class 3/4 hitch

bamalongroof wrote:

Not sure if you discussed the hardware required do you have the hardware noted from your install?

As noted above, the design is for 3/4" grade 8 bolts and nuts for strength. 1-1/2" or 2" would be sufficient in length. To position and retain the nuts inside the frame while tightening, I tacked the washer to the nut and tacked a long (12 or 14") piece of metal (eg: coat hanger) to the washer and ground a flat on one side of each washer. The rod is used to insert the nut through another opening in the frame and position it, while the ground flat edge on the washer jams against the inside wall of the frame to hold the nut while tightening the bolt.

Here is the original sketch:

I bought a Class 4 Putnam hitch off a '92 RMW from a junk yard between Traverse City and Petosky MI in May for $50. Had it shipped to one of my brothers in Pinckney MI for $45. Picked it up in early July. Dissasebled it and removed heavy rust with wire brush, sandpaper and sand blasting. Had a friend from church who owns a steel fabricating shop punch a 5/8" hole in the side pieces so that it could be attached to the frame in two places on each side instead of one. He also cut two 1-1/2" x 2-1/2" 1/4" angles for two side pieces for strength. Another frield welded them to the side pieces. I ground the bottom welds smooth. After sand blasting, painted with three coats of Chassis Saver Paint. Bolted to vehicle with 4-2" 1/2" grade 5 black phophate carriage bolts and 4-10mm x 1.0 8.8 hard bolts to the bumper shocks. The side pieces were bolted to the lateral piece with 4 each side 1-3/4" 7/16 fine thread grade 5 bolts. total cost ~$175. If I can figure out how I will post pics. Now to wire up the 7 round trailer wire harness to haul boat or 27' Travel Trailer.

27' trailer and grade 5 bolts? You brave, brave person.

Grade 8 bolts aren't very expensive, in some cases they aren't necessary; however when hauling a trailer you don't want to leave anything to chance.

you guys make me laugh,..

1/2" bolts are pretty big,.

fine thread grade 5 bolts,. you really think they will shear off?

too funny,...

Nick, Why take the chance when it's only a few dollars more.

MalibuSSwagon wrote:

Nick, Why take the chance when it's only a few dollars more.

oh please,. don't be so silly,..

Some of you guys think everything needs to be held together with grade 8 bolts,.including exhaust manifolds,.

It's not taking a chance,. as i mentioned 1/2" bolts are pretty big for the job,.

your inexperience in fabricating stuff is obvious,. by your need to over engineer,.

if you read what he built the extra 1/4" angle iron is a pretty damn good bracket,.

It's a common thing in the internet world, if its not over engineered, powdercoated and made to last 40 yrs its no good,.

yet uhaul and other places have been bolting hitches on for years,. and they are just painted mild steel stuff, held on with 3/8ths and 5/8ths bolts,. and they last 10-15 yrs,

Do you think the vehicle can generate enough draw bar pull to shear off the bolts?
don't forget what your pulling may weigh 5-600lbs,. but its on wheels that roll,.


i,m pretty sure if we anchored the front of the car to a solid object, then hooked a D8 to the hitch,.it'd tear the frame before it sheared the 1/2" grade 5 bolts,.

check out the hardware of most tongues on trailer,. no where near as strong as the hitches on the vehicle,.


but you do what you want with your hitch,. and i'll use my 3/4 ton truck to tow anything i need to,..

and i'll go back to the real world and you guys can keep playing in the virtual world,.

and we'll both be happy,.

There is a huge increase in strength (about 60% higher proof load) comparing a true grade 8 bolt (not 8.2) to a grade 5 bolt. This not only applies to the bulk of the bolt, but also the comparatively shallow threads that the tongue weight of your trailer will be hanging on.

When I did the original design, I calculated shear forces due to shock loads, given a 7,000lb trailer. I don't have the calculations at hand, but I designed for grade 8 hardware, and came up with 3/4". Yes, 1/2" grade 2 will hold the hitch on the car with a light utility trailer and no unforeseen shock loading. But I was designing a hitch to match the capabilities of the car.

Your choice. I used grade 8 on my hitch.

shock load for 7000lbs,. interesting,.

shallow threads,. tongue weight,. all interesting points,. doubt you will ever have a 7000lb tongue weight ,. or even be able to generate 7000lbs of draw bar pull as i said,.

but of course if its designed for grade 8 bolts then grade 8 bolts must be used right?
I,m sure your design is a strong design,.

as i mentioned but it keeps getting glossed over,.
perhaps i'll try to explain my point in a different way?

if you bolt a 1/4" piece to another 1/4" piece,.with a 1/2" grade 5 bolt,.
i.m not able to come up with the force necessary to shear the bolt off,. but i,m pretty certain its beyond the limits of a station wagon,.and i think the 1/4" mild steel material will bend/distort

unless of course we are now going to build the hitch out of T1,. which of course would be what i would do, and use huck bolts etc,.

but to be safe,. lets all use grade 8 bolts right? then we can all have bragging rights that the equipment we are operating is so well made and so strong and safe that it bears no merit to argue anything,.over engineered or not,.

We all know i,m not an engineer,.and i,m sure that some egg head will come along with a whole long diatribe on bolt strengths and shear values,.stretch factors,. yada yada,.

but i,m pretty sure the afore mentioned hitch won't come off,.and his bolts are more than adequate for holding it on,.

it is like arguing against a fully auto 10 ga, of course it'll get the bird everytime,. but it it necessary?



carry on,.

phantom 309 wrote:

it is like arguing against a fully auto 10 ga, of course it'll get the bird everytime,.  but it it necessary?



carry on,.

Well it'd certainly save a lot of time chopping it up for soups and salads!

Well, I know I am inexperienced at fabricating, no need to point that out. However, my point is bolts are far cheaper than lawyers......That is all.

I have personally seen a 7500 lb grain dryer section lifted off a single 3/8 grade 2 bolt(forgot to remove) very scary!! I have also seen the heads of 7/16 grade 8 bolts shoot off like 12 ga shotgun slugs when jacking 105' dia grain bins...even scarier. I am not agreeing or disagreeing with anyone, but if an engineer wants 3/4 grade 8, for the 3 to 4 bucks its going to cost why not. by the way if you want to talk overkill, I am using 3/4 A235 structure bolts for mine, just because they are sitting in the bolt bin

My what a cat and dog fight I started.

1/2" grade 5 carriage bolts are what most after market trailer hitches are used to attach to the frame. See installation pdf's at e-trailer. BTW the Cequent hiches 41509 and 33007 use 1 1/2" 1-1/2" long grade 5 carriage bolt on each side into the frame and two M10-1.50 grade 8.8 bolts 35 mm long on each side into the bumper shock mount. Their hitch is rated for 10,000 lbs. or lower if the vehicle's owners manual requires a lower rating, in our case either 5,000 lbs for 1991-1993 or 7,000 lbs. for 1994-96. If you are going to use 3/4" bolts u will have to open up the current holes.

The side frames for the Putnam hitch are made from 5/16" steel. I can not find any grade 8 carriage bolts, at least not in McMaster-Carr. The 7/16" bolts that hold the side frames to the lateral frame on the Putman hitch came with grade 5 coarse pitch bolts and did not fail even though it was evident the right side of the hitch had hit bottom quite hard.

phantom 309 wrote:

shallow threads,. tongue weight,. all interesting points,. doubt you will ever have a 7000lb tongue weight ,. or even be able to generate 7000lbs of draw bar pull as i said,.  

Huh? Who said anything about a 7,000lb tongue weight? This is a Roadmaster, not a semi-trailer! I designed for a tongue weight of 500lbs -- a typical effective tongue weight for a 7,000 lb trailer towed with a weight equalizing hitch (ie: 1/3 of real tongue weight is redistributed to other axles via equalizing bars).

3/4" - 10 class 2A major diameter: .7353" (ie: the nut) Area: .4246 sq. in.
3/4" - 10 class 2B minor diameter: .6850" (ie: the bolt) Area: .3685
minimum ISO engagement length (2x tensile area): 0.04568 x 10 tpi = 4.5 threads
overlap in contact: .0503"  
area: .0561 per thread. x 4.5 threads= .2525 square inches.

I was striving for a minimum safety factor of 2. (A safety factor of 1 implies failure at the design load. A safety factor of 2 is considered a minimum standard of good engineering. Some engineers would cover their asses with a safety factor of 5), assuming the sudden shock of hitting a 6" deep pothole or speed bump. While 4 bolts are specified to distribute acceleration forces of towing against the frame, the vertical shock load would essentially be applied on only the rear two of those bolts. So let's see how a regular 3/4" Class 2 bolt would hold up:

Proof load grade 2 bolt: 55,000psi
55,000 * .2525 = 13,887 lbs
Shock load of 500lb tongue weight, 6" bump @ hitch ball: 11465 ft-lbs.
Shock load @ mounting bolt, assuming 24" total distance from c/l of ball to c/l of bolt: 22,930 ft-lbs
/ 2 bolts = 11,465 ft-lbs
Safety factor = 1.2

So while in theory, even a class 2 bolt would handle that jolt, it does not achieve the 2x safety factor. Let's look at a class 5 bolt:

Proof load grade 5 bolt: 85,000psi
85,000 * .2525 = 21,462 lbs
Safety factor = 1.87

Still not quite there.

And now for the grade 8 bolt:

Proof load grade 8 bolt: 130,000psi
130,000 * .2525 = 32,825 lbs
Safety factor = 2.86

And yes, we finally achieve the designed safety factor.

If you are comfortable with a thinner margin of safety, then use the cheaper bolts. Your hitch, your liability. But please don't say I recommended Grade 8 hardware for no reason, without calculating the stresses involved. I made similar calculations for all aspects of the hitch when I designed it, there was no guessing involved.

well my bad with the 7000lb tongue weight,. slip of the finger there,.

so as i said,.the grade 5 bolts are more than adequate in this application INMO,.almost twice as strong as needed,.
considering it has 12? bolts attaching it to the car?,. i was commenting about the above hitch which is not your hitch actually,. but you have done a wonderful job of deflecting the discussion back to your hitch,.and cleverly posting a lot of data pertaining to your hitch,.NOT the hitch that was questioned regarding the grade 5 bolts,.

How silly of me to be drawn into an argument regarding the wrong hitch,. well done, another opportunity for you to promote yours,.and to educate us with some good info regarding the area of a bolt head and nut etc,.

everybody wants yo use grade 8 bolts to "over engineer" as i said,.and also as you said,( safety factor of almost 3 etc,.)

guess it depends on what margin of safety each person is comfortable with,.OR how many bolts are actually holding something together,.

Nuff said,. engineer wins,.grade 8 bolts everybody,.best thing in the long run,.

phantom 309 wrote:

How silly of me to be drawn into an argument regarding the wrong hitch,. well done, another opportunity for you to promote yours,.and to educate us with some good info regarding the area of a bolt head and nut etc,.

I'm not "promoting mine". The thread IS about the hitch being offered that was based on my design, but I'm not selling it, nor do I intend to. I offered the design free to anyone who wants to use it without any pretension that it is the only possible design or even any better than any other design. Rabalc is the one who deserves all the credit for making them and getting them in the hands of those who do not have the resources. I think it is great that he took the initiative and contributed in such a positive manner to the community.

I specifically clarified that I was talking about the original topic of this thread, but just in case that was not completely clear to everyone else too, I was not talking about Skier's modification of an existing hitch using horizontal bolts and additional metal welded to the hitch.

I did so because your disparaging and sarcastic comments were not specific, followed closely on my comment about the need for Grade 8 hardware with the subject of this thread, and could well be construed to apply to the subject of the thread. I do not want anyone to be mislead. The hitch that is the subject of this thread was designed to be strong, simple to build, resistant to but tolerant of warping during fabrication without any special jigs, but utilizes grade 8 hardware.

buickwagon wrote:

I specifically clarified that I was talking about the original topic of this thread,

but just in case that was not completely clear to everyone else too, I was not talking about Skier's modification of an existing hitch using horizontal bolts and additional metal welded to the hitch.

I did so because your disparaging and sarcastic comments were not specific,

I think my comments were indeed obvious regarding the comment made about skiers hitch using grade 5 bolts which INMO are more than enough,.and so i made the comments i did,.

Then it was my fault that i didn't realize you were talking about your hitch,. my bad for not reading correctly,.

You guys crack me up. Good morning reading. We will be hooking up our Airstream to our class III hitch this morning. Sure hope the bolts are okay. Six months traveling and 9000 miles.
Dick

COL wrote:

You guys crack me up.  Good morning reading.  We will be hooking up our Airstream to our class III hitch this morning.  Sure hope the bolts are okay.  Six months traveling and 9000 miles.
Dick

9000 miles definitely put you in the expert category,..

So, has anyone got around to installing their rabalc hitch? I tried to install mine this weekend and the right side hit the exhaust pipe before it was close to lining up with the frame. I know the original plans were to fit an LT1 wagon and I have a TBI wagon....so better question, is there a difference in the LT1 and TBI passenger side exhaust exit?

You have a TBI with dual exhaust? I did not know that was an available option for the 91 - 93 cars. AFAIK, their is no exhaust on the right hand side of a factory TBI exhaust. Is it possibly an aftermarket system?

I do believe it's the original exhaust, it's a single exhaust exiting on the passenger side.

buickwagon wrote:

You have a TBI with dual exhaust? I did not know that was an available option for the 91 - 93 cars. AFAIK, their is no exhaust on the right hand side of a factory TBI exhaust. Is it possibly an aftermarket system?

TBI got a stock single exhaust that exits on the RIGHT side. However, it exits differently than the LT1 cars.

MalibuSSwagon wrote:

I do believe it's the original exhaust, it's a single exhaust exiting on the passenger side.

let me know if I can help in any way, different plate for that side or something?? I fit it to my 96 with no problems hitting anywhere, my resonators still on. shoot me a picture of interference, maybe we can come up with something

Cadet57 wrote:

TBI got a stock single exhaust that exits on the RIGHT side.

Oooops! Yeah, you are right. I'm not sure what I was thinking about there.

rabalc wrote:

let me know if I can help in any way, different plate for that side or something?? I fit it to my 96 with no problems hitting anywhere, my resonators still on.  shoot me a picture of interference, maybe we can come up with something

Seems like the hitch would need an extra inch of clearance on the passenger side to clear the TBI exhaust. This is not anyone's fault, the hitch was designed for an LT1 car and I bought the hitch knowing that, and assuming the exhaust exited in the same location on the TBI car. I can mock it on my car again and take pics, might take me a few days.

If you could get measurment maybe I could make a narrower one for you,and you could send yours on too someone else, I have had quite are people still wanting hitches

I haven't had the time to install the one I got, so I can compare how it fits between the 92 and the 96 tomorrow.

I went and did a test fit of the hitch on the two wagons.  It fit fine on the 96 obviously, but interfered slightly with the exhaust on the 92. The exhaust pipe is a little further inboard. The first pic shows how close I could get it to centered on the 92 (bolt head isn't centered).  The second pic is blurry but you can see where it touches the exhaust.  The final pic is from underneath looking straight up (front of car is towards the right.
It looks to me like if the square tubes where a little shorter and the bolt hole plates were a little longer it would fit both exhaust systems just fine.

My guess for why the two exhaust systems are in different positions is that they needed as much space as possible between the two pipes for the LT1 gas tank (which is smaller than the LO5 tank) so they moved the exhaust as far outboard as they could to squeeze every bit of fuel capacity possible.

I installed my hitch on the 96 today. without a welder I needed to come up with my own mounting method.
It went relatively painlessly, I was able to mount it with the rear 2 bolts, then drill the other 2 holes, then I took it off again and used a telescoping magnet to fish a 1-1/2" bolt and narrow washer into the frame and dropped it into the hole (the magnet held the washer onto the bolt fine). I had used my angle grinder to cut a slit into the bottom of each bolt so that I could use a flat head screw driver to keep the bolt from spinning until it had enough clamp load to hold tight on it's own.
I had to first ream out the bolt holes a bit on the hitch, the powder coating reduced the holes to slightly less than 3/4" so the bolts wouldn't fit. It was too dark by the time I finished so no pictures.

Glad to hear it went ok for you, any suggestions for modifications if I make more?

I think the only thing (other than clearing the LO5 exhaust) would be to drop the crossbar and hitch receiver by about 3/8 inch. My hitch receiver is pressed up against the bumper back plate. It held the the hitch off the frame a bit until I tightened it down. The bumper back plate sits a little differently on each car because it depends on the body and frame tolerances.
I'm quite happy with the way it turned out and I'll probably be trying it out next weekend.

Put me down for the next run. This is a must-have for me.

Here it is on it's maiden voyage with 1.5 cubic yards of topsoil.
It went great, I might turn my hitches upside down to raise the level of the ball. The car sits a wee bit lower than my truck did.

Yeah, I would flip the hitch. That load should be nothing for the wagon.

I'm interested in one of these. I'm in western Canada. When is the next batch coming?

I think I have need for 2 if you decide to build more, I think $100 is underpriced personally. My way of saying I will pay more.

Rabalc,
Check your PM's

I think a couple of us Boxie guy's are interested...

Thanks, Paul

Anything happening on more hitches? Would really like one!

I am still getting lots of requests for hitches, still very busy at work, 70 hrs last week. should be slowing down in a couple of weeks. I will consider running some more, this time I will offer no coating, last time they did not turn out as nice as I would have liked and it took a lot of time and running to get them done, and trying to wrap them for shipping was a nightmare. Trying to figure out shipping cost was also a huge chore. I would say the majority of shipping except the one to Canada was around 50 to 60 bucks, the trip to fedex is a 50 mile round trip. all that being said I think what I would offer is 225 flat price for hitch in raw form shipping included. For those in Canada it would be 250. I know it sounds like a pretty big jump in price, but I way under estimated the amount of time I got tied up in these, mainly in the shipping. Once again I know the hitch works on the 96, and I have no way of testing the fit of the boxies or tbi cars. Any one still interested let me know

I am interested. I have a friend with a Roady here in Portland as well who wants one.

I will confirm with him, let me know how you want confirmation. Here, PM, email, etc.

And I totally understand if you're swamped and can't do it, but hopefully we'll get enough orders to cover your time this time!

Thanks!
Ian

rabalc wrote:

all that being said I think what I would offer is 225 flat price for hitch in raw form shipping included.  For those in Canada it would be 250. I know it sounds like a pretty big jump in price, but I way under estimated the amount of time I got tied up in these, mainly in the shipping. Once again I know the hitch works on the 96, and I have no way of testing the fit of the boxies or tbi cars. Any one still interested let me know

That price sounds eminently fair to me. I know it cost me around $100 just for the materials when I built mine.

Can you incorporate the suggested changes in dimension? ie: 1" narrower and 3/8" lower. That would, in theory, accommodate the earlier models yet still fit the LT1s.

Sounds fair to me. Can you ship in 3 pieces, and i could get welded here? Maybe make it easier to ship?

shipping is easy if they are not coated, fedex takes them with no packaging. If I make any changes I will need to do them soon so I can test fit as I have sadly sold my wagon, will be gone in a couple of weeks a fellow member will be giving it a good home

Can ship it to Canada or to an address in NYS.

I haven't been on here in a while , but do you still have any tow hitches available ? The price is not bad at all considering the only options are rusty or nothing .

What we need to find now, is a member, with a Boxie, close enough to you, that can stop by for a test fit/measure it session. I know of at least 4 other Boxie owners looking for a hitch.

Any volunteers??????

I think your shipped price, unfinished, is a good idea, and very fair.

Thanks,

Paul

I still really need one if you can find the time.

autoarcheologist wrote:

I still really need one if you can find the time.

I just braved the elements to remove this draw tite monstrosity,.