So I packed up my east coast digs and headed west to San Marcos Ca. to work with Arie Vanschyndel at JDAmfg. First on the plate was doing a notch and bag job in a 1953 Belair. Then we cut out the notch kit
Lookin good Big Nick! Glad to see you are getting settled in. Gotta love that plasma cutter table. My ears are ringing looking at that second picture! TP
Ok I slacked on the some of the pictures but here they are, we left the trunk open for the show at Chicano Park to show the work but the car is back in the shop now to have the trunk floor put back in so more to follow. We pulled it all out and did all the finish welding:
While this is some really nice welding and fab work (Kudos to you!) this is destined for a failure. The design does not accounted for any twisting motion during articulation. The front of the arms appears to be a urethane bushing, they will not allow much twisting. The arms themselves are square tubing that also resists twist. The mounting to the rear axle is via a single U Bolt and this is going to be that weak point. During bump or going in a driveway on an angle, The axle is going to lift on one side, this creates a need for the trailing arm to twist and since in this design it can't, the flat pale on the axle is going to try and pull away from the square tubing which will bend or flex the U Bolts eventually causing them to fail. It is also not going to allow much movement - I can see it lifting the inside wheel right off the ground going in and out of driveways. The rear roll stiffness is going to be extremely high.
Two questions, why remove the entire trunk floor? instead of just the notch area (above the rear end) was it rusted out? what size are the astros and tires.
THe entire truck floor is being raised 2" so the tank can be mounted in the stock location and appear stock. The wheels were 14s, I am not sure of the tire size.
Don, I did not design the set up and cant give you an answer either way about it but I will turn Arie onto your post and he can answer the question. Not speak for him but he was building trophy trucks for Camburg Racing for the past 10 years and involved in developing suspension kits for them so I am sure he built it this way with reason but I can understand the concern. I can say that we did have the car aired up on each bag in the rear and drove the car with out any issue but like I said that is all I can say, I am completely new to this.
Don, I spoke to Arie, this is what he told me: The front of the arms are on bushing so they have some give and the amrs themselves are very long so alittle give goes a long way. We cycled the rear (like I said) and it didnt resist reasonable twisting. Round tubing actually resists twisting, not box tubing, not that that comes into play here. The U bolts are also much larger than stock and grade 8. I understand where Don is coming from in theory but again it just doesnt come into play on this car. The car has a total of 7" of travel. This isnt a new design, its a 70's truck suspension on a 50s car, and I havent seen it fail on any 70s trucks even with 35" tires and with a lot of horsepower and off road abuse. I appreciate the constructive criticism, its what keeps us on our toes and helps keep the CRAP off the street. When I get the car back I will do a video showing it articulating. I hope this clears things up and please if you or anyone has any other questions please do not hesitate to ask.
There is a big difference between what you guys have done here and the original GM truck style (which started in the 60's, not 70's) The GM "truck Arm" design, which is still in use by NASCAR today, triangulate the rear arms (in otherwords the fron tof the arms point inward towards a common point, these appear to be parallel. That is a HUGE difference in the loads that are placed on the arms, amounts and bushings during articulation. They were also made of I Beam style material and this is mandated in NASCAR to this day, for very good reason. While you are right that Square tubing is less resistant to torsional twisting than round tubing, the Moment of Inertia is still quite high and square tubing is generally not going to be spec'd for anything that requires repetitive twisting motions. This is another one of those cases where you MIGHT get away with it, but it is not a good solid engineering design and should really be rethought. And Thanks for having an open mind and listening to other views, something more folks on here need to do at times.
I hear what you are saying and I will pass it along. Like I said, I am not as well versed in suspensions so I can not comment either way.
The Jalopy Journal
