Engineering an easy way out?

GPster · November 04, 2005, 01:18:58 PM

My project ('51 Chevrolet truck cab on a '53 chevy car frame) needs a little tweaking to get the steering column to fit in the depression in the bottom of the truck dash. When Chevrolet made the "Top Hat" style frame they used reinforcement so that you wouldn't crush the frame when you tightened up the bolts holding the steering box. The box was originally mounted using 3 Grade 5 fine thread 3/8" bolts. I can get the column where it needs to be without doctoring the frame stiffeners using 5/16" bolts and a couple of exrta washers for spacing. My Dorman book shows 5/16" grade 8 fine thread bolts kind of over-lapping the low end of the strength of 3/8" grade 5 fine thread bolts so I'm looking for an opinion. The car chassis was steered by a psuedo "drag link" going to a "bell crank and the box has the stock full length column so it is also supported by the mount under the dash. Because of the "drag link" the bolts would fail in shear rather than in stretch and the dash mount would add positive strength in that direction. I thought of trying to go one better and using metric bolts because #8s are a little beefier than 5/16" but I got lost trying to convert their strength to our torsion. All of the original enginneering is overdone for what it's use will be now in both weight and tire size but I do have a tendency to overlook the obvious when I concoct strenuous studies. Opinions (a dangerous word to use)? GPster

enjenjo · November 04, 2005, 04:39:20 PM

If I understand correctly, you are putting washers between the frame and the steering box. In addition, there are more washers behind some bolts than the others. Correct? Why can't you still use 3/8" bolts? I don't think the reinforcement plates fit that tight on the bolts.

GPster · November 04, 2005, 06:20:37 PM

Quote from: "enjenjo"If I understand correctly, you are putting washers between the frame and the steering box. In addition, there are more washers behind some bolts than the others. Correct? Why can't you still use 3/8" bolts? I don't think the reinforcement plates fit that tight on the bolts.

I need the steering column at the dash to move in 1 1/2" and up 2". There are 3 bolt holes at the box arranged like a "V". With 1/4" under the front bolt and 1/8" under the center bolt with nothing under the back bolt the column moves in far enough but the coming up 2'' requires all 3 bolt sites to move a little. Just replacing the 3 bolts with 5/16" bolts let it happen but I didn't get far enough to see if using 2 or 1 smaller bolt would allow it. I was just trying to get it in the right place so I could see about building the floor and I don't want to use a smaller steering wheel because I'll need the leverage to steer. Maybe when I get into it a little closer I'll find that the re-inforcement between the frame sides has a bigger I.D. than the holes in the side rails and I can do some work with a "rat tail" file and make it work. Sometimes you look for the easiest way first. GPster

Sean · November 04, 2005, 06:34:40 PM

Grade 8 bolts are hardened, and they will break, where Grade 5's would more likely bend. If something happened to the steering, I think I would prefer that the Bolts got bent, instead of breaking and possibly letting the steering box fall free of the frame.

Of course, if you hit something that hard, the steering box coming free would probably be the least of your worries anyway...

tomslik · November 04, 2005, 06:54:49 PM

Quote from: "Sean"Grade 8 bolts are hardened, and they will break, where Grade 5's would more likely bend. If something happened to the steering, I think I would prefer that the Bolts got bent, instead of breaking and possibly letting the steering box fall free of the frame.

Of course, if you hit something that hard, the steering box coming free would probably be the least of your worries anyway...

might even be prefered...
might not go ALL the way thru your chest if they broke...

enjenjo · November 04, 2005, 08:01:30 PM

I'm sure you can flie the holes out 1/16" with no ill effects. And you still want grade 8 bolts in it.

GPster · November 04, 2005, 09:17:15 PM

When I run out of ideas it's good to use the ideas of somone else. The only place the bolts are tight is the mounting bosses on the steering box. As beefy as those ears are and the fact that they aren't threaded but rely on a through bolt, I'm sure that they can stand some clearancing. I don't know how big the holes are through the frame sidewalls but they are considerably larger than 3/8" bolt size. On top of that the I.D. of the support piece inside the frame are consideably larger than the hole size. I may be able to sneek it back together. And thank you for the comments. I had completely forgotten about the fact that there is no collapseable column and this thing could end in my chest. I was concerned about not being able to steer and hurting someone (else). GPster

GPster · November 05, 2005, 09:14:22 PM

News for today. I moved the steering box up and out of the way. The holes through the side of the frame railsl were probably 13/32"so I inlarged them to 1/2". They were still not as large as the I.D. of the holes in the bracing inside the frame. I used a little bailing wire to hold the column against the bottom of the dash like I want it and all three of the stock 3/8" bolts went in. Also the amount of spacing I need between th box and the frame looks even less, like 1/8", 1/16" and none. Just a little confusion though. Frank, you suggested going with Grade 8 bolts. The original bolts were only Grade 5 and the original bolts can be used again now. Do you think I should up-grade the bolts? what about the breaking rather than bending suggestion? GPster

enjenjo · November 05, 2005, 10:47:01 PM

Go ahead and use the original bolts. They will be strong enough.

Grade 8 bolts being brittle is an old wives tale. The forces needed to bend a grade 8 bolt enough to break it, far exceed the force needed to shear a grade 5 bolt. Some time back I did an analysis of bolt strength, and the grade 8 won hands down. I think there was a post on it here.

Crosley.In.AZ · November 06, 2005, 09:50:01 AM

Joe,

sounds like you got it figured out.

GPster · November 06, 2005, 11:36:17 AM

Quote from: "Crosley"Joe,sounds like you got it figured out.

Isn't it amazing how much better your trifocals work with some natural light when it's early enough in the day to have the strength to get down (and be able to get back up) to within 17" of what you're working on. Now I can be content that The problem is solved and I learned something too. GPster

GPster · November 07, 2005, 08:17:26 AM

At the start I must've been looking at this with my left eye. Now that I have the holes inlarged so the stock bolts will go through them I dug through my parts and found the stock column/dash mounts. With them in place and the back steering box mount bolt in place and finger-tight the spacing looks like it can be done with washers. It looks like 2 washers between the box and frame at the front boss and one washer at the center boss will do it. OK, you can all relax now and get ready for the next problem I imagine I have. GPster