should hold just fine. I don't mean to sound rude but I think you're over thinking this.

[CG]

I'm sure you already did this, but if you had all the cross members out make sure you get your frame back in square before you start tightening everything up again.

Saw someone do this once and just "bolted it all back up" and it made it almost impossible to assemble the truck correctly because it was off just a little.

[LockDoc]

-
I also think you are going overboard on this. Make sure your bolts fit snug in the holes and use these.

http://www.fastenal.com/web/products...endingMachine=

I used them with no lock washers, nor locktite, just washers and the nuts and have had zero problems.

LockDoc

[Kennuck]

If you want the lock washer to be effective don't use a flat washer under it. The lock washer needs to be able to bite into the frame and nut.

[hugger6933]

The only time I've seen problems with the self locking nuts or the nylock the ones with the plastics in them is when the person either installed them or removed them with air and then tried to reuse them. That don't mix. If you zip them on or off with a airtool their effectiveness is nil. Have you thought of shake proof washers? you know the ones with the serrated edges? Think about those see what that may do. I can tell you in the course of my rebuilding of many late model trucks that I have I have on occasion replaced a spring hanger once in a while. I also have traded back for lots of those trucks because of repeat customers and whatnot and get one of my trucks back after 100 thousand miles or so off of farm abuse. On some that I have had come back to me with replaced hangers grade 8 bolts that were double nutted still were right where I put them. On one or two of the first I had done that way I placed a weld tack on the end a single nut and threads to prevent any movement. It held up wonderfully as well. Jim

[slowcpe]

Porterbuilt sends their kits with Grade 8 bolts and nylock nuts. Just mocking things up I don't forsee them to ever back out. Just tightening with a 3/8" ratchet and wrench takes quite a bit of effort.

[bbcmudtruck]

LocDoc, those are the nuts that I'm wanting to use, just without the flange. I'll agree that I may be going over board a bit, but I don't mind spending a little extra for insurance. CG, I'm mostly done mocking my frame up and had to do a little tweaking on the frame before I could bolt it back together, thanks for the heads up!

[bbcmudtruck]

I'll got ahead and ask this question here since it seems to be relevant. When installing the front cross member, why are the bolts installed from the bottom up? Can I put them in from the top? It looks cleaner in my opinion to install them from the top. Also, If a nut did manage to back off, the bolt might have a chance of staying in place. The factory had 7/16" bolts in those locations, but I put 1/2" bolts in. They fit in the holes perfectly without any work. Are they supposed to be a little loose in the holes?

[LockDoc]

Originally Posted by bbcmudtruck

I'll got ahead and ask this question here since it seems to be relevant. When installing the front cross member, why are the bolts installed from the bottom up? Can I put them in from the top? It looks cleaner in my opinion to install them from the top. Also, If a nut did manage to back off, the bolt might have a chance of staying in place. The factory had 7/16" bolts in those locations, but I put 1/2" bolts in. They fit in the holes perfectly without any work. Are they supposed to be a little loose in the holes?

They can be installed either way. I think that way myself sometimes. Also, in my way of thinking all of the bolts should fit the holes snug without any movement. I don't have anything scientific to back that up but I think it is just common sense..... The less movement, the less problems down the road.

Just my 2¢ worth.

LockDoc

[bbcmudtruck]

I'm on the same page Doc! I put new 7/16" bolts in there and realized they were a little loose. So on a whim, I grabbed a 1/2" bolt and they fit perfect with out any drilling or filing. I just wanted to check and make sure since GM put them in upside down and used smaller bolts. To me, its a common sense approach, however I'm not an engineer!

[oldertruckfan]

from a fabrication standpoint, the holes are bigger due to the tolerance in the print when they were built, being this allowed a little 'slop" for ease of installation. I build for a couple of different companies at the fab shop I work at. we always go to the top side of the tolerance in the holes. Less chance for rejected parts on the line that way

[mechanicalman]

Originally Posted by Orange Crate

"but I've heard of cases where the nuts still backed off"

The nut may not have actually "backed off" A riveted joint is an interference fit which helps greatly when trying to minimize the shear movement of two plates. A common bolted joint does not have this same shear prevention property. A bolted joint can easily match a riveted joint in tensile strength, but most common bolted joints are not installed as interference fit joints. But they can be, by drilling and reaming the hole to a size that is actually smaller than your bolt diameter by a few thousands and then cooling the bolt with dry ice and installing it cold. Anyway....a nut "backing off" is more likely due to the plates moving in shear allowing the bolt to also move and deform (stretch). When you have two different types of joining styles (rivets & bolts) in one system the weaker style will show up as a failure of some form (stretch in tensile or shear load). The style of lock nuts you linked to are used in aviation in high temerature aplications all the time and obviously work very well.

Very scientific and well thought out. Thanks I'm getting a reamer.

[Fatherflash]

I agree with a lot of others on this thread....I believe you are over thinking this situation.

I will give you this though: I know of a helicopter that has 9 driveshafts installed in it with each drive shaft connected to the next held together by three 3/4" bolts and with nuts and no other safety device provided. Each nut has nylock on the end to act as the safety for the installation. These driveshafts are spinning at about 12,000 rpm and I never saw a failure due to a failed fastener. Also, vibrations due to a stressed aluminum frame, airframe flex, etc. are much greater than your truck will ever experience. If I am ever in a position to install bolt with nuts nylock acting as a safety device, I would gladly do so in a heartbeat. I may add safety wife as a visual safety however, I don't think I would ever see or encounter an issue due to a failed fastener.

Also, learn from Orange Crate, LockDoc, hugger6933, and others concerning this discussion. They are absolutely correct on how to address your question.

[Keith Seymore]

Originally Posted by bbcmudtruck

I'll got ahead and ask this question here since it seems to be relevant. When installing the front cross member, why are the bolts installed from the bottom up?

Because the frame is upside down when they are installed.

Originally Posted by bbcmudtruck

Can I put them in from the top?

Sure.

A lot of times it depends on the orientation of the tool that is used to secure the bolts (particularly if it is a right angle driver with an integrated backup wrench), which could also be used for another attachment that is not obvious to us 50 years after the fact.

Also - at the factory bolts are often oriented one way vs the other to prevent the excess from sticking out and causing a clearance problem.

K

[Keith Seymore]

28 years as a daily driver; 206k miles; I recall that I used regular nuts, flat washer and a dab of red locktite.

The factory did not use any locktite for a bolted rivet repair; just torqued 'em down.

K

[bbcmudtruck]

Wow, thanks for all the help! I was a little hesitant about asking what I thought was sort of a silly question, but I'm glad I did. I learned quite a bit from people with all sorts of experience and back grounds. My only complaint about nylon nuts is that they lose their locking capability after you torque them down once. Since I'm mocking my frame up right now, I have been putting it together and taking it apart alot. I'm comfortable with moving forward and getting very close to being able to have the frame blasted and painted. Thanks for all the help and guidance!

[Davidf]

Originally Posted by Kennuck

If you want the lock washer to be effective don't use a flat washer under it. The lock washer needs to be able to bite into the frame and nut.

+1 and the right answer. Lock washesr do nothing when installed on top of a flat washer. The lock washer locks to the washer, but the washer can still turn and hence the nut can loosen. When I restored my '52, I would remove one rivet at a time and drill the hole the proper size for a 3/8" bolt which I installed before moving the next rivet. This insure perfect alignment/fit of all the holes and greatly reduced the chance for movement between the two pieces (shear). Worked for me.

[mechanicalman]

Originally Posted by Fatherflash

I agree with a lot of others on this thread....I believe you are over thinking this situation.

Yeah well we think things to death around here LOL. But I do think there is something to the "shear forces" and the extent of that IMO depends on what cross-member we are dealing with. The front cross-member is bolted, and it has the frame captured from both sides.

The rear suspension cross-member, on trailing arm coil spring suspensions, IMO has a great deal of shear forces at play. All the acceleration forces, all the braking forces from the rear axle, towing, and think about how long those trailing arms are and all the leverage generated on that member when cornering. Those rivets are forge pounded into the frame and have absolutely zero give and do not allow any movement at all.

Even if the bolts are as snug as you can get them in the hole they will never come close to being as secure as the rivets so really I don't think in the instance of the rear suspension cross-member that anything less than the factory rivets (all the above) is overkill.

I'm glad I read this discussion it made me think. I'm moving my rear suspension cross-member forward as part of a frame shortening modification. I'm going to use the locking nuts, grade 8 bolts, maybe SAE threads if I can get the locking nuts for that, as tight a fit size bolts as I can get, plus I'm welding it in after that.

That may in fact be overkill, but I'm OK with it.

[MARKDTN]

For a frame bolt, you really should have the type that is not threaded all the way to the head. The smooth shank part will help keep the joint snug. They may be hard to find with exactly the right shank for what you need.

[jeffahart]

Well, coming from a construction background. We're always told that nails are better than screws for shear because they are generally more ductile than screws. Better ductility means better absorption of seismic energy. In earthquake prone regions the engineers are strict on fasteners for seismic code. The city of Los Angeles has some of the most strict seismic building code anywhere.

Just wondering if one might apply that theory to what's being talked about here. Maybe grade 8 is not over kill but possibly inappropriate for shear force. Maybe you want a bit if elasticity?

I'm not an engineer but, all things equal, you would think the same principles apply.

[Kennuck]

There is lots of misinformation regarding the difference in shear strength of grade 5 vs grade 8 bolts with many statements that grade 5 are more suitable in shear applications. This is absolutely not true Grade 8 bolts are stronger in every way including shear strength.

I think most of this conjecture comes from the way in which they shear. Grade 5 bolts when sheared will do so with less of a shock but at a lower load than grade 8. Grade 8 tend to go off like a gun shot so people believe they are brittle when it is actually the higher force required to shear.