Front Subframe Replacement

[RallyX-SX/4]

I've been looking for an SX/4 for a long time, and this past spring, I finally found one that was a suitable start for my project.  I had to go all the way down to Columbus, Ohio, to get it, but I found a 1981 with a four speed and AC.  At some point in its life, someone had bolted on a Mustang hood scoop and applied a Shelby-esque paint job, so it was perfect for my rally car plan.  I currently race a 1989 Mustang in the Detroit Region SCCA RallyCross series, but I've been looking for something my daughter could race.

So far, I've removed the factory AMC 15 rear axle and sourced a Ford 8.8 with 3.73's, disc brakes, and 31-spline axles.  I found a used NP129 transfer case and a T5 transmission from a 1982 Eagle that are being rebuilt, and I got a 1998 4.0L from Grand Cherokee that I will have built into a 4.7L stroker using the original 4.2 crank.

The biggest issue I have with the car is rust.  I sourced a set of reproduction rocker panels to replace the disappearing original set, but the front subframes are also equipped with a lot of holes.  I found a clean set in Idaho, and I'm having them sent back here to Michigan, but I'm wondering how much work it will be to remove the originals and weld the new ones back in.  I've seen some posts about people doing some pretty extensive repair work to their rotted front subframes, but I haven't seen anyone completely replace them.  I'm afraid the ones on my car are too far gone to repair, because I don't think there's enough good metal left to weld patch panels to.  If anyone else has replaced a set, please let me know if I should attempt it.  Thanks.

[amcfool1]

hi, and welcome to the den! I just had the drivers side front subframe repaired on my 84 Sedan. It IS a lot of work, but doable if you are a good welder. AMC sub frames rust from the Inside out, so check carefully. The issue here is that the "frame" really  isn't a traditional frame rail, but about 3 sets of sheet metal body panels wrapped around each other. good luck, gz

[lonestar1947]

I bought a Kammback this Summer on Craigslist, the drivers floor board has rusted through, I'm afraid to look underneath!  I was going to part it out, but it's nice and original, and has a title.  Going to have it delivered this weekend, and I'll see how bad or good things look!

[RallyX-SX/4]

I made a little more progress taking the car apart.  One of the bolts that holds the engine cradle to the front subframe started to turn, but then the weld nut in the frame broke loose.  I had to cut a hole in the one part of the frame that was still solid to get a wrench on the weld nut.

Once that was done, I was able to remove the entire front suspension, so now I have much better access to the subframe.  As soon as I figure out how to remove the speedometer cable, I'll drop the transmission and the transfer case, and then I can get the whole car up in the air a little more so it's at a better working height.

I had a local shop quote rebuilding the front axle and upgrading to 3.73 gears, but they wanted $1,600 to do it.  I was able to get the gears, a new carrier, a Timken bearing and seal kit, shims, marking dye, and all of the axle bearings for $340, so I'm going to take a shot at rebuilding it myself.

The 4.7 stroker is well underway, although the cylinder head from the junkyard 4.0 engine had two big cracks through the valve areas of the middle two cylinders, so I had to bring that back and remove another one.  While I was there, I exchanged the 1998 intake manifold for a 2000 manifold, because the shop said they flow a lot better.

The 1982 T5 and NP129 transfer case I bought used will be rebuilt and ready to pick up in a few days.  The transfer case just needed new seals, but the reverse gear and shaft were damaged in the transmission, so I had to have them replaced.  I'm assuming that I'll be able to use any late 1990's vintage Jeep clutch with this setup, but if anyone has a recommendation for a good one, I would appreciate it.  The further I get into this project, the bigger it seems to become, but I'd like to have it ready to race by the spring (although we run right through the winter, and it would be a lot of fun in the snow), so I have to keep at it.  If there were more SX/4's around, I might consider holding out for one that needs less rust repair, but I think I'm committed now!

[RallyX-SX/4]

Here are some pictures.

[RallyX-SX/4]

And a couple more.

[amcfool1]

hi, I wish you well, but, that being said, IMO, that car is toast! Eagles, (or any other AMCs) never had a "frame" in the traditional sense. AMCs are ALL sheetmetal. That front "frame" rail that you are looking at is actually three layers of sheetmetal wrapped around each other. Stamped/ formed/welded together. Repairs CAN be done, but they are fiendishly difficult and expensive, unless you yourself are an ACE fabricator/welder. I just had my left side front frame rail repaired, from a small less than 2" hole, turned out the whole thing was bad. These things rust from the inside out, so sometimes you can't tell till its too late'. took two months and about  $800.  That said , go for it. good luck, gz ps, the guy who did this repair,IS an ACE fabricator, lifetime MOPAR man, and he said this was the most difficult repair he has ever done, and not sure he ever wants to try it again:)

[eaglefreek]

Based on some of the other modifications you are doing on the car, it sounds like you guys will be running in a modified class. What do they allow as far as frame and suspension mods in that class? You might come out ahead if you lop it all off and start from scratch, if allowable.

[RallyX-SX/4]

This will definitely be the biggest project I've tackled, but there are very few things in this world that can't be fixed if you take the time.  We will be running in the modified class, where there are almost no restrictions on what you can do with the frame and suspension.  The Mustang that I currently race has a full Griggs Racing suspension system, including a Panhard bar and torque arm in the rear and a tubular engine cradle, tubular A-arms that relocate the front wheels 1.5" forward, and adjustable coil overs all the way around.  I've only been doing Rallycross for a little over a year, and the modified class puts me up against some full stage rally cars, but it's what I had to start with.  Hopefully my driving skills will catch up.

Looking at the stock drivetrain in the Eagle, I just didn't think it would hold up, so that's why I chose the Ford 8.8 rear axle, which should easily hold up to the 4.7.  The Mustang would be a handful for my daughter to race, but I think the Eagle will be something that she will be more comfortable in.  With the 4WD, I just had to add a little more power and durability to make it competitive and to make sure it's fast enough for her to have fun with.

The engine, transfer case, and transmission will be ready shortly, so I really have to get to work on the rust repairs.  I just go the new carrier and the 3.73 gears for the front axle, so when the bearing and seal kit arrives, I'll be able to rebuild that too.  I'll keep you posted as I go.  I did see an SX/4 shell for sale down in Florida that already had a full cage in it, and I may have to reconsider something like that as an option, but it depends on what the replacement front subframe rails look like when they get here.  If they're solid enough, I think I can make this car work.

[eaglefreek]

Have you had the opportunity to see Leon Drake's VW pickup? I chatted with him for a little bit at a cars and coffee event and apparently his VW is at the very edge of the rules.

[RallyX-SX/4]

I found some pictures of his truck online and it looks like he has a lot of work into it, and it sounds like he's been doing well.  I'm not a supporter of the front wheel drive approach, but I race with plenty of people who've found ways to make them go fast.  I bought my daughter a VR6 Jetta with a 5-speed for her first car so she would learn to drive a stick, but after having to remove the engine twice, I decided that I would never own another FWD car.  Steering with the throttle is one of the great joys of racing and of growing up on a gravel road, and it just doesn't work with a front wheel drive car.

[RallyX-SX/4]

I removed the hatch carpet and to my surprise, found a lot of solid metal in the center, with only a couple of rusty spots in the corners.  Unfortunately, those spots are over the spring mounts, so they will have to be fixed.

[RallyX-SX/4]

I also found what appeared to be some middle school woodworking projects taking up some of the spaces in the hatch.  The interesting thing is that the carpet fits over them, almost as though they came with the car from the factory, although I've never seen anything like that in a production car.

[RallyX-SX/4]

The engine shop is bolting the cylinder head onto the 4.7 tomorrow, so the long block will be ready soon.  I also got the 3.73 gears, the new carrier, and the bearing and seal kit for the Dana 30 front axle, so I can tear into that if it rains this weekend.  It's the smallest differential I've ever worked on, but it seems like it should hold up.  I picked up the rebuilt T-5 and the NP129 transfer case, so those are now sitting in the barn ready to go as well.  All of which adds even more urgency to the rust repairs.  My brother's welder is now sitting next to the car, so I'm running out of excuses not to get started, other than swapping out the hatch on the Mustang before the race next weekend at Thistle Hill.  I can never seem to finish one project before starting another!

[eaglefreek]

Supposedly to go lower than a 3.54, you might have to do some special stuff. I think the Eagles front carrier is actually the same as the 3.73 and up carrier found in Jeeps. But, I personally don't have any experience, just going by what I've heard over the years with others trying it.