LRT_frame

Frame Plan...

This page is to document the various elements of the planned changes to the Little Red Truck's frame. Think of this as practice for the OldSub...

First a few notes about what I'm thinking. The Little Red Truck is intended to my my wife's daily driver. I don't have any illusions that she will abandon her cute little wagon to drive this truck all the time, but I want her to feel comfortable that this truck can get her wherever she wants any day she likes, and do it, if not in luxury, at least feeling safe, and comfortable.

I believe accomplishing those goals means updating the truck with modern power, automatic transmission, power steering, power disk brakes and independent front suspension. Driving the OldSub I can tell you that speed bumps are rough, and even my driveway can jar one's teeth a bit. Now those obstacles are noticeable in a modern car, but with the leaf spring solid axle in the front, and tired 'truck' springs in the rear, it can be unpleasant. I'd like this old truck to ride as nice as my '72 Chevy pickup. In some ways that's not asking much, but the '72 handles speed bumps without pain and is just a whole lot easier to drive.

So what do we do with the '54? Well my thinking is that this truck is really a car with a box. I do not plan to ever use it to tow another vehicle, not do I expect to load gravel or a big block or anything heavier than groceries in the back. I plan a beautifully finished wooden bed and expect to require people to remove their shoes before climbing into the back.

With those elements as the basic criteria, when I was offered a '78 Monte Carlo, complete and running, I figured I had the modern parts for this truck. This car was built after I graduated from high school, which makes it modern, since I refuse to believe it could be called old. It has a 305 V-8 and at Turbohydro 350, please the rear is 2.29 with positrac. The posi is a plus, but since I've seen the day when an empty pickup with no load and an open read would not move because it lost traction, I'm happy with the posi.

I've removed the body from the car, and have the frame sitting in the yard (Monte Carlo Day). The next step is removing body and box from the pickup and start melding the two frames together. My plan is currently a little outrageous. If you've read Tex Smith's book "How to Build Custom Cars" he has a section about modifying a later perimeter type frame to fit under a '40 Ford or similar car. What they do is remove the part of the frame between the axles that swings out to the perimeter and replace it with rectangular tube. Its similar to subframing, but tosses the entire original frame.

If you subframe one of these trucks, you end up cutting the frame off at about the firewall, and then have to build a new mount for the radiator and front sheet metal. Lots of guys have done it an though its not easy, its done.

Its not uncommon to update the rear leaf springs and mount the rear axle that way. Others will buy a four-link kit to mount the rear. The Monte has a four-link already.

So instead of subframing, and doing something else at the rear, I figure subframe both ends, and take advantage of matched suspension components that I already know give a nice ride (Yes, I drove it fast over some speed-bumps before buying it).

Now I could use the rectangular tube approach and described in the Tex Smith book, but if I instead use the channel that makes up the existing frame I avoid having to create cab and bed mounts. And I don't have to create mounts for the running boards.

<< In this picture you can see how the frame narrows to go between the wheels. Once the bend is complete, the frame is 46.5 inches wide and stays that width until it bends out behind the wheels. At the bend in front you can see the brackets that hold the front of the longer links. This area is almost flat on top. I'm thinking the existing frame can be cut and shaped to lay on top of that area, and be joined to the frame as it raises to go over the axle.

The pickup frame is about 44 inches where it would meet the Monte frame. It widens to 46 inches just behind the axle.

Comparing dimensions with the frame, and no body and 14 inch wheels, against the truck with body and 16 inch wheels, it appears this would lower the truck just a couple inches in the back.

I see cutting off the Monte frame at about the point that the turn back out occurs, and rejoining the rear of the pickup frame to provide bed and bumper mounts.

<< This shows what we are dealing with at the front. I've not measured all of this yet. The existing pickup frame is 28 inches at the axle center line, and wider further back. I need to determine where this frame can be cut, and how wide the pickup frame is at various points, to make sure we match them up correctly.

Since this subframe is one of the ones everyone recommends I'm sure it can be make to work. What I don't know is exactly where the various cuts and welds should be, nor have I worked out how high its going to be.

These are important things...

The image below is scanned from the Chevrolet 1954 Pickup Assembly Manual. This diagram shows the dimensions of the frame, including important figures such as width at the firewall, and width at the rear axle centerline. I wish I could find a diagram like this for the Monte Carlo frame...

So what's next? I need to measure some things, perhaps make some templates to make sure things will fit, and I need to make decisions about how high I want this truck to sit, and what size tires and wheels to put on it.

I want the stance to be low, but not so low its a problem to drive in the real world. So its a little lower than stock, but not radically lower. Remember this is my wife's daily driver. To finalize the stance I have to decide about wheels and tires. I want to use the same tires that are on the OldSub, which are BF Goodrich 235-70/15s. One reason to use the same tires is that I have some I can use for measurements.

Next steps are to remove the engine and transmission from the Monte frame to improve my ability to measure things. With that done I can swap the wheels and tires from the Sub onto the frame, and get some measurement that may not correctly show how the final wheels will act when turning, but which will allow checking ride height and getting a feel for the backspacing needed.

I also need to clean all the tubes and such off the Monte frame and to facilitate making some templates so I can see how the frames will meld together.

And of course, it will help to get the pickup frame cleared off too, so I can make measurements on it too...

And that's the way it is, at lunch on April 1st 2003, as my notebook battery is failing and I need to save and quit....

April 6,2003
Measurements are important.

I've learned that Chevs of the 40's makes a wheel that looks like a Chevy Rally wheel, and takes an old Chevy pickup hub cap. They make the wheels in several versions, including chrome wheel with painted center. And most important, they can make the wheel in a 2 or 2.5 include backspace, which moves the wheel away from the inner fendor (bed in this case) far enough even using my Monte Carlo axle.

BF Goodrich says the tires I've chosed are 9.1 inches whide if mounted on 7 inch wheels. The distance from inner fendor to inner lip of fender is 11.5 inches, so more than 2 inches clearance allows a full inch both inside and outside. If the axle is 58 inches, and we use wheels with 2 inches backspacing instead of the 3.5 currently on the car, the tires should be about 1.5 inches away from the inner fendor, and if the width is 9.1 inch, 9.1 plus 1.5 is 10.6. My approximation of the width in the fender well means I'd have .9 inch on the outside edge of the tire. Based on similar wheels and tires on the OldSub I'm believing that is going to work just great.

I've not yet determined what the front must be, but since the Monte IFS is several inches narrower than a Camaro, I'm expecting to find that I could run the same wheels on teh front and have plenty of room. I need to measure the fendor opening on the truck, and measure the width of the Monte to be sure I know what I'm doing....

Last updated: December 31, 2006