Mcgaughys 2/4 Wobble Solution - Pinion Angle

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Canadian_Ram

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TL;DR: Pinion Angle

I know, another wobble thread, how original. My solution was found by my friends dad who was in the Canadian Rally Championship in the Late 90s and has experience with both lowered cars and trucks both personally and professionally.

My 4WD single cab shortbox Ram wobbles significantly when exceeding 90 MPH and only gets worse as I accelerate. Nothing in this thread is to discredit anyone I asked for advice or any other thread on RF's. I will add good quality pictures after work possibly to aid others hopefully. Here is the steps I went through including what realistically was accompanied by 10's of hours of research and note taking. All Mcgaughys parts I reference were from their 'Deluxe Drop Kit - McGaughys Part# 44050'

Step 1:
Took my truck in for alignment, tire rotation and balancing. No real noticeable change.

Step 2:
I had my front left CV which was failing from unknown reasons replaced under warranty and had the dealer also align my truck while It was in for warranty work.

Step 3:
Under advice of other 2/4 owners and Hemi450HP, I purchased a Sphon Adjustable Panhard Bar. It was installed in combination with my Mcgaughys panhard relocation bracket and adjusted to get the tires as close to possible using a plumb bob and tape measure. It was noticed that the tires seemed to have a very slight camber in, where the tops appeared to be slightly farther under the fender than the bottoms. Tires were checked for bulging and wear and were ensured to be at the proper PSI and had the lugs torqued to spec after.

The wobble felt as noticeable as ever before even with the panhard adjusted and triple checked to ensure it was also torqued and installed correctly.

Step 4:
Next up was the Hellwig Rear Sway Bar which bolted right up as-per the instructions to the Mcgaughys shortened end-links to the most aggresive frontward mounting point on the bar. This aligned the bar perfectly horizontal, everything was torqued back to Chrysler's specs and double checked. The panhard was also double checked after to ensure both bars together had the axle were where it should be. One comment about the sway bar, its quality is amazing, also ensure you are installing it in the exact same orientation as stock, I am pretty sure its not symmetrical and has a left and right side one causing the center to be higher than the other orientation (possibly contact panhard or diff) but I don't know if that's labelled or mentioned in the instructions. It can be done done on your driveway with most of the proper tools but if I had a lift it would have taken 1/4 of the time that it did.

The truck's rear end feels solid when taking corners at high speeds such as on-ramps, you still feel the wobble over bumps and at high speeds but its just a stiffer wobble instead of being mushy like it was before. This wobble is much safer and much easier to handle for the average driver, I can see how some people feel confident calling this a fix, I want next to no movement at high speeds. So I am not done.

Step 5:
I have QA1 rear shocks ordered, TS905's that Hemi450HP verified to be direct bolt on's and no modification needed. Will verify when they arrive. In my eyes the rear shocks are no good. The rear is dropped using coils and changed 4", 4" results in a very large angle change in multiple components of the stock set-up and I think shocks are one of them. I believe that the factory shocks add to the wobble because they are not operating at their optimum angle nor design distance like they do when the rear is 4" higher.

Wondering if I NEED to replace the front shocks also or if only the rears will be acceptable. I personally think the front ones will be fine because we used a spindle drop which is intended to keep the front geometry AS CLOSE AS HUMANLY POSSIBLE to factory while still achieving a drop. At the cost of pushing your tires out 1/2" - 3/4".

Step 6:
My friends dad who was in the Canadian Rally Championship in the Late 90s and has experience with building and working on both lowered cars and trucks, especially suspension wise, both personally and professionally looked at my truck and very quickly told me my pinon angle is off and that it is causing wheel hop. These problems compound together and causes the rear end to eventually start wagging or wobble even with Step 3 & 4. I am in the process of calling Spohn or Matt (whoever can get me the delrin bushings the easiest) and ordering Spohn Upper & Lower Rear Control Arms in order to recenter and correct the pinon angle to one that is correct for the new geometry of the truck and the way I want to drive it.

He mentioned over text message to me if I wanted to almost ensure this was the problem I could by: Removing/unbolting/undoing what holds the rear drive-shaft in safely and drive the vehicle in 4WD. It would be very unorthodox and something you don't want to do for a large distance or time period AT ALL but it could confirm if the drive-shaft/angle is the culprit. I'm not going to try this even with his help, I wanted the control arms anyways this just gives me justification to spend more $$ without feeling guilty. After I install them, adjust them the best I can and most likely take it to a professional alignment shop and let them adjust all the Spohn components in combination with the rest of the truck I should see no wheel hop at any speeds and definitely no more wagging or wobble. I will be putting on perfect Nitto 420's that are staggered to account for the 1/2" - 3/4" that the front spindles push out the front tires and the tires will be perfectly aligned and weighted.

Step 7:
Profit??

I should have no excuse within a couple weeks time. I hope this might help anyone currently with problems that is on the fence about the Spohn Upper and Lower Rear Control Arms, or anyone in the future with problems as well. I will post again when I get the Shocks and the Control Arms in. If anyone can tell me if not upgrading the front shocks is acceptable or not and if it isn't which shocks I need? Thanks.
 
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WadXpress

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I hope this fixes your issues. Definitely in for results
 

Dubstep Shep

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In the end, the issue will never be 100% resolved until you put a watts link on it.
 

brad65ford

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have the same issue and went as far as step #3 only. Love the way the truck looks but its really shakes the truck at different speeds i hate it. Don't think the 22" SRT heavy logs (rims) are helping the issue either. OP are you running stock wheels?
 
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Canadian_Ram

Canadian_Ram

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have the same issue and went as far as step #3 only. Love the way the truck looks but its really shakes the truck at different speeds i hate it. Don't think the 22" SRT heavy logs (rims) are helping the issue either. OP are you running stock wheels?

I have the 20" stock rims and running the factory tires still for arguments sake. When I correct the Pinion angle I will be swapping my tires for Nitto 420's. I think I will be satisfied after that.
 

sicmadek

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I know thad has stock shocks with cut bt springs. The only thing he added was adj. control arms and he said it cured his wobble. He also said all wheel hop is gone.
 

R/T_Fire

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In the end, the issue will never be 100% resolved until you put a watts link on it.

Hey don't giv out all my secrets... I was thinking of this same thing and ben kicking around ideas and looking for a diff cover I can use to do this. may also just build a cage like a skid protection cover for a rock crawler.

Saw it on the show Americarna and been thinking of it since.
 

Dubstep Shep

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In my opinion the diff cover mounted units are vastly superior to all otgers, especially on unspring weight.

That said, go look at S-10 WLs that go over the stock diff cover. Much less fab work needed, just a couple tabs on the axle.
 

keg184

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I have a rcsb 4x4 and lowered the back 2" and front 1". I redrilled the chassis side of the panhard bar raising it 1" and I have had it over 100 mph with no wobble.
 

N1ck

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I have a rcsb 4x4 and lowered the back 2" and front 1". I redrilled the chassis side of the panhard bar raising it 1" and I have had it over 100 mph with no wobble.

I don't think you're low enough to cause serious wobble.

I have a friend that has the mcgaughys 2" drop spindles with factory chopped springs giving him a 2/4 drop he also added a new swaybar and redrilled his panhard bar like you, he has had it over 200kms / 120+ mph and he says its sturdy as could be.
 

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charonblk07

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I don't think you're low enough to cause serious wobble.

I have a friend that has the mcgaughys 2" drop spindles with factory chopped springs giving him a 2/4 drop he also added a new swaybar and red rilles his panhard bar like you, he has had it over 200kms / 120+ mph and he says its sturdy as could be.

This morning I hit 220KM/H on the way to work with no wobble.

100mph = 160km/h

Slowpokes :roflsquared:
 

N1ck

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You guys are nuts!

I've been 200+ only a handful of times in the 10 years I've been modding my car... A few times in my old SRT4 and twice in an old Audi TT.
 

charonblk07

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My '07 had a top speed of 235km/h on the bottle and the '09 will do 240km/h with the blower and 273km/h with the bottle. Important things to know though, I run W rated tires, have friend with a 10km stretch of paved private road to do this on, and my trucks are all geared/built towards 'safe' top speed which means the suspension, aero, and brakes are meant to handle the requirements. Only addition I would make is there is a time and a place, and I don't agree with doing it on public roads where others can be put at risk by my stupidity. I don't drive 200+ regularly but it is nice to know that I can.
 

R/T_Fire

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Hell I'm still stuck with the governor at 105.... and I hit that in 4th maybe it was 5th.... I dont remember... but I know it has so much more left.... gotta get tuned soon... better brakes first....

as for the wobble, exactly what is the wobble is it in the steering? body wobble, or more a vibration? just curious..
 

R/T_Fire

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Driveshaft velocity difference from improper input and output angles.

This video pretty much explains the whole issue
https://www.youtube.com/watch?v=gmV4qwLfOMY

Interesting video, Ive been telling guys this on the farm for years when hooking up well pump motors to gearheads... I can hear the gear head runs with funny sounds when this happens and they don't set them up right and I have to fix it to get rid of the vibration.

I was more wondering what it felt like in the truck... I get a vibration every now and then ht a bump or something and I'll pick it up.. kinda like a wheel balance and I have read alot on 22's and tires doing similar so I've kinda always chalked it up to that...

Now I'll have to look into this. I'll have to put a angle gauge on the pinion and see what the angle is at. now if its odd how is this corrected other than a set of adjustable links?
 

charonblk07

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Interesting video, Ive been telling guys this on the farm for years when hooking up well pump motors to gearheads... I can hear the gear head runs with funny sounds when this happens and they don't set them up right and I have to fix it to get rid of the vibration.

I was more wondering what it felt like in the truck... I get a vibration every now and then ht a bump or something and I'll pick it up.. kinda like a wheel balance and I have read alot on 22's and tires doing similar so I've kinda always chalked it up to that...

Now I'll have to look into this. I'll have to put a angle gauge on the pinion and see what the angle is at. now if its odd how is this corrected other than a set of adjustable links?

Basically the back end just begins to wobble from side to side, picture an excited dog who's tail is shaking the whole ass end around. It's more than a vibration that's for sure, I've never had the issue in my truck because I dealt with it before it even started, but it's a symptom even if the axle is offset to the side because of the panhard bar length but that's more of a vertical eccentricity compared to the horizontal eccentricity of the pinion angle issue since the long portion of the oval travel path is always perpendicular to the free axis of the smaller angle's plane. So a side angle will affect the up/down vibration and a vertical angle will affect the left/right vibration.

You'll get it with any big bump because there's a change in CV angle which will change the velocity of the joint temporarily and will also change the side angle as the suspension cycles. For your vibration on bumps you are increasing both the side and vertical angle when the diff moves up and to the right as it travels along the control arms and panhard bar paths. You could eliminate almost all of the side angle with a watts link but you can't get rid of the vertical angle change.

Your tire's will absorb some of the lateral motion from the vertical angle change before it begins to move the vehicle but the shorter the side wall the less is absorbed, same goes for the up/down motion and that's wheel hop from the tire loading and unloading. Soft sidewalls will absorb a lot of both types of motion but we don't drive around on soft side walled tires on 22+ wheels.

Vertical angle is changed with adjustable control arms, horizontal angle is changed with adjustable panhard bar, only other way to change this is to properly measure out the angle change required and drill holes accordingly and never change the ride height again.
 
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