Let's revisit this topic... I've been putting this off for a few years now due not really needing a new rear suspension, the car being my alternate daily driver so I was avoiding down time, not having a garage and not being super comfortable with the strength of the kit I got. Now I know theres a million 4 link threads out there and I'm pretty sure I've read them all at least 5 times but I swear theres not a word on this topic. I'm sure most people aren't building 4 linked daily drivers so it might not be a big deal but I am which is why I'm apprehensive. I have the Paul Horton triangulated 4 link kit. The tubes are 1" od .188 wall dom and the brackets are all 1/8" thick. I got the larger of the two bushings, I think 3/4". I have a '51 Belair just for reference. My concern is A) with the tubing. I remember one of the go to guys on here said it would be ok but I'm wondering if he was saying that for a daily driver (as in highway at 70 - 75 mph, exit ramps at 50 mph and winding hilly back roads type driving) or just for just slow speed cruising. I have 81 which is pothole land at 70 mph and I'm not far from DC and Baltimore where the closer to them you get, the more nascar style driving becomes lol. B) with the brackets. I would think at a minimum 3/16" would be used if not 1/4". They just seem kind of thin to me, especially with the forces that'll be put on the top bars during the type of driving listed above. And C) the bushings and smallish bolts. I see Suicide Doors bars are 1.5" dom with .25 walls, their bracket plates are all .25 thick and their bushings and bolts are huge compared to mine. So what do you guys who daily drive with 4 links think...roll with what I have or sell this kit and go with the beefier parts?
Like a lot of parts, application makes a difference. The 1" , 0.188" wall DOM is pretty bullet proof in a light weight hot rod. Your Belair doesn't really fall into the light weight class. And it sounds like you are going to thrash it a bit. And then there is the peace of mind factor. So if I was in your position, I would probably go with a set of 1.250" or 1.500" bars and 3/16" brackets. The brackets are probably the only thing that you need, but the bigger bars let you run the bigger ends.
I used 1.5" OD, 0.188 wall seam welded tube for the 4-Link in my '62 Merc Monterey wagon. I also used 1/8" plate for the brackets. Lots of miles on the car, with no issues, but the brackets are all short and have added stiffeners. As a side note, I am a Validation Engineer at a Heavy Duty Truck Suspension manufacturer and we use 1.5" x 0.188" wall tube for all the torque and reaction links. If it holds up on a 23,000 lb axle weight rating suspension, it should be fine (read overkill) for a Belair.
I would suggest you contact Paul Horton (Welder Series) directly and ask his opinion. I've dealt with him/them before and they are good people. In my opinion, 1" DOM is extremely strong material. That being said, peace of mind is a good thing too. If it bugs you that much, you already know the answer ... sell the kit and go with a heavier duty product.
have used a range of stuff personally ....1" 6061 aluminum with .250 wall to start, bore to tap drill size and tap to needed thread size ( generally 5/8 nf. for a four bar application or panhard. for a heavier car with some nose weight; 1" DOM tapped the same. I have used 3/4" tapped tube in some applications, but with slightly larger tubing o.d. if a high stress deal. The disclaimer here is that I also have seen tube as small as 7/8's used in a lot of locator situations, but personally I've never felt comfortable going that light, mostly due to mine field roads and absurd power applications.
Food for thought. Potholes and other road impacts and hazards put very little energy into and create very little damage since they occur over a very small amount of time. Most of the energy and load is taken up by the springs, and in accelerating the mass of the car upwards (i.e the bump you feel in your hind parts). Suspension links see very little load and it's associated damage from these events. Suspension Links are meant to react cornering and braking / accelerating events. Braking events especially can cause very high, sustained loads. The amount of torque generated by a max brake effort can be very large, and is a function of the weight of the car, radius of the tire, and friction coefficient between the tire and road. The good news is that the links are designed to be in tension and compression under braking and cornering events. Even cheap A36 mild steel has a tensile strength of 50,000 psi which means a 1" OD, 0.125" Wall tube will support over 17,000 lbs in tension (assuming you properly welded the bushing ends on correctly) before pulling apart. The thing you have to worry about is the compression loading and buckling. A longer tube is more likely to buckle. That same 1" OD tube, at 24" in length will buckle right around 16,000 lbs, and that value drops in a non linear fashion as length increases. If designed and built correctly, the suspension links should see very little to zero bending load. Bending is what drives up the cross sections of the tubes.
Take a look at the beefy bars Art Morrison uses on his chassis. They look like at least 1.25 with bungs welded in the ends for the adjusters. I've used 100's of P&J 4 bars and triangulated 4 bars on the 28-34 chassis I've built over the years with no problems.
Thanks for the responses everyone. My "main" concern is with the top bars, bushings and especially the thin brackets being able to keep the axle under the car around the backroad curves. Some of them are 40+ mph curves but still kind of sharp.
I wanted to hop on and add some clarification... "all" the brackets are not 1/8". We use formed 10ga (.134” not .125”) brackets for the bar mounts on the frame, top and bottom. The rest of the brackets are 3/16" (upper axle tabs, lower formed axle brackets, and the lower frame brackets that the bar mounts weld to). We make street rod chassis parts - nothing leaves here that I wouldn't install on a street rod then load up my family to drive across the country... and have done. The question about bar size is good and valid. What we usually say about questions like this is if you're confident in the installation, we're confident in the parts. For decades, we built our four link kits with 5/8-18 adjusters and 1-3/8" wide bushings with zero failures... pro/street cars, big cars, little cars, didn't matter - they all used the 5/8" adjusters and small bushings. Then, once another company comes out with a larger bushing kit and claims all the other kits are too weak (we first heard of this in the mini truck market!), the small bushing kit becomes obsolete even though there were no issues. We feel the bar size is a similar issue... 1" bars have been used for (more) decades on every size of car and truck, driving hundreds of thousands of miles, and just because there's now a larger bar available doesn't mean the other bars are too small. But like someone else said, it's your car, and if you'd rather have a larger bar - that's up to you. For reference, I have 50k+ miles on my '32 coupe. It's a daily driver and has also been across the country on every type of road (and non-road) imaginable. It has one of our old four link kits with the 5/8-18 adjusters, small bushings and 1" bars. My '68 Dodge pickup is also a daily driver. I have pulled my vintage Scotty camper to Louisville and Syracuse several times with it, and the truck gets used for truck stuff like picking up patio stones, mulch, trees, etc. Check out our Instagram for more #thingsyoucantdowitha32ford. It has a newer triangulated four link with the 10ga brackets, large bushings, and 3/4-16 adjusters. I would have been fine using the smaller bushings on it too, but our inventory is 99% big bushing kits now anyways. Thanks for your business. I hope that you feel confident using our parts.
Just to clarify I wasn't knocking your product. I'm just building this car with the ability to drive with modern traffic so I want to make sure the parts I'm using are up to it. I have to admit I was mistaken. The axle brackets are indeed 3/16" so that changes things entirely. I apologize for the misinformation. I'll be using the front leaf spring mounts to mount the front of the lower arms to and using the kits angled upper arm brackets for the front but I may reinforce them.
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