Banging from underneath when shifting

[Budweasel]

Thanks in advance to everyone who can shed some light on this issue.

I recently purchased a 1968 camaro and I am learning about its idiosyncrasies.

When shifting from 2-3 or 3-4 with 3/4 or more throttle I get a loud clunk from what seems like right side of car. Possibly near subframe connector or right leaf spring. Tonight I went into fourth with some more exuberance than before and the clunk came followed by the rear of the car mildly swinging to the left, (I'd guess no more than a foot). Shift happened near 60 mph as I was exiting an onramp to the interstate.

What could be causing this? What should I look for? Broken leaf spring? Loose subframe connector? Axle out of alignment? After losing traction at highway speeds right after the "klunk", I'm having safety concerns.

Background on the car: 489 cubic inch crate motor advertised as 575/575. Transmission is TKO 5 speed. Global West upper and lower control arms, Heidts lowered ball joint, Wilwood brakes, Hotchkis subframe connectors, leaf springs, and front and rear anti sway bars. Caltracs traction bars. Tires are 255 BFG g-Force KDW. I have not identified rear yet, (was told 3.55:1 ratio).

[Sieg]

Get it on a lift or jack stands asap and thoroughly check the health of all suspension components, mount locations, and frame rails.

On throttle application the top of the rear end housing is rotating back toward the fuel tank, during a hard shift it's snapping back.

Is the pinion bump stop on the car?

With 575/575 you roughly have twice the power the chassis was engineered to handle.

Let us know what you find.

[Vince@Meanstreets]

I'd like to hear about the pre load or lack of in them cal tracks


Your gonna be looking for pounded rust dust somewhere on the suspension.

[Budweasel]

I have the car on stands now. I will report with my findings hopefully by end of weekend.

Cheers!

[Sieg]

Good for you!

[GregWeld]

My guess is it's the pinion hitting.... Look for a "witness" mark of fresh metal or "damage" to the undercoating or paint above the pinion.

My guess is also that the dance / side step - is caused by the rear end not being in correct alignment with the front -- or "square" to the front of the car... you might take it in for a FOUR wheel alignment.

[Budweasel]

So far here is what I have found:

1. Front drivers side spring mount has one of the three bolts missing. Threads are bad, need to chase with tap in order to get the bolt back in.

2. When measuring between center of wheels on drivers side versus same dimension on passenger side there is a 7/8" variance. Passenger side of axle is farther back. Center pin on leafs is bent, looks consistent with out of square axle like Greg said.

3. U bolts on axle are not torqued properly. A couple on passenger side were less than 40 ftlbs, should be 120 ftlbs according to specs I found on Eaton's site. Could these being loose contribute to the bang?

4. All other fasteners, subframe connectors, body mounts, anti-sway bars, were tight.

5. I found no evidence of rotation between the shackles and the axle tube, (looked for fresh scratches, no grease, etc.). There is a pinion bump stop present and as far as I can see there has been no contact between pinion and stop or body.

6. I will check the caltracs preload when I get the car back on the ground. Maybe the right one has no preload and is "slapping" into the front spring mount?

For what it's worth. This has happened before but never so violently and it's only been me in the car. Last night when this happened there were three of us in the car; two in front and one in back. The person in back did not feel anything with his posterior NVH receptor. In case it matters: driver 215lbs, front passenger about 170lbs, rear passenger (sat behind driver) 280lbs.

Thank you all so much for your help. It's the people that make this site so wonderful!

Here is a picture of the right rear from in front of the axle.

[GregWeld]

It's hard to see from this one picture and the angle -- but it appears you may possibly be bottoming out the shocks. You said you had 3 pretty good sized boys in the car which would also be a contributor to that.


Tie a piece of string around the shock "rod" - and push it down against the top of the body.... then go out and hammer it just a bit so you're loading the rear end... come back and see where that string ends up as it's pushed towards the top of the rod.... Do this on both sides because that will be measurable to see the loading as well -- left vs right side.

The shock should have sufficient length so that you have an equal amount of compression and extension... and when sitting with weight on the axle (as though it were on the ground on its tires) the exposed rod should be about half of the total (so 2" of compression and 2" of extension = for 4" of total travel)...

Put the jack stands under the axle --- and then measure the exposed rod length. It looks short to me.

[Vince@Meanstreets]

Good eye, if that's full droop I'd say you are right.

Nevermind stand is under the rear.


You can see the dirt and clean section from the shaft seal.

[GregWeld]

Originally Posted by Vince@MSperfab

Good eye, if that's full droop I'd say you are right.

Nevermind stand is under the rear.


You can see the dirt and clean section from the shaft seal.

Yeah -- but that's the driver side --- I learned a while ago (50 years?) that the passenger side loads pretty hard during throttle use.... LOL