How To: Subframe Gravel Guard

[John E Davies]

This could go in Modifications, but it really has to do with protecting the suspension and subframe from gravel rash and water while towing off pavement. Moderators, you can move it there if you like.

 

This is an easy mod, you just have to get over your fear of drilling into your frame. Why would you want to do this?

 

It will stop the paint on the axles, hubs and shocks from eroding and rusting (gravel rash). It will help to protect the plated finish on the steel subframe. It will reduce or at least soften the high pressure water blast that sprays up onto your spring bearings in wet weather from your tow vehicle, washing out the lubricant. It may help to reduce the blast on the rear bumper and bumper compartment. And it looks cool.

 

 

The material is 1/8 inch sheet neoprene, cloth reinforced. I think it is used for conveyor belts. I located it in bulk at a local rubber supplier. A 3 x 4 ft sheet cost $90. The rest of the material was used elsewhere on Mouse. I cut two strips 12"x 26". They meet in the center and extend about 3 inches beyond the frame angle. The extended part will protect the shocks, which are pretty far outboard.

 

Hardware is 1/4" x 1 1/4" stainless bolts, washers and nylocks (locking nuts).

 

To keep the rubber off the steel I used 5/6-18 nylon nuts (full plastic, no steel) as spacers. They are a little hard to find - the box stores and Ace Hardware keep only a few in stock. You might be able to use circular nylon spacers, but these nuts work fine and are half the cost (about $0.60 each).

 

Drill a neat row of 1/4 inch holes at 6 inch spacing along the bottom of the front-most steel cross angle.  Use a sharp pilot bit first and it is not difficult, just a little messy. Wear eye protection and old clothes! Drill the rubber to match the spacing using a 5/16" bit.

 

Clean the steel with a good solvent, not alcohol. Use of alcohol for prepping the parts before sealing will prevent the sealant from curing!

 

Install the bolt and washer with the threads facing forward, with a dab of 3M Fast Cure 4000 or another excellent marine sealant under the head.

 

Add another dab of sealant on the shank and push the nylon nut into place, and add a flat washer.

 

Place the flap onto the threaded part of the bolt, add another washer and a nylock.

 

Repeat for all the holes and tighten evenly. Unless you were frugal with the sealant this could be MESSY!

 

 

 

You can use a good solvent like Acetone or MEK to clean up any messes.

 

The rubber I used is curling since it was in a tight roll for six weeks. I think it will straighten out when exposed to wind blast and heat, if not I can install some stainless strips along the bottom to weight them down.

 

John Davies

 

Spokane WA

[John E Davies]

Teaser: rear mudflaps, a future thread:

 

 

John Davies

 

Spokane WA

[Geronimo John]

John D:

 

First, really cool way to avoid deterioration of the under side of the Ollie!

 

A.  I assume you are standing off the rubber from the frame with the spacers to avoid corrosion of your steel sub-frame.  Correct?

 

B.  Scrap used conveyor belting is very available.  It is used at airports, warehouses, mining, bulk material yards, equipment rental places and many more.  Just look for an conveyor in a yard and you will find the old belts piled up.  The former users of it are generally very willing to just give it away.  What happens is that it physically gets damaged and they usually replace a lot more than just the damaged section.  So there is just about always a lot of good belt sitting there waiting to be cut off.

 

Another quality idea and execution from John D!

 

Thanks, Geronimo John

[John E Davies]

Geronimo John,

 

Thanks for the kind words and the headsup on the material. I did not know where to find it used. My new stuff is probably a lot prettier;)

 

The reason you want to use standoffs is to keep crud and moisture from collecting and sitting against the steel. With about 3/8 inch distance, dirt will tend to wash out naturally, and you can always shoot the area with a pressure washer.

 

You could probably use stainless spacers, but I think inert plastic is a better choice here.

 

The sealant is to preserve the raw steel where you drilled the holes by completely excluding air and moisture.

 

Finally, the reason I chose thin material is that it is lighter, it will “sail” at high speeds to hopefully lessen drag, and the steep angle will deflect gravel down towards the pavement. A heavier, more vertical flap would tend to ricochet them back up onto the underside of the hull. At slow road speeds the thin flaps will tend to hang more verically.

 

John Davies

 

Spokane WA

 

 

[taylor.coyote]

John,

 

thank you for your thoughtful post/reply on this topic a couple of days ago.

 

I like what you have done with the gravel-guards. You have covered the sub frame gravel-guards pretty well but i have few questions:

 

you defined the size and the ground clearance will be the result of the size. can you give a rough guideline for the resulting ground clearance from the bottom of the guard to the ground? the reason i ask is many roads have much of the gravel in crowns between the tire groves worn in the road. I want to insure the guards are not dragging on the crowns and contributing kicking up more gravel. I had this issue with tampers. I set up my hitch / truck hight before fully loading my truck that includes a 30gal water tank. needless to say, the truck squatted a little thus contributing to the the tampers taking rocks off the gravel crowns.

 

you have made a significant effort to keep steel components away from the Aluminum frame, why are you not using Aluminum fasteners?

 

i'm thinking the open gap in the front of the rear bumper needs some protection. the inside of my bumper is filled with rocks and grit.. do you have any thoughts?

 

----

 

Questions and thoughts about your stompers.. I see the value of the stompers and what i perceive to have has solved the rock problem. Even as a proven solution I'm struggling with what I perceive to be a lot of extra stuff to "futz with". I can’t see myself dealing with all that stuff to hitch and unhitch each time, maintaining and carrying extra service parts.

 

when i had my 1/2 ton truck, i hated dealing with the extra stuff using the Anderson weight distribution hitch. I used the hitch because i think it was the best in-class and I really needed it. I like the gravel guards because they seem to be a good solution with a one-time investment on the front-end doing the installation. Once together, just use it with a small amount of maintenance required.

 

If push come to shove, I'm not unwilling to use stompers if it is the only way to get good rock protection. I'm still seeking a solution that does not require dealing with it every time the trailer is hitch and unhitched. The Oliver owner calling himself "bugeyeddriver" seems to be satisfied with the Vortext coating with a few limitations.

 

I'm inclined to try using Line-X (no experienced Vortext guys near by) with good mud-flaps on the truck + modified Tampes (close of the gap between the flaps), open tread tires with next tires before sub-coming to managing a Stomper system.

 

I have read pretty much all that has been written in the forum on rock protection. Knowing my aversion to managing a stomper system, do you have any general advice or things I should consider before pulling the trigger?

 

Unfortunately, I just purchased a new set of Cooper AT3's. This is my third set and I really love the way they handle on and off road and they last 55K+. I thought all tires threw rocks and it was just part of being off road until you mentioned mud/open tread tire throw a lot fewer rocks. Makes a lot of since now you have brought to my attention.

[taylor.coyote]

John,

 

thank you for your thoughtful post/reply on this topic a couple of days ago.

 

I like what you have done with the gravel-guards. You have covered the sub frame gravel-guards pretty well but i have few questions:

 

you defined the size and the ground clearance will be the result of the size. can you give a rough guideline for the resulting ground clearance from the bottom of the guard to the ground? the reason i ask is many roads have much of the gravel in crowns between the tire groves worn in the road. I want to insure the guards are not dragging on the crowns and contributing kicking up more gravel. I had this issue with tampers. I set up my hitch / truck hight before fully loading my truck that includes a 30gal water tank. needless to say, the truck squatted a little thus contributing to the the tampers taking rocks off the gravel crowns.

 

you have made a significant effort to keep steel components away from the Aluminum frame, why are you not using Aluminum fasteners?

 

i'm thinking the open gap in the front of the rear bumper needs some protection. the inside of my bumper is filled with rocks and grit.. do you have any thoughts?

 

----

 

Questions and thoughts about your stompers.. I see the value of the stompers and what i perceive to have has solved the rock problem. Even as a proven solution I'm struggling with what I perceive to be a lot of extra stuff to "futz with". I can’t see myself dealing with all that stuff to hitch and unhitch each time, maintaining and carrying extra service parts.

 

when i had my 1/2 ton truck, i hated dealing with the extra stuff using the Anderson weight distribution hitch. I used the hitch because i think it was the best in-class and I really needed it. I like the gravel guards because they seem to be a good solution with a one-time investment on the front-end doing the installation. Once together, just use it with a small amount of maintenance required.

 

If push come to shove, I'm not unwilling to use stompers if it is the only way to get good rock protection. I'm still seeking a solution that does not require dealing with it every time the trailer is hitch and unhitched. The Oliver owner calling himself "bugeyeddriver" seems to be satisfied with the Vortext coating with a few limitations.

 

I'm inclined to try using Line-X (no experienced Vortext guys near by) with good mud-flaps on the truck + modified Tampes (close of the gap between the flaps), open tread tires with next tires before sub-coming to managing a Stomper system.

 

I have read pretty much all that has been written in the forum on rock protection. Knowing my aversion to managing a stomper system, do you have any general advice or things I should consider before pulling the trigger?

 

Unfortunately, I just purchased a new set of Cooper AT3's. This is my third set and I really love the way they handle on and off road and they last 55K+. I thought all tires threw rocks and it was just part of being off road until you mentioned mud/open tread tire throw a lot fewer rocks. Makes a lot of since now you have brought to my attention.

Unfortunately, I just purchased a new set of Cooper AT3's. This is my third set and I really love the way they handle on and off road and they last 50K+. I thought all tires throw rocks and it was just part of being off road until you mentioned mud/open tread tire throw a lot fewer rocks. Makes a lot of since now you have brought to my attention.

 

[John E Davies]

Taylor, I will answer to the best of my ability.....

 

I used stainless fasteners for strength, they are not at all ideal in aluminum (but Oliver uses them everywhere in the frame). But these mid-flaps and also the flaps behind the tires, are not mounted into aluminum, but into the galvanized mild steel of the subframe. So if you used aluminum bolts here, you would still have the possibility of some dissimilar metal corrosion. Joining aluminum brackets to steel parts is a little spooky, you need to bed the parts completely and seal off the holes 100% with an excellent sealant to exclude all moisture, which would accelerate corrosion.

 

Ground clearance. I chose this height because I felt it the best compromise between good coverage and not scraping the ground. I have no way of telling at what angle they actually “fly” at say 30 mph or 60 mph, I would have to mount a camera under there to see. But I do not see any signs that they are kicking up rooster tails of debris. Very stiff flaps would be a problem, IMHO.

 

I did add stainless strips along the bottom to weight the flaps, I will try to add some pics. The rubber stayed curled and I needed the strips to keep them straight along the bottom edges.

 

Sealing the bumper compartment. Yes, it does fill up with dust and grit. You could seal the big gaps in the sides and leading edges where it joins the hull, that will help a lot, but you can’t seal it up tight. It needs to drain and dry out after you spill grey water or worse there. You could mount a rubber stone guard strip across that area underneath. It would catch the larger stuff but I doubt that it would help with the fine dust.

 

Rear mudflaps. If I were to recommend just one of these mods, it would be these. They stop debris from impacting your water fittings, and the lower curve of the hull, and from ricocheting off the front face of the bumper and back into the rear lights.

 

Futzing. There is no doubt that a Stone Stomper requires a small amount of constant futzing. When unhitching, you have to unclip all the bungees in front and drag the mesh under the tongue to clear the jack. By clipping the outer bungees to the rear mounts, the fabric is help up off the ground, looks tidy and won’t blow around in a cross wind.

 

When hitching, you have to bring the fabric back into place, and attach the front bungees. You cannot access the rear cargo area with the fabric in place, but it is dead simple to unclip two of them and let the fabric fall, or clip those bungees to the coupler handle.

 

When it is clean, this is no problem. If it is wet and filthy, then it is not pleasant. I do try to not unhitch at all, if possible. I prefer to stay hooked up overnight and it greatly simplifies things. I prefer a dead level site or one that slopes slightly down from the road, so I can use no jacks at all, or lower just the rears to level the butt.

 

You have to consider the many hours of drudgery and expense you save, not having to deal with chips, filth or damage to your trailer or  TV. If you don’t care about how they look, and can live with a steady increase in chips and erosion, then you don’t need a Stone Stomper.  I am actually astonished that boaters do not use these. An unprotected boat hull can get really damaged by just a few miles of gravel roads, or thirty miles of freshly chip sealed highway, even with Rock Tamers. Nobody likes to do gelcoat or paint chip repairs or pay a shop many hours of labor to fix it.... as I mentioned in another thread, after 10000 towing miles my trailer and frame look like new. The system works.

 

If you don’t want to go with a Stone Stomper, consider a fixed wire mesh barrier like you see on many Australian caravans. They direct the debris up and outward. Which is good for your truck and trailer, but not so good for cars approaching that might get blasted by the stuff getting thrown into that lane...

 

Tires: I am a huge fan of Coopers, and I have used AT3 s before on a couple of vehicles, but the bottom line is that they are not a great choice for graded gravel roads. They are rock slingers..... though not as bad as say a set of snow tires. My Nittos do not throw gravel much and they are very fine tires, but they are a very soft compound and short lived. I will probably replace them in a year with Cooper ST Maxx or Goodyear Duratracks.

 

John Davies

 

Spokane WA

[John E Davies]

The fabric “pinned up” to allow access to rear hatch.

 

 

Instead of swearing at the fabric, embrace its usefulness to hold groceries or the doghouse while you are doing other stuff.

 

 

Here are the mid-guards, showing the stainless strips I added to stiffen them.

 

 

John Davies

 

Spokane WA

[taylor.coyote]

John,

 

Thank you for sharing your experience and this is very thoughtful information. For sure, I'm going forward with the undercarriage gravel guards and mud flaps. I'm sold on the functionality and performance of the stompers but need to sleep on it. Seems another level of fabrication skills is needed to set up stompers plus futzing factor makes me pause. your point about camping "hooked up" mitigates some of this as we too camp "hooked up" good share of the time.

 

You are correct about the AT3's being rock flingers. Darn, thought this was just the ways it is when off road. I'm a day late on this one.

 

 

the Aussi wind screen guards mentioned.. do you mean like the image below?

 

 

 

 

[John E Davies]

I have never seen a guard like that, it attaches to the front of a vehicle,  it looks very effective, but you couldn't see past it.... No I meant one to attach to the tongue of the trailer.

 

 

This is interesting, it shows the low pressure areas behind the Land Cruiser and trailer at speed on a dusty road.

 

 

The Stone Stomper prevents most of that forward cloud, except at low speeds. You don't get that vast accumulation of grit and dirt on the front of the trailer, as in the upper pic.

 

John Davies

 

Spokane WA

 

 

[Geronimo John]

John:
What is the purpose of having the nylon washers between the conveyor belting and the steel sub-frame?

Thanks.

[John E Davies]

40 minutes ago, Geronimo John said:

John:
What is the purpose of having the nylon washers between the conveyor belting and the steel sub-frame?

Thanks.

They don’t need to be nylon, they are there to space the rubber away from the steel, so water and gunk will not accumulate there and cause corrosion on the frame. When washing the trailer I intentionally spray that area to remove any dirt.

John Davies

Spokane WA

[Trainman]

Those are some pretty nicely thought out systems and a first class job was done building and installing them. For ourselves we don't plan to travel any back roads (gravel or rocks) and boondocking is not to our liking, I see no need for me to invest in a system like that, but I will say here it looks like great protection for those who wish to camp that way. As you can see we probably won't be going to Alaska with our trailer, or camping beyond the paved roads. 

trainman