canbaufo

To be clear, I've had the vibration with three different shafts; stock, Denny's HD, and Denny's Nitrous Ready. All are steel shafts and all became noticeable at critical frequency speeds based on gearing used at the time. Using sound deadening undercoating on the stock shaft and the Denny's HD shaft helped very significantly, but I have not done that yet on the current Denny's NR shaft and prefer not to. In the past with the other two shafts I sprayed undercoating on them very meticulously and evenly so as not to introduce an imbalance.

What I attempted to do with the adj LCA's was loosen the rear torque arm bolts and lengthen the LCA's, then retighten the torque arm bolts. My hope was that it would shift the axle/diff housing just enough to introduce a tiny bit of negative pinion angle. Not so. In fact, all it did was preload the axle and transmit more vibes to the body. Worth a try anyway. I have reset the LCA's to where they "want to be" at ride height so there is no preload at all.

Crazy that there's no way to get negative pinion angle, but that's just how it is on this lowered car. Now that I realize the tranny slip yoke is being pulled out of the trans on acceleration with a positive pinion angle, I guess I've come to the realization that it would be wise to get an Adj Tq Arm....whether it cures the vibes or not. Perhaps actually having a bit of negative pinion angle (about 1.5 - 2* ...heck I'll try for 1.8* since it works so well) will cure most of the vibes ...would be nice! It appears that I should be able to get the trans output shaft equal and opposite, which could really smooth it out.

I'm almost 43 and just getting tired of annoying noises. Hence the reason I'm focusing on this and accumulating parts for a true dual exhaust project that should be more mellow than the current Borla catback. Switching to X-pipe and slightly larger Borla Pro XS ("Turbo") mufflers. Not sure why they call them turbo-style when they're still a straight through design but whatever.

Injuneer

Just because an aftermarket DS is made of steel does not mean it will have the same critical frequency as the stock steel shaft. Tube diameter, wall thickness and steel composition all play a part. Since you have had the same vibrations with three different shafts, you have an alignment problem, not a critical speed problem.

Surprised loosening the rear torque arm bolts would do anything. Those thru-bolts are tight in the holes. The torque arm can't move more than a tiny fraction of an inch on the diff housing. What I think you accomplished was pulling the front of the torque arm backward in the front bushing, and pulling the slip yoke out of the tail housing.

canbaufo

Yes, there was only a very minor shift of the diff housing in the rear of the tq arm due to the through bolts like you said. Great points, I didn't think about that last one, but I am sure you're right because the vibes were worse with the lengthened LCA's. I have to just go ahead and get an adj tq arm, obviously. Do you have a recommendation for a good one at a reasonable price?

Injuneer

You have two choices in mounting - one that will use the stock bushing, or one that attaches to a cross-member that bolts in place of the sheet metal brace that spans the driveshaft tunnel. There are more articulated designs, like the one by Global West, that would offer an advantage in a road race application. Most people get what they need with a simple lever.

The arm that fits into the stock front bushing will typically cost $100 less than an arm that comes with the new cross-member. I prefer the chassis mounted design, because it takes the load off the tailshaft of the trans housing, and eliminates the huge uplift on the trans mount under heavy acceleration.

You also need to consider the type of bushing used on the front mount. A poly bushing will work well, and limit transmission of noise and vibration. A spherical rod end is stiffer, but transmits more noise and vibration. The rod ends will also wear out over time.

I personally like and use the Spohn Performance suspension parts.

canbaufo

I've read complaints from some who've used the chassis mounted designs. They claim that more vibration and road noise comes into the cabin, which stands to reason. I can appreciate what you're saying about the rear of the trans being lifted during load though, which throws the angles off of course. Sure looks like a nice piece you have there and it's very solid. I think I already have a poly tq arm mount, although if so it has some rubber on it's outer perimeter ....so maybe not. Whatever it is it has held up well for a long time. My car isn't abused much, so rubber may be fine. Thanks for the info!

canbaufo

This is the most inexpensive adj tq arm I can find at the moment (QA1 PN: 5282):

http://www.summitracing.com/parts/ha...ions/year/1994

Comparing apples to apples, meaning transmission mounted adj tq arms ...is this one of pretty good quality? I cannot find any reviews or threads where it is discussed or compared with UMI, Spohn, etc.

Here are my other two candidates:

Spohn
http://www.ebay.com/itm/Transmission-Mounted-Adjustable-Torque-Arm-1982-2002-F-Body-Camaro-amp-Firebird-/271418874184?_trksid=p2054897.l4275
UMI
http://www.ebay.com/itm/82-02-GM-F-Body-Transmission-Mounted-Adjustable-Torque-Arm-/271492082784?pt=Vintage_Car_Truck_Parts_Accessories&hash=item3f36306c60&vxp=mtr
Not a huge price difference, so I guess whichever is best is what I should go with. However, if the QA1 is plenty sufficient for my rarely abused '94 ...may as well save a few bucks. What do you all think?

canbaufo

Has anyone used the QA1 PN: 5282 adj tq arm???? Any opinions on product quality? Oddly it seems that very few have used it.

Found it for $260 - shipped at Jegs:

QA1 5282 QA1 Camaro/Firebird Torque Arms - Free Shipping on All Orders @ JEGS

canbaufo

I bought the QA1 for $260, too good of a deal to pass up and I couldn't find any negative feedback on it. Well ...after installing the adj torque arm and some pinion angle vs trans angle adjustments, I am STILL at square ONE .

So far, nothing I have tried has changed the vibration at all. It still kicks in around 70 MPH. I am using 1.8* negative pinion angle, since that has worked so well for many. Due to the car being lowered with an Eibach Pro Kit, it is not possible to achieve perfectly opposing pinion vs trans angle. With the trans shimmed about 3/4" off of the crossmember, the LEAST amount of negative angle (trans pointing DOWN at rear) I can get is 3*. With the pinion angle set to the ideal 1.8* V down relative to the DS, the DS is going uphill by 1.5* ...as in the DS is going UP pointing toward the front. This unfortunately means that BOTH, the pinion AND the trans output shaft point DOWN at the driveshaft. So there is no way to cancel vibration frequencies by having opposing angles (ideal would be pinion pointing DOWN relative to DS and trans shaft pointing UP relative to DS.

I have also implemented the following measures to reduce the vibration frequencies:

1. Rubber sheeted the stock rubber trans mount.
2. Rubber sheeted the trans crossmember at mounting points
3. EVENLY sprayed rubberized undercoating onto the DS and torque arm

So far I've used 3 different steel driveshafts and two completely different rear ends and still have the same vibration. Also, different wheels and tires ....same vibration. I have noted that rubberized undercoating does help some, but not enough for me. Also brand new tires mask the vibration fairly significantly in the first few thousand miles.

I have a few more things to try before I finally break down and get an aluminum shaft.

1. Turn the DS 180* in the pinion yoke, independent of any other changes.

2. Spray some more rubberized undercoating on the DS and torque arm (I have a very precise procedure for getting the undercoating on the DS evenly so as not to introduce an imbalance). I didn't put much on and it was the regular stuff. There is "sound deadening" undercoating that may be more effective that I could spray on a little thicker. Laugh, but this has helped significantly before with other DS and rear.

3. I may try a little more negative pinion angle and see what it likes in increments. If you picture what happens during acceleration and high speed loads ...the pinion is lifting, perhaps too much and creating a positive angle. This also lifts the DS at the rear a little more than at the front ...increasing the trans output shaft to DS angle.

WOW, all I can say is this takes a lot of patience. I have scrutinized everything, including PHB adj, LCA adj (both spot on), centering of the trans mount, etc. I suppose it's possible that there's an issue with the trans output shaft being slightly warped. Perhaps the fact that it's impossible to achieve an offsetting transmission angle due to the car being lowered just defeats everything?

In the end, my gut is telling me I need an aluminum DS to mask the vibration. I just wanted to at least have the pinion angle correct before going that route....so I tried and at least the pinion is now a negative angle relative to DS as it should be.

Injuneer

The perfect configuration is to have the trans output shaft centerline and the pinion shaft centerline parallel to each other. That insures minimal variations in rotational speed. Neither the transmission nor the pinion shaft needs to be absolutely level (horizontal). The centerlines just need to be parallel.



You shouldn't have to shim the trans to level it. Have you checked for vibration without using the 3/4" shim? If it's pointed down (hard to see why lowering the car would cause the trans to not be level, unless you dropped the back end of the car more than the front end) the pinion shaft needs to be parallel to it.

I think by shimming the trans mount, and going negative on the pinion angle, you may be creating the vibration.

canbaufo

I cannot get the trans and pinion angles parallel as in the diagram without creating positive pinion angle relative to the DS. Without a shim my trans output shaft points down nearly 5* ! ....you can easily see it by eye. The car was lowered equally at all four corners with a brand new Eibach Pro Kit years ago and does not sag in the rear. I read of many others with lowered F-bodies curing their vibrations with a trans shim ...I assume for the same reason (excessive downward angle toward the rear).

I completely understand what you're conveying but as far as I can tell the only possible way for me to have the centerlines of the trans output shaft and pinion yoke parallel is to have the pinion UP, relative to the DS ....which everyone says is a no-no. Basically the exact opposite of the diagram you posted. Just imagine it reversed due to the trans being angled down too much (even with maximum allowable shim). Crazy huh?!?!? ...I agree! I believe that if the car wasn't lowered, the situation would be more fixable due to the entire engine/trans assembly being higher relative to the pinion (I would be able to have the angle of the trans lesser than the angle of the DS).

To clarify even more, this vibration was present when the car was bone stock (yes, stock suspension, rear, DS, everything). Back then I was using 3.42 gears ...so it was noticeable at 90 MPH whereas now it's noticeable at 70 MPH with 3.90 gears (this may strongly suggest that it's simply the limitation of any steel DS). It is present with negative pinion angle, positive pinion angle, shimmed trans, non-shimmed trans, different rear ends, different driveshafts, different torque arms, etc, etc, etc, LOL ...it is seemingly INDOMINABLE!!!

Thank you for explaining the importance of the rear and trans angles needing to be horizontal, I suppose that's another thing I could try even though I hesitate to. The reason for hesitation is that the ONLY way this will happen is with quite a bit of positive pinion angle (relative to DS) ...I don't think that's good.

So IIUC you are saying if my trans is pointing down 3* I want my pinion pointing up 3* ??? Never mind the fact that the pinion will be UP relative to the DS (I doubt that's exactly what you're suggesting)????

I wonder why the trans points down nearly 5* without a shim? Makes me want to pull the motor mounts and trim them but of course I won't be doing that. To shim the trans any more than 3/4 leaves a dangerously low thread count in the nut for the trans mount ...as well as putting everything so close to the tunnel it would likely bang on hard shifts (I have already trimmed the rubber isolaters on top of the trans).

Finally, I noted something today when I turned the DS 180* in the yoke; the cap or whatever you call it on the pinion seal is not pressed on perfectly evenly. As I spin the whole assembly I can see a slight wobble when looking at that cap. I haven't driven the car yet to see if the 180* trick helped any (seriously doubt it). The pinion seal is not exactly right for this rear and has a slow leak, I have simply been topping it off as needed and don't mind that as it keeps fresh gear oil in use.

I totally see your point. The fact that the trans shaft and pinion BOTH point DOWN at the DS can't be a good thing (along with both pointing down independent of the DS ...which is nowhere near parallel). I just don't know what the heck to do about it. Maybe I've misunderstood something, but I thought it was pretty much imperative that the pinion angle is DOWN relative to the DS, allowing the angle to be reduced upon acceleration when the pinion inevitably rotates UP. No???

Injuneer

It's beyond my capability to resolve. All I ever did to set the pinion angle was measure the pinion shaft and the driveshaft to get the "\/" at the pinion/DS interface. Steve Spohn has worked on my car, installing various prototype devices, and he never set the pinion angle any different than I did.

With three different transmissions (all sitting on the same ES poly trans mount), two different rear axles, four different driveshafts, three different torque arms, and the car at stock ride height, lowered and higher than stock in the rear, I never had a vibration problem.

At this point I'm wondering if your trans output shaft is bent.

canbaufo

Me too, I've suspected the trans shaft as a potential culprit all along. I have an old write up in a paper file on removing the rear of the trans to replace 5th and/or 6th gear(s) along with the output shaft. I just hate to go down that road, especially if it's not really the culprit.

I haven't tried simply setting the trans and pinion angles exactly parallel to each other. At the very least out of curiosity I will try it at some point if this continues to be unresolved, regardless of the pinion being up relative to the shaft like this>>>> "^". FWIW I've put many miles on the car with the stock torque arm having the pinion slightly up relative to the shaft and I never had U-joint problems. If it will rid me of the vibs to get the trans and pinion parallel I will HAPPILY replace the rear U-joint every few thousand miles (if it gets toasted due to the pinion being up relative to DS). That's one really good thing about this adj tq arm, I will be able to play around with it and experiment with different settings to potentially resolve or minimize the problem.

What do you think about this (setting the trans and pinion parallel regardless of pinion being up relative to DS)? ...does it pose additional risk for items other than the U-joint? FWIW my car doesn't get launched hard on slicks (ever) and is rarely even shifted hard .....throttle roll ons that are usually not even WOT but somewhat high load are usually the worst abuse it sees.

Thanks for the responses.

Injuneer

I would think you could measure the straightness of the trans output shaft by using a dial indicator, and rotating the output shaft, placing the indicator plunger on one spline at a time.

canbaufo

Good idea. I also thought of attaching something to the trans shaft and watching it while running, but that's a stretch. I finally drove it after turning the DS 180* in the pinion yoke and there is no change.

What do you think of attempting to use it long-term with the pinion and trans angles being parallel, in spite of the pinion angle being UP relative to the DS? I don't mind the idea of putting a new rear U-joint in a couple times a year if I can be free of vibration. I do think it may be a concern if I were to use it that way for racing, as it might blow the rear U-joint up. I could always adjust it to negative pinion angle for rare heavy-street/track use.

Injuneer

Since you have an adjustable torque arm, see if it cures the vibration problem. Worth a try.