MTL_4runner
07-11-2007, 04:38 PM
My install from 3 years ago. Works awesome!!! :thumbup:
OK, well I finally got it all installed but it was not as easy as I would have hoped. Lucky that I did the experimentation so you don't have to. I also did calculate all the forces so as far as I can tell the design is very solid and should be more than adequate for keeping a baby safe in all but the most extreme of accidents.
Assumptions:
Assume baby and carseat weigh no more than 50 lbs, thus in a survivable crash we assume potential G force of 30 for several milliseconds. This would turn the 50 lb load into a 1500lb projectile of force you need to keep contained and still have some safety factor to the system.
Calcs (each bracket get half the 1500lb load):
1/4 bolts in tension (fine threads) = A x P = 0.033 insq x 92,000 psi = 3000+ lbs per bolt (clearly we will not fail here SF=8)
Nuts - very important to get fine threads because 6 threads are needed to carry 99% of the load
Homemade brackets are far too thick to be a weak link
3/32" Sheet metal tearing from bracket pulling at impact = F/A = P
Area of bracket = (0.0625 x 1" x (2) 0.0625 x 2" x (2) = 0.375 insq
so 750 / 0.375 = 2000 psi in shearing (fine too SF=25)
Honda anchor shear of tabs = F/A = P
Area of tabs = 0.09375 x 1" x 2 tabs = 0.1875 insq
so 750 / 0.25 = 3,000 psi in shearing (still fine with SF=6)
Honda anchor shear of LATCH attach point = F/A = P
Area of anchor bar = pie x R sq = 3.14 x 0.09375 sq = 0.0276 insq
so 750 / 0.0276 = 25,000 psi (so this is the weakest link whith still a SF=2, reality is higher since it will deform before shearing occurs)
Now that we have proven it will work.....lets build it.
What you need:
Hardware:
1 foot of 1" x 1/8" flat steel barstock (most hardware stores have this)
(8) 1/4-28 (fine) nuts (Grade 5 or better!!!)
(10) 1/4-28 (fine) bolts (Grade 5 or better!!!)
(8) 1/4" washers
(4) Trunk strikers from a 2002 Honda Civic LX, P/N 74862-SE3-003 (I called them anchors in the writeup)
Tools:
1.5" bimetal hole saw
Drill (cordless works best)
1/4-28 thread tap (just in case after welding nuts)
1/4-28 thread die (just in case after making transfer punch)
1/4" Drill bit
torque wrench
hammer
hacksaw
bench grinder
Ratchet set (12mm for seat and whatever fits the bolts you bought)
sharpie marker
1) First thing is to mark a line on the sheetmetal floorpan to keep all the brackets in line with where the seat back and bottom meet. Do this by flipping the seat bottoms forward and mark a line from one end of the seatback to the other along the floor (you may need to move some of the little strips of carpet that go between the belts).
2) Now that we have a way to keep all the anchors in line after we remove the seatback, you need to then unbolt it, there are a total of 8 bolts holding it in place (2 on each side and 4 in the middle). Take the seat back and push it into the rear cargo area (it will still be attached to the rear carpet, just give yourself as much working room as possible).
3) Next we need to enlarge the access holes so you can get the brackets in and have enuf room to hold the bracket (will tell you how to make these in a sec) while you bolt the achors down in place. When you moved the seatcak into the rear, under the carpet you will find (4) 1/2" holes in the floorpan covered with stickers. Use the holesaw to enlarge all 4 to 1.5" so you have ample access to behind the sheetmetal. It can be a pain so take your time on this step.
4) Now we will start to make the rear brackets that will hold the anchors behind the sheetmetal. You start by simply lining up the anchors on the barstock lengthwise (first anchor will be lined up on the edge of the barstock and centered on the width) and drill a 1/4" hole in the center of the anchor mount hole. Then bolt the anchor to the barstock (bolt and washer on top of bracket and nut on the bracket side.....nut will get tack welded to the barstock when we are done) and repeat for the second hole (2 holes per anchor). You will then put the next bracket about 1/8" away (enuf to hacksaw the brackets apart later). Just center them width-wise the best you can but it is not entirely critical. Now you should see a line of anchors attached to your barstock....leave them like that for now (having the bar makes it easier for someone to clamp and weld) and take it to someone who can tack weld the 8 nuts to the barstock (I don't know anyone who welds so I took it to Mineke and they charged $5 to tack em down, took like 10 min max....works for me!!!). Ok now use the hack saw to cut the brackets apart and now you should have 4 brackets about the same length as the anchors. Unbolt the anchors from the brackets and make sure the bolts turn freely in the nuts (if not use the tap on the nut threads) Finish them by rounding off all the corners, then use a wire wheel to deburr all the edges (a sharp edge may cut into the sheetmetal in an accident and allow shearing at lower force)....so don't skimp here!
5) Now you have finished the brackets, you need to locate the anchors and drill the bolt holes. We are going to make a transfer punch in this step. Take 2 of the bolts and grind them to a point on your bench grinder. Use the thread die on them if the threads got buggered in the process of grinding. Now screw the 2 bolts you made into a bracket and locate it about where you want to place it. Now hit the top of each bolt so as to make a mark in the sheetmetal. Then go ahead and use your 1/4" drill bit for the holes you just located. Then repeat this step for all the brackets (you may need to sharpen the bolt tip again.....also DO NOT use the same bracket for all anchors because the centers may be different when you drilled them by hand!!!!), so also make sure to keep in order as to which bracket goes in what location (numbering them with a marker helps). You can discard the sharpened bolts after this step.
6) FINALLY we can bolt these in! You need to now slide the bracket into the access hole you made, hold the flat side against the sheetmetal and line up the holes (the middle 2 brackets were a pain in the ******* and you may need to use a screwdriver to pry them sideways into place....there is another piece of sheetmetal in close proximity you need to get the bracket in between in order to secure it). Now with the other hand locate the anchor and use a bolt and washer and hand tighten the assy. Do the same for the second bolt. Then torque down both in place according to this chart http://www.fandisc.com/tti.htm (remember they are in in*lb NOT ft*lb).
7) Now that they are all in, I didn't get very creative on covering the holes so if someone has a great idea let me know. I just used about 7 layers of duct tape over each to ensure no water can enter and corrode inside (remember the holes were covered before we enlarged them).
8) I did have to trim some of the carpet that goes between the seatbelts so they fit around the anchors nicely, just use a pair of scissors to trim as needed.
9) Lastly reassemble the seatback and crack open a cold one!
I am quite confident in the design and it came out very well I think. This is only my design (not tested, not sanctioned, etc) and if you decide to use it, I accept NO liability for anything that results from the use of it. This should be common sense but too many people are sue happy now a days so it always needs to be said it seems. If you are worried you can also use the lap belt in combination to be doubly sure.[/
OK, well I finally got it all installed but it was not as easy as I would have hoped. Lucky that I did the experimentation so you don't have to. I also did calculate all the forces so as far as I can tell the design is very solid and should be more than adequate for keeping a baby safe in all but the most extreme of accidents.
Assumptions:
Assume baby and carseat weigh no more than 50 lbs, thus in a survivable crash we assume potential G force of 30 for several milliseconds. This would turn the 50 lb load into a 1500lb projectile of force you need to keep contained and still have some safety factor to the system.
Calcs (each bracket get half the 1500lb load):
1/4 bolts in tension (fine threads) = A x P = 0.033 insq x 92,000 psi = 3000+ lbs per bolt (clearly we will not fail here SF=8)
Nuts - very important to get fine threads because 6 threads are needed to carry 99% of the load
Homemade brackets are far too thick to be a weak link
3/32" Sheet metal tearing from bracket pulling at impact = F/A = P
Area of bracket = (0.0625 x 1" x (2) 0.0625 x 2" x (2) = 0.375 insq
so 750 / 0.375 = 2000 psi in shearing (fine too SF=25)
Honda anchor shear of tabs = F/A = P
Area of tabs = 0.09375 x 1" x 2 tabs = 0.1875 insq
so 750 / 0.25 = 3,000 psi in shearing (still fine with SF=6)
Honda anchor shear of LATCH attach point = F/A = P
Area of anchor bar = pie x R sq = 3.14 x 0.09375 sq = 0.0276 insq
so 750 / 0.0276 = 25,000 psi (so this is the weakest link whith still a SF=2, reality is higher since it will deform before shearing occurs)
Now that we have proven it will work.....lets build it.
What you need:
Hardware:
1 foot of 1" x 1/8" flat steel barstock (most hardware stores have this)
(8) 1/4-28 (fine) nuts (Grade 5 or better!!!)
(10) 1/4-28 (fine) bolts (Grade 5 or better!!!)
(8) 1/4" washers
(4) Trunk strikers from a 2002 Honda Civic LX, P/N 74862-SE3-003 (I called them anchors in the writeup)
Tools:
1.5" bimetal hole saw
Drill (cordless works best)
1/4-28 thread tap (just in case after welding nuts)
1/4-28 thread die (just in case after making transfer punch)
1/4" Drill bit
torque wrench
hammer
hacksaw
bench grinder
Ratchet set (12mm for seat and whatever fits the bolts you bought)
sharpie marker
1) First thing is to mark a line on the sheetmetal floorpan to keep all the brackets in line with where the seat back and bottom meet. Do this by flipping the seat bottoms forward and mark a line from one end of the seatback to the other along the floor (you may need to move some of the little strips of carpet that go between the belts).
2) Now that we have a way to keep all the anchors in line after we remove the seatback, you need to then unbolt it, there are a total of 8 bolts holding it in place (2 on each side and 4 in the middle). Take the seat back and push it into the rear cargo area (it will still be attached to the rear carpet, just give yourself as much working room as possible).
3) Next we need to enlarge the access holes so you can get the brackets in and have enuf room to hold the bracket (will tell you how to make these in a sec) while you bolt the achors down in place. When you moved the seatcak into the rear, under the carpet you will find (4) 1/2" holes in the floorpan covered with stickers. Use the holesaw to enlarge all 4 to 1.5" so you have ample access to behind the sheetmetal. It can be a pain so take your time on this step.
4) Now we will start to make the rear brackets that will hold the anchors behind the sheetmetal. You start by simply lining up the anchors on the barstock lengthwise (first anchor will be lined up on the edge of the barstock and centered on the width) and drill a 1/4" hole in the center of the anchor mount hole. Then bolt the anchor to the barstock (bolt and washer on top of bracket and nut on the bracket side.....nut will get tack welded to the barstock when we are done) and repeat for the second hole (2 holes per anchor). You will then put the next bracket about 1/8" away (enuf to hacksaw the brackets apart later). Just center them width-wise the best you can but it is not entirely critical. Now you should see a line of anchors attached to your barstock....leave them like that for now (having the bar makes it easier for someone to clamp and weld) and take it to someone who can tack weld the 8 nuts to the barstock (I don't know anyone who welds so I took it to Mineke and they charged $5 to tack em down, took like 10 min max....works for me!!!). Ok now use the hack saw to cut the brackets apart and now you should have 4 brackets about the same length as the anchors. Unbolt the anchors from the brackets and make sure the bolts turn freely in the nuts (if not use the tap on the nut threads) Finish them by rounding off all the corners, then use a wire wheel to deburr all the edges (a sharp edge may cut into the sheetmetal in an accident and allow shearing at lower force)....so don't skimp here!
5) Now you have finished the brackets, you need to locate the anchors and drill the bolt holes. We are going to make a transfer punch in this step. Take 2 of the bolts and grind them to a point on your bench grinder. Use the thread die on them if the threads got buggered in the process of grinding. Now screw the 2 bolts you made into a bracket and locate it about where you want to place it. Now hit the top of each bolt so as to make a mark in the sheetmetal. Then go ahead and use your 1/4" drill bit for the holes you just located. Then repeat this step for all the brackets (you may need to sharpen the bolt tip again.....also DO NOT use the same bracket for all anchors because the centers may be different when you drilled them by hand!!!!), so also make sure to keep in order as to which bracket goes in what location (numbering them with a marker helps). You can discard the sharpened bolts after this step.
6) FINALLY we can bolt these in! You need to now slide the bracket into the access hole you made, hold the flat side against the sheetmetal and line up the holes (the middle 2 brackets were a pain in the ******* and you may need to use a screwdriver to pry them sideways into place....there is another piece of sheetmetal in close proximity you need to get the bracket in between in order to secure it). Now with the other hand locate the anchor and use a bolt and washer and hand tighten the assy. Do the same for the second bolt. Then torque down both in place according to this chart http://www.fandisc.com/tti.htm (remember they are in in*lb NOT ft*lb).
7) Now that they are all in, I didn't get very creative on covering the holes so if someone has a great idea let me know. I just used about 7 layers of duct tape over each to ensure no water can enter and corrode inside (remember the holes were covered before we enlarged them).
8) I did have to trim some of the carpet that goes between the seatbelts so they fit around the anchors nicely, just use a pair of scissors to trim as needed.
9) Lastly reassemble the seatback and crack open a cold one!
I am quite confident in the design and it came out very well I think. This is only my design (not tested, not sanctioned, etc) and if you decide to use it, I accept NO liability for anything that results from the use of it. This should be common sense but too many people are sue happy now a days so it always needs to be said it seems. If you are worried you can also use the lap belt in combination to be doubly sure.[/