Pinion angle question.

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75slant6

75slant6

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Quick question, I finally measured my driveline angles last night and is is what I found. My transmission is 3* down and my differential is 1* down. So in theory, if my pinion rotates up 4* under acceleration, that would put the trans at 3* down and the diff at 3* up and should be right where I want it, correct?

I’ve had a driveline vibration for quite awhile and was thinking it was my pinion angle but when I pulled the driveshaft, I discovered the front u-joint is stiff and “notchy”. So now I’m thinking my pinion angle is fine and it was that joint causing the issues
 
you want them to be parallel under load.so under load the drive shaft will rise 2-3 degrees.so you are good with the setup you have.unless ss springs race car
 
jdsduster said:
you want them to be parallel under load.so under load the drive shaft will rise 2-3 degrees.so you are good with the setup you have.unless ss springs race car
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Awesome. Thanks. Not sure what springs are in it but they’re not SS’s, I’m guessing they’re the originals.
 
Here is a chart

Driveshaft info Mark Williams.jpg


you can save it and it should blow up so you can read it
 
So u measured the angles on the tail housing and on the pinion? Ur thinking back wards. U need the pinion at least 3* down from the tranny. If u leave ur tranny 3* down ur pinion would have to be 6* down. Then when u torque on it the pinion will move up to match the trans angle to cancel out any vibrations. Of our e there is cars with angles outta whack that don’t vibrate, which doesn’t make sense. Kim
 
oldkimmer said:
So u measured the angles on the tail housing and on the pinion? Ur thinking back wards. U need the pinion at least 3* down from the tranny. If u leave ur tranny 3* down ur pinion would have to be 6* down. Then when u torque on it the pinion will move up to match the trans angle to cancel out any vibrations. Of our e there is cars with angles outta whack that don’t vibrate, which doesn’t make sense. Kim
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Here’s where I’m thinking that I should be alright with how it is. My tailhousing is down 2-3* so under acceleration the front of my differential should be pointed up a 2-3* to match the tail housing. I think. Lol

 
According to ur measurements the pinion is already up 2* compared to the tranny. Or should I say the tranny is lower than the pinion by 2*. When the pinion goes up let’s say 2* u r now up 4* instead of even to the trans. Kim
 
oldkimmer said:
According to ur measurements the pinion is already up 2* compared to the tranny. Or should I say the tranny is lower than the pinion by 2*. When the pinion goes up let’s say 2* u r now up 4* instead of even to the trans. Kim
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Here’s a rough sketch of what I’m talkin bout. Sitting still the rear of my trans is pointing 3* down and the front of my pinion yoke is pointing 1* down. Now if it makes any difference, the driveshaft goes down from the tail housing to the differential at 1* as well.
Then as you can see in the lower part of my chicken scratchings, if the yoke of the differential rises 4* under acceleration, it would then be 3* up to match the 3* down of the tail housing.

image.jpg
 
One thing to keep in mind is that these angles were all taken with my iPhone and a cheap harbor freight angle finder. I would really like to get ahold of a good, digital smart level or something to really nail the angles down.
 
Put in ur u joints and see if it vibrates. There is a 1/8 inch flat plate that fits in between the tranny mount and the tranny. Does urs have it? Kim
 
Replace the U joint and then re assess.
There is zero point in questioning this with a binding U joint.
 
oldkimmer said:
Put in ur u joints and see if it vibrates. There is a 1/8 inch flat plate that fits in between the tranny mount and the tranny. Does urs have it? Kim
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Yea I’ll see how it is after new ujoints. I have a few plates in the transmission mount but I also have a homemade mount since I’m running an AX15 transmission from a dakota.
 
the angle is the difference between the pinion/trany angle and driveshaft angle ...not the trany vs pinion.

So if your trany is at 2.5 down and the driveshaft is at 6 ... you take 6 - 2.5 = 3.5

then measure pinion angle... lets say 4 down for that as well.. your driveshaft is still 6 so..
6 - 4= 2
you would need to shim the rearend.
If you have a negative angle you would add the numbers
 
mbaird said:
the angle is the difference between the pinion/trany angle and driveshaft angle ...not the trany vs pinion.

So if your trany is at 2.5 down and the driveshaft is at 6 ... you take 6 - 2.5 = 3.5

then measure pinion angle... lets say 4 down for that as well.. your driveshaft is still 6 so..
6 - 4= 2
you would need to shim the rearend.
If you have a negative angle you would add the numbers
Click to expand...
Well that makes sense. So my tail housing is 3 down, driveshaft is 1 down and pinion is 1 down. So sitting still, my front and rear angles are both 2, right?
 
yes... but you qant 2.5 or less for trany and between 5-7 for rear pinion.

Feel free to correct me if I am wrong.
 
mbaird said:
yes... but you qant 2.5 or less for trany and between 5-7 for rear pinion.

Feel free to correct me if I am wrong.
Click to expand...
Ooohhh. Now I think I get what you’re saying. I just realized I may have been measuring wrong. I was measuring the differential and trans angle off of level/the ground and not off of the driveshaft. I’ll see if I can’t get the u joints changed this weekend and get the driveshaft back in and measure again and take pics.
 
If the car is level then the top of the carb should be level too because the intake tips the carb forward to make up for the motor trans angle. Full weight should be on the rear springs when measuring the pinion angle. However much the trans angle is mismatched to the pinion angle at cruising is the amount of vibration you can expect and the amount of u-joint wear you can expect as well. It can also wear out the yoke and trans bushing. If you're getting that much spring wrap up then you need bars.
 
U r not measuring the drive shaft angle per se. That only becomes relative when u r under load. The way I measure it is on the bottom of the tail housing and the bottom or top of the pinion flange. I have never had a problem once doing it this way. Kim
 
So here’s where I got my angles from, on the end of the transmission output shaft and the face of the pinion yoke. REAR of the trans was 3* down, FRONT of the pinion yoke was 1* down.

84A96F96-7B97-4BAE-8A88-B087F89ED902.jpeg


993387BD-A0FC-42D2-983E-A69329581ACC.jpeg
 
So from ur measurements u r up 2* at the pinion. U need to be nose down with the pinion. If u can’t raise ur tranny u have to lower the pinion. If u lower the pinion 5* u will be 3* nose down. Kim
 
The output shaft will flop around some with the yoke out; find a place on the block that is vertical or one that is horizontal; like the pan rail.
 
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