Ripped the crossmember

[ironadict]

OK well my truck has been pulling some weird stuff on the freeway. Kind of swerves on its own and can be a little scetchy at times. So i had the best guy around align it, got new shocks and a stiffer bag up front. It rides better but still moves around on freeway.
Checking out my chassis I noticed the trailing arm Xmember is split on the bottom and pulled back. Must have caught a pothole or something when riding low. The bottom is pulled back so I know the frame rails must be pulled in on the bottom.
My first question is could this be the cause of my steering problem at higher speeds (55 and up)?
My second question is what crossmember do you recommend for replacement. PB or cpp or other? My exhaust has already been tucked up so I'm guessing it'll have to come down for it to be installed. I have a 2 piece drive shaft.
Third has anyone installed one without removing the cab?
Hope to order one of these soon and get this swerving prob out of the way.

[Bagd72Chevy]

That could definitely be your problem. As the crossmember flexes the rear axle moves around. I put the CPP one in my truck. pretty easy if you're not concerned about ruining the stock one, which you probably arent at this point!

[davepl]

Well, even if its not the cause I wouldn't be driving it over 55 until that was fixed anyway! But there's a good chance it's the cause, I'd say.

Remember GM built 875,000 of these in 1972 alone and it was a 6 year run. That means there are a lot of old factory cross members out there, but the repops might be decent too. Unless it's bagged/chopped/lowered or whatever you kids are doing these days and requires a special crossmember for ground clearance or exhaust routing.

Just a random thought, and I'd check with a frame guy first, but: if you could get a bottle jack in there and place to seat it, I wonder if forcing the crossmember out straight again might push the outer rails back into position.

I guess you'll know when you try to install a new one whether it fits or not!

[lolife99]

Get a Porterbuilt crossmember.
http://pbfab.com/63-72-tubular-fully...rm-crossmember
Were the holes put in the original crossmember, (for the exhaust), reinforced with pipe or tubing?

[Xeen]

While the PB piece is superior the CPP piece is more bang for your buck.
The PB piece is $249 with no carrier bearing.
The CPP piece is $279 and includes the high quality Billet Carrier bearing.

PB http://pbfab.com/63-72-tubular-fully...rm-crossmember
CPP http://www.ebay.com/itm/19631972-CHE...-/281263897807

[Turbo1dr]

By the way that looks, you've been riding around like that for a while. Look how much of it you've grounded off already making sparks fly out.

[ironadict]

Thanks for the responses. Yes my truck is bagged that's why I'm looking into these crossmember because the stocky lays too low. I have a custom triangulated 4 link so the stock trailing arms or mounts aren't used any more.
I've never dragged this part for sparks. That's what my trailer hitch balls are for in the back. I originally grinded about an inch off the lip so it didn't sit so hard on it. This happened from rolling slow down the strip and one of these F'd up california roads clipping it.
I do like the fact that the cpp comes with the bearing and mount so far.

[lolife99]

If you have a triangulated 4-link,... the trailing arm crossmember has nothing to do with your problem.
It just mounts the driveshaft carrier bearing.
I've heard these 67-72 frames are too narrow for a triangulated 4-link to control side to side movement,... but don't know from actual experience.

[jjzepplin]

Do you still have a panhard bar?

[see ten]

Yes... that crossmember can be changed without removing the cab.
We installed an ECE xtreme drop crossmember in my 72 when it was lowered.

[ironadict]

Nope no panhard bar. Seems to be pretty solid with the 4link. I just figured maybe this crossmember twisting up my frame rails can be the cause. Guess ill replace it anyways and keep looking for the cause.

[Blown06]

I know you had it aligned but have you thought about a caster angle issue? Not sure if you are running homemade control arms or z'd frame or what, but it was just a thought.

[ironadict]

I got it aligned twice. Once at les shwab (garbage) then I took it to a highly recomended shop in my town that deals with a lot of old schools. He did go through the caster. He spent like 3hrs adjusting my front end and it helped a lot. However still does the weird sh*t on the freeway.
I have cupped control arms and drop spindles up front. Rode straight for a while with the set up so I do t think that's it. I guess next stop is to pop the brand new upper ball joints and see if they are getting too stressed when dumped.

[davepl]

Originally Posted by ironadict

Nope no panhard bar. Seems to be pretty solid with the 4link.

Does it though? I mean it might be hand, but a truck in freeway ruts at 60mph is a lot more force than anything you can generate. It's not really the walking side to side that's the problem, it's unwanted rear wheel steering.

Imagine that one end of the axle manages to get even 1/4" in front of the other. That's going to noticeably steer the rear end, at least at speed. You'd never notice it at slower speeds though. That's why I bring it up.

Normally you need a panhard bar unless the four links are "triangular" enough to center the axle well. This is what the Chevelle has.

If at least the upper links aren't directedinboard pretty aggressively, you need the panhard bar like the Impala has. Random trivia: GM was so cheap that if you ordered a Biscayne (or maybe it's with all 6 bangers) you only got 3 links, not 4.

The coil spring trucks don't have a super-aggressive angle to them, but they're loooong, so they still step in by quite a distance.

I know nothing about your setup, just speaking in generalities.

[72MARIO]

How do you set your ride height ? Even a 1/4" lower or higher can mess with your geometry.

[ironadict]

Yes I here you about the rear wheel steering. When it does it it does kind of feel like its steering in the rear. The thing is though that the rear set up is the better part of 10 years old and its never done this before. That's why I'm looking for recent mods and events.
My 4 link is a much greater angle then the stocks. I would say close to 45*. I also replaced all the bushings in the traingular bars. Not the straight bars yet though.
I do think your on to something though with the rear end steering cause when I replaced the bushings I noticed the holes on the arm mounts were a little ovaled. Did some little burn outs on the 4th of july while dragging the rear. I can imagine this put a lot of stress on the holes the bolts go through as the right side of the axle tried to go forward and the left wanted to go back or stay in place. Sounds good anyway
I have to pull one of these off soon to reinforce a crack so I'll look more into it. I hope this is it. It would be a paint to re do the whole rear but at least it would be solved!

[jjzepplin]

Hmm. Crack in one of your links? That means it IS stressing quite a bit. That's the reason I brought up the Panhard bar or lack there of. GM felt it was necessary so removing one and not replacing it could be your issue.
Look up the "Watts Link". A fine replacement for the panhard and looks pretty cool too. Took me a minute to figure out how it works, But then I thought it was nothing short of genius!

[ironadict]

Originally Posted by 72MARIO

How do you set your ride height ? Even a 1/4" lower or higher can mess with your geometry.

Well when we aligned it we used a tape measure cause at the time I had not put in gauges yet. So we set the ride height and aligned it. Then I installed gauges to better know where it's at. But the last 2 years of owning the truck I just used the old feeling ti out method.

[ironadict]

Originally Posted by jjzepplin

Hmm. Crack in one of your links? That means it IS stressing quite a bit. That's the reason I brought up the Panhard bar or lack there of. GM felt it was necessary so removing one and not replacing it could be your issue.
Look up the "Watts Link". A fine replacement for the panhard and looks pretty cool too. Took me a minute to figure out how it works, But then I thought it was nothing short of genius!

The crack in the link was because the original installer thought it was ok to put the bags right in the middle of the triangulated bars (get good lift)and instead of using a bag plate on the bottom just drilling THROUGH the middle of the bar that gets the most stress and mounting to the center bag mount there

I like the idea of the watts. Does it restrict the lift at all?

[Blown06]

Watts link will not interfere with your lift. It is designed to keep your rear end perfectly centered no matter the height.

[jjzepplin]

I have never had one but I plan on one for my dropped Blazer. I have seen them on racing vehicles and I think you would not want to move the suspension much but it looks like it does not restrict any movement up or down but keeps the rear centered no matter where it sits. Ideally you would want this about how the pic looks at ride height. You might look up the "make it handle" thread and take a good long read. Or you could start a new thread for the watts or search it as well. Nice piece.

[ironadict]

I looked it up. I saw a youtube vid of a "longtravel" watts link https://www.youtube.com/watch?v=-P2CtC0rCfE. I definitely think this thing is in my future. Especially if I can set it up to not restrict my lift.

[72MARIO]

Well unless you get your ride height the exact same height every time you will never get a truck to handle properly. If your rear right corner is 1/4 lower than the front that greatly affects your caster.

[bs46488]

Can we see a pic of the rear setup?

[72BigBlockBurb]

Originally Posted by davepl

Does it though? I mean it might be hand, but a truck in freeway ruts at 60mph is a lot more force than anything you can generate. It's not really the walking side to side that's the problem, it's unwanted rear wheel steering.

Imagine that one end of the axle manages to get even 1/4" in front of the other. That's going to noticeably steer the rear end, at least at speed. You'd never notice it at slower speeds though. That's why I bring it up.

Normally you need a panhard bar unless the four links are "triangular" enough to center the axle well. This is what the Chevelle has.

If at least the upper links aren't directedinboard pretty aggressively, you need the panhard bar like the Impala has. Random trivia: GM was so cheap that if you ordered a Biscayne (or maybe it's with all 6 bangers) you only got 3 links, not 4.

The coil spring trucks don't have a super-aggressive angle to them, but they're loooong, so they still step in by quite a distance.

I know nothing about your setup, just speaking in generalities.

I'll agree here. I've had a number of Corvettes over the years and never had any type of tracking issue. PO of one of my latest cars must have banged a curb or something and didn't replace the left rear tie rod end...Bought the car anyways...but when you floored it, the slight shift of that tie rod end (we are talking VERY slight) would cause the car to push sideways. I think this may be your issue...the four-link is allowing just a little shift that translates into BIG issues at highways speeds.

I know a Corvette and a pickup are much different beasts suspension-wise...but I see some similarities in what you are describing and what I experienced with a shift in rear tires. I'm shocked that the "recommended" shop didn't mention your torn cross-member. Good luck!