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Old 11-08-2006, 09:55 PM
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Should Output Shaft Wiggle on THM200 4R?

I dropped my driveshaft today trying to find the cause of a rapid rat-tat-tat noise under the car on hard acceleration. Sounded like something in the driveline was contacting the frame as the driveline rotated. Was constant not rythemtic.

Anyway, after pulling the driveshaft I was looking at the transmission output shaft that goes into the front U-joint yoke. The output shaft isn't fixed in place. It doesn't pull in or out but I can wiggle it around up or down, side to side, about 1/16 inch.

Is this normal?

I also measured the free end play of the driveshaft as .367 inches with the car sitting on the ground. There is a shiny band on the u-joint yoke about .150 inches wide outside the transmission oil seal indicating the yoke moves into the transmission case this far under normal operation. This would still leave .217 inches of frre end play.

Anyone know what the end play should be on an automatic transmission with a 50 inch one piece driveshaft?

John

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Old 11-08-2006, 10:07 PM
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Normal. It is centered by the yoke in the output bushing.
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Old 11-09-2006, 06:15 AM
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You gotta put the drive-shaft back in place, then you can try to lift it up and down. There should be no "wiggle around" then. The yoke is just slipping into the bushing in the rear-housing. If you got 1/16 play with the axle in place, then your bushing is totally gone.
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Old 11-09-2006, 06:21 AM
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If there is too much wiggle as you call it...you will know it because your seal will be leaking as a result.
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Old 11-09-2006, 06:59 AM
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should output shaft Wiggle on thm2004r?

Ok,you now know the output shaft is gonna move a bunch,with driveshaft out,good info from posts.Now on to that rat-tat-tat noise.

You said constant not rhythmic.Do you mean the noise level stays the same at all speeds? I know it's under hard acceleration,will it intensify?

Any marks on driveshaft? Engine and trans mount ok? Will it make any noise under a load sitting still?
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Old 11-09-2006, 08:46 AM
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I've had bad universal joints do exactly that, but I'm more accustomed to driveline noises driving more 4X4's than not over the years.
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Old 11-09-2006, 09:02 AM
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I think the output shaft is okay, only wiggles when the driveshaft is off and no leakage of oil whatsoever.

This noise started after I adjusted my upper rear control arms to reduce the pinion angle -- changed it from 6.5* up toward the transmission to 1.5* up toward the transmission. This obviously changed the rear geometry and pretty much eliminated some drivetrain vibration I was having.

However, when I give it WOT, not immediately, but very quickly this very metalic screeching starts (it does have a rapid beat to it, not a squeal) -- I think it was increasing in speed as the engine rpm rose but I quickly backed off when it started.

Before removing the driveshaft I looked for any sign of the driveline makeing contact with the frame, brakcets, shocks and couldn't see any. After removing the driveshaft I did find one short mark that might be a contact scar that is located exactly where the shaft goes through a frame cutout. The scar was short, no more than 3/8 inch around the circumference of the shaft. The frame cutout might have some paint rubbed off, but it is not obvious it was contacted by the shaft.

Clearance on the frame cutout is closest on the passenger side with about 3/8 inch clearance with the car at rest. I don't have any experience with this -- would a driveshaft move 3/8 inch to the side? The driveshaft was custom made and 50 inch in length. The mark is 24 inches back from the front u-joint. The rear suspension has a 28 inch panhard bar which sits level under normal load. With 200 lb rear springs the car doesn't squat much.

At first I thought maybe rotating the pinion down more level may have pushed the front u-joint yoke too far into the transmission and it no longer had sufficient free play. But based on dust on the exposed yoke, it doesn't appear to have moved into the transmission enough to bottom.

I guess I will touchup paint the scar on the driveshaft, put it back together and see if it rescars in the same place.

Thanks,

John
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Old 11-09-2006, 09:04 AM
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Oh, and no noise when reving the engine in neutral. The noise definitely started after repositioning the rear control arms.
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Old 11-09-2006, 03:50 PM
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Since the driveshaft is a little closer to the passenger side of the frame cutout hole than the drivers side of the hole, I decided to try and measure whether the axle is centered under the frame.

I measured from the upper shock mount to the inside of the rubber of the tire and got 2 1/4 inches on the drivers side and 2 7/8 inches on the passenger side. Also, the shock angle is 4* inward on the drivers side and 7* inward on the passenger side.

I also measured from a reference point forward on the frame on each side back to the front edge of the axle and got indentical measurements. So, the axle appears to be square to the frame.

Now this is no stock rear suspension. It was to some extent cobbled together by the shop that installed the cutlass front suspension and rear axle onto the 1939 chasis. So there is no garantee anything is exactly in the right place. But it does have a lot of adjustablility -- coil over rear shocks, adjustable upper control arms, and adjustable panhard bar.

So, it appears that if I move the axle 5/16 toward the drivers side using the panhard bar, the axle will center under the car, I will get a little more driveshaft clearance through the cut out, and the rear shock angles will come closer together.

Here I go.

John
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Old 11-10-2006, 12:10 AM
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John - If you changed the upper control arm height, you have also changed the anti-squat characteristics of the car. In turn the squat change under hard acceleration will react in a manner that sees more lateral movement of the rear end due to the panard bar traveling farther and in a wider arch. The longer panhard bars have less lateral movement than shorter ones but all panard bars exibit some form of lateral movement of the rear end. Where the drive shaft is already a little askew, the longer arch of the panhard bar may have been just enough to have made the contact problem become obvious. You can stretch a string on a pair of jack stands from in front of the front bumper to behind the rear bumper on both sides of the car. Measure and set up the string so it is say 4" inches out and parallel the frame rails. I usually measure a little behind the front wheel and again the same distance off the frame a little in front of the rear wheel. The same general area you'd use to take frame height measurements. Then you can take your tape measure and see how far the front tire is away from the string vs your rear tire. I usually measure axle flange to axle flange at the rear as well because I've seen wheel offsets get in the way of getting a narrower rear tracking width centered in the car. You are definitely correct in the decision to move the rear end over with the panhard bar so that it is centered in the chassis. Also raising the panhard bar will increase oversteer and decrease body roll. Lowering the bar will decrease oversteer but increase body roll. Depending on the length of the panhard bar, increased roll translates into increased rear end lateral movement. It can be a balancing act sometimes. I hope this helps.
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Old 11-10-2006, 06:55 AM
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Hammerlane,

Thanks for your comments. I reinstalled the driveshaft last night but didn't take the car off the jack stands yet. I am going to put masking tape around the edge of the frame cutout so I can tell if the driveshaft makes contact with it.

I can adjsut the panhard bar for length but not for height without having it removed and rewelded.

The measurements you are talking about are for the purpose of determining if the front and rear wheels are centered relative to the frame, correct?

John
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Old 11-11-2006, 09:59 AM
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John - You are welcome and yes that's correct - determining if the front and rear wheels are centered relative to the frame. Smart idea with the tape. Most likely you are already on top of the problem and adjusting the panhard bar will eliminate the problem. Some other things to perhaps consider in the event it does not go away though might be.

Shock measurements - Shock travel can help tell you if you are sprung properly, if you have a bad shock, or help in isolating a suspension bind. Do your coilover shocks have gromets on them to show the amount of travel the shocks are seeing? If they do you may also want to plug that information into the picture. If one side is getting buried and one is getting normal travel it may help shed some light on the problem. I've seen instances where the LF suspension had a bind in droop and buried the RR suspension hard on acceleration.

If you don't have shock grommets and you want to measure shock travel, you can use a small zip tie wrapped around the shock shaft on top of the shock body. Slide the zip tie down to the shock body before you start and as the shock sees the travel it will record it on the shaft with the zip tie. After a test drive, measure the travel preferably without jacking up the car. Sometimes that may mean finding a friend with a drive on type car lift or an oil change place with a pit to get the exact measurements but if none of those are available just try to jack it up evenly and support the rear end to simulate it sitting on the ground and take the mesurements.

I'm assuming you have high aircraft quality 1/2" or 5/8" hiem ends on both ends of the panhard bar correct? Is the panhard bar long or short? Is the panhard bar mild steel, chrome moly, or aluminum? Could the bar be flexing and causing excessive lateral movement?

How far inboard from the centerline of the rear tires are the lower coilover mounts? What motion ratio are they installed at? What are the compression/rebound ratings of the shocks? Are they gas shocks? Have they been mounted upside down to reduce unsprung weight? Hydraulic shocks won't live more than a few strokes mounted that way. How heavy is the car? Do you know the individual wheel weights? Front weight vs rear? Left side weight vs right side?

How large is the fuel tank? Gasoline is 6.042 pounds per gallon. A 22 gallon tank can change weight transfer a lot especially given most fuel tanks are mounted outside the wheelbase. ( Example - a 108 wheelbase car will see 133 pounds of fuel as 142 pounds of rear weight when a full 22 gallon tank is mounted 115 inches back.) Does the noise only show up when the tank is full? After the upper link change did the car squat more than usual? Does the car seem to brake differently?

Let us know what you discovered John, and good luck with it!
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Old 11-11-2006, 01:33 PM
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Hammerlane,

I can supply much of the data you mentioned in your post. Let me bring you up to date on how we got where we are.

We started with a rust free, straight, original 1939 Olds that my wife inherited from her father 3 years ago. We decided to street rod it for enjoyment and improved driveability.

We turned it over to a nearby shop which located a donor 1988 RWD Cutlass to take the front clip, motor, trans, and rear axle off of. Since they had done a lot of this before. I didn't get involved in picking the donor or overseeing the work. I spent my time looking for various parts for the project while two different shops collaborated on chasis work, body work, and driveline installation. As a result when we got the car on the road 1.5 years ago, I didn't really know much about how the chasis work and driveline was done.

It is obvious now that the car was the victim of a "just get finished" attitude at the chasis shop and inexperince at the driveline shop. Among the problems that have surfaced which my wife and I took upon ourselves to understand and correct are:
1. camshaft installed 45 degrees advanced -- fixed by degreeing within 2*
2. harsh ride due to drag shocks, soft rear springs -- fixed by installing QA1 adjustable shocks and 12 inch 200 lb springs
3. overheating -- fixed by installing 15 inch shrouded Cooling Components fan

More recently we have dealt with the driveline vibrations. By changing the pinion angle I eliminated those but somehow introduced this new metalic screeching sound.

After reinstalling the driveshaft, it is centered in the frame cutout which is not the way I remember it before taking it out. But I adjusted the panhard bar to move the rear axle 1/4 inch toward the drivers side. This equalized the distance between the upper shock mount and the tire on each side at the rear, but the shaft is now slightly off center in the frame cutout.

On a test drive I still get the metalic screeching sound under WOT, but it wasn't quite as loud.

But now I am more concerned about the overall squareness of the chasis before worrying anymore about the screeching.

I have a top view engineering drawing of the 1939 chasis with all the dimensions between frame connections and specific locations.

I am going to put the car back up on jack stands and use a plumb bob to mark on the floor the layout of the chasis and orientation of the front wheels and rear axle. I fear the front clip is skewed -- a quick measurement from center of wheels gave me a wheelbase of 113 inches on the drivers side and 112 inches on the passengers side.

As for some of your questions:
- the shocks are new with 3.0 inches of free travel at ride height. The grommets have moved up 1.75 inches over 700 miles of driving since July, but no rear passengers.
- shocks mounted right side up, rebound setting 3 of 12 (toward soft)
- bottom shock mount 8 inches inboard of tire centerline
- driver side bottom shock mount 1/4 inch lower than passenger side, compensated by raising coilover bottom spring mount ring
- shock angle 5 degrees inboard
- hiem ends on each end of panhard bar and upper control arms
- 28 inch panhard bar, not sure of the material
- 16 gallon fuel tank located behind the rear axle
- with half tank gas, no driver, 1900 lb front, 1560 lb rear weight
- 200 lb rear spring compression: driv side 2.38", pass side 2.75 "

So, getting out the jack and jack stands for the weekend.

John
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Old 11-14-2006, 09:38 PM
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John Ė Wow! Sounds like you have already endured more than your fair share of calamities with the old girl. A couple of things come to mind about professionals who donít seem to sign their work with excellence but ma always said if you donít have anything nice to say wellÖgoing there wonít help anyway. Suffice it to say that I really hope the chassis folks did not mount that front clip skewed.

I canít even comprehend the possibility that a chassis shop would not reference a squared chassis centerline when they front clip a car so Iím more inclined to believe the spindle measurement being off could be a result of caster offset, A-arm adjustments, and/or the base design parameters of the 88 Olds chassis itself. I wouldnít be too worried just yet.

Definitely use the plumb bobs to figure out what you are dealing with though. Whereas the 39 frame rails were straight, use them to determine the centerline of the chassis. That line will tell you how well they did or didnít do when the put the front clip on. When you jack the car up so you can get under it easier be certain to return the chassis to a leveled ride height attitude with the suspension loaded as if it were still on the ground before you set about measuring. You are most likely already doing that but where it is as critical as it is, and for others following or referring to this thread, it warrants reiterating the point. Also if you are using equal height blocks for under the tires make sure all of your tires are aired up properly and you have enough room to safely chock the wheels.

No doubt the most accurate way to see if the front clip is in square is putting the chassis on a jig but most of us donít have access to one. Thousands of short track racers though square their chassis without the benefit of a jig on their garage floors many times during the course of a racing season. There may be some pro chassis guys or racers out there who can chime in and even shed some light on a simpler more efficient way of going about it. Unfortunately though I can only share what I know and have done in the past with good results.

I use the lower A-arm mounting points. I measure in to the chassis centerline, forward to a 90-degree to centerline reference line, (I call it the frontline), derived from the 3,4,5 triangulation method, and then X measure from the opposing lower A-arm mounts to the measurement points I brought forward to the frontline, and again X measure to the inside of the old frame rails at a point equally distant back from the frontline just behind where the front clip was mated up with the old frame rails. I usually check A-arm lengths and angles and the lower ball joint to centerline measurements as well.

This link shows the 3,4,5 triangulation-stringing method used: ( http://www.circletrack.com/techartic...surement_tech/ ). Although this is a racing link, and it relates to squaring a rear end in a racecar, you can apply the same information to measure the front-end suspension points in your car.

Given what you had to say about two different shops coordinating the efforts to assemble the car, you may also want to ensure the driveline alignment measurements are correct. There are two planes to be concerned with, the horizontal plane, (the driveline as viewed from the rear of the car), and the vertical plane, (the driveline as viewed from the side of the car).

The crank, transmission, drive shaft and rear end should ideally be parallel with one another in the horizontal plane. They can be offset from the chassis centerline without too much of a problem as long as they all remain in alignment with one another. It is ok to sacrifice some rear spring/shock angularity to accomplish this too. Springs and shocks donít begin to lose rate until they get above 10 degrees of angularity.

That may explain why the chassis shop set your springs and shocks a little off from one another. It is more important to keep the driveline parallel. So when you have your plumb bobs out and have your centerline, frontline and rearline reference lines transferred onto the floor see where the motor, transmission, drive shaft, and rear end are all sitting in relation to one another and with your centerline. Check out the frame member hole the drive shaft goes through as well to ensure that it is where it has to be. Speaking of that frame member; when you took the car out for a test; did any marks show up on the tape you put around the hole in the cross brace?

The vertical plane is where pinion angularity comes into focus. Under acceleration the torque tries to spin the rear end housing upward (positive) as the pinion tries to climb the ring gear. The objective in setting the pinion angle is to have the entire driveline angle at or near zero degrees under hard acceleration when the drive train is seeing itís highest load. This means that our pinion angles have to be set according to the type of rear suspension control we have and how much the rear end is actually being allowed to flex or twist upward under the torque load we have going into it.

The angularity of the crank/transmission output shafts also have to be brought into the equation. Hereís why. If your transmission output shaft is at +2 degrees and your pinion is at Ė2 degrees, then your true pinion angle is at zero degrees. Most four-link suspensions need to have a negative 1 to1.5 degrees of pinion angle set into them to bring the angle to zero under hard acceleration wrap up. In the example above the pinion would need to be set to Ė3 to3.5 degrees with a four link set up to get the correct negative 1 to1.5 degree static pinion angle.

By comparison a leaf spring rear suspension does not have the same wrap up control and might need as much as negative 4 to 6.5 degrees depending on spring stiffness. See this link ( http://buickperformance.com/Pinion.htm ). Getting a handle on the crank/transmission angles will tell you where you need to be with your pinion angle and rear end alignment. Going slow, using thin lines so you can be precise with your measurements, and staying methodical in your approach wins the day. Hang tough, with it man. Good luck and keep us posted.
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Old 11-14-2006, 09:57 PM
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Hi john I had a hard time with my ISP staying on-line lately. So I worked out a response to you in a word document. I figured I'd just cut and paste it into the post but for whatever reason it didn't post. I'll try it in shorter blocks ok?
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