Transmission/pinion angle issue... '68 Charger shakes hard on the freeway. Help!

[ncmiller1]

So I've read numerous if not all of the pinion angle threads on this site and I think I have my issue narrowed down, I just wanted some expert advice.  I just swapped out the 318/904 in my '68 Charger for a 440/727, had the driveshaft shortened and balanced, and did no work on the rear end.  I put all new front suspension in (except for lower control arm bushings, strut rod bushings, and torsion bars) before the swap and the car drove fine.  After the swap when I drove on the freeway above 70 mph, the car started to shake slightly, and then build up to a fairly violent shake.  This was with just me in the car.  When I put three others in the car with me to help diagnose, the car still shook but with all the extra weight it didn't seem to get to the violent shaking.

After reading up on this site it seemed I had a pinion angle problem, so I borrow a magnetic angle finder and got to work.  On level ground, the drive shaft was at a 2 degree angle downward from the transmission to the rear end (see picture below).  I pulled out the drive shaft and measured the pinion angle (also on level ground, not jacked up) and it was pointing 2 degrees upward.  This meant that at rest the pinion and the driveshaft were parallel which I immediately knew was not good.  Furthermore, when I measured the transmission angle, it was pointed downward at 4 degrees, meaning that it was 2 degrees in the wrong direction in relation to the driveshaft. 

My first thought was to get the transmission tail up, so I bought a new transmission mount and used shims as well to get the tail as far up as it would go without hitting the tunnel.  This helped a little putting the transmission angle AND the driveshaft angle at 3 degrees downward, making them parallel at rest, and the rear end at a 1 degree angle in the correct direction. 

This was not the drastic fix I was hoping for, so I am going to shim the rear end in hopes I can increase the pinion angle more.  My questions are: does it seem like I'm heading in the right direction in this fix? Does it seem unusual that the transmission was pointed so far down and is shimming a transmission normal?  I'm also curious if replacing the shot LCA and strut rod bushings would help the problem (I am going to replace them this weekend regardless)?  Thanks for any help, I want to get out and drive on the freeway!

[bobs66440]

The transmission and rear should be on the same plane (ie: trans 1-3 deg down/rear 1-3 deg up is common). As you have it now, the two u-joints are fighting each other by traveling in different circles, effectively pushing and pulling the drive shaft with every revolution.

Here is a good article describing the procedure.
http://www.carcraft.com/howto/91758/index.html

[Musicman]

Yes, you are heading in the right direction, just a little more to go maybe, and yes they do make shims for shimming engines, transmissions and rear ends for this very reason. Regardless of what others may tell you however, there is no one "all perfect" setting... Example: A 4 link suspension system requires far less correction than a leaf spring system. Then there is the average driving condition to be considered... The car running the 1/4 mile at the track all day should be set up differently than a street driven vehicle.
Also remember that you have to account for side to side angles too... the engine was mounted slightly off center for a reason.

[elacruze]

Pinion angle shims are available through speed shops but ridiculously expensive. I worked with heavy truck drivelines, knowing that I went to the local RV shop with alignment rack and bought two shims for $4. Any heavy alignment shop, or an old automotive alignment shop should have these shims as they were used on beam type front axles.

To your shaking issue, 4* difference (nor any of the angles you show) should *not* result in shaking. What is your gear ratio? Who built the driveshaft, how did they balance it? Did you verify the u-joint clocking? What else changed since the driveline swap other than transmission/driveshaft?

[Budnicks]

Here's a previous posted drawing by someone else below... Just spitballing here, it may not be any of these things... Sound like if you didn't change anything in the rear end, it shouldn't be that, maybe just a too tall or too short of a trans mount, or totally wrong mount all together or possibly the front suspension changes you made, could also be the culprit, scrubbing the tires or something, bad Caster/Camber angles, bad toe in setting, loose bolts, loose/hub spindle bearing, or maybe excessive slop in the Upper control arm bushing, did you feel it bad thru the steering wheel ?  did you have it realigned after the suspension parts changes ? to proper toe in, camber & caster settings/alignment...

[ncmiller1]

Thanks for the replies everyone.  To answer some questions, my gear ratio is still an open 2.73 (I haven't swapped out my rear end yet, so nothing has been done to the rear end).  My driveshaft was built by Drivelines in Mission Viejo, CA and I'm not sure how they balanced it or what RPM they spun it up to when testing it, so I will give them a call and ask more details. 

I have been having an issue with the drive shaft that may or may not be another symptom; shortly after putting in the new shaft and discovering this shaking problem, the plug on the back of the yoke that goes into the transmission started leaking trans fluid (not out the trans rear seal, but through the yoke and out the back where the u-joint is), so I brought it back and had them replace it.  After a little more driving the plug started leaking again, so now i'm curious if that is indicative of a problem with the u-joint on the yoke or transmission, that it is possibly being tweaked during the shaking on the freeway? 

As far as u-joint clocking, I'm not sure exactly what that is so I will do my research tonight and see if I can get an answer to that.  The only thing changed from the swap was the engine, transmission, and then the shortened drive shaft.  All the new suspension worked fine with the 318 in the car, but when I got it aligned afterwards, the shop said that the car could not be fully aligned due to the shot LCA bushings and strut rod bushings.  I am going to replace those this weekend (if all goes well) and hopefully get the car realigned.  Even though the car didn't shake with those bad bushings before the swap, it could be possible the weight of the new engine could have affected the car enough to cause a problem, so I hope new parts will help.

The shaking I felt seemed to be coming from everywhere (helpful, I know) including the steering wheel, but also the change in the ashtray was rattling and I could feel it when putting my hand on the dash as well.

Thanks for the tip on the shims, I will search out an RV shop and see if I can score some for a good price.  I want this car to be all around driveable on the street so I want to adjust everything to allow for that.  Thanks again for all the replies!

[elacruze]

Check that the tailshaft bushing isn't worn out, allowing the yoke to go into a resonant gyroscopic vibration (circular) that would explain both the shaking and the plug coming out.

[bobs66440]

To your shaking issue, 4* difference (nor any of the angles you show) should *not* result in shaking.

Every tech article regarding pinion angle I've read states that any difference in alignment of the u-joints to each other can and will cause a vibration. It can sometimes be difficult to distinguish from a unbalanced drive shaft. Sometimes it may not be enough to be annoying. Sometimes, when combined with other issues as suggested it may be severe. In any case, when they are out of alignment, they are spinning at different speeds and will cause vibration.

I'm not saying for sure that it is the cause of the problem, there are many other factors to consider. Just that it's possibly a cause.

Read this article and you will understand.
http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

[elacruze]

To your shaking issue, 4* difference (nor any of the angles you show) should *not* result in shaking.

Every tech article regarding pinion angle I've read states that any difference in alignment of the u-joints to each other can and will cause a vibration. It can sometimes be difficult to distinguish from a unbalanced drive shaft. Sometimes it may not be enough to be annoying. Sometimes, when combined with other issues as suggested it may be severe. In any case, when they are out of alignment, they are spinning at different speeds and will cause vibration.

I'm not saying for sure that it is the cause of the problem, there are many other factors to consider. Just that it's possibly a cause.

Read this article and you will understand.
http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

Thanks Bob, but I understand perfectly. I'm not just repeating information I Googled and bench raced about, I've been factory trained in driveline theory and diagnosis by Hunter Engineering and Navistar, and have ~35 years of direct experience diagnosing and repairing drivelines, along with about every other part of automobiles, over-the-road trucks, heavy equipment and material handling equipment.

Excessive u-joint angle *alone* will not produce vibration at a single speed, it will produce a vibration which worsens with increasing RPM. Joint angle produces a torsional vibration along the driveshaft axis, which translates back into the transmission tailshaft and pinion shaft. In a manual transmission vehicle this will sometimes be felt in the shifter as well as the chassis. In an automatic transmission there is more slippage and hydraulic cushioning so vibration may be felt primarily in the rear axle. What our customer here is describing sounds like a resonant frequency at a given MPH not RPM, which indicates and off-axis imbalance somewhere. If the shaft is perfectly balanced, a worn output bushing can allow the shaft to rotate off center and act as if it is out of balance.

We have two separate concepts to distinguish and define here;
1. The oscillation of the driveshaft tube, which happens when one or both ends have excessive joint angles.
2. The tube oscillation which may be passed through the shaft assembly into the pinion gear.
3. Axial vibration which passes perpendicular to shaft axis.

#1 occurs any time there is any joint angle at all, and increases exponentially with increasing angle.
#2 occurs when there is a *difference* of angle between the front and rear joints in the shaft.
#3 occurs when there is a static or dynamic (off-axis operation) imbalance.

With #1 and #2 vibration is mostly turned to heat in the transmission and differential. Torsional vibration must be very severe to be felt through the directional changes and cushioning effect of suspension, tires, rubber mounts, etc.

#3 is very obvious even at slight imbalance due to a more direct path to the chassis, and because of likelihood of harmonic multiplication at a given frequency is much higher.

Driveshaft dynamics is not a simple subject, obviously. What's important to keep in mind is to look for the high-value targets first, and torsional vibration due to joint angle doesn't seem very likely to me in this case. Look for the simple stuff.

'Clocking' (or 'phasing') simply means to be sure the joint bosses on both ends are perfectly in line.

I'm thinking your shake is tires or a worn trans output bushing. Jack up the car and rotate all the wheels, checking that they are round and true from every angle. If so, have them checked for balance. If that doesn't out the root cause, we can get deeper in. There are a number of driveline vibration threads in the forum archives too.

[FLG]

I agree, check the tailshaft bushing...if its bad replace it while your there replace the bearing in the tailshaft as well. I'm pretty sure when I did mine I got all the stuff from tsr racing (something to that name,ill double check when I get home) all was pretty inexpensive and a fairly simple job.

[bull]

This is simple, basic stuff (and I'm sure it's moot) but be sure all your bellhousing bolts are good and tight. It's an easy thing to overlook but it will cause a vibration too.

[Cooter]

Hope you figure the shaking out, as I don't think there's any way to keep these older cars from shaking at aanything over 50 MPH. For whatever reason, they just shake. My Charger ('69) will rattle your teeth out at anything over 55 MPH. Drove to Carlisle one year(80 MPH in OD) and had to stop at rest stops for a break from the shaking.

[bobs66440]

To your shaking issue, 4* difference (nor any of the angles you show) should *not* result in shaking.

Every tech article regarding pinion angle I've read states that any difference in alignment of the u-joints to each other can and will cause a vibration. It can sometimes be difficult to distinguish from a unbalanced drive shaft. Sometimes it may not be enough to be annoying. Sometimes, when combined with other issues as suggested it may be severe. In any case, when they are out of alignment, they are spinning at different speeds and will cause vibration.

I'm not saying for sure that it is the cause of the problem, there are many other factors to consider. Just that it's possibly a cause.

Read this article and you will understand.
http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

Thanks Bob, but I understand perfectly. I'm not just repeating information I Googled and bench raced about, I've been factory trained in driveline theory and diagnosis by Hunter Engineering and Navistar, and have ~35 years of direct experience diagnosing and repairing drivelines, along with about every other part of automobiles, over-the-road trucks, heavy equipment and material handling equipment.

Well, I certainly can't match all that formal training. You obviously have a lot of knowledge and I respect that (most of  mine comes from 30+ years of fixing crappy cars because that's all I could afford  )
Though, I admit, I'm guilty. I do sometimes use Google and bench race occasionally  

The OP was asking about pinion angle and since it's known that his is wrong, and it's known that can be a cause of driveline vibration, I was simply suggesting he correct it, if nothing else, to eliminate it as a possible cause. A side benefit would be avoiding premature u-joint wear.

I agree with you, (as I stated) this alone may not be the cause and there are other factors involved. I don't think it's likely a wheel imbalance because he stated that it was fine before the swap, and he hasn't changed wheels/tires since, but, I agree, it certainly wouldn't hurt to check. Maybe as you said, it's a worn output bushing (different trans with possibly unknown history) and the pinion angle is amplifying the problem.

I used to sell Competition Engineering (Moroso) products and they have 2 deg shim kits, but as previously stated, they aren't cheap. Bell Tech also makes them but they are more expensive.

http://www.competitionengineering.com/catalog/CategoryDisplay.asp?CatCode=10002

[Musicman]

Check that the tailshaft bushing isn't worn out, allowing the yoke to go into a resonant gyroscopic vibration (circular) that would explain both the shaking and the plug coming out.

After reading your latest update I have to agree with elacruze... this seems like an obvious place to start.

[ncmiller1]

Thanks again for all the replies.  Is there a way to check the tailshaft bushing without removing it from the case?  Or is the only way to do it to drain the trans fluid and remove the tailshaft?  I tried to search for info on tailshaft bushing issues and somewhere it was recommended to use the yoke and a hammer to try and recenter the bushing by inserting the yoke all the way into the tailshaft and then hitting it.  Is this something to consider doing or is it detrimental?

[elacruze]

Thanks again for all the replies.  Is there a way to check the tailshaft bushing without removing it from the case?  Or is the only way to do it to drain the trans fluid and remove the tailshaft?  I tried to search for info on tailshaft bushing issues and somewhere it was recommended to use the yoke and a hammer to try and recenter the bushing by inserting the yoke all the way into the tailshaft and then hitting it.  Is this something to consider doing or is it detrimental?

You can lift the car and check by hand how much you can move the yoke in the trans, but that's really not good enough. To be sure, you have to remove the yoke from the driveshaft and the seal from the transmission so you can feel exactly how loose it is, then you have to have a lot of experience and/or a service manual to know if what you feel is within tolerance.

Perhaps one of the auto trans experts can chime in with specifics on specs, procedures and perhaps tools for checking.

[64dartgt]

Sounds like where I am.  I had the tranny, engine and rear rebuilt.  Had a bad rotational vibration on the highway about 50-60mph.  Figured it was the rear end.  Rear end guy looked at it once before and has it again.  Now seems like it is the tailshaft bearing, which has about 3x more play than normal, according to him.  It was likely wiped due to the fact that the guy who put the engine in neglected to tell me that there was no tranny mount in it for a few days.  He only told me after I complained of a noise.  Any way, I hope this cures it.  The rear diff guy has done everything else...pulled and straightened the axles...checked the drive shaft twice....etc...

[ncmiller1]

Okay, so it took longer than I had hoped to work on the Charger, but here is an update on the issue... which, sadly, still exists.

First, I ended up shimming the rear end down 2 degrees.  This didn't fix the shaking issue on the freeway.  When I drove the car after shimming, the shaking did seem to be much more prominent in the front end and in the steering wheel than in the rear of the car.  I don't think the shaking changed at all due to the shimming which was a little bit of a letdown.  Maybe I didn't shim enough?  The pinion is only pointing 2 degrees down in respect to the driveshaft, so that may not be a large enough angle.  But, I had someone else with me while driving, and we both agreed that the issue seemed in the middle or front of the car, which could mean the pinion wasn't the issue (but I'm no expert so I'm not positive).

Next, I replaced the lower control arm bushings and strut rod bushings (which were completely shot) in hopes this may help.  It didn't. But on the lighter side, the steering is really tight now and the 6 inches of slop that was in the steering wheel is completely gone.  Driving is much, much, much more fun now that everything is crisp and responsive.

So my new plan is to put the rear end of the car on jacks, or hopefully something sturdier, and slowly run up to freeway rpm's and see if the issue resides in the driveline.  I think it must be the transmission bushing mentioned before or the torque converter, I just want to do this test before ripping the transmission out (again) and paying people to test and replace parts if it isn't the issue.  

After all the new parts I put in this last round, I took the Charger on the freeway a few times to recreate the shaking and get a good, consistent feel of what was happening.  What I came up with was this:  
 1.) When I first get to freeway speeds, the car drives very smooth with no signs of any shaking problem.  Then over the course of 2 miles the shaking slowly builds, first manifesting lightly in the steering wheel, and then increasing to a fairly violent shaking felt in the wheel, the dash, and what seems to be the front of the car.  
 2.) When I exit the freeway, the shaking seems to increase a little when I apply the brakes, then when I come to a complete stop all returns to normal.  
 3.) I immediately repeated the test with the same results; at freeway speed the car is smooth at first then slowly starts to shake harder and harder until my eyes rattle after around two miles.

Another random addition (maybe related, maybe not) is something I noticed while removing my front disc brake calipers.  I had to open the hydraulic bleed vent in order to allow the caliper piston to release the rotor so I could remove the caliper/brake pads (I have power disc's up front and drums in the back).  This is due to the fact that there is a 2 psi check valve installed in the brake line going to the front calipers from the master cylinder.  It seems that it would be a bad thing that my brakes are always applied whether I'm braking or not to the degree that I can't slide the caliper off the rotor without venting the system.  Should I take the check valve out of the system?  Is it a normal thing to have a check valve holding a constant 2 psi on the rotors?

And just to add more information to this already too long post, I didn't replace the shocks or torsion bars after the engine swap, mainly because I thought it wasn't completely necessary and all it would do was make the car more boat like.  The shocks are new but I replaced them before the swap and they are 318 shocks (if there is a difference).  Was this dumb of me and could this be part of the issue (318 shocks and torsion bars under a 440)?

I guess my question after that novel I just wrote is; does this information help anyone to help me fix this issue, more so than the original post?  And feel free to tell me to just suck it up and take out the transmission tail shaft and replace the bushing, or replace the torque converter, etc. if you have mentioned this before, and the next step is to just start replacing parts until the issue is resolved.  I want to drive this car! (haha)

Thanks again to all who have replied to try and help with this issue already!  This site has been amazingly life-saving when it comes to Charger issues.  Happy Holidays!  (I'm unfortunately working graveyards tonight, Christmas Eve, and Christmas night 6:00pm to 6:30am)

[Dodgecharger74]

did you have the tires checked for a broken belt or bubble in tire  tires warm up & shake gets worse  This happens on my work trucks often

[ncmiller1]

I haven't checked the tires yet, and the only reason is because they are the same ones from before the engine swap when the car used to ride smoothly on the freeway.  I should check them though just to positively remove them as the culprit.

[Musicman]

You do not put residual pressure valves (check Valves) in the front lines of a Disc/Drum system!!! Get rid of them and your problem will more than likely disappear.

[elacruze]

You do not put residual pressure valves (check Valves) in the front lines of a Disc/Drum system!!! Get rid of them and your problem will more than likely disappear.

Surely! likely what happens is your pads are on the rotors, and when the rotors heat up they have hard spots which have a different coefficient of friction, causing a brake pulse. It takes a couple minutes to develop because they need time to heat up sufficiently.

[ncmiller1]

I am going to be so happy if such an easy fix solves my problem!  I can't wait until next week to remove the check valve and take the charger for a spin.  Should I also remove the check valve thats on the line to the rear drums?  Thanks for the awesome tip!

[elacruze]

Drums need the residual pressure to keep the shoes near enough to the drum to prevent excessive pedal travel. Disc calipers by design don't pull back much so they don't need the help. Keep the rear RPV.

[Musicman]

Drums need the residual pressure to keep the shoes near enough to the drum to prevent excessive pedal travel. Disc calipers by design don't pull back much so they don't need the help. Keep the rear RPV.

Yea that