Just put the chervele away for the winter and I decided to check the operating angles. I have had no issues regarding vibration since going to radials from diamond back tires two summers ago. Just wanted to check for understanding.
I measure the transmission angle using a digital level on the engine heads and got -3.90 on each side. I check the driveshaft all along the length from the transmission to the pinion and got from -1.15 to -1.20 so thinking it is -1/20. Then I check the pinion level at the webs on each side of the carrier housing and got +0.70. Not sure how good this reading is, I wonder if there might be a better way.
So I think the operation angles are 2.70 at the transmission yoke and 1.85 at the pinion. I think they are suppose to be within 0.50, whereas my vary by 0.85. Maybe a better way of reading the pinion angle would get closer results. Any thoughts?
Am I correct in thinking if I shim between the transmission mount and the crossmember a little that will increase my driveline angle a little to say -3.50 and decrease my driveshaft to say -1.50. Thus changing the angles to 2 degrees and 2.20 respectively ( Am I correct in assuming the pinion angle will not change?).
Also Bob Wall has mentioned to me that even though the operation angles might be equal when measured the standard way, that there is still and operation angle between the yokes because the center line of the pinion shaft is slightly offset from the Driveline/transmission center line, due to the design of the rear axel housing and location of the pinion with respect to the center of the rear axel assembly,.
Bobs_Place said
Dec 5, 2018
Yes, adding a shim to the rear trans mount will should bring the two working angle closer. That is if the numbers are correct. So to simplify things the Nos. are as fallows:
Engine/trans is -3.9*
Driveline -1.2*
Pinion +.7
Because the slop of both eng/trans and the D/L are the same (both down towards the rear) the foreword operating angle is calculated by subtracting the smaller no. from the larger no.
3.9 - 1.2 = 2.7* Foreword working angle
With the pinion slopping down towards the front(opposite the D/L) the rear working angle is calculated by adding the numbers of the Pinion and the D/L.
So 1.2 + .7 =1.9 Rear working angle
This gives a difference of 0.8* not bad, very driveable and should not cause any problems.
Now, back to my original statement That is if the numbers are correct. All measurements should always be taken from machined surface, ether parallel or perpendicular to the crankshaft center line. On a BBC I have found the best place to measure the slop of the eng/trans is on the pan rail just ahead of the left engine mount. Jim you said that you are measuring at the cyl heads, If you are on the machined vertical surface at the front of the engine, that would be acceptable, just subtract 90* from the reading. As for the diff/pinion measurement, disconnect the D/L from the yoke, the bolt surface of the yoke is 90* to the pinion center line, measure and subtract 90*.
With the car up on blocks or jack stands (under the axle)in the rear and car at ride height, I would get a more accurate measurement at the pinion, than reassemble the D/L to the yoke. Once you have the pinion measurement you don't have to remeasure it again when calculating your working angles after shimming the rear of the trans. Hopefully by adding a shim to the trans mount both working angle would be reduced and the difference between then would be minimal. Always much better to have lower working angles.
Your last statement about the pinion not being centered causes what is called a compound angle. You have to know your "Trig" to figure and add the offset into the vertical angle (not me). Because the offset to the side is so minor, I never get concerned with it. Again if the working angles are very low, adding in the offset would still be well within acceptable tolerances. And with the pinion offset to the side you can never get a zero working angle which can prematurely ware Ujoints.
jim larson said
Dec 5, 2018
Thanks for clarifying Bob. I will re-calculate the pinion angle. I removed the drivers side valve cover/gasket and set the digital gauge along the surface where the valve cover gasket meets the surface of the head. The oil pan would be less work. I will do that to check my other method and see how close they are.
So I am correct in assuming the pinion angle will not change when you shim the transmission. Also if springs were to be changed which slopes change, driveline, driveshaft, and pinion?
Bobs_Place said
Dec 5, 2018
The gauge needs to be position upright to get an accurate reading, so by placing directly on the gasket surface or tipping the gauge upright in the edge I would think leaves a lot of room for error. When I say "pan rail" I mean the gasket surface just ahead of the left engine mount, it is a wide spot on the block that is machined. Do not use the pan or pan bolts to measure. Just looked at my Impala (396),there is a narrow spot, not as big as the chevelle 454. Always recheck to see if your reading repeats. If the bell housing is machined out far enough past were the trans bolts up, take a vertical reading. If nether spot will work remove the alt and alt bracket and measure there.
If you are measuring both vertically and horizontally you should check your gauge for accuracy. If I calibrate my gauge in the horizontal position than vertical is off, if I cal for vertical the horizontal is off. Some times placing a square on the vertical surface with the gauge placed on the horizontal part of the square make readings easier.
As long as you don,t move the car the diff shouldn't change, but raising or lowering the rear of the car will alter the readings. Also the front tires should be on block not jack stands on the frame as that will unweight the rear of the car. The car should be up close to level to distribute the weight and to gain access.
jim larson said
Dec 5, 2018
I found the flat machined surface you were referring too next to the engine mount. So I rechecked the angle and got the same -3.9.
Then I put the rear axel on jack stands dropping the rear axel just a tad. Checked engine drive line angle and it dropped to -4.20, Drive shaft changed to -1.50; so Operation angle would be 2.7 degrees which was the same.
Since the rear is supported by the jack stand I will removed the drive shaft shortly to check the pinion angle as you suggested.
-- Edited by jim larson on Wednesday 5th of December 2018 06:01:51 PM
Bobs_Place said
Dec 5, 2018
Is the the car some what level? 3.9/4.2* seems abet steep for eng/trans, usually see them around 3 give or take a little. Not concerned if the car is not level of the car for measuring angles, just wondering what the eng/trans is at with car level/normal ride height
jim larson said
Dec 6, 2018
Bobs_Place wrote:
Is the the car some what level? 3.9/4.2* seems abet steep for eng/trans, usually see them around 3 give or take a little. Not concerned if the car is not level of the car for measuring angles, just wondering what the eng/trans is at with car level/normal ride height
Car was pretty much level when the measurement of the driveline was -3.9. I then set the rear axel on jack stands and got the -4.2. I replaced the engine mounts and transmission mount a few years ago. I have spacers in the rear springs due to them being pretty weak from years of use. The distance from the top of the rear axel to the bottom on the frame is 5 1/8 on each side. Specifications from the 66 service manual says 5 1/8 +- 3/8.
Just thinking the garage floor is not level as I have it sloped a little from front to back for water to drain; thus car would not be level, don't know how to get it really level unless using some kind of level later beam to get the center line of the rear axel level with the centerline of the front axel.
Bobs_Place said
Dec 6, 2018
Probably raised the engine with the engine mounts, were they aftermarket or std replacement from the auto store?
When I installed my engine, I couldn't find one or both mounts. I bought one new, found one or two on the shelf. I ended up with different height mounts, used the thick one on the left to get header clearance and thin mount on the right for a/c box clearance. Eng/trans cam in low 3*s. After I installed the Gear Vendors I raised the rear(didn't like the low rider look) which rotated the diff and reduced the slope of the D/L ,adjusted the diff a bit to end up with very good numbers.
I also measured axle to frame and then frame to ground per the assembly manual and service manual, after accounting for the larger tires, when the frame to axle was correct the frame to ground was low. So, I through the books away and used my eye ball and protractor the determine the best ride height.
The quick way to check the garage floor slope is to find a place on the car that you easily measure, turn the car around and remeasure the car. If you find a difference of say .4*, the garage floor is sloped .2*, than add or subtract that from the eng/trans* (with car on the ground) reading.
jim larson said
Dec 6, 2018
I measured the garage slop at the front tires, it was -0.20. To much work to turn car around at this point.
I just remeasured the driveshaft and got -1.60, so with the new engine at -4.20 Those new measurement that give me an operating angle of 2.60. Considering the floor slope my engine would be down at approximately -4.0 give or take a bit.
I will now drop the driveshaft and measure the pinion angle.
I got the engine mounts from Long Island Corvette, they were suppose to be exact replacements for the original BB mounts; but who knows. They were made in the USA and did not have the updated locking tabs that started in 68 that most replacements have.
jim larson said
Dec 6, 2018
Well I got +0.60 when I measured diagonally across the front of the pinion flange both ways. The surface is flat; but not machined flat. This is the new position with the rear dropped just a bit, it was +0.70
This would make the rear working pinion angle at 2.20.
So the forward working transmission angle would be 2.60 and the rear working pinion angle would be 2.20 or differ by 0.40. This is all stock non-adjustable CA's.
I don't think the pinion measurement is very accurate because the flange not being machined.
jim larson said
Dec 6, 2018
I don’t think there is a good way to measure the pinion slope. Unless you are removing the rear axel cover to change fluid. Then you could use the backside of the pinion shaft.
Can't tell from the pic but make sure the protractor is vertical when placing it on the yoke, then get a reading, rotate the yoke 180*and recheck, recheck2-3 you should get good repeating numbers, then average the numbers. Another way to check the pinion is by installing a ujoint then read across the caps.
The angles look very good, should have no problem with these number, also the 3.08 gear (I think is what you have) helps a lot. You could try a shim to raise the trans, that should make both working angles less, and as along as they stay close that would be even better yet. But really not needed. If you have any future suspension plans I would not make any more changes now.
Just put the chervele away for the winter and I decided to check the operating angles. I have had no issues regarding vibration since going to radials from diamond back tires two summers ago. Just wanted to check for understanding.
I measure the transmission angle using a digital level on the engine heads and got -3.90 on each side. I check the driveshaft all along the length from the transmission to the pinion and got from -1.15 to -1.20 so thinking it is -1/20. Then I check the pinion level at the webs on each side of the carrier housing and got +0.70. Not sure how good this reading is, I wonder if there might be a better way.
So I think the operation angles are 2.70 at the transmission yoke and 1.85 at the pinion. I think they are suppose to be within 0.50, whereas my vary by 0.85. Maybe a better way of reading the pinion angle would get closer results. Any thoughts?
Am I correct in thinking if I shim between the transmission mount and the crossmember a little that will increase my driveline angle a little to say -3.50 and decrease my driveshaft to say -1.50. Thus changing the angles to 2 degrees and 2.20 respectively ( Am I correct in assuming the pinion angle will not change?).
Also Bob Wall has mentioned to me that even though the operation angles might be equal when measured the standard way, that there is still and operation angle between the yokes because the center line of the pinion shaft is slightly offset from the Driveline/transmission center line, due to the design of the rear axel housing and location of the pinion with respect to the center of the rear axel assembly,.
Yes, adding a shim to the rear trans mount will should bring the two working angle closer. That is if the numbers are correct. So to simplify things the Nos. are as fallows:
Engine/trans is -3.9*
Driveline -1.2*
Pinion +.7
Because the slop of both eng/trans and the D/L are the same (both down towards the rear) the foreword operating angle is calculated by subtracting the smaller no. from the larger no.
3.9 - 1.2 = 2.7* Foreword working angle
With the pinion slopping down towards the front(opposite the D/L) the rear working angle is calculated by adding the numbers of the Pinion and the D/L.
So 1.2 + .7 =1.9 Rear working angle
This gives a difference of 0.8* not bad, very driveable and should not cause any problems.
Now, back to my original statement That is if the numbers are correct. All measurements should always be taken from machined surface, ether parallel or perpendicular to the crankshaft center line. On a BBC I have found the best place to measure the slop of the eng/trans is on the pan rail just ahead of the left engine mount. Jim you said that you are measuring at the cyl heads, If you are on the machined vertical surface at the front of the engine, that would be acceptable, just subtract 90* from the reading. As for the diff/pinion measurement, disconnect the D/L from the yoke, the bolt surface of the yoke is 90* to the pinion center line, measure and subtract 90*.
With the car up on blocks or jack stands (under the axle)in the rear and car at ride height, I would get a more accurate measurement at the pinion, than reassemble the D/L to the yoke. Once you have the pinion measurement you don't have to remeasure it again when calculating your working angles after shimming the rear of the trans. Hopefully by adding a shim to the trans mount both working angle would be reduced and the difference between then would be minimal. Always much better to have lower working angles.
Your last statement about the pinion not being centered causes what is called a compound angle. You have to know your "Trig" to figure and add the offset into the vertical angle (not me). Because the offset to the side is so minor, I never get concerned with it. Again if the working angles are very low, adding in the offset would still be well within acceptable tolerances. And with the pinion offset to the side you can never get a zero working angle which can prematurely ware Ujoints.
Thanks for clarifying Bob. I will re-calculate the pinion angle. I removed the drivers side valve cover/gasket and set the digital gauge along the surface where the valve cover gasket meets the surface of the head. The oil pan would be less work. I will do that to check my other method and see how close they are.
So I am correct in assuming the pinion angle will not change when you shim the transmission. Also if springs were to be changed which slopes change, driveline, driveshaft, and pinion?
The gauge needs to be position upright to get an accurate reading, so by placing directly on the gasket surface or tipping the gauge upright in the edge I would think leaves a lot of room for error. When I say "pan rail" I mean the gasket surface just ahead of the left engine mount, it is a wide spot on the block that is machined. Do not use the pan or pan bolts to measure. Just looked at my Impala (396),there is a narrow spot, not as big as the chevelle 454. Always recheck to see if your reading repeats. If the bell housing is machined out far enough past were the trans bolts up, take a vertical reading. If nether spot will work remove the alt and alt bracket and measure there.
If you are measuring both vertically and horizontally you should check your gauge for accuracy. If I calibrate my gauge in the horizontal position than vertical is off, if I cal for vertical the horizontal is off. Some times placing a square on the vertical surface with the gauge placed on the horizontal part of the square make readings easier.
As long as you don,t move the car the diff shouldn't change, but raising or lowering the rear of the car will alter the readings. Also the front tires should be on block not jack stands on the frame as that will unweight the rear of the car. The car should be up close to level to distribute the weight and to gain access.
I found the flat machined surface you were referring too next to the engine mount. So I rechecked the angle and got the same -3.9.
Then I put the rear axel on jack stands dropping the rear axel just a tad. Checked engine drive line angle and it dropped to -4.20, Drive shaft changed to -1.50; so Operation angle would be 2.7 degrees which was the same.
Since the rear is supported by the jack stand I will removed the drive shaft shortly to check the pinion angle as you suggested.
-- Edited by jim larson on Wednesday 5th of December 2018 06:01:51 PM
Is the the car some what level? 3.9/4.2* seems abet steep for eng/trans, usually see them around 3 give or take a little. Not concerned if the car is not level of the car for measuring angles, just wondering what the eng/trans is at with car level/normal ride height
Car was pretty much level when the measurement of the driveline was -3.9. I then set the rear axel on jack stands and got the -4.2. I replaced the engine mounts and transmission mount a few years ago. I have spacers in the rear springs due to them being pretty weak from years of use. The distance from the top of the rear axel to the bottom on the frame is 5 1/8 on each side. Specifications from the 66 service manual says 5 1/8 +- 3/8.
Just thinking the garage floor is not level as I have it sloped a little from front to back for water to drain; thus car would not be level, don't know how to get it really level unless using some kind of level later beam to get the center line of the rear axel level with the centerline of the front axel.
Probably raised the engine with the engine mounts, were they aftermarket or std replacement from the auto store?
When I installed my engine, I couldn't find one or both mounts. I bought one new, found one or two on the shelf. I ended up with different height mounts, used the thick one on the left to get header clearance and thin mount on the right for a/c box clearance. Eng/trans cam in low 3*s. After I installed the Gear Vendors I raised the rear(didn't like the low rider look) which rotated the diff and reduced the slope of the D/L ,adjusted the diff a bit to end up with very good numbers.
I also measured axle to frame and then frame to ground per the assembly manual and service manual, after accounting for the larger tires, when the frame to axle was correct the frame to ground was low. So, I through the books away and used my eye ball and protractor the determine the best ride height.
The quick way to check the garage floor slope is to find a place on the car that you easily measure, turn the car around and remeasure the car. If you find a difference of say .4*, the garage floor is sloped .2*, than add or subtract that from the eng/trans* (with car on the ground) reading.
I measured the garage slop at the front tires, it was -0.20. To much work to turn car around at this point.
I just remeasured the driveshaft and got -1.60, so with the new engine at -4.20 Those new measurement that give me an operating angle of 2.60. Considering the floor slope my engine would be down at approximately -4.0 give or take a bit.
I will now drop the driveshaft and measure the pinion angle.
I got the engine mounts from Long Island Corvette, they were suppose to be exact replacements for the original BB mounts; but who knows. They were made in the USA and did not have the updated locking tabs that started in 68 that most replacements have.
Well I got +0.60 when I measured diagonally across the front of the pinion flange both ways. The surface is flat; but not machined flat. This is the new position with the rear dropped just a bit, it was +0.70
This would make the rear working pinion angle at 2.20.
So the forward working transmission angle would be 2.60 and the rear working pinion angle would be 2.20 or differ by 0.40. This is all stock non-adjustable CA's.
I don't think the pinion measurement is very accurate because the flange not being machined.
I don’t think there is a good way to measure the pinion slope. Unless you are removing the rear axel cover to change fluid. Then you could use the backside of the pinion shaft.
Can't tell from the pic but make sure the protractor is vertical when placing it on the yoke, then get a reading, rotate the yoke 180*and recheck, recheck2-3 you should get good repeating numbers, then average the numbers. Another way to check the pinion is by installing a ujoint then read across the caps.
The angles look very good, should have no problem with these number, also the 3.08 gear (I think is what you have) helps a lot. You could try a shim to raise the trans, that should make both working angles less, and as along as they stay close that would be even better yet. But really not needed. If you have any future suspension plans I would not make any more changes now.