Pinion Angle/Tailshaft Bushing

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MOPARJ

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Working on my 4 speed Dart with minor humming, grumbling vibration in 4th above 2000 rpm/55 mph. Still there when in neutral gliding but reduced. Can feel roughness when pushing clutch in at that speed. It is noticed in the float zone of the throttle while cruising only and from the trans forward. Can feel it in the shifter and even a bit in the steering wheel. 3.91 gears are in the rear and new 3” driveshaft was built to potentially help issue with new u joints, but it didn’t help. Tires are all good and balanced. There is some very minor side to side play of the slip yoke into the trans, so I am suspecting the tailshaft bushing has some wear (the trans needs a re-fresh anyways). Either than, the pinion angles, although look parallel, may not be perfect, causing this symptom.


Had a similar issue on another car of mine recently.


Being that this vibration/hum isn’t violent and shaking the car to pieces, and I am suspecting either the tailshaft bushing to be worn, or pinion angle to be off slightly, do you think the car should be fine operationally until I can get a chance to refresh the trans and get the pinion angles just perfect? The car is driven a few times a week, about 100 miles total over a week.
 
It should be ok if it isn't that bad.


Nah, not violently shaking at all. More of a grumbling pulsation that rhythmic.


Main concern was just snapping or dropping the driveshaft somehow, but I don’t see how that would happen. Likely would just keep doing what it is doing, either from the angle being off slightly or wobbling in the tailshaft from a worn bearing.


This will be remedied soon, because a very prolonged period will slowly wear on the front ujoint or both over time.
 
If it only does it in 4th gear and not the rest it could be the pilot bushing in the crank.
 
Nah, not violently shaking at all. More of a grumbling pulsation that rhythmic.


Main concern was just snapping or dropping the driveshaft somehow, but I don’t see how that would happen. Likely would just keep doing what it is doing, either from the angle being off slightly or wobbling in the tailshaft from a worn bearing.


This will be remedied soon, because a very prolonged period will slowly wear on the front ujoint or both over time.

Usually the first thing to go with a vibration is the thin little tail shaft housing of the automatic transmissions, but it does take a pretty serious vibration to do it.
There was a Road Kill episode where that happened to them because they shortened and rewelded their own shaft in a Barracuda and didn't get it straight.
 
If it only does it in 4th gear and not the rest it could be the pilot bushing in the crank.


It may very well do it in 3rd, but revs are around 3100 rpm at the same mph, so it is very tough to notice if so due to the added engine noise. Would need to get it up at least to that point in revs to duplicate the same driveshaft speed that is seen at 55-60 mph in 4th. I will experiment on the way home with that.


Pilot bearing on crank is pretty new, only about a year old and less than 5000 miles.
 
The only reason I ask is I had a bad experience with a lakewood bell that some one put on and didn't use offset dowels to center it and it kept wiping out the pilot bushing, so in 4th gear the input and out put are going the same speed and it would whip the output and cause a rumbling noise, in 3rd the shafts are going different speeds so it seemed to cancel out the noise.
 
Did you indicate the bellhouse, before slaming the tranny in? that is to say; can you say with surety that the crank and the tranny are on the same centerline?
A)Still there when in neutral gliding, B)but reduced.C)Can feel roughness when pushing clutch in at that speed.D)It is noticed in the float zone of the throttle while cruising only and from the trans forward.E)Can feel it in the shifter and F)even a bit in the steering wheel.
This says you have multiple issues; 4 or 5 by my count.and possibly a 6th.
A) Still there Could mean some of it is after flywheel
B)Reduced vibration with the engine now idling, could mean that some of the vibration is in the engine.
C)Could be in the bellhouse
D)could be in the rods or wristpins or the tune.
E) Something is going on inside the tranny, or at it's tailshaft
F) if you feel it in the steering wheel this rarely has anything to do with the powertrain. The most likely is a blown cord in a front tire, followed by out of balance wheels, then too much toe-in, and lack of caster.

g) Sometimes these all conspire to set the body itself into an oscillation of it's own. It typically happens at 55 to 62 in our A-bodies.

I once had your problem pretty much exactly as you describe. I about tore my hair out looking for it. I spent huge blocks of time searching for it. In the end, I pulled the 4.30s out and swapped in 3.55s. This made it bearable.
The engine,flywheel and clutch were dead smooth. It was there with an indicated and checked for parallelism bellhouse,with multiple trannys, and two balances of the D/S. lt did not go away with pinion angle adjustments. Nor by removing the wheels, drums,axles,or by swapping out the chunks. I concluded it was the body.
It is still there today.
 
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Did you indicate the bellhouse, before slaming the tranny in? that is to say; can you say with surety that the crank and the tranny are on the same centerline?

This says you have multiple issues; 3 by my count.


Yes, everything was lined up before installing about a year ago. Bellhousing is a stock piece.


This issue is popped up about a month or so ago shortly after a gear change, which has led me to suspect that the increased driveshaft speed is making a worn tail bushing or slight pinion angle misalignment more obvious.


As for the issue described, all of the symptoms popped up at once. Sorry if it seems like three issues; hard to describe these things sometimes without someone else actually feeling them.
 
Assuming no tire changes,and no ride height changes,with the new gears, only one thing changed; the power train speed,at any given mph. That is from crank to pinion gear.
If you previously had 3.23s you are now at about a 21% higher rpm for any given mph. ( the Speedo was corrected, yes?). So the vibration, if pre-existing, should have been there at a 21% higher speed, with the old 3.23s. This maths out to about 67 mph, previously, as compared to 55mph, now.
If you did not have an issue at that earlier mph, then I would have to ascribe the issue directly to the chunk, or that the new rpm is exciting the natural body oscillation.
 
Assuming no tire changes,and no ride height changes,with the new gears, only one thing changed; the power train speed,at any given mph. That is from crank to pinion gear.
If you previously had 3.23s you are now at about a 21% higher rpm for any given mph. ( the Speedo was corrected, yes?). So the vibration, if pre-existing, should have been there at a 21% higher speed, with the old 3.23s. This maths out to about 67 mph, previously, as compared to 55mph, now.
If you did not have an issue at that earlier mph, then I would have to ascribe the issue directly to the chunk, or that the new rpm is exciting the natural body oscillation.


Your thinking is in line with mine. Cruising at 65 mph with 3.21s was 2000 rpm and that is usually where I hang out on the highway. Now, 2000 rpm is 55 mph with the 3.91s. So, I need a bit more engine speed and driveshaft speed with the 3.91s to get to the same 65 mph, which might be why I am now noticing this sensation. The driveshaft is 3” and .083” thick, so half critical speed shouldn’t be anywhere close at 65 mph.


No tire changes were made. I thought about the rear having the issue after the gear swap, but I don’t feel much of the sensation/vibes coming from the mid driveshaft to rear area at all.


During lunch, I put the car in 3rd and ran it up to 60 mph. Not near as much noticed in that scenario, but that trans gear is 1:1, so the driveshaft speed is a bit slower.
 
I ran 3 different units of those, and every one did that in o/d. And I blew all three of them up. Two of them stripped off the O/D teeth and on a third I stripped all the teeth off the input gear.So take it easy on the o/d part.
In od the engine torque goes into the input gear and down to the cluster. Then over to the third gear drive , and then up into "third" gear (which is now OD). From there the torque exits the tranny thru the mainshaft. This means that the input gear and the mainshaft are turning at different speeds. 37% different! When the crank is going 2890 rpm@60 mph, the M/S is going about 2110.
It was my conclusion that,that speed difference was setting up an oscillation right inside the tranny.It also means that the cluster gear is constantly under load. And so are the front rollers,and the back bearing. The back bearing. I put a new one in to no effect. $138 Canadian, plus taxs. I have pulled od boxes apart,in the which, the front nose of the M/S was all chewed up. When this happens the input torque forces the cluster and the M/S apart. This creates noise as the teeth are no longer in mesh, and a huge amount of force is pushed into the back bearing. You can bet it is going to complain. I'm not saying your tranny has this issue, nor did mine when I got them, nor when I yanked them. I'm just saying it happens. If you find silver streaks in your oil, as you agitate it, it's time to drop that box and see what's going on inside.No streaks, means carry on.
My combo seemed to work Ok with 3.55s or less. It did not like 4.10s,4.30s, 4.86s,5.13s, nor my 3.91s.
I got out of od boxes.
If you think about it, at 2890 rpm, Our hotrod engines are putting out a pretty good amount of torque.Probably siting fairly near the fattest part of the torque curve. I wonder what harmonics are running up and down the powertrain that find their origins in no mechanical issue at all, but in the tune.
I got out of od boxes.
If you are running the OD box, you are running a starter gear of 3.09 x 3.91=12.08. This is a great starter gear for drag-racing. I found it much to deep for street.But I understand that to run that box, second gear needs that stinking 3.91, or even more. Second thus is 1.67x3.91=6.53, which is the same as (in the std box) 1.92x3.40s. That is the price you pay to get overdrive,namely; too much starter gear to get; a so-so second,a third you almost never use, and a great od gear.
I got out of od boxes.
The only way that box ever worked for me was with a GVOD, used as a spitter. The ratios were 3.09-2.41-1.67-1.30-1.00-.78-.57 GV in red.
The splits were---.78---.68---.78--.77---.78--.73
I ran this with almost every gear in my arsenal. For street,I liked 3.55s, for a 10.97 starter gear and a 2.02 double overdrive.I ran it with a 223/230/110 cam; what a hoot! 65=1630rpm .....
I also tried it with 4.86s,and with 4.30s, in an attempt to have a dual purpose tranny, skipping first and attempting to start in second or first over, on the street. But that didn't work out at all.
That was a fun two summers.
But I got out of those boxes

During lunch, I put the car in 3rd and ran it up to 60 mph. Not near as much noticed in that scenario, but that trans gear is 1:1, so the driveshaft speed is a bit slower.

I'm sure you meant something different than what you wrote here,lol. Cuz the driveshaft rpm at 60mph is the same no matter what gear you are in. And the point that there is less vibration in direct at about 2750,vs, 2000 in o/d, kindof answers your question.
It's either in the box, or in the tune; is my guess,cuz I have never seen engine/flywheel vibration get better with an increase in rpm.
 
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I ran 3 different units of those, and every one did that in o/d. And I blew all three of them up. Two of them stripped off the O/D teeth and on a third I stripped all the teeth off the input gear.So take it easy on the o/d part.
In od the engine torque goes into the input gear and down to the cluster. Then over to the third gear drive , and then up into "third" gear (which is now OD). From there the torque exits the tranny thru the mainshaft. This means that the input gear and the mainshaft are turning at different speeds. 37% different! When the crank is going 2890 rpm@60 mph, the M/S is going about 2110.
It was my conclusion that,that speed difference was setting up an oscillation right inside the tranny.It also means that the cluster gear is constantly under load. And so are the front rollers,and the back bearing. The back bearing. I put a new one in to no effect. $138 Canadian, plus taxs. I have pulled od boxes apart,in the which, the front nose of the M/S was all chewed up. When this happens the input torque forces the cluster and the M/S apart. This creates noise as the teeth are no longer in mesh, and a huge amount of force is pushed into the back bearing. You can bet it is going to complain. I'm not saying your tranny has this issue, nor did mine when I got them, nor when I yanked them. I'm just saying it happens. If you find silver streaks in your oil, as you agitate it, it's time to drop that box and see what's going on inside.No streaks, means carry on.
My combo seemed to work Ok with 3.55s or less. It did not like 4.10s,4.30s, 4.86s,5.13s, nor my 3.91s.
I got out of od boxes.
If you think about it, at 2890 rpm, Our hotrod engines are putting out a pretty good amount of torque.Probably siting fairly near the fattest part of the torque curve. I wonder what harmonics are running up and down the powertrain that find their origins in no mechanical issue at all, but in the tune.
I got out of od boxes.
If you are running the OD box, you are running a starter gear of 3.09 x 3.91=12.08. This is a great starter gear for drag-racing. I found it much to deep for street.But I understand that to run that box, second gear needs that stinking 3.91, or even more. Second thus is 1.67x3.91=6.53, which is the same as (in the std box) 1.92x3.40s. That is the price you pay to get overdrive,namely; too much starter gear to get; a so-so second,a third you almost never use, and a great od gear.
I got out of od boxes.
The only way that box ever worked for me was with a GVOD, used as a spitter. The ratios were 3.09-2.41-1.67-1.30-1.00-.78-.57 GV in red.
The splits were---.78---.68---.78--.77---.78--.73
I ran this with almost every gear in my arsenal. For street,I liked 3.55s, for a 10.97 starter gear and a 2.02 double overdrive.I ran it with a 223/230/110 cam; what a hoot! 65=1630rpm .....
I also tried it with 4.86s,and with 4.30s, in an attempt to have a dual purpose tranny, skipping first and attempting to start in second or first over, on the street. But that didn't work out at all.
That was a fun two summers.
But I got out of those boxes



I'm sure you meant something different than what you wrote here,lol. Cuz the driveshaft rpm at 60mph is the same no matter what gear you are in. And the point that there is less vibration in direct at about 2750,vs, 2000 in o/d, kindof answers your question.
It's either in the box, or in the tune; is my guess,cuz I have never seen engine/flywheel vibration get better with an increase in rpm.



All of that makes sense. And yes, what you were saying about running in 3rd gear is what I mean. You are right. Lol.

I do think its trans related being how I feel it through the accelerator, steering wheel. And clutch as well. I'm just feeling more with the 3.91s. The trans was a used unrebuilt unit that leaks from left side a bit, so its a little tired. But it was near free. It will have to be rebuilt sooner or later, prolly sooner.

Forgot to mention my rear is an 8.25.
 
Ok good, nothing wrong with that combo now Eh? 12.08 is just the starter gear she needed.

If you ever decide to get out of that box, I highly recommend the 3.09/direct box. The ratios are much tighter, and you could go back to 3.21s or 3.55s.Your current Road ratios are;
>12.08-6.53-3.91-2.85 with splits of;.54-.60-.73
The above recommended 3.09/D box with your 3.91s has ratios of
>12.08-7.51-5.47-3.91, with splits of .62-.73-.71 Notice the much tighter splits. Your 268 will like those splits much better. The Rs will not fall nearly as far on the shifts. Notice you get an extra gear, where you need it. But IMO 12.08 is way more starter than you need. Because you have an extra gear, you could drop back down to the 3.21s, but that starter of 9.92 would be a little soft with your compression ratio.3.55s will be just right. The road ratios with 3.55s are
>10.97-6.82-4.97-3.55, and splits are same as above,namely .62-.73-.71
Notice 2nd gear is about the same as you currently have, then you get two more tight ratios. The 10.97starter should be adequate, requiring just a smidge more Rs to get rocketing. Second gear will take you to 70plus mph,the rpm at 65 will be bang-on at 5500;being about just a little over peak, and 65 will be about 2850.
As a comparison here's what it looked like with; the 3.21s and o/d box
>9.92-5.36-3.21-2.34 Remember that second gear? It's about like 3rd gear with the 3.09/D and 3.55s,lol,
So if you go shopping, there's my opinion. I have this box, and have not been able to break it in about 10 years or more.And I love it. My 367 has enough torque that I could easily run 3.21s. But with my GVOD, the Rs would be a tad low at 60mph =1866, and the engine would be back into reversion, with the current cam.
If you go looking...... the 3.09D box and 3.55s will be killer for street.
 
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Ok good, nothing wrong with that combo now Eh? 12.08 is just the starter gear she needed.


For what it is, it runs pretty well. Original block and heads. 1.88/1.60 valves. 60k since I rebuilt it, so its a little rough and one of the Comp lifters is noisey, but it'll last another summer or so.
 
Ok good, nothing wrong with that combo now Eh? 12.08 is just the starter gear she needed.

If you ever decide to get out of that box, I highly recommend the 3.09/direct box. The ratios are much tighter, and you could go back to 3.21s or 3.55s.Your current Road ratios are;
>12.08-6.53-3.91-2.85 with splits of;.54-.60-.73
The above recommended 3.09/D box with your 3.91s has ratios of
>12.08-7.51-5.47-3.91, with splits of .62-.73-.71 Notice the much tighter splits. Your 268 will like those splits much better. The Rs will not fall nearly as far on the shifts. Notice you get an extra gear, where you need it. But IMO 12.08 is way more starter than you need. Because you have an extra gear, you could drop back down to the 3.21s, but that starter of 9.92 would be a little soft with your compression ratio.3.55s will be just right. The road ratios with 3.55s are
>10.97-6.82-4.97-3.55, and splits are same as above,namely .62-.73-.71
Notice 2nd gear is about the same as you currently have, then you get two more tight ratios. The 10.97starter should be adequate, requiring just a smidge more Rs to get rocketing. Second gear will take you to 70plus mph,the rpm at 65 will be bang-on at 5500;being about just a little over peak, and 65 will be about 2850.
As a comparison here's what it looked like with; the 3.21s and o/d box
>9.92-5.36-3.21-2.34 Remember that second gear? It's about like 3rd gear with the 3.09/D and 3.55s,lol,
So if you go shopping, there's my opinion. I have this box, and have not been able to break it in about 10 years or more.And I love it. My 367 has enough torque that I could easily run 3.21s. But with my GVOD, the Rs would be a tad low at 60mph =1866, and the engine would be back into reversion, with the current cam.
If you go looking...... the 3.09D box and 3.55s will be killer for street.


Good advice. I may be looking to switch to a 3.09/D transmission at some point down the line since I would assume the only thing that might need to change is driveshaft length a tad and the pilot bearing size. For now, I will most likely just refresh what I have down the road a few months.


Like you were saying, I don’t hang out in first gear long and usually into second by about 20 mph to keep revs down. I try to run in 3rd gear up to about 60mph/3000 rpm, then when I go to OD, I ease off the gas and gently put it into 4th. I certainly make it a point to be gentle on that OD gear.


In the interim, I am going to check the balance of the front tires again just for kicks. Checked the relatively new balancer on the front of the engine last night and no wobble, and not loose. It’s a cheapie replacement from Autozone. Drove 30 miles into work this morning with zero change in severity of what I had described and no change of mph or revs as well. All engine vitals good at 185° temp and 58 psi of oil pressure at anything above 1200 rpm, 25 psi at warm idle.
 
All A/F-body A833s have identical dimensions, except for certain od boxes had the small output shafts. That would require upsizing the yoke to the 727 dimension

That cam likes to be reved.
Put a vacuum gauge on it and slowly rev the engine up to at least 3000. The vacuum will steadily increase. When it tops out, that is when the engine first becomes efficient.That is the minimum cruise rpm for best fuel economy. That can be considered the minimum engine speed.Reversion has stopped, and the air in the intake is now all moving in the same direction. The headers have finally stopped yanking fresh charge out into the exhaust system.This is where you start leaning it out to get some mpgs.And the oil starts to say thank you.
If this is 1800 rpm, then 1st will want to be buzzed up to 3300,and second to 3000.
>If it is 2000, then 2000/.54=3700 into 2nd, and 2000/.599=3340 into direct
If 2200, then 2200/.54=4074 into 2nd, and 2200/.599=3673 into direct.
Of course the engine will be happy to be shifted earlier,But then a smaller cam would be a great investment. It will make more torque down below the vacuum peak, possible even up to 3000/3500. More torque down there means more power. And less fuel useage. And cleaner,longer-lasting oil. And longer lasting cylinder walls.
If you are keeping the revs down, It seems to me that you and that combo are not so well-matched.I say this with no animosity, or criticism, only as gentle as I know how to.

Now that makes me curious, What was your thinking for installing the 3.91s?
 
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All A/F-body A833s have identical dimensions, except for certain od boxes had the small output shafts. That would require upsizing the yoke to the 727 dimension


That cam likes to be reved.
Put a vacuum gauge on it and slowly rev the engine up to at least 3000. The vacuum will steadily increase. When it tops out, that is when the engine first becomes efficient.That is the minimum cruise rpm for best fuel economy. That can be considered the minimum engine speed.Reversion has stopped, and the air in the intake is now all moving in the same direction. The headers have finally stopped yanking fresh charge out into the exhaust system.This is where you start leaning it out to get some mpgs.And the oil starts to say thank you.
If this is 1800 rpm, then 1st will want to be buzzed up to 3300,and second to 3000.
>If it is 2000, then 2000/.54=3700 into 2nd, and 2000/.599=3340 into direct
If 2200, then 2200/.54=4074 into 2nd, and 2200/.599=3673 into direct.
Of course the engine will be happy to be shifted earlier,But then a smaller cam would be a great investment. It will make more torque down below the vacuum peak, possible even up to 3000/3500. More torque down there means more power. And less fuel useage. And cleaner,longer-lasting oil. And longer lasting cylinder walls.
If you are keeping the revs down, It seems to me that you and that combo are not so well-matched.I say this with no animosity, or criticism, only as gentle as I know how to.

Now that makes me curious, What was your thinking for installing the 3.91s?

The 3.91s were installed to mainly bandage the gap from 1st to 2nd as you had mentioned. And to give this mill with slightly less low end torque a bit of help.
 
Yeah that is what I kindof suspected.
I once put a 340 cam and Xheads into/onto an otherwise stock 73 teener. Yeah with 2.76s that was a bit of a disaster. It had great passing power on the hiway, but out of the gate,To say it had"slightly less low end torque" would be too kind. It flat out sucked. The addition of a 2800TC improved things a bit. But when the 4.10s went in well, that was the magic. I won't ever put a 340 cam etc onto an 8/1 teener again.
>When that Dart died, I pulled the powertrain and junked the rusted hulk, which today would still fetch good coin. But in the late 80s who could have known.....
>So fast forward 15/20 years or so, and in 2000 I un-mothballed that same engine.I yanked the 340 stuff in favor of the teener equivalents. I freshened up the rings etc. and plopped it into my FormulaS clone as a winter engine.( I used to pull the 367 every September and go thru it in the snowy season). Some winters the teener had an auto, and some it had a stick. Sometimes a 2.66 low and sometimes a 3.09od and sometimes a 3.09od and a GVOD for a double od. One year it had that 2800TC and 3.55s . Of course it had the TTIs on it and a small-port intake with a TQ on it. It was still the 8point something factory compression.And I put some 360valve springs in it, (or 340, not sure), with the 273 rocker gear. I still have this engine.
>Well I'll tell you, that lil teener surprised the dickens outta me.Best lil teener I ever had. It was so sweet, I just hadda mess with it. Every May I pulled it out and stuck the freshened 367 back in. So then,I would contemplate the next winters combo.
>One winter,I put an A999 in it with the wide ratios and a semi-auto shift kit in it, that allows both auto mode and full manual. And then, Then, I put 2.76s in it.Now if you have never heard a mellow 4 barrel teener running WOT, in high gear, from 20mph to 65 mph, screaming obscenities at me through full-length dual 3 incher exhaust and Dynomaxers, Man; I can't tell you how sweet that sounds. That is just one long pull at about one continuous rpm!
I used to nail it from a stop, get her into 3rd as fast as she would take full throttle and then, let that TQ moan, for what seemed like forever.65mph was still near 2800.Hyup, that brings me a huge smile just remembering it. The starter gear with the A999 was 7.56, and with a 2800TC, and with the teener top-end back on, she had plenty enough giddy-up for a winter motor.That combo pulled about 75/80 mph still at 2800ish,before the Rs started to climb,lol.
>I mean imagine the dyno-operator pulling the lever, flat-footing it,and keeping the Rs at 2800 for about 14 seconds,lol. That poor teener! I used to torture it so bad.
>One winter I had the od/GVOD combo in it with 4.30s.That teener pulled the od ratios all by themselves, but I had set the GVOD up as a splitter. The starter gear was 13.29, and double OD was 2.45. Well set up like this, the teener hits shift-rpm real quick. I used to shift it at 5000; sometimes 5500, just because.
First topped out at about 30mph,and 1st-over at 39. Second was 56, and 2nd-od was 72. Third was 94,and 3rd-od was 120. But I rarely went past 72@5500; That was 4 ratios, with just one tug on the stick, and two electric fast-as-lightning splits........ 65mph was a tic under 2000,lol.
I gotta tell you, a teener with 4.30s, and split-shifting, is pretty neat.
Those winter combos were not fast. Nor quick. But it/they were hands down,the funnest I ever had. They were not about being fast or quick. They were just about being mellow, and having fun.
I stopped doing that after the 5th winter or so. The 367 was no longer having issues, that I was catching in the nick of time,and she was in her final iteration. I was no longer broke; the kids were on their own, and doing well. I bought a second car, and no longer needed the S for winter. Hallelujah, no more swapping powertrains.
I still miss that teener now and then.............
But 93 in the 1/8 is funner, oh yeah
 
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