Crossmember/frame differences (a rant)

[shifty]

Ok, so, I jsut want to have a little "Mythbusters" session about frames and crossmembers.

There are two major differences that make a '73-87 front crossmember (possible 71-72 as well) NOT a "direct bolt on" to a '68-'68 frame.

Back story: I picked up an entire '73-'87 front clip and rear end recently to swap into my '68 from another board member/friend. I got a killer price from him, and it's in great shape, so I can't complain now that i'm finding I can't easily use it. I want all of you to learn from my experience.

I cannot even BEGIN to tell you how many different times I read all over this forum that this would be a direct bolt-on swap, that the '73-87 front crossmember would fit like a champ in my frame with nothing more than "warbling" out one or two holes a bit. THIS IS ABSOLUTELY NOT TRUE.

I'm here to set the record straight after spending 5 hours today taking off brake lines, unbolting parts, cleaning up suspension and brakes, pulling off wheels, and finally swapping to my mid-70's crossmember.

Here's the problem:

1) The framerail on '73-87 trucks is 6" tall at mid-crossmember. The framerail on 67068 trucks is 5.5" tall at mid-crossmember.

This matters to me because I'm using the ECE GenIII engine mounts for my LS1 swap, and they incorporate the '73-87 stands, so while they are a perfect bolt-in for the '73-87 frame+crossmember, they require drilling with the 67/68 frame using a 73-87 crossmember.

2) There are four bolts that hold the crossmember to the frame on the side. They use a completely different pattern in 67/68, so when you go to bolt that 73-87 crossmember to your frame, two of the four holes line up perfectly, one hole needs to be "warbled" out to make it work, and you will need to completely drill a new hole for the fourth bolt. Be aware. The other pair of three holes on the bottom of the framerail seem to work like a champ. On a positive note, the access holes for the press-in studs for the upper control arm are perfectly accessible .

Anyway, that is all for my complaining for now. I just wanted to share my experience with others so you can learn from my mistakes.

I know some guys would be like, "Dude...just modify it!" But you know what? I already modified my old one and it was working. I swapped to 73-87 so my ECE GenIII mounts would fit like a champ...I dunno about you, but I don't want to do work I've already done, and swiss-cheese my frame in the process

[CG]

Ive never done this, but I have read several times that one hole needed elongated and one hole needed to be drilled.

Must be more than a pain in the tukas to do than it sounds.

[shifty]

It's not really a pain at all. I'm sure it's actually fairly easy.

This is my beef:

My reason for upgrading to 73-87 front crossmember were simple:
- beefier U-bolts for the lower control arm
- already have the proper bolt pattern drilled for my ECE GenIII mounts, direct bolt-up
- the upper control arm bushings are rubber vs. metal that mine have stock
- the arms are a little bit beefier
- My original '68 crossmember was already drilled and fitted for my GenIII mounts

Now, I still walked away with $150 in parts, so I'm not upset by any means, nor did I "lose" money in this case (I can bounce back).

I am going with ART tubular ams b/c I'm bagging the truck. This negates the ruber vs. stell bushing situation, and they're just as beefy. The framerails are different n my '68, so I'm swapping drilling the crossmember for drilling the framerail. It's a lose-lose situation IMHO.

I dunno, just sucks. I don't mind, but I want to make sure others know that this isn't a direct swap, because I'd read it was one too many time.

I'm kicking myself afterthis. I should have listened to board member uncle all this time. Tim, if you are reading this, please slap me next time you talk to me or see me.

Oh - but hey - can someone with a 71 and 72 truck measure the height of the framerail at mid-crossmember mount and tell me if it's also 5.5"? Or is it 6"? I'm curious, myself. Want to make sure I don't misinform anyone in the future when talking about the ECE GenIII mounts.

[slammed1]

Hey shifty,Im up and can go measure for you if youd like right now,I have a 72 and it wouldnt take 5 minutes for your answer.

I added this picture so you could point to the area needed.

[lolife99]

Shifty,... that's why I like leaving the original crossmember and changing everything from the a-arms out. Then use all the 73-up steering linkage. Seems easier to me. You still have to deal with the "hard" brake lines. Thanks for the input from someone who has done it. What was the exact year of the donor truck?

[67ChevyRedneck]

71/72 cross members are NOT any different than the 67/68's. I took a complete suspension from a '71 and bolted it into my '67. Direct bolt in. No hole drilling or wallering required.

What is different between 67-69 and 71/72 (that I can think of)? Most of the differences have to do with the disk spindles vs drum spindles:

On the lower control arms, the bump stops for steering are different. You can use 67-69 A arms with 71/72 spindles, but you have to grind the tit down on the spindle.

Outer tie rod ends are different.

On the cross member itself (I'm a little fuzzy on this one) but I think the location of where the steel line/rubber hose meet are different.

Is it truely 73-87 suspensions that can be used? I though I'd read a few times that the ones around 80 or so and newer won't work?

[shifty]

Originally Posted by lolife99

You still have to deal with the "hard" brake lines. Thanks for the input from someone who has done it. What was the exact year of the donor truck?

It is a '77 or '78 crossmember. I have a '68 pickup. The control arms don't look much different, honestly. In fact, the holes for the hard brake lines are in the same spot.

The main differences I see between the '77-'78 crossmember and the '68 crossmember is this:

- '77 has larger holes for the lower control arm u-bolts.
- '77 has a 1/4" reinforcement plate riveted to it around those larger holes.
- '77 crossmember has wider flange area where the u-bolts pass thru on each side.
- '77 bolt hole pattern is different for the four side bolts. The '77 is nearly a perfect 4-square pattern, the '68 is not even close to a square pattern.

Originally Posted by 67ChevyRedneck

On the cross member itself (I'm a little fuzzy on this one) but I think the location of where the steel line/rubber hose meet are different.

On the '68, they meet on the area of the control arm absolutely closest to the upper shock mount on the frame.

Originally Posted by 67ChevyRedneck

Is it truely 73-87 suspensions that can be used? I though I'd read a few times that the ones around 80 or so and newer won't work?

I've had at least a dozen people tell me this is an absolute bolt-in affair - that is, if you keep your 67-72 crossmember, you can simply bolt in the arms. I also had two people tell me that around 1980 or so, they started using metric brake fittings, so you need to get converters - I DO NOT know if this is true, but wouldn't be surprised.

Things I can tell you:

* '77 control arms look damn near identical in diameter and whatnot.
* The cross shafts look identical as well, and the upper arms appear to direct-swap (interchangeable).
* The lower control arm U-bolts are relatively different in diameter and width BUT the lower control arms have the same diameter shaft, so you can theoretically use your '68 crossmember and u-bolts and directly bolt a '73-87 LCA to it.
* 73-87 u-bolts DO NOT fit into a '68 crossmember for two reasons, possibly just one reason: The holes in your '68 are smaller diameter. I personally believe it would be a perfect fit if you just opened up the holes on the '68 crossmember, BUT you wouldn't have the advantage of the beefier reinforcement plate. So - seems like a catch-22...you either upgrade to the larger stronger u-bolts and possibly weaken your crossmember, or you use weaker u-bolts and maintain the original structural strength of your crossmember.

I've still got a lot of work to do today. If I have any epiphanies or find any other quirks, I'll post on it. I guess my big interest is the framerail height at the crossmember of a 71-72 pickup. I have someone checking that out for me.

[shifty]

PS - crappy picture of the u-bolt size diff'ce.

I did not measure them from center-to-center on the posts to check for width, but ... I probably will do that when I head back down to get a couple more hours work in.

[TravisH]

What diameter are the new ubolts? The ones I used when rebuilding my front suspension were larger than original because the original are either hard to locate or not being made. I believe the ones I have are 9/16 but its been more than a year since I had to drill out the mounts

Just so I'm clear, you wanted to change the front clip so you could avoid using two holes on the crossmember you'd already drilled? I read your list above but to be honest those seem more like justifications

[SCOTI]

73-87 u-bolts DO NOT fit into a '68 crossmember for two reasons, possibly just one reason: The holes in your '68 are smaller diameter. I personally believe it would be a perfect fit if you just opened up the holes on the '68 crossmember, BUT you wouldn't have the advantage of the beefier reinforcement plate. So - seems like a catch-22...you either upgrade to the larger stronger u-bolts and possibly weaken your crossmember, or you use weaker u-bolts and maintain the original structural strength of your crossmember.

The lower a-arm cross-shafts are the same diameter so the u-bolts are the same I.D. but are a smaller thread diameter (1/2" vs. 73-up @ 9/16").

The larger u-bolts fit once the holes are drilled to the larger size. The reinforcement plate can be swapped into place as well (shave to fit). Once done, the arrangement is equally strong = no catch-22.

As I've stated previously, I don't understand why one would go through the extra effort to use the later crossmember if the swap is just to swap in disc brakes. If there's a specific reason it makes sense (LS motor mount conversion, powder-coating, original c.member is damaged). Otherwise, all the parts will swap over (I've done more than one disc swap on pre-71's).

[shifty]

Originally Posted by SCOTI

As I've stated previously, I don't understand why one would go through the extra effort to use the later crossmember if the swap is just to swap in disc brakes. If there's a specific reason it makes sense (LS motor mount conversion, powder-coating, original c.member is damaged). Otherwise, all the parts will swap over (I've done more than one disc swap on pre-71's).

In this case, going GenIII that was the main reason to swap (bolt holes were already present, had no way to know my framerail was taller ), stronger hardware was a secondary perk.

Oh - and I just realized that I should probably tell you - this thread isn't aimed at you or 'gringoloco' or any of the guys on the suspension forum that have been helping me out. I actually should have paid attn to what you guys were saying, but went off and read a bunch of threads around here about crossmembers instead. You guys were basically spot-on with everything.

[SCOTI]

Originally Posted by shifty

In this case, going GenIII that was the main reason to swap (bolt holes were already present, had no way to know my framerail was taller ), stronger hardware was a secondary perk.

Oh - and I just realized that I should probably tell you - this thread isn't aimed at you or 'gringoloco' or any of the guys on the suspension forum that have been helping me out. I actually should have paid attn to what you guys were saying, but went off and read a bunch of threads around here about crossmembers instead. You guys were basically spot-on with everything.

No harm, no foul. I knew your reasoning was the GEN III mounts. I also included the info on the reinforcement plate to ease your mind.

[slammed1]

Shifty,my truck is a 72 and in the area you wanted a measurement I got between 5 1/4" and 5 1/2" height as best I could measure.This was as best I could get which was from the bottom of the frame rail to the top of the frame rail in the center of the crossmember where you wanted. If you need any other measurements I can easily go get more in certain areas.

[LockDoc]

Shifty,

Maybe I'm not understanding your post but I have replied in most of the following threads (with pictures) about the differences in the frame holes. The last link mentions the difference in frame height.

http://67-72chevytrucks.com/vboard/s...ember+enlarged

http://67-72chevytrucks.com/vboard/s...ssmember+holes

http://67-72chevytrucks.com/vboard/s...ssmember+holes

http://67-72chevytrucks.com/vboard/s...ssmember+holes

http://67-72chevytrucks.com/vboard/s...ssmember+holes

http://67-72chevytrucks.com/vboard/s...ssmember+holes

LockDoc

[chevymad]

Another point for confusion. There are 2 different height frames in the 73 up trucks. I parted out 3 different 73-78 trucks and used parts on my 70C10. The truck that I used the front crossmember from was a 74gmc C10 454 truck. Crossmember bolted right in. But that frame was something like 3/4" taller then either of the 2 3/4 ton trucks I parted out at the same time. One of the 3/4 tons was a 73, the other was a 78 crewcab. Both frames were shorter then the 74 454 trucks. I do wish I'd moved the motor mounts forward though. I left them in the same position that it came out of the 74.. and the 454 fits pretty tight when that far back.

[shifty]

Well, for prosperity, here are some pics of '68 control arms and '77 control arms, for comparison. They're basically the same. Just thought I'd post em here for the future.

1st pic is '68 arms, second is '77 arms.

[Blue_71]

i put a 76 crossmember in my 69, 3 of the 4 bolts that go sideways lined up dead even.. the lower front bolt had to be elongated though. i did have to make all new brake lines, but i used a 76 prop valve which has 2 outlets for the front lines instead of one. my reasoning behind doing the whole crossmember was because i dont have a coil spring compressor and i absolutly HATE compressing coil springs

[shifty]

Originally Posted by Blue_71

i put a 76 crossmember in my 69, 3 of the 4 bolts that go sideways lined up dead even.. the lower front bolt had to be elongated though.

This is what I read in all of the threads I was checking out here. I didn't see a single one of LockDoc's threads/posts. I had several folks tell me your same experience. Leaves me to wonder: WTF?!

Why would we have two drastically different experiences? Were there more than one type of frame for halfton trucks, or is the 3/4 ton truck setup with diff't bolt holes for the crossmember or something?\

Originally Posted by Blue_71

i did have to make all new brake lines, but i used a 76 prop valve which has 2 outlets for the front lines instead of one.

it looks like all of the brake provisions are the same between my '77 and '68 crossmember and shouldn't cause any problems. Although, there are no tabs for the hard-to-soft line on the '77 as there were on my '68.

[Blue_71]

im just as confused as you are, lol. mine came from a plain jane bonanza-10 light duty half ton. here are some pics i took back in october

[Blue_71]

pic of the 69 M/C, and the two victims

[SCOTI]

I used the post-73 prop valve & hard lines on my 68. The prop valve is installed in the same location as a post-73 truck vs. up @ the master cyl like on a pre-73 truck.

It required slight spacing where it mounted on the splash pan up front, but everything worked.

[PipsC10]

On factory disc brake trucks the hard brake lines ran on the front of the crossmember. The junction block where the hard lines meet the soft lines was also on the front of the crossmember. On pre 71 crossmembers, the hard lines and junction blocks are on the rear of the crossmember.

[shifty]

Sounds like I need to order brake lines for a '68 when I pick those up down the road, just to stick with what is supposed to be there.