My frame isn't square... shocking!

[jerimy75]

Hey guys - looking for some experience from others that have installed DMs before. I have a '72 SWB that I am adding PB's Mild DM front and rear. I have the front mocked up already and have moved to the back. I bought the weld in notches and am mocking them up to tack weld in place. I have two possible issues:

1. I've measured back the specified distance to place the notch CL (bump stop hole). Passenger side is pretty close if not dead on. With the bridge in but bolts loose, the driver's side is about 1/4" if not more forward of the specified CL. If I center the notch, I won't be able to get the bridge in. I don't have the axle in yet but am thinking if the trailing arms are the same length and the axle is centered in the frame and notch I should be good. Has anyone had this issue before? Am I on the right path?

2. Not sure it's an issue but want to confirm my thought process: Frame is not square, it's about 1/8" out measuring between cab mounts. My question is should I square up my notches (see issue 1 above) or mimic the frame 'out-of-squareness'?

I don't know the history of the truck and don't know if it was in any accidents. Any insight you guys can give will be greatly appreciated, thanks!

[sduckworth13]

I'd suggest taking it to a frame shop just to relieve yourself of any doubt. I'll be doing the same thing since installing tubular crossmembers has moved things around a little

[PBFAB.COM]

Originally Posted by jerimy75

Hey guys - looking for some experience from others that have installed DMs before. I have a '72 SWB that I am adding PB's Mild DM front and rear. I have the front mocked up already and have moved to the back. I bought the weld in notches and am mocking them up to tack weld in place. I have two possible issues:

1. I've measured back the specified distance to place the notch CL (bump stop hole). Passenger side is pretty close if not dead on. With the bridge in but bolts loose, the driver's side is about 1/4" if not more forward of the specified CL. If I center the notch, I won't be able to get the bridge in. I don't have the axle in yet but am thinking if the trailing arms are the same length and the axle is centered in the frame and notch I should be good. Has anyone had this issue before? Am I on the right path?

2. Not sure it's an issue but want to confirm my thought process: Frame is not square, it's about 1/8" out measuring between cab mounts. My question is should I square up my notches (see issue 1 above) or mimic the frame 'out-of-squareness'?

I don't know the history of the truck and don't know if it was in any accidents. Any insight you guys can give will be greatly appreciated, thanks!

First off.... it's a rare thing to find one of these frames that is actually "dead on" when measuring for squareness. The 1/8" number you gave will be well within the "factory tolerance". I have noticed this same thing arise on a handful of installs from many different chassis years. They are just mass produced and were never intended to be perfect.

How far off are the notches in regards to the one being further back than the other?

I would pick a couple other reference points to measure from to try and confirm how far out of square the chassis really is.

Let us know what you find.

Nate

[jerimy75]

Originally Posted by sduckworth13

I'd suggest taking it to a frame shop just to relieve yourself of any doubt. I'll be doing the same thing since installing tubular crossmembers has moved things around a little

Thanks - I had thought about that, but with the bolt in crossmembers (ability to separate the frame rails completely, thereby negating a square frame) I wasn't sure if it would be worth it except to confirm the rails are straight.

Originally Posted by Porterbuilt Street Rods

First off.... it's a rare thing to find one of these frames that is actually "dead on" when measuring for squareness. The 1/8" number you gave will be well within the "factory tolerance". I have noticed this same thing arise on a handful of installs from many different chassis years. They are just mass produced and were never intended to be perfect.

How far off are the notches in regards to the one being further back than the other?

I would pick a couple other reference points to measure from to try and confirm how far out of square the chassis really is.

Let us know what you find.

Nate

Thanks Nate. Your directions actually say that the tolerances back in the day would drive today's engineers crazy, I'm an engineer, so you are right on! I'll double check when I get home but the passenger notch appears to be right at the 26.5" measurement (if I remember the directions correctly), while the driver's side appears to be about 1/4" forward of the specified measurement. I'll take some measurements from other locations but it sounds like you might suggest to keep the notches square. I'm also going to mock up the rearend and make sure that it is centered in the notches, if it is I should be good, right?

Thanks again!

[jerimy75]

So I took some additional measurements and the frame is only about 1/8" out max which I'm OK with based on your comments Nate.

I was also able to get the drivers side notch to the correct location (26.5" from the bed mount as directed). But this brings up another question:

With the axle housing 8" below the bottom of the notch, the center of the housing is about 1 1/8" behind the center of the notch. I can't imagine at the axle housing will swing that far forward in the 8" of remaining travel. This guy had the same issue but this issue was not addressed in the thread:http://67-72chevytrucks.com/vboard/s...otch+placement

I could move the trailing arm crossmember toward the front to help make up the difference but just want to confirm that this is normal before I finish welding the notches in and cut the frame sections out.

I'll try to give your shop a call tomorrow Nate but I've been pretty busy at work so I might not get a chance. If you have a chance to reply here I'd appreciate it. Or if anyone else has some feedback that would be great as well. Also, I can load some photos if needed. Thanks again!

[PBFAB.COM]

Originally Posted by jerimy75

So I took some additional measurements and the frame is only about 1/8" out max which I'm OK with based on your comments Nate.

I was also able to get the drivers side notch to the correct location (26.5" from the bed mount as directed). But this brings up another question:

With the axle housing 8" below the bottom of the notch, the center of the housing is about 1 1/8" behind the center of the notch. I can't imagine at the axle housing will swing that far forward in the 8" of remaining travel. This guy had the same issue but this issue was not addressed in the thread:http://67-72chevytrucks.com/vboard/s...otch+placement

I could move the trailing arm crossmember toward the front to help make up the difference but just want to confirm that this is normal before I finish welding the notches in and cut the frame sections out.

I'll try to give your shop a call tomorrow Nate but I've been pretty busy at work so I might not get a chance. If you have a chance to reply here I'd appreciate it. Or if anyone else has some feedback that would be great as well. Also, I can load some photos if needed. Thanks again!

I designed the rear suspension so that the rear axle center-line lands in the middle of the notch when fully compressed. The 26.5" notch placement measurement will put the notch center-line in the middle of the rear fender well on the fleet-side bed.

At ride height, the axle center-line will be approx. 1" behind the notch center-line... so it sounds like you should be good. The arc of the rear suspension will cause the differential to plunge forward... it's normal (that's why you see a lot of trucks that have the rear axle center sucked forward in the wheel well opening when fully deflated).

I would go ahead and compress the suspension to confirm that it lands in the center of the notch... it should.

Let me know if you have any questions. I don't frequent the forum much on the weekends, but try and keep up with it during the week. If there is ever a specific question and it doesn't seem like I reply, one could always send me a private message and I will make sure I get back.

Nate

[jerimy75]

Originally Posted by Porterbuilt Street Rods

I designed the rear suspension so that the rear axle center-line lands in the middle of the notch when fully compressed. The 26.5" notch placement measurement will put the notch center-line in the middle of the rear fender well on the fleet-side bed.

At ride height, the axle center-line will be approx. 1" behind the notch center-line... so it sounds like you should be good. The arc of the rear suspension will cause the differential to plunge forward... it's normal (that's why you see a lot of trucks that have the rear axle center sucked forward in the wheel well opening when fully deflated).

I would go ahead and compress the suspension to confirm that it lands in the center of the notch... it should.

Let me know if you have any questions. I don't frequent the forum much on the weekends, but try and keep up with it during the week. If there is ever a specific question and it doesn't seem like I reply, one could always send me a private message and I will make sure I get back.

Nate

Thanks for the quick reply Nate. I'll cut my frame sections out this week and let you know if I run into any issues with the axle housing not landing in the center of the notch. Again, thanks.

[jerimy75]

Hey Nate - I was finally able cut the frame sections out this weekend. I took a few photos to show the alignment of the axle housing at the bump stops (not the best photo, sorry), at the notches without the bump stops, and the point from which I measured my 26.5 inches back from to locate the center of the notch. Without the bump stops the axle housing centerline is about 1/8" back from the center of the notch which I don't think is that big of a deal. Not sure any of it is a big deal, just want to confirm this is what I should expect. I look forward to your thoughts, thank you!

[PBFAB.COM]

Originally Posted by jerimy75

Hey Nate - I was finally able cut the frame sections out this weekend. I took a few photos to show the alignment of the axle housing at the bump stops (not the best photo, sorry), at the notches without the bump stops, and the point from which I measured my 26.5 inches back from to locate the center of the notch. Without the bump stops the axle housing centerline is about 1/8" back from the center of the notch which I don't think is that big of a deal. Not sure any of it is a big deal, just want to confirm this is what I should expect. I look forward to your thoughts, thank you!

The only thing I noticed, is that it looks like we sent you the tall bumpstops instead of the short bumpstops. Other than that, it looks good. I would be happy with the 1/8" number.

Let me know if those are the bumpstops we sent you, and we can get you the correct ones.

Nate

[jerimy75]

Originally Posted by Porterbuilt Street Rods

The only thing I noticed, is that it looks like we sent you the tall bumpstops instead of the short bumpstops. Other than that, it looks good. I would be happy with the 1/8" number.

Let me know if those are the bumpstops we sent you, and we can get you the correct ones.

Nate

Thanks for the quick response Nate. Those are the bumpstops I recieved. I'll reach out to you to get the short bumpstops because I need to order the front crossmember too.

Do you see any need to move the trailing arm crossmember forward and lengthen the hemi joints a little to get the axle housing centered?

Again, thanks for all of your input and assistance!

[PBFAB.COM]

Originally Posted by jerimy75

Thanks for the quick response Nate. Those are the bumpstops I recieved. I'll reach out to you to get the short bumpstops because I need to order the front crossmember too.

Do you see any need to move the trailing arm crossmember forward and lengthen the hemi joints a little to get the axle housing centered?

Again, thanks for all of your input and assistance!

There will be adjustment in the rod end on the trailing arm IF you wanted to scoot the x-member forward and then adjust out the rod end. I don't think it will be necessary. Keep in mind that the frame will have some flex in it once the weight of the vehicle and all the components are mounted. Experience tells me you will land dead center once you are done.

Nate

[jerimy75]

Originally Posted by Porterbuilt Street Rods

There will be adjustment in the rod end on the trailing arm IF you wanted to scoot the x-member forward and then adjust out the rod end. I don't think it will be necessary. Keep in mind that the frame will have some flex in it once the weight of the vehicle and all the components are mounted. Experience tells me you will land dead center once you are done.

Nate

10-4 Thanks Nate!