Flipping trailing arm mounting brackets?

[loridr]

I've seen in several threads about guys flipping the trailing arm mounting brackets which raises the mounting point on the crossmember. The claim is that this improves the geometry on a lowered rear setup. Seems like a simple thing to do if there is a real gain.

Is there any real advantage to doing this? If so, what is the gain related to?

Steve

[gringoloco]

Changes pinion angle back to a more stock-like position. Maybe a few degrees difference... If you are planning on going extremely low, this is a bad idea, as the arms will hit the frame where they cross under sooner. Also, not quite as simple as it sounds, that crossmember is a BEAR to remove.

All that said, not a bad idea if you're already moving it and don't plan on going super-low.

[robnolimit]

If you lower the truch (chassis) the mounts move down, and the pinion angle goes with it. This was the way chevy designed it, but the 'sweet' spot for the pinion angle was at stock hieght. Flipping or raising the front mount helps get it back. The other thing is the percentage of "anti-squat", or, how the truck loads the rear tire. Raising the mount helps to plant the tires. It's onlt 12 rivits, drill 4 holes, and put in 12 grade 8 bolts, and you know its better.

[oldblue1968chevy]

So with 4" drop it'd be a good idea?

Cut the rivits out, flip em upside down, then bolt back with grade 8 hardware, right?

[loridr]

That's the way I understood the modification Oldblue, just pop em off an flip em.

Not sure why Gringoloco is saying you need to move the crossmember, maybe only in an extreme drop? GL, can you elaborate?

[gringoloco]

Two ways to skin this cat: First, remove the crossmember and flip the entire thing; second, pull the mounts and flip them. You will, as Rob posted, have to drill two holes per side when swapping the brackets due to the middle rivets being off-center. Really not sure which method would be more work, honestly. Those rivets are a pain no matter what they're holding, especially when lying in your driveway, on your back, with an angle grinder and an air chisel (or BFH). Kind of a rite of passage of modifying these trucks though...

At 4", it sounds like it would be a good idea, but I would measure the pinion angle to be sure that a) you need to do it, and b) if you do need it, you are ending up with the correct angle when all is said and done. There are also shims available to more precisely correct pinion angle, but not quite as inexpensive as a handful of grade 8 hardware...

[jayman68]

Here is a link to a great thread hosted by Rob. Post 270 on page 11 shows how it is done. Good luck.
http://67-72chevytrucks.com/vboard/s...d.php?t=419251

[loridr]

I was thinking about modifying the crossmember for pass through exhaust anyway.... but if the only gain from flipping the arm mounts is improved pinion angle then it would seem to me that shims would be more precise. I thought maybe there was something more to it.

[SCOTI]

Originally Posted by loridr

I was thinking about modifying the crossmember for pass through exhaust anyway.... but if the only gain from flipping the arm mounts is improved pinion angle then it would seem to me that shims would be more precise. I thought maybe there was something more to it.

Answered here....

The other thing is the percentage of "anti-squat", or, how the truck loads the rear tire. Raising the mount helps to plant the tires.

[Hart_Rod]

Has anyone swapped the mounts on an ECE crossmember? I'm assuming it will give the same benefit......

[SCOTI]

Originally Posted by Hart_Rod

Has anyone swapped the mounts on an ECE crossmember? I'm assuming it will give the same benefit......

Correct. Mine are swapped.

[Hart_Rod]

Originally Posted by SCOTI

Correct. Mine are swapped.

Cool. Looks like I'll have to drill a couple extra holes. Do you have any pics?

[SCOTI]

Originally Posted by Hart_Rod

Cool. Looks like I'll have to drill a couple extra holes. Do you have any pics?

Page 21 of my build thread in the 60-66 section. Posts 506 & 508 have some closer shots of the brackets flipped.

[loridr]

Originally Posted by SCOTI

Page 21 of my build thread in the 60-66 section. Posts 506 & 508 have some closer shots of the brackets flipped.

Good stuff Scoti. Sounds like I may as well do this swap while I'm conducting surgery. Going to use your poor-man shock relocator swap as well, at least for the bottom brackets; up top I'm going to modify and relocate my custom crossmember.

Anti-squat is good........... FREE IS ALSO GOOD!!!

[Hart_Rod]

Here's how I did mine, . The sawsall, air chisel and punch made this a pretty simple job. I also have some rear end pinion shims just in case this doesn't fix all the angle mismatch. After reading everything here, I "assume" I should put them in to help rotate the pinion up in the front???? Also, another advantage seems to be that it pushed my rear wheels back approximately an inch, which helps better center them in the wheel well.

[gringoloco]

Looks good, Rob Any clearance issues, either at the floor cross-sills or where the arms pass under the frame? Also, have you re-installed the driveshaft? Since it moved you back an inch, any issues at the trans yoke?

[lolife99]

Rob,... just curious how this mod pushed the rearend back 1"?

Is the ECE crossmember located in a different set of frame holes?

[SCOTI]

Originally Posted by lolife99

Rob,... just curious how this mod pushed the rearend back 1"?Is the ECE crossmember located in a different set of frame holes?

The ECE x-member mounts in the OE location unless it's modified/moved by the installer.

The rear end on a T/A set-up swings up & forward on its natural arc as it gets lower. By raising the pivot point in front, it's like you're not lowering it as much in the rear as it swings through the arc of travel.

As we know, the lower the truck, the farther forward in the wheel opening the axle C/L shifts. Not being as low in the arc should mean the rear end sits slightly farther back & yields positive pinion angles.

[lolife99]

I see the 6" drop spring and a 2" block moving the rearend forward.
I just don't see the bracket flip moving it rearward as much as 1 inch.
(with the pivot point being the coil spring)

I do see the advantage of gaining a better pinion angle.

[Hart_Rod]

Originally Posted by lolife99

I see the 6" drop spring and a 2" block moving the rearend forward.
I just don't see the bracket flip moving it rearward as much as 1 inch.
(with the pivot point being the coil spring)

I do see the advantage of gaining a better pinion angle.

I don't know that it's exactly 1", I just kinda swagged it, . I do know visually it has moved back... When I get it back on the ground I'll see if I can get a before and after picture.

[SCOTI]

Originally Posted by lolife99

I see the 6" drop spring and a 2" block moving the rearend forward.
I just don't see the bracket flip moving it rearward as much as 1 inch.
(with the pivot point being the coil spring)I do see the advantage of gaining a better pinion angle.

Which is why I stated this.....

Originally Posted by SCOTI

Not being as low in the arc should mean the rear end sits slightly farther back & yields positive pinion angles.

I feel that 1" measurement is unlikely, but it will move it back.

[scrapmetalart]

how low is too low to do this? I have 5" rear springs & am adding 2" blocks & might go to 6" springs...will this cause a clearance issue with the bed?

[72gmcshorty]

Is this crossmember flip recommended for someone with a mild c-notch, airbags, shock relocators?

[WAAF]

silly question, hope is doesn't highjack the o/p thread..
I understand the flip of factory bracket= cheap and easy
but,(always the but)
would making or useing mount like they use on a 4 link set up.. with 4 mounting points.. allow you to tune the rear set up more?
or is this overkill on this.

[SCOTI]

Originally Posted by WAAF

silly question, hope is doesn't highjack the o/p thread..
I understand the flip of factory bracket= cheap and easy
but,(always the but)
would making or useing mount like they use on a 4 link set up.. with 4 mounting points.. allow you to tune the rear set up more?
or is this overkill on this.

A spec built mount w/several mounting points for the front bolts would allow the end user to 'tune' the set-up per their application & be better vs a one size fits all approach.

Porterbuilt @ http://www.porterbuiltfabrication.com/ makes a T/A x-member like this. Hotchkis offers something similar too (I can't remember but I think it might be just the brackets as part of a rear kit).