Technical T5 Swap Vibration Woes

Hey all,

About 6 months ago I finally bit the bullet and swapped a T5 into my driver ‘60 Falcon. I used the Modern Driveline 8.5” adapter, Ranger 8.5” clutch disc, stock bellhousing, flywheel, pressure plate, and a rebuilt 86 World Class T5. At the same time I installed a fully rebuilt 74 Maverick 8” rear with new bearings, 3.55 gears, 4 lug axle shafts, brakes, billet yoke, etc. I also had an old driveline modified to accept the 1310 u joints and T5 slip yoke.

I was thrilled to get this on the road again. However the glory was short lived as I ran into some substantial vibration issues around 70mph and they continued to worsen at speeds above that. It starts off harmonically, as if I’m driving back and forth over a rumble strip. It progresses into full fledged high frequency shaking at higher speeds.

Let me give you a run down of the tests I’ve performed, the measurements I’ve taken, and its current status.

T5 is 3 degrees pointed down, rear axle is shimmed up 3 degrees. Working angle of the driveline is 4 degrees on either u joint.

I strung a line from harmonic balancer to rear axle yoke and measured the transmission being about .4” off centerline at 45.5” back from the harmonic balancer. This is about a .5 degree angle.

Replaced pinion bearings twice, T5 tail shaft bushing twice.

Removed driveline from the car and flat towed it to observe rear axle vibrations. None were observed at 80mph.

Removed the driveshaft and spun the transmission up to 80+ to observe any unloaded vibrations. Some were present but nothing I’d consider abnormal.

Installed a slip yoke and measured output shaft runout against the slip yoke and got .01”.

Turned the brake drums and changed the tires as an effort to diagnose to no avail.

Had 3 different driveline companies make drivelines and all exhibited the vibration issues to varying degrees.

I’ve now cut grooves in 3 yokes substantially as a result of the continued vibration.

I’m pulling what little hair I have left out with this one. I’m thinking maybe its a bent output shaft, my driveline is at its 1/2 critical speed, or my .5 degrees engine rotation is causing this issue.

Anyone experience this or have any advice to offer?

 

I'm thinking that you are just looking for confirmation that you need to dig into the car kitty and come up with enough coin for a properly built driveshaft.
You have done everything that I could think of and beyond to already confirm that the driveshaft is the issue.

First though you might take it to a real driveshaft shop and have them check the runout and balance and see if they can balance it. It just may need balanced but personal experience says that if there is a ding or dent in it it will have to be replaced.

 

Did you overhaul the T5?

 

I’m on my 3rd driveshaft. I’ve had 3 different local shops build them. First two were 52” eye to eye leaving about 1” exposed slip yoke and the last was 52.5” leaving 1/2” exposed slip yoke. All 3 have been steel. Each of them has chewed up a slip yoke in about 50-300 miles depending on the shaft. The more I drove it at or above 70 the quicker the slip yoke grooved out.

Yes the T5 was rebuilt by a guy here in town that specializes in them. New 2nd gear, input retainer, carbon lined synchros, input shaft checked out good, new input retainer, new tail shaft bushing, seals and a Pro 5.0 shifter.

 

Since you changed trannies, & I'm assuming bellhousings, did you dial-in the bellhousing? *Very* important in some makes(Stude being one), but just because GM, Ford n Chrys allowed slop in the bellhousing to crank-flange alignment(s), doesn't mean it shouldn't be done. It's not a hard procedure, but the explanation can get a little long. Esp iffen you aren't familiar w/the term or concept.

Yes, I concur on having the driveshaft checked by a *competent* shop/tech. Make sure it is straight, undamaged, in-phase, & balanced. Same guy/shop should be able to do this, easily.

If & when that's ok, the next thing I'd suggest, is to research the weights gm has hung on the tailshaft in the past, to absorb/change vibrations(by altering the vibrational frequencies there). They weren't the only ones to do so, by any means, & even some automatics had the attachments. Some bolted onto the trans tail-mount, others hung out on a bracket. Weights varied. I've seen weights hung on trannies, cowls, & a few other places, to "cure"(change the noticeable) vibration frequencies. Worth a try.

Marcus...

 

I used the stock bellhousing that came behind the little 6, I didn’t index it or change dowel pins. I was planning to do that here soon when I pull the trans out next. I’m only on my 6th time pulling the trans!

 

Question. What does the vibration do if you hold the clutch down or knock it into neutral at say 75 mph?

 

I have had bad tires cause vibrations.

Ben

 

When tossing into neutral or pushing in the clutch at 70+, the vibration doesn’t change.

 

What about putting in neutral and killing engine? Possible the steeper gears are amplifying a previously muffled engine imbalance

 

Explain the yoke damage or do a pic. I've been working on cars and trucks for a living 60 years, and I've never heard of chewing up yokes...and seems impossible at 50-300 miles, so something is way wrong. I can't be the only old guy here that's never seen that before.... especially in such a few miles.

As far as a vibration drone that has a rhythm, like I think you describe, it's usually not the slower rotation of wheels or axles, it's usually the higher rpms of engine and driveshaft speeds.

But chewing a yoke three times? Bushing replaced multiple times. Is it possible that the tail bushing ID is too big for the OD of the yoke? That would cause the driveshaft to not run true and might explain tearing up the yoke. Is it possible that the inner splines are not the correct size for the transmission, allowing it to wobble? The seal might fit tight enough so you didn't notice it was sloppy fit.

You said you changed driveshaft length as to change yoke position, but you would definitely get vibration if the yoke is bottomed out in the trans, however it should change the vibration or sounds as the car goes over rises or dips in the road.

 

I agree , I have never saw a yoke stripped out. Pics please.

 

Here is a picture of the latest yoke. This was in excellent shape when installed it and this is about 50 miles. I can catch my fingernails on the grooves you see.

The other yokes were replaced when I took the driveshafts in to have new ones made, so unfortunately this is the only one I have pictures of.

This is why I was thinking perhaps a bent output shaft. I also know I’m close to the 1/2 critical speed of the driveline which can cause natural frequency vibrations, but this seems a bit excessive.

 

It's not easy for us to examine that wear on the yoke. Could be trash that scored it, or the outer edge of bushing was peened during assembly. IDK. And we'd want to measure with a vernier or Helios to know if it's worn. Shouldn't have lost any amount of diameter in those short miles.

Anyways, there should or could be a center hole in the output shaft, I'm not sure if you could indicate off of that center to know if it is bent.

This vibration won't be easy to diagnose over the Internet

 

Definitely have the driveshaft checked and re-balanced.

With the stock cars, we often made our own and would run the cars at an industrial park access road, to ferret out a balance issue.

Sometimes they were fine. We carried a 1 ounce tire weight and a big hose clamp, I'm case there was a vibration. Clamp it close to where the factory weight was, take it for a run.

Then reposition it 90 degrees at a time until we were happy with it. Then weld the factory weight in place. I had accurate scales at work so we were about as precise as possible.

 

I personally had an 8 inch rear with a 4.61:1 ring and pinion that I bought already set up that vibrated like that. It was almost undrivable. Kind of a really bad cyclical drone. I took it apart and reset it up and the vibration went away. Not sure this would explain your driveshaft yoke problem though. I guess it could transfer up the driveshaft and cause that yoke to wear.

 

After all you have tried I would slide the axles out and see if anything feels amiss in the rearend. Maybe the housing is bent, as Ardinger stated maybe it is set up wrong .

 

Do you know anyone that has the same trany? You seem to have pulling it out to a fine art after 6 times. I would try a different trany.

 

Is there any oil at the tail shaft bushing?
How about the wheelbase from side to side, this will add to the driveline angle.
Worn rear spring bushings?
Install driveline and dial indicate the shaft just behind the weld at the front, a bent output shaft should show up on the indicator. Can the tail shaft housing be easily removed? If so pull it and check for run out of the shaft, ( might need install a yoke on to indicate off of ).

 

Internet diagnostics are difficult at best.
Have you had a discussion with your transmission builder about the vibration and the yoke wear? You may have and not shared it here. The builder may have insight from past experience.
A magnetic base and dial indicator can check the rotating trueness of a driveline real fast plus it can be used to test for looseness with a 'lift test'. It can also be used to check your output shaft/yoke assembly to see if it is bent and/or concentric.
Have you run the car up in the air, resting on jack stands or a lift to see what you can observe?

My thoughts and worth what it cost you....or not. good luck

 

Just to toss in a bit of musicology, a rhythmic, or harmonic vibration as you described is the result of two or more things vibrating at different speeds. An individual single vibration might not be so noticeable, but when combined with a second vibration would be exaggerated.

So it could be a combination of the driveshaft, along with clutch, clutch disk, flywheel, balancer, or some other engine component. Quick test to confirm that it is two or more things would be to run it up to vibration speed in 4th gear, (1-1 ratio) which means the engine and driveshaft RPM are the same. Is it still a harmonic vibration, or is it a steady vibration?

 

I think I'd try putting in a different 5 speed to see if it is specific to the one in it? If same result then it's probably driveshaft or rear end related.

 

From your description and the picture of the yoke, it sounds like the yoke is trying to seize in the tailshaft bushing. I don't know how the bushing gets lubricated, but I'd be examining the oil path carefully. I've seen vehicles with driveline vibration run for a long time without damaging the slip yoke like yours has.

Also, have you actually measured the off center side angle? Basically measuring the driveline U-joint working angles at 90 degrees.

 

I would concentrate on finding the source of the driveshaft yoke wear problem.

 

Interesting! Did you notice these vibrations only at high speeds? I certainly could carry a few hose clamps to see if it helps.

We did check the wear pattern on the gear but didn’t see anything abnormal. We could see evidence of the vibration issue due to some wear pattern on the pinion bearing. We replaced it and reset the crush sleeve but no change in vibration.

I did run a dial indicator off the slip yoke and measured about .01” of runout. I haven’t removed the tailshaft housing since we replaced the tailshaft bushing.

There is some side-to-side offset, about .5 degrees of the engine from the pinion angle which does add a bit of working angle to the slip yoke side of the driveshaft.

Absolutely. I’ve spoken at length to the transmission builder, axle builder, and taken it to a few friends that also work as mechanics as I’ve been fighting this for months now.

We did run this on jack stands and watched the previous driveshaft lobing in the center quite significantly, but we haven’t run it with the latest driveshaft that’s experiencing the same vibration.

Great thought! We did replace the harmonic balancer to eliminate some engine vibration as a possibility. Unfortunately I can’t get up to 70 in 4th with the little 144, it’s pretty gutless. But I do notice a bit of a harmonic hum at lower speeds in 5th gear when I lug it around. Nothing crazy, just noise around 50mph. Then that goes away until about 70 when it becomes a real vibration not just a faint noise. Seems like there might be something to this.

I can try to find one, unfortunately T5’s are now treated like gold. They are pricey around the NW and somewhat hard to find these days.

I definitely get oil out every time I replace or remove the shaft, that said it’s possible if the fit is too tight it’s not lubricating sufficiently between the bushing and yoke. Installing them doesn’t seems to be a big issue, they seem to slide in and out fairly easy. I’m not sure if there is a spec on the radial gap between the bushing and yoke.

The engine is .5 degrees rotated side to side. Very slightly, but that would add to the working angle of the front u joint.

Absolutely, I think that is the culprit. I’m just struggling to understand if the vibration is the cause of the wear, or if the wear is the cause of the vibration.

 

I'm not sure how I'd set up to measure this, but it sounds and looks like the slip yoke centerline is parallel to the driveshaft center line but not inline with it. If that makes any sense. In other words the yoke center is moving in little circles relative to the shaft. Or trying too, setting up the vibration and wearing the yoke.

Wild guess but that's all I got!


.

 

I missed your post(#4), since I was posting at the same time. Lots here in this thread to consider.

Thought I remembered seeing a NVH(Noise/Vibration/Harshness) thread on the HAMB somewhere, but since I can't find it, I do a bit of guessing here:

Since you're pulling the mill/trans again anyway... ;

I don't see the engine/trans non-parallel-slight-offset being a big problem, but iffen you could correct it somewhat easily, maybe slightly slotting the engine & trans mounting holes, it couldn't hurt. Ideally, everything would be perfectly parallel & perpendicular, but that is what the u-joints are for, since the angles end-up being a sum total anyways.

I'd still do the bellhousing dialing-in, as a precaution, then that's a known "done-right".
If that's off by more than a very little, I'd check the trans input shaft bearings/bushings for wear; then that = a known-done-right.

Then concentrate on the tailshaft parts: output splines/shaft itself, + the t/s housing. To check n verify that both are w/i spec as to clearances, out-of-roundness, & being straight(stuff does happen - & it's not your or the builders' fault), & not worn. Other than being beyond anal in checking *everything* every-which-way-including-loose... Then that is another known-done-right.

I've also made the assumption that the trans mount-cushion is good, not sloppy/weather-checked/rotted/broken?

Also next in-line, looking at the d/s harmonics. Since you've mentioned the d/s lobing, I'm thinking you need a new d/s. This d/s must have a very slight bend near the middle or some weld-induced stress(s) that cause it to bounce. Had that happen on a Shelby pickup, when I had the trans rebuilt(wasn't there prior to the rebuild, was after), & the cure was a correctly-built d/s. Since you also mentioned being close to the 1/2-critical-speed-frequencies, I'd do a d/s w/a different dia, & maybe wall-thickness, possibly a different material. Some d/s have cardboard "tubes" rolled up w/in them, to dampen freqs. Maybe a cut-down large-dia Aluminum one from a late model SUV-thingy, idk? I haven't done the calcs for that for 50+yrs, but then at least you know... .

& when all that checks out correctly, & vibration issues still exist, then investigate weights at the back of the trans mount/tailshaft-housing. The machined pads should, or very well may be, still be there, as a lot of cars & trucks had them. Lots of folks threw them away as they didn't know the why/what-for aspect(s). It's not a band-aid, as things need to be right/correct prior to the weights - both in amount of & location, but it will change/absorb some frequencies, up to a point. & all you really need is the change - to a different freq, so it'll show-up in the situation(s) you don't get into. .

I am very interested in what you eventually find, & the correction(s) needed.
Sadly, this is a whole lot like the Chinese curse of "living in Interesting Times". *If* you can keep ahold of your insanity long enough to keep from going stark-raving-sane, then you'll end-up with:
1st-hand knowledge of NVH-issues & correcting them; both the "book-learnin' " & "empirical-testing" versions. .
&, the "Opportunity to Upgrade" ;D .
Or at least I would...

Marcus...

 

I'm trying to recall...wasn't there a weight (mass) hung off the 8.0 differential on some application...or am I needing to check my meds

 

Why is the engine not straight in the frame? That sounds like a good place to induce bad things. As mentioned, fix that when you have the engine out next.

 

I fixed a 78 ford pickup in early eighties hit in rear axle put a new housing and axles chased a bad vibration went thru everything you have ,turned out the bodyman didn't put the small wedge shims that set the axle where it originally was that fixed it. Even pull c6 and had main shaft checked in lathe for bent