trailing arm mount?

[sumtercleaner]

Did some searching on here and saw where some of yall were swapping/flipping the trailing arm mounts to get better pinion angle. Can some one elaborateor post pics?
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[CC69Rat]

I have several pictures in my GMC build if you want to check it out (the second one in my signature)

When you lower the rear of the 67-72, assuming you're doing 5-6" springs (?) What happens is the distance betwen the axle housing and the frame rails get closer (duh.. I know you know this.. ) BUT, when you factor in the position of the front mounting point of the trailing arm does no change, think of that upward swing of the trailing arm vs. that pivot point on the trailing arm cross member. The angle of the 'perch' where your rear axle housing sits will roll the nose of the pinion down. By flipping / raising the brackets up is corrects some of this pinion adjustment. In theory the truck will only think it has been dropped about 2-3 ".

The only negative drawback is by doing the flip mod, you will loose about .75" of your rear drop. So, 6" springs now = 5.25" net drop. .. so, just add a 1" block and it's all set.

I won't lie man, it is a PAIN to do it. There are 6 rivets in each bracket. It is ridiculous to try to do it with a grinder. If you have a plasma, or air hammer I would high suggest the mod. .. If you're going really low, Cnotching, bags, etc. .. and staying with the stock trailing arms especially.

Take a look at mine, I used the Hotchkis bracket designed specifically for this issue. This will also keep your truck from 'squatting' during hard acceleration and it gives you back some of the original geometry of the 'truck arm' suspension. .. What I'm saying is your trailing arms are not sitting "flattened out" in paralel with the ground. you actually have more of a Nascar type rear suspension geometry. I personally feel it's one of the best things you can do to relieve some of the future suspension issues. I'm running the bracket mod, 6" springs, 1" block, and 3 degree shims. My rear pinion angle is exactly where it was before the drop.

Hope this helps ..
Later
Chad

[BugzC10]

Originally Posted by CC69Rat

I have several pictures in my GMC build if you want to check it out (the second one in my signature)

When you lower the rear of the 67-72, assuming you're doing 5-6" springs (?) What happens is the distance betwen the axle housing and the frame rails get closer (duh.. I know you know this.. ) BUT, when you factor in the position of the front mounting point of the trailing arm does no change, think of that upward swing of the trailing arm vs. that pivot point on the trailing arm cross member. The angle of the 'perch' where your rear axle housing sits will roll the nose of the pinion down. By flipping / raising the brackets up is corrects some of this pinion adjustment. In theory the truck will only think it has been dropped about 2-3 ".

The only negative drawback is by doing the flip mod, you will loose about .75" of your rear drop. So, 6" springs now = 5.25" net drop. .. so, just add a 1" block and it's all set.

I won't lie man, it is a PAIN to do it. There are 6 rivets in each bracket. It is ridiculous to try to do it with a grinder. If you have a plasma, or air hammer I would high suggest the mod. .. If you're going really low, Cnotching, bags, etc. .. and staying with the stock trailing arms especially.

Take a look at mine, I used the Hotchkis bracket designed specifically for this issue. This will also keep your truck from 'squatting' during hard acceleration and it gives you back some of the original geometry of the 'truck arm' suspension. .. What I'm saying is your trailing arms are not sitting "flattened out" in paralel with the ground. you actually have more of a Nascar type rear suspension geometry. I personally feel it's one of the best things you can do to relieve some of the future suspension issues. I'm running the bracket mod, 6" springs, 1" block, and 3 degree shims. My rear pinion angle is exactly where it was before the drop.

Hope this helps ..
Later
Chad

I'm trying to learn all I can about our trucks, but having difficulty visualizing what your talkin about.......could you post pictures for us newbies...
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[CC69Rat]

Theres a good picture of it on post #1197 in my GMC build. I think its page 54.. something like that. 55,56 maybe.
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[Robznob11]

I don't see how you figure your going to loose .75 of your drop the front should not affect the drop it only affects pinion angle and IC. by doing this you are doing the same as the aftermarket kit and creating anti squat. you by changing the IC the weight transfer shifts and hits the tires with more tq making it bite harder and not blow the tires off. on another thread we discussed this and a guy put it a way that you can picture it in your head. the lower the front mounting point the more the tires try to drive over the axle the higher the more they try to drive under the axle causing more leverage and lift and biting harder into the pavement. I would do the mod if you have lowered it past 5" with springs. you can get an aftermarket xmember and they will be move up already. note that not all do tho classic industries is in the stock location but they are bolt on so you could probably flip them.

Originally Posted by CC69Rat

I have several pictures in my GMC build if you want to check it out (the second one in my signature)

When you lower the rear of the 67-72, assuming you're doing 5-6" springs (?) What happens is the distance betwen the axle housing and the frame rails get closer (duh.. I know you know this.. ) BUT, when you factor in the position of the front mounting point of the trailing arm does no change, think of that upward swing of the trailing arm vs. that pivot point on the trailing arm cross member. The angle of the 'perch' where your rear axle housing sits will roll the nose of the pinion down. By flipping / raising the brackets up is corrects some of this pinion adjustment. In theory the truck will only think it has been dropped about 2-3 ".

The only negative drawback is by doing the flip mod, you will loose about .75" of your rear drop. So, 6" springs now = 5.25" net drop. .. so, just add a 1" block and it's all set.

I won't lie man, it is a PAIN to do it. There are 6 rivets in each bracket. It is ridiculous to try to do it with a grinder. If you have a plasma, or air hammer I would high suggest the mod. .. If you're going really low, Cnotching, bags, etc. .. and staying with the stock trailing arms especially.

Take a look at mine, I used the Hotchkis bracket designed specifically for this issue. This will also keep your truck from 'squatting' during hard acceleration and it gives you back some of the original geometry of the 'truck arm' suspension. .. What I'm saying is your trailing arms are not sitting "flattened out" in paralel with the ground. you actually have more of a Nascar type rear suspension geometry. I personally feel it's one of the best things you can do to relieve some of the future suspension issues. I'm running the bracket mod, 6" springs, 1" block, and 3 degree shims. My rear pinion angle is exactly where it was before the drop.

Hope this helps ..
Later
Chad

[BugzC10]

Originally Posted by CC69Rat

Theres a good picture of it on post #1197 in my GMC build. I think its page 54.. something like that. 55,56 maybe.
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Thanks....
BTW...#1197 is on pg 48
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[CC69Rat]

48, 54 .. whatever it takes.

[CC69Rat]

Does this help?

[BugzC10]

Instead of moving the training arm mounting points, is it possible or practical to install a wedge shim at the axle mounting points to improve Pinion angle?
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[CC69Rat]

The trailing arm mod will fix about 3" of the drop and I used an additional 3deg shim to correct the rest of it. So,.. yes absolutely.
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[BugzC10]

Originally Posted by CC69Rat

The trailing arm mod will fix about 3" of the drop and I used an additional 3deg shim to correct the rest of it. So,.. yes absolutely.
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Do you have a source for the shims, or did you have to make them?
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[CC69Rat]

Here's the link where I got mine. This is the lowering block (obviously) but they have the shims too.

http://www.stockcarproducts.com/cont...ock-aluminum-2

I'd suggest 1 deg shim for every 1.5" drop. .. but that's just ballpark. LWB might be different (?) .. measure, measure .. These things are not cheap nor is your driveshaft when it drops a Ujoint and either sticks into the pavement and catapults you across into the oncoming lane .. or drops the rear joint and you're stuck on the side of the road.

I guess I worry too much but in a lowered truck with the pinion angle as close to perfect as you can get it .. man, the truck just floats on air. No vibrations, jump roping, etc. It's a lot of trouble but well worth this correction in geometry to do it 'correctly' the first time.

Not saying none of the other trucks / drop kits are correct .. there's a 1,000 different ways and combinations out there. I'm just sayin, .. just my opinion. This is a good way to do it on a budget and keep your stock trailing arms. I just couldn't lay down $500+ for aftermarket trailing arms. (Yet anyway ... )

[CC69Rat]

For the record, I'm not taking credit for this. Big props to my buddy Gringo for posting this idea. This is not the post, but it will put you in touch with him if you have other questions maybe I can't answer. Follow his build, this guy is sharp.

http://67-72chevytrucks.com/vboard/s...d.php?t=251017

edit:
Somewhere around in here:
http://67-72chevytrucks.com/vboard/s...444746&page=36

He's talking about the trailing arm mods.

[BugzC10]

Rat,
You've posted / passed along some great information....appreciate it.
My truck is Lowered in the rear 5.75". ...4" with CPP springs. 1.75 with block/shim. Should I be concerned at this point about pinion angle / drive shaft failure. Or maybe just adjust with wedge to make it perfect +/- and ride comfort.
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[CC69Rat]

Concerned -- probably not if it has a shim in it now (?)

Particular -- you might put a degree / angle finder on it to just see where you are. Do you have a one piece drive shaft or two?

[BugzC10]

Originally Posted by CC69Rat

Concerned -- probably not if it has a shim in it now (?)

Particular -- you might put a degree / angle finder on it to just see where you are. Do you have a one piece drive shaft or two?

No shim in it now. I have 1.5" block + .25 plate. Plate is extended adjustable panbar.
I have one piece drive shaft. I'll have to pick up an angle finder to see where she sits.
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