commando1
Old Man with a Hat
Critter, how many miles have you put on this beauty?
1971 Plymouth Sport Fury GT Brogham & U code Super Comando
- Thread starter CanCritter
- Start date
Probably both not enough and too many.
I'm about half way through this thread. Absolutely awesome car!
Great Work !!! Really enjoying a few pages at a time.
Great Work !!! Really enjoying a few pages at a time.
When I took it for a drive last month it had 1100 I believe. Derek is definitely spending more time behind the wheel which is great to see. We were trying to diagnose a vibration as the car gains speed over 40mph. It gets quite bad the faster you go so thinking wheels/tires or possible rear diff as it does have some diff howl.
You need to check the rear diff pinion angle. Rear diff and trans tailshaft MUST be parallel. There are wedges you can buy to help "clock" the rear.
Check tires for shifted belts (not uncommon).
Thanks Ross good suggestions. The tires are new and have been balanced more than once I believe and Derek has had the driveshaft balanced and checked for straightness. Thinking the pinion angle could be a possibility.
Well, get it checked asap, as you'll wear out the tailshaft bushing and bearing plus the U joints in short order.
@CanCritter ^^^^
CanCritter
Senior Member
close to 400 this year lm thinkin...now that cars home get out whenever l can with it...
exactly....
vibration shows up around 75 mph.....have rechecked front tires for balance...driveshaft had a slight bend shop said when l took it in to be checked..they said they straightened it and rebalanced...
Rear tires need to have balance rechecked as well yet....
will have rear tires rebalanced and checked and go from there..
straightening out a driveshaft...not having much confidence in that ...no diff than straightening out a bent wire...is never gona be bang on... will probally have a new driveshaft made.....
Does the vibration pulsate? Or is it constant? Pulsating vibration is a number 1 marker for pinion angle. Constant vibration is more tires, U joints, bent shaft etc.
From the innerweb:
"The pinion angle is simply the angle between the rear end’s pinion shaft and a true horizontal line. The transmission angle is the angle between the transmission’s tail shaft and a true horizontal line.
Together, these angles form the driveline’s phase angle. Pinion angles can make the difference between a smooth ride, or a noisy and vibrating ride. Correct pinion angles are also very important to the life of your u-joints. Yes a driveline will work with 0* degree pinion angle, but the u-joints need a slight angle for proper lubrication. Without the correct angles, the needle bearings in the u-joint caps do not rotate. Those needle bearings need to rotate in order for the u-joint to operate reliably and smoothly. These u-joint angles should always be at least 1-degree to avoid wearing out the yoke bearings."
Simple angle gauge:
From the innerweb:
"The pinion angle is simply the angle between the rear end’s pinion shaft and a true horizontal line. The transmission angle is the angle between the transmission’s tail shaft and a true horizontal line.
Together, these angles form the driveline’s phase angle. Pinion angles can make the difference between a smooth ride, or a noisy and vibrating ride. Correct pinion angles are also very important to the life of your u-joints. Yes a driveline will work with 0* degree pinion angle, but the u-joints need a slight angle for proper lubrication. Without the correct angles, the needle bearings in the u-joint caps do not rotate. Those needle bearings need to rotate in order for the u-joint to operate reliably and smoothly. These u-joint angles should always be at least 1-degree to avoid wearing out the yoke bearings."
Simple angle gauge:
polara71
Old Man with a Hat
Then the question that begs to be answered is " how does that angle get out of whack"?
The transmission and engine are set by the mounts. The gear housing is set by the rear tube and springs.
What am I missing?
CanCritter
Senior Member
in looking at rear tires see no weights so next weeks project will consist of removeing & checking rear tires for balance
I asked the same question... apparently welding the perches on and trans/engine mount placement is not an exact science!
70bigblockdodge
Old Man with a Hat
Sometimes there is a plate on top of the mount. The pinion angle should be set at perches and should be evident if someone ever moved them.
The drive like is built so trans is to one side and pinion is to the other so even when full bottomed out to flying through the air you will always have u joint angles. Trans points down and rearend should point down at ride height so the chance of those angles lining up are slim.
Unless the parts have been changed I will agree. How does it get wrong?
Most vibrations go toward something loose or worn, and of course the tires which suck. 150 years of pneumatic tires and they are hardly better than the first ones. The wear out too fast, not enough tread and are truly impossible to balance in all conditions.
LocuMob
Fluid Technician with a hat
Sounds like a quick fix.
The vibration was constant and increased with speed which to me usually is a tire balance/bent rim issue as rpms are affecting the dissonance. However the diff howl is a concern as well. I am sure Derek will get after it with his usual tenacity.....
polara71
Old Man with a Hat
I realize how it could possibly with modifications. This is a bone stock 100 % original. Nothing should be off.
I also learned from my dads 73 the perches were not put in place with a template or at least they had a good range of side to side tolerance.
I get a similar vibration in my ‘68 Polara. Every thing is smooth until I hit 80 mph and then I get a resonance/ vibration. I rotated my tires around and it did not change. Next step is probably the drive shaft. Earlier this summer It seemed like the vibration was happening at around 70, one of my new U-joints after just 2,000 miles was shot. I was getting about 1/16 - 1/8” of radial play. I replaced it and was good until somewhere between 80 & 85. I do have a few gravel road dings in my drive shaft so maybe it is a little off balance. It seems my angles are fine.
Bone stock as well. Am looking forward to what you May find.
Bone stock as well. Am looking forward to what you May find.
70bigblockdodge
Old Man with a Hat
Wow, that was more than gravel. Mine in my Charger has a ding like that where the fork hit it when they picked up the 74 fury that I parted. It's okay till around 80, it is also homemade.
(fixed)
@polara71
I agreed with your comment on that if everything was stock things should be aligned. But I think after 50 years things start to sag, or new parts change the angles a little. Rear spring sag or new or re-curved springs could change the angle of the rear differential. Also new motor or transmission mounts being taller or shorter than the original could affect the angles. It doesn’t take much to change 1 -2 degrees.
I was on the lift and decided to see if I could attribute my high speed vibration to the drive line. The answer is maybe. It is so close, but at an opposing angle of about 1/4 degree up in relation of the engine and transmission down 3.6 degrees. I started measuring driveline angles, trying to replicate the Chrysler method outlined in the service manual using a 6” bubble level with a adjustable leg. Too bad they don’t give actual angle measurements. Front angle between engine and drive shaft, looks to be in spec, but the differential was too steep. Full disclosure, my bubble level doesn’t have the gradients the same as the Chrysler tool, but based on the pictures I estimated pretty close.
To verify I did some googling and found a Tremac app that uses your smartphone to measure.
Driveline Angles 101
The free app is in the article that explains the angles.
Anyway my angle calculations failed as my diff was at an opposing angle to my transmission. It will also fail if the end calculation is 0 degrees as U joints need a little load, 3 degrees is too much.
Anyway by putting a bottle jack under my pinion I found that at a 1/2 of degree it started to solve good in the app, but close to zero.
Result: I am very close different car loading will change the angles. I may order a 1 degree wedge shim to see if does anything. They originally sold them in 1/2 degree increments.
@polara71
I agreed with your comment on that if everything was stock things should be aligned. But I think after 50 years things start to sag, or new parts change the angles a little. Rear spring sag or new or re-curved springs could change the angle of the rear differential. Also new motor or transmission mounts being taller or shorter than the original could affect the angles. It doesn’t take much to change 1 -2 degrees.
I was on the lift and decided to see if I could attribute my high speed vibration to the drive line. The answer is maybe. It is so close, but at an opposing angle of about 1/4 degree up in relation of the engine and transmission down 3.6 degrees. I started measuring driveline angles, trying to replicate the Chrysler method outlined in the service manual using a 6” bubble level with a adjustable leg. Too bad they don’t give actual angle measurements. Front angle between engine and drive shaft, looks to be in spec, but the differential was too steep. Full disclosure, my bubble level doesn’t have the gradients the same as the Chrysler tool, but based on the pictures I estimated pretty close.
To verify I did some googling and found a Tremac app that uses your smartphone to measure.
Driveline Angles 101
The free app is in the article that explains the angles.
Anyway my angle calculations failed as my diff was at an opposing angle to my transmission. It will also fail if the end calculation is 0 degrees as U joints need a little load, 3 degrees is too much.
Anyway by putting a bottle jack under my pinion I found that at a 1/2 of degree it started to solve good in the app, but close to zero.
Result: I am very close different car loading will change the angles. I may order a 1 degree wedge shim to see if does anything. They originally sold them in 1/2 degree increments.
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