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Discussion Starter #21
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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Discussion Starter #22
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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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.


Z
 

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Discussion Starter #24
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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Discussion Starter #25
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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Discussion Starter #26
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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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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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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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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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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Discussion Starter #31
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"!
I caught a good deal on a 9 with the old style big bearing ends in the right length for the stang.. I've found some 31 spline axles too. I'll need a centre and some brakes when the pocketbook allows and I'll be ordering from Shaun! Its just a slow process as money these days is scarce. Had to drop $$ on new tires for the daily and replace the dishwasher my soon to be ex wife broke.
 

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Discussion Starter #32
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.
We spun the new raybestos drums and they were good. No change from the previous ones either in vibration..
 

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Discussion Starter #33
Thanks Shaun!

I've got a steel shaft that was built and balanced to 4k rpm locally. Far more than this shaft should ever turn.. but I do keep hearing of people swapping to aluminum which dampens better. Better critical speed ;) Someone else mentioned that 28oz motors through the t5 sometimes create a harmonic that is also solved with aluminum shafts... Perhaps if this round of 'fixes' doesn't go in my favour I'll be getting a shaft and probably the 3 link from you. I mean might as well right. You have options for rear Brakes for a 9in old big bearing right?

The post with pinion angles is old info. We've tried a couple of different spots to see if it liked anything different. Currently have a spacer in the trans mount so we could go to 3.3 up (pinion) and 3.4 down (trans) No change from the past 2.6-2.7!

The 8in in the cars axle tube is almost 1.5cm bent. No wonder it was eating wheel bearings. Hopefully that is the source of this vibe thats been troubling me :)

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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Thanks Shaun!

I've got a steel shaft that was built and balanced to 4k rpm locally. Far more than this shaft should ever turn.. but I do keep hearing of people swapping to aluminum which dampens better. Better critical speed ;) Someone else mentioned that 28oz motors through the t5 sometimes create a harmonic that is also solved with aluminum shafts... Perhaps if this round of 'fixes' doesn't go in my favour I'll be getting a shaft and probably the 3 link from you. I mean might as well right. You have options for rear Brakes for a 9in old big bearing right?

The post with pinion angles is old info. We've tried a couple of different spots to see if it liked anything different. Currently have a spacer in the trans mount so we could go to 3.3 up (pinion) and 3.4 down (trans) No change from the past 2.6-2.7!

The 8in in the cars axle tube is almost 1.5cm bent. No wonder it was eating wheel bearings. Hopefully that is the source of this vibe thats been troubling me :)
You do NOT want to go UP with the pinion... you want to go DOWN. D-O-W-N as in pointed to the ground.
 

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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.

I actually have that wheel balancer. They work awesome! Unfortunately I only have the 13",14"&15" wheel adapters.
 

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As @Woodchuck we said, you want to go down, not up on pinion angle. They need to be at complimentary angles and with in 3° under normal use. As you apply torque to the rear axle, the pinion angle is going to rise. So if it's adjusted just sitting, it's going to be not at good operating angle. You need to go lower for what looks like a wrong angle.

Here is a really great demistration of universal joint operation. As far as changing the rear yoke you could have just bought a 1310/1320 combination. Very common and cheap.

 

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You do NOT want to go UP with the pinion... you want to go DOWN. D-O-W-N as in pointed to the ground.
Pinion down sounds so wrong but it is indeed right especially in a leaf spring car when all the angles change a bunch when a load is applied. Didn't believe it when I first heard it. Theoretically the engine and trans run parallel with rear axle under load but the pinion climbs as as you hit the gas.
 

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Discussion Starter #38
Guys.. Its NOT PINION ANGLE! Yes I'm aware I typed that post out wrong. The car was on it's wheels at ride height each and every time. I've gone through and measured pinion angles multiple times, Chassisworks has gone through it, Pats Driveline has gone through it. Pinion angle on the car is FINE! We simply tried adding some to at pats when they rebalanced the shaft to see if that changed anything. it didn't make a lick of difference whatsoever.

The car was hit in the 90's.. thats what resulted in the rear quarter being replaced and the car being painted. Thats why the drivers axle flange was bent. Thats why it had new wheels on it. Thats 99% the reason why the axle housing is bent. I'm still shaking my head that it wasn't caught when IWE went through the whole thing. You can see it with bare eyes when the rear end is out of the car.

I did not want to run a combo joint. IIRC its now a 1330.
 

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Discussion Starter #40
I appreciate the response, but it's just been gone over and over and over again and again. It was the first thing that got sorted. I knew with the T5 in the car it was going to be a potential culprit. I've driven myself crazy with it. I was even tempted to put the car on the dyno and run it up to 75mph under load and look to see just how much change there was and whether or not that was causing it. We did run it up on a set of stands and watched. Safety third right? haha I just feel burnt out.

As an aside, I believe the crank and rods/pistons are back from being balanced.

I'm off to my US mailbox tomorrow to pick up a pile of other parts for it.

Saw Blair this AM and my 8in was up on the bench and into his jig. Told me he'd have it done sometime next week.
 
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