Drivetrain vibration - possible transmission issue

[Gumball]

Well, this is turning into the summer of no-fun. From rusted side pipes - pending replacement with my new Gas-N pipes that are at the ceramic coater - to the on-going carb issue, I can now add a potential transmission issue.

This is the third summer my car has been on the road and it's covered just a tick over 8,100 miles so far. Last year, I began feeling a bit of a vibration in the seat of my pants - definitely a rear issue, as there was no feedback from the steering wheel to indicate it was a problem with the front wheels, steering, or suspension. Shortly after it began, I got a flat tire on the left rear and found a leaking shock. Well, I thought that was the issue, but since it was late in the season, I just drove it a couple more weeks, then parked it for winter. This spring, I replaced the bad shock and was surprised to find that the vibration continued.

Recently, I put it on the lift and re-did my usual nut and bolt check, paying close attention to the driveshaft and rear end. I also confirmed that the weight was still in place on the driveshaft. Next thoughts were to pull the driveshaft and have it rebalanced, as well as having the rear tires checked for out-of-round condition and balance. Also on the list is looking into getting hub-centric rings for the wheels to make sure it's not an issue resulting from mis-mounting due to the lug centric nature of the FFR wheels.

Well, while checking the driveshaft and U-joints, I discovered that the output shaft bushings/bearings seem to have worn out on my T5. There is a significant amount of movement of the slip yoke (not in-and-out, but up and down) and a slight knocking or clicking noise coming from inside the transmission when I move the front U-joint up and down. So, not sure if this is the source of my vibration or the result of some other imbalance that wore the bushings/bearings out prematurely.

The transmission was not rebuilt when I put my car together - it was a donor unit from a car with 120k miles. But, a friend who owns a transmission shop went through it and said it was in great shape and only needed a shim to take up some thrust and new gaskets.

So, I think I'm going to learn whether the transmission can be removed without pulling the engine..... sigh...... and then I'll have it completely rebuilt. I'll also continue to look at the other possible sources of the vibration, just to make sure that this wasn't caused by something else being out of whack.

Looks like my driving season was just shortened somewhat.

[scottiec]

keep in mind that T5's will have some shaft play. I literally just rebuilt mine and it is on the garage floor waiting to meet its motor. When I get home I will check the play on the output shaft so you can compare it to a freshly rebuilt trans.

[CraigS]

Also research whether the tail shaft could be removed w/ the trans in the car.

[Gumball]

Thanks guys - I'd sure be interested to know how much vertical thrust - i.e., play - is acceptable on the output shaft. That said, I think mine is way loose.

[NAZ]

Better double check the pinion angle and condition of the u-joints while you're at it. Having a trans output bushing go from your friend's assessment of "it's in great shape" to worn out in 8,100 miles is unusual -- unless he didn't do a very good job of checking this part.

[scottiec]

Pm sent

[GoDadGo]

Make sure you check your pinion and transmission output shaft are in phase.

https://youtu.be/Idk3BVDVHq4

If your upper link was not set properly, then your pinion angel may have been more than couple of degrees out of phase causing all sorts of issues.

[Gumball]

Was pretty careful during final assembly and set-up / alignment to get the pinion angle right, but will certainly add that to my investigation.

[GoDadGo]

Was pretty careful during final assembly and set-up / alignment to get the pinion angle right, but will certainly add that to my investigation.

Just Trying To Help Brother Gumball!

I had major issues with getting my pinion angle correct, so much so that I had to shorten lower control arms to get the transmission output shaft and pinion on the pumpkin in phase. My next issue was the driveshaft that I had made was was 2-3 degrees out of phase from end to end so this issues is near and dear to my heart.

Steve

[scottiec]

Gumball,

sent another PM. I have very minimal output shaft play. a clunking is when wiggling the shaft about since the counter shaft is knocking up against a floating main shaft.

[Mountain-Metalworks]

Hey Gumball, sorry to hear about your troubles. Good thing is that summer is just getting started, so once this is sorted out you'll still have lots of play time. I'm familiar with manual transmissions but not the T5 tranny specifically, but I'm pretty sure you found the vibration. If there is noticeable radial/vertical/horizontal play in the output shaft(not in/out from the slip joint like you mentioned) then you're definitely going to feel that. There can be some play, but with a dial indicator you shouldn't get more than a few hundredths at most. If you can wiggle it around either the bearings are shot or somehow the preload/thrust is way off.
I would never intend to question your buddy that checked it out, but if he added a thrust shim could it be possible he put too much preload in the system and you toasted a bearing after 8K miles? If you're interested in a second set of hands to get the tranny out just let me know, I'm right over the border and definitely willing to offer the help.

Good luck!

-TJ

[NAZ]

The T-5 Service manual doesn't give a dimensional tolerance for the yoke bushing (and I didn't see a replacement bushing listed) but does call out to inspect it & replace it if there is "scoring or other damage". My guess is if the clearance is anything .004" or greater (that's four-thousands not hundreds and four-thousands for that size journal is a lot of clearance for something that rotates at that speed) it should be replaced. But again, the manual does not give a specific clearance spec. Excessive clearance may be the vibration you're experiencing but again, what caused the wear in just 8,100 miles? If your friend says he checked this then you have another problem to address. If he missed it then simply replacing a warn bushing may be the cure. But where do you find a replacement bushing? Do you have to order a new tail shaft housing to get a new bushing?

[CraigS]

.... Having a trans output bushing go from your friend's assessment of "it's in great shape" to worn out in 8,100 miles is unusual -- unless he didn't do a very good job of checking this part.

If he didn't have the driveshaft along w/ the trans it would be kind of hard to check.

[Gumball]

It's been a while since I did my suspension set-up, but I remember putting a fair amount of thought into it back then. However, now I'm doubting my accuracy, so I'm throwing myself on the mercy of the collective group of experts and looking for confirmation or correction of my pinion angle.

From what I remember, the two are supposed to be at the same relative angle, but not necessarily on the same plane. With that in mind, at ride height on compressed suspension, my transmission output shaft points down towards the rear at approximately 1.5 degrees and my pinion points up toward the front of the car at 1.5 degrees. This means that in relation to each other, the centerline of the transmission and centerline of the pinion are parallel, but not on the same plane as the pinion flange is a little higher than the transmission tailhousing.

This difference in plane leads the driveshaft to have a downward slope towards the front of the car, which I haven't measured, but will do so when I can get back to the shop. I am concerned that even if the pinion angle is correct, that the fact they are not in the same plane and the driveshaft angles downward is putting too much static angle into the U-joints and that it just gets more extreme under suspension compression.

So, with that info, any thoughts?

Would any more info be helpful?

Thanks in advance for your comments and suggestions.

[Gumball]

Oh, and one other thing..... it appears that some play in the tailshaft bushing is acceptable, so I'm going to pick up a magnetic dial indicator to measure the amount of play in mine. Any excuse for another tool and dial indicators are cool, so it seems like as good of an excuse to get one as any.

[NAZ]

In an ideal world you want the driveline angles to match under load (acceleration) as under load is where a miss matched angle will cause the greatest vibration. Typically that will require the static pinion angle to be a bit less than the trans output shaft angle as the elastomer suspension joints flex during acceleration and the axel housing rotates (pinion rises). So if your transmission output shaft is angled 1.5-deg your pinion shaft will be something less than 1.5-deg when at ride height. How much depends on several factors that all contribute to the amount of flex in the joints which allow the axle housing to rotate. On a solid rear axle there is also suspension squat to consider and how much the pinion angle changes in squat. When the car accelerates it transfers weight to the rear axel and the rear suspension squats. The suspension moves just like it does going over a bump. If the upper and lower control arms are not the same length and parallel then the pinion angle will change during suspension travel. How much depends on the pinion angle gain built into the suspension design and how much the car squats. So every car will be different but you will get a variety of angle offset settings when you ask what to set your static pinion angle at.

As for the amount of play in your yoke bushing the rule of thumb for plane bearings (AKA bushings) is .001" clearance per inch of shaft diameter. So for a 1.5" O.D. yoke you would expect the designer to have spec'd .0015" (that's one and a half thousands) of clearance in the bushing when new. In all the years I've been wrenching on cars I've never measured the clearance on a yoke bushing.

[phileas_fogg]

I found this post explained pinion angle really well: http://thefactoryfiveforum.com/showt...-Pinion-Angle)

Likewise, I found this post explained drive shaft phasing really well: http://thefactoryfiveforum.com/showt...t-Is-Important


John

P.S. Dial indicators are cool, and AMAZINGLY useful to boot!

[Mountain-Metalworks]

Chris,

It sounds like you've got the pinion and tailshaft angles setup correctly. This is a doc I've used over the years but it simply explains what you already know.

Universal Joint Alignment

It's always good to understand what caused a problem, but since your tranny was used you may have a hard time narrowing down the issue. If it had been brand new, then it would be almost mandatory to find the root cause but it's possible you're going to chase a ghost knowing that your driveshaft angles are correct.

-TJ

[GoDadGo]

Chris,

Just Throwing These Foods For Thought Items Out There:

1. If the universal joints were in phase, but the ride height was causing excessive driveshaft angles, then could that have caused the vibration by wearing out the u-joints or tail shaft bushing?
2. Are the universal joints still in good shape because I'll pick up major vibrations in my daily driver when the universal joints of my half shafts get worn on my C-4 Corvette?
3. How far into the tail shaft does the yoke go in and does have any wobble in it?

Sorry to pile on again, but your issue is sticking in my brain like a bad tequila hangover.

Steve

[Gumball]

Some follow-up....

1) Confirmed that the current transmission tailshaft angle is 1.5* down towards the rear of the car.
2) Confirmed that the current pinion angle is 1.5* up towards the front of the car.
3) Verified that the pinion is higher than the transmission and the resultant angle on the driveshaft is 3* down towards the front of the car due to the pinion flange being higher than the trans tailhousing.
4) This gives me a working angle on both the front and rear U-joints of 4.5*, which is over the recommended maximum of 3.5*.
5) The U-joints appear to be okay, no play or other issues.
6) Apparently I was way overly pessimistic about the amount of play in the slip yoke bushing - dial indicator is showing around .005" of movement just outside the rear seal on the trans, so even less inside at the bushing.
7) Trans guy came by and confirmed that the amount of play in the slip yoke is not concerning.
8) Ride height is 4.25" front and 4.75" rear, but this is with tires that are approximately 1" larger in diameter than spec'd by FFR, meaning the tires are giving me 1/2" of that ride height and resulting in the suspension being off a bit in relation to the chassis.
9) The transmission mount was never shimmed - the isolator is resting directly on the transmission crossmember.
10) My transmission and bellhousing is out of a '94 SVT Cobra, meaning that the input shaft is 1" longer and the bellhousing is 1" deeper than a T5 from '87 - '93. This pushes the end of the tailshaft back a corresponding 1". My driveshaft is from Breeze and was a new unit made specifically for this transmission - i.e., it's a bit shorter than normal.

What all of this is telling me is that there are a few things that add up to result in the U-joint angle of 4.5*: 1) suspension that is "out-of-spec" due to the taller tires; 2) the shorter span between transmission tailshaft and pinion flange due to two-year-only trans/bellhousing combination; and 3) failure to shim the transmission up a bit.

So, I'm going to do a couple things......

First, I'm going to swap my current tires for the set of 17" wheels/tires that I have hanging around and see if the vibration goes away or if it changes.
Second, if that doesn't solve the problem, I can pretty much count on it being driveshaft angle. Regardless, I think that I have to do something with the 4.5* working angle on the U-joints, so I'll do a slight tweak on the ride height to bring the pinion down in relation to the tailshaft, shim the transmission mount to reduce the angle from 1.5* down to around 1* or less, then readjust the three-link to get the pinion angle down to the same as the tailshaft (perhaps just a little less, to account for rear axle rotation under load/squat).

This should get the working angles of the U-joints down under 3.5* and reduce any vibration or unnecessary wear, even if the actual vibration ends up being the result of an out-of-round or imbalanced tire.

Thanks again guys, I'll keep you posted on results.

[CraigS]

One other thing to consider re; driveshaft angle. I like the front to be slightly higher than the rear. this is because I like to have slightly more bump movement than droop movement for the axle. IE;, if the axle has a total of 5 inches of movement I like to set things up so there is maybe 3 in bump and 2 inches droop travel. Or a little closer to equal but definitely not equal. So, the driveshaft needs to be able to move up further than down. This doesn't have much to do w/ working angle but does have a lot to do w/ u-joint binding. look at your joints here

This is usually a problem that crops up on big bumps w/ a full tank and a passenger, but good to keep in mind.

[NAZ]

I would not mess with ride height to get out of a vibration issue -- adjust the driveshaft angle. Ride height on these cars should be set so that the lower control arms are parallel to the ground to minimize roll steer. FFR does not provide much adjustment here so you're limited on optimum ride height.
Adjusting chassis settings to achieve a more optimum driveshaft angle will result in changing handling characteristics. Your plan to shim the trans to decrease the output shaft angle is a better course of action. If you can't get the driveshaft operating angle range where you want it consider going to a double cardan u-joint if you have to but don't play with chassis tuning to change driveshaft angles.

As for using a dial indicator to check slip yoke bushing clearance -- this is the wrong tool for the job. The correct method is to use a bore gauge or telescoping gauge to measure bushing diameter and an outside mike to measure the yoke journal. Yes this will require removing the tail shaft housing but will give you an accurate clearance measurement. A dial indicator will not give you a true reading but will give you a "relative" assessment if you can measure a known good trans. I expect you will get varying readings depending on the yoke engagement with the output shaft and point of measurement.

Another consideration is the engagement of the yoke with the output shaft (see the GoDadGo post above). You can get a vibration from too little engagement and you see this more often with short driveshafts and lots of travel. Your driveshaft builder will have an opinion on the minimum engagement you should have. Since you have a shorter than typical shaft you may need to use bump stops / limiting straps to maintain that minimum engagement. Another short wheelbase vehicle that sees this issue is the Jeep Wrangler, especially lifted vehicles with lots of travel. Here a slip yoke eliminator can help with this problem. There are many ways to deal with driveshaft issues but again, adjusting ride height is not one I would consider.

[Avalanche325]

I am chasing a vibration myself. I will stay tuned to this. I'll start my own thread so I am not hijacking.

[Gumball]

Craig - thanks for posting that U-joint pic... mine look fine and show no damage or wear, but I have heard a bit of a noise on just a few occasions when going over bridge transitions from asphalt to concrete and when I have a full tank of gas, so I'm guessing I was getting at least some bind. At the time, I chalked it up to tire rub on the inside of the body, but never saw any actual sign of wear up inside the wheel wells.

NAZ - thanks for the continued tech info... I'll do the transmission shim and give the pinion a little less static angle so that under load and squat it will be at the same angle as the output shaft. I'll hold off on making any ride height changes until I determine whether those first two tweaks get me down to (or below) 3.5* of working angle on both the front and rear U-joints.

Too many others to thank for your continued encouragement and suggestions - I'll keep you all posted on the results of these adjustments and also the swap to my 17" wheels. Going to do the wheels first, to rule out any issues with my 15" wheels and tires, then the driveline adjustments.

[Gumball]

Well, well, well.... thanks to Craig, I gave my U-joints a little closer scrutiny and found what is obviously the source of the noise I remember hearing on a few occasions when crossing bridge transitions. What I thought was tire rubbing was, in fact, the ears of the front U-joint binding. Here are a couple pics......

Note the spot to the far left of the U-joint in this pic that appears to be hammered over slightly along the edge.....



And here is what it was hitting - just a slight amount of paint loss on the slip-yoke as seen directly under the numbers.....



I did a rough fit of the shim I made for under the transmission mount (3/16" aluminum) and found that it reduced the angle of the output shaft from 1.5 degrees to 0.0. Once I adjust the pinion angle to compensate for this change, it should also reduce the forward down angle of my driveshaft somewhat and I'm guessing the working angles on my U-joints will go from 4.5 to around 2.5 - well within recommended specs.

I'll keep all of you posted, but won't be able to test for a while as the carb is still off the car for it's rebuild.

Thanks to everyone for tips and suggestions.

[NAZ]

Good catch, persistence pays off and now you'll have an improved driveshaft angle.

[Al_C]

Not helping with your adjustments, but look at the bright side - now you have more time to spend in the GT350...

[GoDadGo]

Congratulations On Finding The Culprit!

[Gromit]

I would suggest that if that U joint was binding to replace it even if it feels good. I would be concerned that the u joint has been Brinelled

https://en.wikipedia.org/wiki/Brinelling

Chris AKA Gromit

[Ducky2009]

Well, well, well.... thanks to Craig, I gave my U-joints a little closer scrutiny and found what is obviously the source of the noise I remember hearing on a few occasions when crossing bridge transitions. What I thought was tire rubbing was, in fact, the ears of the front U-joint binding. Here are a couple pics......

Note the spot to the far left of the U-joint in this pic that appears to be hammered over slightly along the edge.....



And here is what it was hitting - just a slight amount of paint loss on the slip-yoke as seen directly under the numbers.....



I did a rough fit of the shim I made for under the transmission mount (3/16" aluminum) and found that it reduced the angle of the output shaft from 1.5 degrees to 0.0. Once I adjust the pinion angle to compensate for this change, it should also reduce the forward down angle of my driveshaft somewhat and I'm guessing the working angles on my U-joints will go from 4.5 to around 2.5 - well within recommended specs.

I'll keep all of you posted, but won't be able to test for a while as the carb is still off the car for it's rebuild.

Thanks to everyone for tips and suggestions.

I started with a small shim and found other issues.
Engine/Trans height - Leveling the drive train
I know several people talked about leveling the drive train. With the engine oil sump in the rear, I didn't think it needed to be completely level. I originally added a 1/4" shim to the trans mount to prevent the drive shaft from rubbing the frame. While installing the headers I realized the oil pan (at the rear of the engine) was below the frame rails. I have now added a 3/4" trans shim, which brought the oil pan up above the frame rails. Time to revisit the pinion angle. The first pic is at a little too much of an angle to have a good view of how much the oil pan is down below the frame.

First pic is with small shim. Second is with 3/4" shim. Not the best angle on the first pic.

Oil Pan Height BEFORE adding .750 Trans Shim.jpg Oil Pan Height after adding .750 Trans Shim.jpg

[Gumball]

A little progress - I finished the 3/16" aluminum shim and put it in place. Confirmed that the output shaft is at 0.0 now (at least relative to the car's position on the lift, which is pretty level) and reset the pinion to just below that to account for a slight upward rotation under load. Since the carb is still off the car, I wasn't able to drive it to allow the suspension to resettle after all the up-and-down, including raising and lowering the rear axle while the chassis was supported on jack stands so that I could make fine adjustments with it at droop and then jacking the axle back up into place to check alignment.

As soon as I get the carb back together and on the car, I'll roll it around a bit and recheck all of the alignment. But, at first glance, it appears that this has given me a much reduced working angle on both the front and rear U-joints - down in the 2* range.

Hopeful that this solves the vibration problem.

[steno]

Hey Chris! How did your pipes turn out?

[Gumball]

Hey Chris! How did your pipes turn out?

Still up in Delevan - he said a couple weeks as he had to get some aluminum oxide media to take the shine off them so that the satin black ceramic would have something to bite into... oh the sacrilege!!!!

[GoDadGo]

Chris,

I think you've got your driveline vibration solved.
Sorry that you had to deal with this, but your problem made me go back to double check my drive line angles.
Your post most likely saved me issues down the road so this thread that you started is appreciated.
Have A Fantastic 4th Of July Which Is Only 12:23 minutes away!

Steve

[Gumball]

Resurrecting a year-old thread to comment on the vibration issue. After I got the car back together last summer - new pipes (stainless that I had black ceramic coated to preserve the old-school look), blue printed carb, ignition tune, etc.... continued to chase the vibration. It's most noticeable at 45 - 50 mph, which is a sweet spot for cruising on the back roads in my area, so it's really annoying. Just a subtle vibration in the seat of the pants and a wiggling of the shifter.

Yesterday, I finally pulled 7074 out of my trailer where it's spent the winter (all tucked away in a corner of my shop) and it still has the storage wheels / tires on it - these are the 17" wheels that originally came with the kit and a set of 245 / 315 Sumitomo tires. Since I went old-school with my build, I never used these for the road, but decided to try them last night. Sure enough, no vibration.

The new rear shock (to replace one that sprung an oil leak) and the changes to the driveshaft / pinion angle were surely needed, but obviously not the source of my vibration. I took the 15" wheels in this past winter and the shop did a re-balance (this time, a dynamic balance that places weights both along the rear edge and on the barrel of the wheel nearer to the back of the spokes), so I'm hoping this will eliminate the vibration once I get the 15"s back on the car. If not, then I'm going to consider it to be an out-of-round issue with one of the rear tires and will replace them in an effort to finally rid the car of this last little gremlin.

Just over 10,500 miles on it and loving every minute of it now, though, so I can't wait to finally have it back on the road this week!

[CraigS]

If you continue to have a vibration do some research to find a shop w/ a Hunter Road Force balancer. This is the best machine available but you also need to find someone who knows how to run it and cares.

[Murd]

Just read through this thread, wondering why no one recommended the 2deg down pinion angle that seems to be suggested in all the pinion angle threads?
Good luck with the re balance!

[Gumball]

If you continue to have a vibration do some research to find a shop w/ a Hunter Road Force balancer. This is the best machine available but you also need to find someone who knows how to run it and cares.

Bingo - this was recommended by my local shop. They don't have one of these, but did the re-balance. Operator said that if this doesn't fix it, to search for the machine you mentioned, as it'll verify if the issue is the result of either an out-of-round condition or some other issue with the tire, such as a bulge or belt separation.

The good news is that this is about the last little bug - and I have to say that the vibration is now very minor... just one of those things that I can sense, given the amount of time I have in the seat and my critical nature.

[Avalanche325]

Posting incase this helps someone. I posted earlier that I was chasing a vibration....

My symptoms were throttle lift off and pick up vibration. Right in that second where there was no torque on the drive train.

I chased it for a long time. Replaced the U joints, rear axle bearings (had a seal leak anyhow), check the pinion, ring gear, etc. Of course, I checked the pinion angle half a dozen or more times. Set it to -2, -1, 0. +1, +2. Every time I made a change, it would go away for 50 - 100 miles and slowly come back. A real head scratcher.

Then I checked my rear ride height, that I had lowered to get more rear grip at autocross. It was about 1/2" lower than I had set it. Hmmmmm. I raised it up a bit, and put another 1/4 spacer under the transmission mount. I wanted to keep it on the lower side for traction. Reset the pinion angle and it was cured. My pinion angle was good. My u-joints were not binding. But my driveshaft angle was too severe.

Apparently, it takes more than I thought for the suspension to settle after being jacked up. That is why it would seem to be fixed and come back after driving for an hour or so.