These aren't my kinda vibes - Page 2 - Vintage Mustang Forums
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post #16 of 41 (permalink) Old 12-02-2018, 08:07 PM
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Originally Posted by Woodchuck View Post
Take the car to a shop that does "on the car" balancing and have the rears done.
I remember in 1980 working at a tire place in Ocala that did on vehicle tire balancing using the machine pictured below. While the electric motor was spinning the wheel at speed you would adjust using the 4 little round knobs at the end of the rim adapter the amount and position on the rim of the necessary weight by grabbing them with your bare hand while they were spinning. Looking back, that was friggin stupid! Hopefully the practice has advanced since then.
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post #17 of 41 (permalink) Old 12-03-2018, 12:09 AM Thread Starter
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And if the problem is a brake drum or an axle flange your problem STILL won't be resolved...
I'm thinking I'll put it up on the stands and check the axle flanges/drums.
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post #18 of 41 (permalink) Old 12-03-2018, 12:33 AM
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My brother had a fox body with a similar issue. Come to find out the new pinion gear shaft was not true. Replaced the gears and smooth as butta.

Scott

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post #19 of 41 (permalink) Old 12-03-2018, 12:35 AM
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I chased a vibration for a long time. I finally had a drive shaft made that was a little longer and solved the problem. How much slack do you have in the slip joint after you install the universal into the rear end yoke. It should not be any more than about 3/4". Just something else to check when all else fails. My driveline had been balanced and had new universals also.
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post #20 of 41 (permalink) Old 12-03-2018, 02:07 AM
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IWE should be able to help you out !

6r07a143871 --owned since 10/83
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post #21 of 41 (permalink) Old 12-03-2018, 07:39 PM Thread Starter
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Originally Posted by CRUZZAR View Post
I chased a vibration for a long time. I finally had a drive shaft made that was a little longer and solved the problem. How much slack do you have in the slip joint after you install the universal into the rear end yoke. It should not be any more than about 3/4". Just something else to check when all else fails. My driveline had been balanced and had new universals also.
We bottomed the slip yoke and then came out to 3/4in and had the driveshaft built to that! I chatted with Colin and he said anywhere from 1/2 to 1-1/4in is acceptable. 3/4in being ideal. So it's right in spec.
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post #22 of 41 (permalink) Old 12-04-2018, 12:20 AM Thread Starter
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Put the car up on stands.. started it and ran it up into 4th gear and you can see the wobble. Much more pronounced on the pax side. Took the wheels off and still see the wobble with the drums on. Pulled the drums and measured the flange surface. the pax side is .013 out! The drivers side about .006.

Me thinks me found the problem!

Looks like I'll be replacing at least one axel and most likely the carrier when they pull it apart. Perhaps it's time to just pull the trigger and build a 9.
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post #23 of 41 (permalink) Old 12-04-2018, 12:30 AM
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Congratulations Bent axles are pretty easy to check, but they usuallly aren't the first thing you think of when chasing a vibration.

When first working in a shop, I was taught to eliminate all the easy to check items first, even if they might be a remote possibility. Then go after the time consuming checks. Over the long run, that methodology is a big time saver.


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post #24 of 41 (permalink) Old 12-15-2018, 07:00 PM Thread Starter
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I replaced the passenger side axle with one from a local mustang friend. That seems better. Still a vibration. Car went back up on thew stands and I can see the driveshaft moving around a bit near the tail shaft while running. I can feel some play in there now too. So out it came. Theres a bit of scoring on the yoke and I'd imagine the tailshaft bushing is toast too? Perhaps from the bad angles previously and wobbly old shaft?

I also get a bit of a vibration out of gear as I go through the rpm with the car out of gear. Perhaps its time to pull the trans out and have a look at the clutch/flywheel/balancer. I wonder if something ended up 'wrong'.
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post #25 of 41 (permalink) Old 03-17-2019, 04:59 PM Thread Starter
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Figured I'd provide some update.

I got annoyed and yanked the trans out. Input shaft had a lot of play in it, so opened the whole thing up. Worn bearings, trashed synchros and a 5th gear cluster that looked like it had been sitting at the bottom of a swamp! So much for being 'rebuilt'. Rebuilt the the whole thing. Checked the bell housing for concentricity and for lateral deviations as well. Everything lined up nicely. Had the flywheel and pressure plate checked for Balance. Got the driveline angles spot on. 2.5 and 2.6. Checked the joints. Ran it on the stands again and noted that it appeared good.. felt vibration in the rear leaf.

Pulled both axles out and got some new ones from Dutchman. Seems a bit better.

Still notice a harmonic/vibe at around 120km/h. Also notice an engine derived vibration under load around 3000rpm and onward.

I swear this thing just enjoys fighting me and causing me grief.

By the end of this, hopefully it'll be smooth as glass. I kind of wonder if that vibration is just the way it goes with strokers?

Someone else suggested having another shop rebalance my new driveshaft, or maybe getting an aluminum one as they tend to absorb or not transmit as much in the ways of harmonics.

I'm all open to suggestions on this..
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post #26 of 41 (permalink) Old 09-08-2019, 02:23 PM Thread Starter
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Figured I'd come back and update.

Motor is out of the car being rebalanced. It also was detonating and had burnt a valve. I guess a crappy balance led to the intake bolts loosening and draw oil/air in from the lifter valley. Getting that all fixed up. doing some mild porting and a cam change.

Further to that, on the recommend of a good friend, I measured the rear axle housing. Almost an inch out. One tube was obviously bent. I should have checked that when I swapped in the dutchman axles, because obviously if the axles were bent, so was the housing. I guess that was something that didn't get looked at when the car was hit in the 90's and repainted. I should have also noticed that it kept eating drivers side rear wheel bearings. Once I had the whole rear end out and on the floor it was plainly obvious. Blair is going to put it in a jig and straighten it and weld on a new drivers side housing end. I've already dumped too much into this 8in to just ditch it. I did however find a screaming deal on a small web large bearing 9in housing in the right length. I'll slowly piece that together and then add SorT's 3 link. As funds allow of course.

I'll report back on 'this' fix when the cars back together...
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post #27 of 41 (permalink) Old 09-10-2019, 09:37 PM
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I find myself in the similar position as you on my upgraded 8" rear end. New TJ center section, new Moser axles, and in my case it works fine but I am at a dead end on installing a 3 link and have $1500 in the 8" setup. Had I known I was going to catch the racing disease I would have started with a big tube 9"!

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post #28 of 41 (permalink) Old 09-10-2019, 09:56 PM
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Check the dynamic balance of your brake drums individually. Way cheaper than a new set of skins. My gremlin was an out of balance brand new brake drum from a reliable vendor. I couldn't drive 74 mph for years till I figured it out. Good luck.
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post #29 of 41 (permalink) Old 09-11-2019, 08:22 AM
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What kind of driveshaft are you using? I didn't see mention in the thread.

We build a 3" dia. aluminum shaft with CNC machined forged aluminum yokes. The vibration dampening of the aluminum shafts has fixed a few customers issues when they switched from steel.

Also, I like to run my pinion angle in the 3-4 degree range. Equal and opposite. Engine down, pinion up.

Wheels, tires, bent axles, trans., engine, lots of rotating parts that can cause vibrations. Sounds like you are working your way through it!
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post #30 of 41 (permalink) Old 09-11-2019, 08:42 AM
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When all else fails, go back to your driveshaft/pinion angle. You want a total of -5 to -7 degrees total... that means if your driveshaft is, for example, 3* down you want the pinion yoke 4* DOWN, not up. If the driveshaft is down 2* you want the pinion DOWN 3*. You want to measure angles with the weight on the suspension as it would be going down the road (occupants, fuel, etc.).
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