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!!!

[SCOTI]

Originally Posted by loridr

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!!!

I raised the OE shock x-member 3" in addition to the upper shock mount mod in my 68 Beaters last incarnation (before disassembling everything). For my 64, I decided to use Bilsteins but they didn't make them for the rear coil application GM trucks. I opted to use another coil application GM spec shock (GM g-body) as the g-body shock was a better length for my packaging/spacial limitations.

[loridr]

Originally Posted by SCOTI

For my 64, I decided to use Bilsteins but they didn't make them for the rear coil application GM trucks. I opted to use another coil application GM spec shock (GM g-body) as the g-body shock was a better length for my packaging/spacial limitations.

I'm reading the entire 64 thread now. Really nice x-member, lotta work. I'm diggin the frame work as well.

I was working my way backward from the arm mount page so I wondered what the heck the plate was behind the mounts... until I saw you were relocating the axle position. So much to think about, am I glad I found this site?!! With a little luck maybe I'll build this thing right this time.

Is there a build thread on your 68? I'd like to see that raised x-member as well.

Steve

[SCOTI]

Originally Posted by loridr

Is there a build thread on your 68? I'd like to see that raised x-member as well.

Steve

No build thread for it. It was done before these build threads picked up momentum.

Basically, I cut the rivets out of the 'upper' portion on the OE shock x-member so it could be removed. The upper portion of the shock x-member is riveted just under the top lip of the frame rail. It is also riveted to two lower flanges (one on each side L&R) that are riveted to the bottom lip of the frame rail.

I then bolted it back into place & marked the edge of the bolts where the upper & lower flanges come together. I cut the upper flange pieces off where I scribed the lines (cut straight across scribe mark to scribe mark; L & R sides). I then welded a piece of 3" angle to the upper piece on each side (L&R) & in turn welded the two flange pieces to that. This effectively raised the upper shock mounting position 3". Once it was fully welded, I was able to bolt it right back in like it originally was installed.

[loridr]

Originally Posted by SCOTI

Basically, I cut the rivets out of the 'upper' portion on the OE shock x-member so it could be removed.

Thanks, I can picture it. My OE x-member is long gone though so I'll have to cook up something else.

That entire area was rotted on my 69' including the spring perches so I cut everything out, repaired the C channel, plated it on all three sides and boxed everything in. To replace the OE shock X-member I fabed an "H" member from square tubing, fully welded it into the C channel boxing plates, and hung the stock upper shock brackets from that. My mistake was locating the H-member so that the upper shock mounts were in the OE location.



So I'll either relocate the H-member, or work some trick brackets off of it depending on how things line up. I like the idea of raising the mounts to get longer shocks on it.

[SCOTI]

You could basically cut & raise it just like I did the OE x-member.

It looks like you have 2 pieces of tubing running across the frame from side to side w/2 shorter pieces running front to rear to tie them together. Cut the longer pieces just outside of where the shorter pieces attach. Use some angle steel & weld it to the center section after raising it the desired amount. Keep in mind the bed floor will need to be raised or a notch made to clear the x-member (I planned to raise the entire floor).

[loridr]

Originally Posted by SCOTI

You could basically cut & raise it just like I did the OE x-member.

It looks like you have 2 pieces of tubing running across the frame from side to side w/2 shorter pieces running front to rear to tie them together. Cut the longer pieces just outside of where the shorter pieces attach. Use some angle steel & weld it to the center section after raising it the desired amount. Keep in mind the bed floor will need to be raised or a notch made to clear the x-member (I planned to raise the entire floor).

That would work. Sure would be easier to cut the tubing at that location than to cut out the welds where the member joins the boxing plate.

Bed clearance issue:

Right now I have tons of room because I have an 89’ step side bed on it. With these beds, in order to get the reveal with the cab correct you raise the entire bed up on brackets. I do plan on swapping out to a stock stepside bed however.

Sounds like I won’t have the clearance with the stock bed to raise the x-member? It’s been so long since I had a stock bed on it that I don’t remember the relationship between the top of the rail and the bed floor, pretty tight huh? Didn’t really want to get into raising the bed floor.

[SCOTI]

Originally Posted by loridr

That would work. Sure would be easier to cut the tubing at that location than to cut out the welds where the member joins the boxing plate.

Bed clearance issue:

Right now I have tons of room because I have an 89’ step side bed on it. With these beds, in order to get the reveal with the cab correct you raise the entire bed up on brackets. I do plan on swapping out to a stock stepside bed however.

Sounds like I won’t have the clearance with the stock bed to raise the x-member? It’s been so long since I had a stock bed on it that I don’t remember the relationship between the top of the rail and the bed floor, pretty tight huh? Didn’t really want to get into raising the bed floor.

Basically, there's no clearance (the floor is directly above the rail). Steppers are the easiest to modify though. Just raise the floor the required 3".

[loridr]

Originally Posted by SCOTI

Basically, there's no clearance (the floor is directly above the rail). Steppers are the easiest to modify though. Just raise the floor the required 3".

So if I go that route and am ordering new bedsides from Mar-k, I'd take the option to not have the angles welded so I can just put em where I need em, right?

I suppose you just weld or bolt a piece of angle to the front panel to support the wood? Smooth panel would end up looking nicer as on a stocker you'd mess up the reveal.

Only thing I can't picture is what you do with the rear cross sill? Section it?

[SCOTI]

Originally Posted by loridr

So if I go that route and am ordering new bedsides from Mar-k, I'd take the option to not have the angles welded so I can just put em where I need em, right?

I suppose you just weld or bolt a piece of angle to the front panel to support the wood? Smooth panel would end up looking nicer as on a stocker you'd mess up the reveal.

Only thing I can't picture is what you do with the rear cross sill? Section it?

I wouldn't think you'd need new bedsides. Just add the angle strips to raise the floor (front, L-side, R-side). The rear will need a filler piece made.

[loridr]

Originally Posted by SCOTI

I wouldn't think you'd need new bedsides. Just add the angle strips to raise the floor (front, L-side, R-side). The rear will need a filler piece made.

I not only need new sides, I need new everything.

The only pieces I saved from the OE bed were the rear cross sill, fenders and steps. Been watching the parts board but I think I'm just going to bite the bullet and buy new from Mar-K. I'll have enough to do with the chassis work and reworking the cab sheet metal. My OE steps and rear fenders need a lot of work as well.

[SCOTI]

Originally Posted by loridr

I not only need new sides, I need new everything.

The only pieces I saved from the OE bed were the rear cross sill, fenders and steps. Been watching the parts board but I think I'm just going to bite the bullet and buy new from Mar-K. I'll have enough to do with the chassis work and reworking the cab sheet metal. My OE steps and rear fenders need a lot of work as well.

Ahh.... Now I understand what you meant.