Skid plate theory? - JeepForum.com

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post #1 of 17 Old 10-28-2013, 07:14 PM Thread Starter
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Skid plate theory?

I am building a new skid for my '72 CJ5 (stock 15gl tank). The original skid was thin and would crush often. The one I am building is thicker (14ga compared to 16 or 18ga) and has ribs welded the length of the skid, this should provide less COF if I am correct. Anyone have any advice? Is there a theory on skids? Any help or ideas are welcome. When it is all done. i'll post the drawing in the file CJ file posting thread.













I used 1/2" angle that was thin, probably under an 1/8" for ribs and hammered the ends flat so it has an easy transition , no sharp edges. The skid was made in two pieces becuase my Swag finger brake is only 19" wide, skid is 23" wide.

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post #2 of 17 Old 10-28-2013, 07:33 PM
mopar346
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Our factory CJ7 tank skid is pretty stout, it also has sides welded to make almost a box for the tank to sit in. Skid plate theory: Protection with airflow and drainage AND floatation in mud is an added benefit - most of the time.

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post #3 of 17 Old 10-28-2013, 07:46 PM
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I would have put those 'rock-grabbers' on the inside, so the plate can 'skid' over rocks etc.
The sides could use some reinforcement too.
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post #4 of 17 Old 10-28-2013, 08:20 PM Thread Starter
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When all done, it will be boxed a little for strength. I need to see a 7 skid to see how it is structured.

Lumpy, the runners are in line with the Jeep, they are "rock grabbers" when sliding sideways ( a good thing I hope). I don't want to skid over rocks, I am hoping to "slide" over them. Am I on something from the pharmacy? My theory is that the ribs have such little surface that they will have a distinctly lower COF. I am not sold on it yet, so talk me off the bridge.

I could put another plate right over the ribs, easy enough and probably light enough, oh ya, I am now "concerned about weight". I have already added helpers, now it is time for the YJ spring swap I fear.

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post #5 of 17 Old 10-28-2013, 08:27 PM
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MOST CJs need a little weight in the rear.

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post #6 of 17 Old 10-28-2013, 08:32 PM Thread Starter
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Quote:
Originally Posted by mopar346 View Post
MOST CJs need a little weight in the rear.
Mine has a serious case of saggy bottom LOL

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post #7 of 17 Old 10-28-2013, 09:58 PM
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OK, now that I'm on a bigger screen. I see how you have it.
SORRY
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post #8 of 17 Old 10-28-2013, 10:24 PM
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Quote:
Originally Posted by mopar346 View Post
Our factory CJ7 tank skid is pretty stout, it also has sides welded to make almost a box for the tank to sit in.
I believe the factory skid with the boxed in sides is for a 20 gal tank, not a 15.
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post #9 of 17 Old 10-29-2013, 01:00 AM Thread Starter
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I do plan on structuring the sides, might not be boxed or go all the way to the top but it will be sealed in some. The rear bend (two bends actually) has enough clearance to put in a three inch (by 23" long) strap or gusset on the inside of the skid. that will make the rear/ bumper side of the skid more crush resistant. This seems to be the spot that gets it the most. The front I will probably leave as it is, even though it is a bit weak in my opinion. I will rely on the side boxing/structuring for the outboard sides of the front and hope nothing hits the center. I did make the diff opening bigger on this one as the BTF cover on the 44 was hitting and I had to cut out a few inches all around for clearance.

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post #10 of 17 Old 10-29-2013, 04:28 AM
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Did you leave enough room for some insulation around the tank to keep it from rubbing against each other? Even though it might be flat and smooth a little foam will go a long way to keep the tank rubbing against the skid plate. Don't want to wear any holes in the tank although if you have a plastic tank it might wear longer.

Are you going to cut an access hatch for the sending unit in the floor of the jeep? I would hate to muscle that plate in and out to work on the tank.
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post #11 of 17 Old 10-29-2013, 05:07 AM
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Before you box it too much, you may also want to think how much crud is going to be collected inside it. Crud is the main contributor to rust and building a box that is impossible to clean out or is closed on the sides may trap that stuff up next to the skid, tank, and frame rails.
Just something to think about.........
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post #12 of 17 Old 10-29-2013, 09:59 AM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
Did you leave enough room for some insulation around the tank to keep it from rubbing against each other? Even though it might be flat and smooth a little foam will go a long way to keep the tank rubbing against the skid plate. Don't want to wear any holes in the tank although if you have a plastic tank it might wear longer.

Are you going to cut an access hatch for the sending unit in the floor of the jeep? I would hate to muscle that plate in and out to work on the tank.

John, I have not cut a hole (yet) for the sender. Four months ago, I put in all new tank, float and sender apparatus. I know I can still have problems though. Regarding the buffer zone, our 5 has a small body lift that i took advantage of and raised the tank 5/8" from the top of the frame, this was important for two reasons, first the fill neck is no longer rubbing the frame (causing the cracks i think) and two gave me some much needed room between skid and tank. The old tank had lots of dings and bends from the skid hitting it. I would be concerned about any insulation holding moisture and causing a rust problem, even here in so cal, the main problem is creek crossing and muddy roads.

Nut and washers under L bracket:


Fill neck, short version:




Quote:
Originally Posted by jeepdaddy2000 View Post
Before you box it too much, you may also want to think how much crud is going to be collected inside it. Crud is the main contributor to rust and building a box that is impossible to clean out or is closed on the sides may trap that stuff up next to the skid, tank, and frame rails.
Just something to think about.........
Yesterday, when I pulled the skid, a bunch of gravel/rocks were in the skid, this could be a problem if they gather and rub on the tank. I could integrate some holes along the side to shed small particles and water but the bigger stuff I might have to live with and check it once in a while.


How many CJs have skids like mine?
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post #13 of 17 Old 11-01-2013, 07:20 PM Thread Starter
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OK, it is on and ready to be tested tomorrow, headed to cougar buttes.

I cut this for the sides in order to structure the sides and still shed debri and water as well as keeping the weight down:



I welded them in just as cut, shown here:



On fit testing, there was some rubbing on the new installed sides. I was able to take a deadblow hammer and bend them enough to fit good. Just a couple of easy whacks and it was done. If it was thicker, it may have needed more persuasion. not a big hurdle, just a small detail.



Overall, I like the fit. It is 7lbs heavier than the stock plate, 11lbs vs 18lbs, not too big a difference really.








I need to make two small changes to the cut file to allow for some clearence at the back near the bumper. I'll do that first of next week and then post the files here and in the CJ file section to cover the bases.

Please post any ideas or problem areas you see in the pics.

Cheers!
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post #14 of 17 Old 11-01-2013, 11:26 PM Thread Starter
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old vs new skid comparison:

OLD



NEW

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post #15 of 17 Old 11-02-2013, 06:04 AM
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Will the square back corner be a problem if you back into a rock? I know you were interested in sliding over rocks, so I figured I would ask. I guess we will find out.
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