Flipping Trailing Arm Crossmember

[damnyankee36]

This is my first attempt at bagging my '66 C10, so I might be re-inventing the wheel here...

While looking at ways to keep the pinion angle close to the proper degree at my target lowered ride height, I was going to flip the trailing arm mounting brackets that are riveted on the crossmember. I then realized, why not flip the whole crossmember?

In doing this, I raised the trailing arm pivot points 3-1/4", plus gained an additional 1-3/8" driveshaft clearance at the top of the hole. It also raises the lower part of the crossmember to help with ground clearance problems for laid out trucks.

Four of the bolts were out of alignment by about 1/8"- 3/16", the other six lined up perfectly. I drilled out the four holes and enlarged the others by a few thousandth's and installed 7/16" grade 5 bolts.

Consequently, this also raised the top of the crossmember 1-1/8", so I'll have to massage the belly of the cab in this area to clear it.

When fully dropped, I have about 7/16" clearance between the frame and the arms. Looks like it will work.

I've never seen this done. Anybody else do this?

Pic#1: Top of crossmember, Before
Pic#2: Top of crossmember, After
Pic#3: Grade 5 bolts
Pic#4: Overall view, After

[texastrendz]

is it going to hit the cab floor? i know it is close!!!

[shifty]

Will the trailing arms contact the frame at full drop?

[ob1monkey]

Subscribed!!

[lolife99]

Cool idea.
Will the trailing arms contact the frame sooner,... since the entire arm has been raised?

I know the ECE and Porterbuilt crossmembers are higher priced than your mod,... but the solve alot of the ground clearance and exhaust problems.
Subscribing to see how this works out.

[Naterman35]

Could you trim the part of the cross memmber that like kicks up to help with clearence?

[damnyankee36]

Originally Posted by Naterman35

Could you trim the part of the cross memmber that like kicks up to help with clearence?

I'd rather not since it would weaken it somewhat.

Originally Posted by lolife99

Cool idea.
Will the trailing arms contact the frame sooner,... since the entire arm has been raised?

Yes, but I have about 7/16" clearance at full drop.

Originally Posted by shifty

Will the trailing arms contact the frame at full drop?

7/16" clearance at full drop.

Originally Posted by texastrendz

is it going to hit the cab floor? i know it is close!!!

I will mod the floor about 1-1/8" to clear it. It's under the seat, should be no problem.

[72 SUPER10]

IT WILL WORK, AND IT ALSO CENTERS THE WHEEL BACK UP IN THE WHEEL OPENING, I FLIPPED MY FRONT BRACKETS AND GOT MINE BACK WERE IT NEEDS TO BE,COOL JOB,,VINCE

[SCOTI]

Originally Posted by damnyankee36

I'd rather not since it would weaken it somewhat.

Yes, but I have about 7/16" clearance at full drop.

7/16" clearance at full drop.

I will mod the floor about 1-1/8" to clear it. It's under the seat, should be no problem.

What's "full drop"? C-notches or step notches?

It's a good idea (I've flipped the brackets) but found little benefit flipping the c.member. The 'hoop' still wasn't tall enough @ dropped height if running more than the standard c-notch & the 'lip' below the frame rail still was too low (1.5" below or so...). But.... it's a good 'budget' idea that works even better w/some mods: exhaust holes, flatten the bottom lip, & add height to the top hoop (all of which can be done on the cheap).

[72 SUPER10]

I DONE THE EXHAUST HOLES ALSO ,

[cap70ss]

I posted a while back on this and got very little response. I have my complete crossmember flipped in my 70 short stepside. With my new complete floorpan sitting on new poly mounts I have 3/4" clearance to the floor pan. That's not with it bolted down but I think it will be fine. I've talked with drag race and circle track friends. They both feel the front trailing arm mount point should be raised up as we shorten the rear spring. This is to maintain the trailing arm angle for better tire down force under acceleration. I'm going with 4.5"/6" drop.

[damnyankee36]

Originally Posted by SCOTI

What's "full drop"? C-notches or step notches?

It's a good idea (I've flipped the brackets) but found little benefit flipping the c.member. The 'hoop' still wasn't tall enough @ dropped height if running more than the standard c-notch & the 'lip' below the frame rail still was too low (1.5" below or so...). But.... it's a good 'budget' idea that works even better w/some mods: exhaust holes, flatten the bottom lip, & add height to the top hoop (all of which can be done on the cheap).

I'll be running a standard C notch, so I'm figuring it should work quite well. The frame won't be on the ground, so the lower lip should be well off the ground. We'll see when I get the cab mounted on the frame.

Definitely agree on the low cost of this mod, (Just bolts).

[damnyankee36]

Originally Posted by cap70ss

I posted a while back on this and got very little response. I have my complete crossmember flipped in my 70 short stepside. With my new complete floorpan sitting on new poly mounts I have 3/4" clearance to the floor pan. That's not with it bolted down but I think it will be fine. I've talked with drag race and circle track friends. They both feel the front trailing arm mount point should be raised up as we shorten the rear spring. This is to maintain the trailing arm angle for better tire down force under acceleration. I'm going with 4.5"/6" drop.

I forgot to add the height of the mounts. I might have clearance after all or maybe as much as you! Thanks for the reminder!

I'm going with about the same drop as you. This is looking better all the time!

[damnyankee36]

Originally Posted by 72 SUPER10

IT WILL WORK, AND IT ALSO CENTERS THE WHEEL BACK UP IN THE WHEEL OPENING, I FLIPPED MY FRONT BRACKETS AND GOT MINE BACK WERE IT NEEDS TO BE,COOL JOB,,VINCE

Didn't think of that benefit!

[damnyankee36]

I finally have the driveshaft in place and with the truck dumped, I have 1 1/4" of clearance between the driveshaft and the top of the crossmember hole. This is with a 3" driveshaft. For reference, my dumped height has the axle housing about 1" into the C-notch.

Soon as I get the cab installed, I'll see what kind of clearance I have between the floor and the top of the crossmember.

I also didn't have to adjust the pinion angle. At my expected ride height, +/- 1", it is within a degree or so of the tranny centerline.

Very satisfied so far.

[kev2809]

do have any shots from the side of the truck at full dump? does this mod keep the truck from laying lower that if you didnt flip them?

[SCOTI]

Originally Posted by damnyankee36

I finally have the driveshaft in place and with the truck dumped, I have 1 1/4" of clearance between the driveshaft and the top of the crossmember hole. This is with a 3" driveshaft. For reference, my dumped height has the axle housing about 1" into the C-notch.

Your 'dumped' height was my 'ride' height.

[damnyankee36]

Originally Posted by kev2809

do have any shots from the side of the truck at full dump? does this mod keep the truck from laying lower that if you didnt flip them?

How 'bout these pics?

At my full dump, I could fit a 7/16" drill bit between the arm and frame on the driver's side. The passenger side was about 1". So, I would guess this would be a limiting factor as to how low the frame could drop. I have 1" lowering blocks; thicker blocks would add some more clearance.

At my projected ride height the gaps are pretty much equal. I'll do a final adjustment on the track bar after the truck is finished.

Since I raised the hole by 1 3/8" by flipping, and I have 1 1/4" clearance now tells me I would have had 1/8" interference between the D/S and crossmember hole without flipping.

Since the area of interference is about the middle of the arm, I would estimate the truck could go another 1" lower before they would touch.