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Old 01-03-2013, 09:20 AM   #1
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Split Lockwashers on Base Plates

Getting ready to install a Roadmaster baseplate on my brand-new Ford C Max hybrid. Parts not here yet, but I downloaded the instructions.

So here's my problem and possible fodder for a big discussion on this forum. Like most baseplates, their's is attached to the vehicle with a total of twelve 1/2" bolts, grade 5. My problem is that they provide split lock washers for each fastener. For at least the last 20 years or so it is generally recognized that split lock washers don't work and in fact compromise the integrity of bolted joints. This is recognized all the way from NASA to most of the fastener professional organizations.

My cunning plan is to substitute all the fasteners with grade 8's, fine thread, with hardened flat washers, torqued to the recommended 96 ft lb. Every source I can find says this is would create a substantially stronger joint and should be trouble free forever.

My dilemma is, I know if anything goes wrong for any reason, Roadmaster will point to my substitution as the root cause. Their instructions, however, have enough cover-their-butt stuff to absolve them from any failure anyway. For example they say it is the owner's responsibility to re-torque all the fasteners every 3,000 miles. I'm not likely to do that and no one else is either and unless you paid to have it done, you wouldn't be able to prove it anyway. You'll note that nothing on your car has to be re-torqued ever - and they don't use lockwashers on critical joints on cars and trucks.

Any thoughts on this, fellow RVers?
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Old 01-03-2013, 09:40 AM   #2
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I'd not use the lock washers and use Locktite Red on each thread to keep them tight.
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Old 01-03-2013, 09:44 AM   #3
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Hi, you are in a dilemma and I know that you have to make a decision to insure that you do not have an issue down the road.
With that said I know what I would do and that is use the grade 8 plated bolts; but maybe coarse thread bolts unless the grade 5 bolts were fine thread to begin with. I would than use grade 8 plated harden washer under the bolt heads and torque to the required bolt torque from the manufacture.
And I would then check the bolt torque once a season on your Road Master base plate for the car. But I would not use the dynamic torque list for installing the fasteners but the Static torque for checking them, this is standard practice in the industry when manufacturing heavy equipment.
I do not like split lock washer because they tend to provide a false torque reading during the installation process due to the bur that can be caused by the soft metal on the parent material and the split washer gouging this parent material. The other issue is you will never have a flat surface to reinstall the fastener on if you need to remove and replace them. There will always be that bur in the material from the split washer.
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Old 01-03-2013, 09:56 AM   #4
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Jim,

I agree with you. The best decision is to do the job right to the latest engineering standards and disregard Roadmaster's outdated design. Like I said, with all their disclaimers, I'd never get them to warranty anything if it did fall off. I'd rather have it not fall off in the first place.

My alternative, of course, is to let a dealer install it and then make them eat it if it does fall off. Bad news is I talked to another guy who had a dealer install and it cost him $700 plus the cost of the base plate. Roadmaster says 3 hours to install.

And, I forgot about the false torque reading due to the gouging at initial installation. That is a significant disadvantage to split lock washers.

My logic for going to fine thread is just to increase the clamping force. Bolt cost is the same, so why not?
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Old 01-03-2013, 12:22 PM   #5
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Why not use a nylock or a castellated nut instead and torqued to the correct spec? JM2¢...
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Old 01-03-2013, 12:46 PM   #6
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GR 8 bolts and nylon nuts

Hello as I mechanic for over 48 years I would use Gr 8 bolts with a harden steel washer on both the head of the bolt and nut end as well with a nylon lock nut and loctited. Torque it and forget it. Once its matting area is cleaned bolts installed Loctited and torqued it will be good to go.
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Old 01-03-2013, 12:56 PM   #7
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Quote:
Originally Posted by Diesel Guy View Post
Hello as I mechanic for over 48 years I would use Gr 8 bolts with a harden steel washer on both the head of the bolt and nut end as well with a nylon lock nut and loctited. Torque it and forget it. Once its matting area is cleaned bolts installed Loctited and torqued it will be good to go.
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Old 01-03-2013, 01:02 PM   #8
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+3 on the loctite. Lockwashers are just so 20th century.
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Old 01-03-2013, 06:43 PM   #9
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Use the supplied bolts, washers and nuts, add some Loctite and be done with it. If you want to go a little overboard, change to grade 8 hardware but still use the Loctite. Chances of you having a problem is slim to none.
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Old 01-04-2013, 01:37 PM   #10
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Quote:
Originally Posted by jmckinley View Post
Jim,

I agree with you. The best decision is to do the job right to the latest engineering standards and disregard Roadmaster's outdated design. Like I said, with all their disclaimers, I'd never get them to warranty anything if it did fall off. I'd rather have it not fall off in the first place.

My alternative, of course, is to let a dealer install it and then make them eat it if it does fall off. Bad news is I talked to another guy who had a dealer install and it cost him $700 plus the cost of the base plate. Roadmaster says 3 hours to install.

And, I forgot about the false torque reading due to the gouging at initial installation. That is a significant disadvantage to split lock washers.

My logic for going to fine thread is just to increase the clamping force. Bolt cost is the same, so why not?

John,
When I was at Cat we rarely used fine thread bolts and nuts just too easy to cross thread them.
What type of joint design are you looking for a Bearing type joint or a friction-type joint?
With a Bearing type joint the fine thread will not help and the cross sectional area of the bolt is what will support the load. With a friction-type the clamp load is what will support the joint and a coarse thread grade 8 will provide plenty of clamp load for the required drawbar pull that you will see. Also coarse thread will be easier to find at a dealer who deals in grade 8 bolts.
Just my $0.02
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Old 01-04-2013, 03:53 PM   #11
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Fine vs Course thread bolts

I agree with most of the previous information. My thought on Fine vs Course would be if you ever plan to remove the base plate. Fine threads have about 10% to 12% increased clamping force. But fine threads can really be a pain to remove.

One note on Thread Lock: Thread Lock will not only hold a fastener from loosening. But will also seal dirt and moisture out of the threads making it easier to remove after a little heat is applied. It takes about 400 +_ 50 degrees to soften Thread Lock back to a liquid like state. A small propane torch will do the trick on anything smaller than a 3/4" bolt/nut.

As to the original question about warranty. I would suspect no matter what hardware you used would be an out for warranty if they wanted to be picky. I think poor welds would be the biggest problem. Mounting with stronger hardware will only improve the final product.

BTW, I have my base plate installed with 3/8" NC grade 8 hardware all torqued and used Lock-Tight red on all. Been in place since Mar 2010 and nothing has loosened at all. I do a visual at every hook up of all the connection points on the Jeep.
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Old 01-04-2013, 04:22 PM   #12
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Quote:
Originally Posted by jimcumminsw View Post
John,
When I was at Cat we rarely used fine thread bolts and nuts just too easy to cross thread them.
Daddy always said that a good tight cross-thread is better than any self-locking nut! Used to install bolts/nuts on farm machinery, then beat the $*^! out of the threads to keep the nuts from coming off. Of course, if you ever want to uninstall it, that's a different story.

Seriously, I ran across this same issue installing the Roadmaster base plate on my CR-V last month. Roadmaster says not to tighten the nuts until all bolts are installed. Roadmaster also says to use LocTite Red on all the bolts. It has a working life of about 15 minutes -- you gotta work fast!

I did pre-fit everything, then put the LocTite on and torqued the nuts to specs. I used the hardware supplied by Roadmaster, including the split lock washers. In more than 50 years of mechanic work, I've never had a split lockwasher fail -- autos, farm machinery, or aircraft. So I trust them.

I do have a bone to pick with Roadmaster. They state that you should use carriage bolts to install the baseplate, and they have the square holes for carriage bolts, but all the supplied hardware was standard hex-head bolts. Not a problem except for the largest bolts which went thru a bracket that was then inserted inside a frame component where there was no access to get a wrench on the bolt head while torquing the nut. I held it as best I could with a prybar stuck inside the frame. I have to trust that the lock washers and LocTite will hold, because I wouldn't bet a nickel that I ever got the max torque on the nut.
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Old 01-04-2013, 04:29 PM   #13
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Is changing out the hardware really worth it in this particular situation? While there is a substantial difference in the tensile strength of a grade 5 vs a grade 8 bolt there isn't much difference in the shear strength. In this case I believe the shear strength is more important. A grade 5 bolt has a minimum shear strength of 14,136.5 lbs., while a grade 8 is 17,670.6 lbs. That's only a little over 3500 lbs difference.

You may have a little larger safety margin on that end of the assembly, but by the time you apply enough pressure to realize the difference the towbar and hitch will have long seperated from the motorhome.

As a point of reference I installed the Roadmaster XL baseplates on our Jeep using the factory supplied hardware (it does come complete with Loctite High Strength thread locker). In over 75,000 miles of towing over some of the worst roads in the lower 48, Alaska, and Canada there has never been a problem with fasteners loosening, deforming or breaking.

The ultimate decision is up to you, but in this case I wouldn't bother to reinvent the wheel. There's always the challenge to make something better, faster, and stronger. Along with that goes the chance that something may not work out the way you planned. If that does happen you've left the door open for the manufacturer to walk away and point the finger in your direction.
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Old 01-04-2013, 07:12 PM   #14
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Long time customer of locktite.. With Locktite read the nut goes on like it was oiled.. and comes off like it was welded.

One thing I would like to know if you can (And I'm going to research this for myself as well cause.. Well I do research for fun) is this:

You said Split lock washers are bad for the bolt (paraphrased) can you explain farther on that issue.. Thanks.

(I can in fact think of one possible reason but I'd like to hear the official one).
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