I'm getting ready to install a Jag IFS on my 54 F100 and I measured from certain points on the front of the frame, meaning crossmember rivits just in front of the cab to the bolt that hold the front bumper on (furthest point on frame). I of course measured in a X pattern and one side is 1/4 of an inch different from the other side. I also did the same on the bed area of the frame and came up with it being off by 1/4 of an inch. Now I'm hoping this isn't a problem and common with these trucks but I'm not sure.

My question is if this is something I should be worried about before attempting my IFS install?
Thanks.

 

The Jag suspension should have enough adjustment to compensate for that small of difference. That's within tolerance, IMO.

 

Well, you could put it on a frame machine, but you could easily get it 1/4" out the other way. My son says that with full frame trucks on a frame machine, they use a tolerance of 1/8 to 1/4". Mine was off 1/8. You could probably install it the way it is, adjusting for the 1/4" when you mount it, but it's not that hard to get it perfect, or close to it. Make sure the rear axle is square, if not square it, and measure from that. The method for checking square is called "stringing" the chassis.First, put it on jackstands. Measure and mark the center of the chassis, then with a carpenters square or plumb bob, stretch a string along the center of the chassis. Use jackstands or some heavy object to fasten the string to. Alternately, after finding center, plumb to the floor, and make marks on the floor. A carpenters chalk line is helpful. You can now run perpendicular lines to check the rear axle square. Use either the carpenters square, the carpenters 3-4-5 method, or the pythagorean theorem to make sure the axle line is at right angles to the center line. Post if you need more info on that point.Also, post again if you need help with squaring the axle. With the rear axle square, measure your wheelbase forward to locate the front axle. Using the same methods, mark a front axle center center line and use that line to install the subframe. . What you're doing here is ensuring both front and rear axles are on the same center and parallel to each other, which ensures the truck will go straight. Btw, I'm assuming that your frame is just "racked", not twisted. Better check. Also, since you're doing the install, I assume your mech knowledge is similar to mine, so I didn't give you step by step, just the concepts. If you need more help, post again. One more point. If you leave the garage after setting up your lines, recheck everytime you come back. Trucks seem to move all by themselves.
Rusty

 

So 1/4 inch is not something that I should really worry about as far as putting it on a frame machine. To be honest I really would hate to go through all of that unless it is necessary for 1/4 of an inch off. I was hoping that was within tolerances but I really had no idea. I figured it would be better to go to the experts before making a difficult to correct mistake.

Rhopper, I think I get the jist of what you are saying about getting the suspension square. I'm planning to do both front and rear jag suspension swaps starting with the front. Over this weekend I will look into what you are saying and post if I have any problems.

 

lowtrkn2k When I put my Jag IFS in I measured 14 1/4 back from the back edge of the cross member and made a mark on the frame. That is where the center of the rear mount on the Jag IFS will bolt. My frame was 1/4 out of square as well. These frames are made to give some. I got mine to 1/8 and gave up. I squared the JAG rear and welded in the cross member. Be sure to check the wheel base. Mine is 113 1/2 should be 114 but that was as close as I could get it for some reason. Look at the pics in my gallery it shows the front and rear. If I can help give me a PM. Be glad to help if possible.

 

Rusty50F1, how did you get it back within 1/8? Did you take it to a frame shop? Also, did you measure 14 1/4 back from the transmission crossmember? Thanks for the measurements and information. I plan on working on it over this weekend as time will allow...this will probably turn out to be a busy weekend with the wife and kid...LOL.

 

Rusty50f1, I was checking out the pictures in your albumn of your install. What type and size steel did you use to make you front mounts? Also, the same question for your IRS crossmember? How low did that cross member lower your rear of your truck? I have looked at a couple of sites that sell the crossmembers and they are pretty expensive. The ones I've seen though are straight across and don't have that kickup that yours has (at least the ones for the trucks). I'm looking to have my truck sit level and low.

 

Measure carefully before "kicking up" the middle of the crossmember unless you are comfortable having to build a hump in the bed floor. I strongly suggest measuring the clearance available from the top of the frame where the newcrossmember will go to the bottom of the bed wood.

 

lowtrkn2k I used 3x3 square tubing for the front gussets. I ordered the rear cross from TCI,(total cost involved) $180 plus shipping. When you order be sure you they understand it is for a JAG rear. The first one they sent me was straight. It wouldn't work. So they sent me another one.(and let me keep the first one free) I measured 14 1/4 back from the cross that the radiator mounts on but mine is a 50f1. On yours you need to mark the center of the front axle on both sides and mark the frame. Some people with the year you have move the axle forward 2 inches to get the tires set more into the front of the fenders. Let me know if I have confused you. And I'll PM my cell# to you and you can call me. It's easier to tell someone rather than type it out.

 

OH I also used a come a long to pull my frame to get it to 1/8 inch. And I boxed in the frame front and back.

 

Thanks Rusty50f1 for the help. I think I understand what you are saying. I'll give it a shot over this weekend and see how it turns out. If I have any problems I'll post or PM you for advice at your convenience. The rear crossmember seems like a pretty good price. The cheapest I've found so far is about $380. TCI has a really good price. Do they sell any of the other bars needed to stabalize the IRS such as the pinion and radius supports?

 

When you order the cross for the rear It only comes in 0, 4, and 6 degree pinion angle. I ordered the 4 and set it to 2 when I tack welded it in. My tranny angle is at about 2 3/4. I may grind the tack welds and reset it to match. The only draw back to the rear is you have to make all your stablizers for the rear. But with the rear welded in the angle will not change when you rabbit take off. I'll try to find the post about the bars and give it to you. It's something you really need to read. Very interesting.

 

When you order the cross for the rear It only comes in 0, 4, and 6 degree pinion angle. I ordered the 4 and set it to 2 when I tack welded it in. My tranny angle is at about 2 3/4. I may grind the tack welds and reset it to match. The only draw back to the rear is you have to make all your stablizers for the rear. But with the rear welded in the angle will not change when you rabbit take off. I'll try to find the post about the bars and give it to you. It's something you really need to read. Very interesting.

 

Sorry about the double post! anyone else having trouble with this site?

 

http://www.uk-hotrods.co.uk/v2/garag.../me/page_1.php This is the site I was talking about. Lots of good info.