Custom Trans Crossmember - Opinions?

I'm not quite done yet, figured I'd post up some pictures and get any opinions before I finish in the next few days. I've got a '99 with an AX15, just finished welding on frame stiffeners from Brian (HD Offroad Engineering).

I bought a new poly trans mount since mine had 200k miles on it, if you want to replace your stock mount on an AX15 '98-'01 don't order from rusty's! It won't fit! But I planned on building a new crossmember anyway since my old one was was rather bent from bashing it on rocks, so I don't care, it actully worked to my advantage. I've always had good experiences and customer service with rusty's before, and if I'd complained about this I'm sure I could have gotten full customer satisfaction from them, this is not the point of the thread so please don't get side tracked, I know some of you don't like rusty's but I do I've ordered from them plenty of times and think they're just fine.

I got a 4' x 2" x 4" box tube and a 4' x 1/4" x 3 1/2" strap, I was only able to get 14 gauge tube, if anyone knows any good scrap steel yards here in Vegas it would be appreciated, I can't find any (I just moved here though). The new trans mount had upper bolt holes to work either on the transmission directly, or on the factory relocation bracket to make it work (I'm assuming, I don't own one) on the same crossmember as the longer AW4, but the new mount is too short and a different lower bolt pattern to work with the stock crossmember. I decided to mount it on the trans directly, since this would make the bottom exactly level with the frame rail, giving me more clearance. Like this



This is the start of my crossmember. I plan on welding nuts to a plate attached to the exposed end of the 2x4 tube on the inside of the frame rail, with some small round tube cut down as spacers between the inner side of the rail and the plate, so the crossmember is bolted through the rail, not to the bottom of it like from the factory, so more strength bolted through 3 layers of frame(frame stiffy and rail) and 2 layers of crossmember, instead of 1 each, and no risk of bashing the bolt heads on rocks.



I welded the 1/4" strap to the bottom to reinforce and protect it, the section under the frame rail and the mount itself are particularly weak otherwise and I was worried about twisting. I plan on welding another 1/4" plate under the mount itself, and using a 1" hole saw around the mount bolt holes, that 1/2" of depth should protect the nuts on the bottom of the trans mount. Here's a picture of my current progress, I've got the 1/4" strap welded on the bottom.

Any suggetions before I finish it up? Think it'll be strong enough? Or should I modify anything before I finish up?

You were talking about not bashing bolt heads on rocks. From the looks of it the studs from your tranny mount are going to be hanging through the bottom of the x member fully exposed? I honestly dont see the point in upgrading the stock x member unless your running long arms off of it or building skid plates and a belly pan off of it. The stock x member is strong enough to do its job and hold up the drivetrain. This looks like a really simple and clean design though. Alot of people get to complicated and caught up in what they are building. I would at least weld a tcase skid off of it.

redrider2911 said:

I honestly dont see the point in upgrading the stock x member unless your running long arms off of it or building skid plates and a belly pan off of it. The stock x member is strong enough to do its job and hold up the drivetrain.

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I've seen plenty of stock xmembers munched up into transmissions.

Especially this past weekend where someone came down hard on it.

Granted it didn't rip off and he drove home on it.

Yea true, It is only sheet metal but Im saying I would be more worried about cracking my t case first and if taking the time to build a crossmember, add a skid to it.

redrider2911 said:

You were talking about not bashing bolt heads on rocks. From the looks of it the studs from your tranny mount are going to be hanging through the bottom of the x member fully exposed? I honestly dont see the point in upgrading the stock x member unless your running long arms off of it or building skid plates and a belly pan off of it.

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That's what I was saying about welding an extra plate directly under the mount, so the nuts will be recessed 1/2", the nuts are 3/8" tall and I'm trimming the ends of the studs so I'm hoping that's recessed far enough. I could make it slightly deeper if you think it needs it?

I just finished welding the long arm mounts to the frame, and they cover the forward stock holes. Possibly adding a skid plate to this in the future, but not in my current set of mods

MoparManiac said:

I've seen plenty of stock xmembers munched up into transmissions.

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Mine was bent up about 1/2" in the center, it was far enough out of line that my t-case linkage wasn't working right, I always had to crawl underneath to shift it

Looks good Matt....I think you have a good design.As mentioned , I agree with adding a TC skid plate.

Glad to hear You well in Vegas.

Nick

Everyone's suggesting adding a t-case skid, so I think I'll look into it. Ideas on how to do it? I'll need to measure to find out how far back it needs to cover, but I'd guess about 12 inches. How would I go about supporting that without a second crossmember farther back? If it was just hanging off the back of what I currently have, one hit could twist the whole thing.

I made a VERY solid crossmember out of 2x8x1/4 wall rect. tube. VERY simple, it took about 2 hours to make. The tranny mount sat on top of the crossmember just like factory. I just drilled 1-1/4" access holes to get to the 4 tranny mount nuts. I angle-cut the ends so I could get into where the factory bolt pattern was on the frame rails. Sat the whole Jeep on that crossmember a few times, with NO issues.

Your design looks good, but 14ga steel sounds thin to me. I would say it would be OK if you made a rect box with the 14ga and the 1/4 strap as the sides, and bolted the tranny mount like factory, but if your just planning on bolting through the bottom layer of 14ga, my feeling is it won't handle a hard hit.

Andy in Pa., two of my stock holes are covered, and one of the others has a broken bolt in it that I don't feel like dealing with, so stock mounting is not an option. And I'm trying to get some extra clearance since I have the chance

Here's my progress, ok maybe more pictures than I need for a small project like this, but whatever

I didn't get much done yesterday, after that visit to the dentist I just didn't feel like it. But today was good. I'll start drilling the frame tomorrow. I was looking at possibly mounting a t-case skid, there's just no way without another crossmember farther back. This member is farther forward than stock, so it would be a very long unsupported skid otherwise. It'll be a lot of extra work and right now I just need this Jeep driveable, my CJ5 is not the most reliable daily driver

I forgot about the driveshaft since I'd removed it months ago cause of bad pinion bearing. So I had to clearance that





And I finished up the holes for the studs, so I was able to bolt it up to the trans and see how it'll look. still need to trim the ends of the studs,they hang out about 1/8" from the bottom

After several very unproductive days, I finally got the frame drilled, the inner nuts welded on, and everything painted up and bolted it on. Turns out the very last nut was misalligned and wouldn't bolt together, so now I got to take it all apart to reweld that nut, maybe I'll finish it tomorrow.

redrider2911 said:

You were talking about not bashing bolt heads on rocks. From the looks of it the studs from your tranny mount are going to be hanging through the bottom of the x member fully exposed? I honestly dont see the point in upgrading the stock x member unless your running long arms off of it or building skid plates and a belly pan off of it. The stock x member is strong enough to do its job and hold up the drivetrain. This looks like a really simple and clean design though. Alot of people get to complicated and caught up in what they are building. I would at least weld a tcase skid off of it.

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every time i have wheeled with a stock crossmember, it got bent up enough to do one or more of the following:

make my driveshaft tear apart my 02 sensor wires
make my driveshaft hit my e-brake cable and sound like a machine gun
make my t-case slap against my floor on bumps
make my t-case slap my floor on hard throttle
make my t-case linkage not work
put my exhaust into my floor


anyway heres my old crossmember



2x6x1/4

i clocked my t-case flat and had no driveshaft clearance issues. had to pound up the floor a bit tho. it hung 1/4" below the framerails i later added a full belly skid and fixed my leaky transfercase

I like that design! That's close to what I was trying for originally but with the bolts through the rail. But my exhaust and driveshaft forced some modification, and I couldn't find any 2x6 1/4" tube.

I may clock mine and rebuild the crossmember again if I still have driveshaft clearance issues, I won't know for sure until I get my axle swap done and go flex it. Any idea if redrilling the transmission housing works for an AX15? Everyone I've seen that's done that had an AW4. I could go crawl up under the jeep but I'm not there right now

Is 3/16 wall heavy enough 2x6 for this kind of task?

Also ktm, I've seen write-ups for clocking the tcase. All in all, how long would you say this process takes. It doesn't seem like it would cost much.

I'm most concerned about front shaft angle since I have the shorter front shaft anyway, and when I go to a d44 front I'll be lifted about 6 inches and a lot of flex with my three link.

Done! I haven't put the front shaft back in, if it hits I'll clock the t-case, it doesn't look like it'd be a problem with an ax-15. I'll do some driving this weekend to test everything out, and flex it on that otherwise useless decorative rock in my front yard.





Got spacers installed between the frame and tube ends so I can tighten down the bolts properly

You should sleeve the framerail also.

DeftwillP said:

Is 3/16 wall heavy enough 2x6 for this kind of task?

Also ktm, I've seen write-ups for clocking the tcase. All in all, how long would you say this process takes. It doesn't seem like it would cost much.

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ive only done the aw4's but ive heard the ax15s have enough meat to do it as well.

i made a little tool so i can get my holes perfect. slid a piece of dom over the output shaft and a plate with a couple holes coming off it.

once the t-case is out and tranny hangin down a little its just drilling 6 holes through aluminum. real quick

Well, I've got the aw4 so that's no problem. I'd assume it's worth it though since you can then build a flat belly plate, right?

DeftwillP said:

Well, I've got the aw4 so that's no problem. I'd assume it's worth it though since you can then build a flat belly plate, right?

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its worth it if thats what you are going for.

i had a perfectly flat belly on my last jeep. also made a t-case linkage using 7/16" heim joints.

the reason the new jeep didnt get the same treatment is because i just wanted to get wheeling quickly and a bolt in belly skid was available to me.

the only real downside to keeping everything real high up is it kept a lot of heat under there. the ventilation for the t-case and cat suffered a bit and the heat was more easily transmitted through my floor. other than that its a pretty worthy mod.

just note some floor modification is needed. i got away with just hammering some room in there but it might be worth it to pull the carpet and re-shape the floor around that area