Tri-4 link: Is a 3.5 degree change in pinion angle during full compression normal? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-12-2012, 09:09 PM
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Tri-4 link: Is a 3.5 degree change in pinion angle during full compression normal?

I am doing a triangulated four link rear suspension. I attached a picture for reference.

I set the pinion angle at ride height to match the transmission (2 degrees). Today I installed the upper bar's front bracket and tack welded the upper rear brackets (the brackets on top of the axle).

I put a floor jack under the axle and cycled it from ride height all the way to the bump stops -- a 3.25" motion. When the axle is against the bump stops, the pinion angle reads 4.5 degrees. I am new to installing 4-links, but I was expecting the pinion angle to remain virtually unchanged.

So my questions are:

1) Should the pinion angle change by ~2.5 degrees when the suspension is compressed?

2) If not, what did I do wrong to cause this?

Thanks!
J
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Old 05-13-2012, 09:43 AM
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Having your axle LCA mounts several inches ahead of the uppers will cause what you are seeing. I would think that (looking at them from the side view) an imaginary line drawn through them should be vertical in order to minimize the angle change. I'd be more concerned about what's happening with the driveshaft, will this deflection cause the trans yoke to bump into the tailshaft?

Russ
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Old 05-13-2012, 11:31 AM
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Thanks Russ. I was thinking that might be the issue. From the side, the upper brackets are 1.5" back from the lower brackets.

I can soak up about 0.5" of the difference by tightening the upper adjusters and re-tacking the brackets. However to make them completely even I would have to either shorten and re-tap the upper bars or re-work the crossmember at the front of the bed and move the front brackets.

I will see what (if any) difference the 0.5" makes and decide from there. I wonder how much driveshaft vibration this issue would cause if left unfixed (not that it will be) -- horrible or just slightly noticeable?

Thanks!
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Old 05-13-2012, 04:56 PM
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Some technical info from a well known expert in the field (Billy Shope of the Ramchargers) is here.
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Old 05-14-2012, 08:04 AM
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Quote:
Originally Posted by cobalt327
Some technical info from a well known expert in the field (Billy Shope of the Ramchargers) is here.
Speaking of Billy, haven't seen any posts from him in awhile. Any word on how he's doing?

Russ
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