Pinion angle

[efnfast]

My T5 tailshaft cracked after ~15yrs (although I suspect it started ~10yrs ago as that's when I developed a mysterious fluid drip I could never figure out). I think it's because either I didn't trim the "fin" enough on it and bottomed it on the road a quite few times and/or my pinion angle isn't good (I found with how i set the pinion and transmission if I jack the car up fully (koni coilovers) the driveshaft u-joints bind at the transimssion side).

I'm working on pinion angle and after reading a few dozen threads my mind is full of fvck, this is confusing :/

The transmission (measuring on the face of the output) is pointing 3* down. Does this mean that I want the pinion (measuring on the pinion face) to point 2* up in order to get to -1* pinion angle?

This is confusing because I read one post that says you want the pinion pointing down to compensate for when you accelerate??

[ggunter]

I read this post and replied yesterday but it didn't post for some reason. It can get confusing try to set up pinion angle but its not that hard. It can be difficult to find a flat place to take engine trans angle from so I use the front crank pulley and measure from top to bottom. For example if it reads 88.5 degrees, subtract that from 90 and you have 2.5 degrees trans down angle. The rear can be dificult to read because you have to read it with the wheels on hard level surface and the car ride height adjusted to where you want it to be. If you have an IRS I think they are fixed as far as pinion angle (not %100 sure as I don't have that set up) but if you have a solid axle you can adjust your pinion angle with the adjustable torque rod. My original engine trans angle was 3.4 degrees. Too much so I added spacers under the trans mount. ( From Forte ) to get it to 1.9. Then adjusted the rear to match 1.9 Degrees. Your drive shaft should be within 1Degree of the other readings either up or down. No more then 2.9 degrees but the closer you can make them to each other the better. You just never want 0 degrees throughout because the needle bearings in your ujoints wont revolve and wer them out.I have a drive line analyzer program at work and factored in the measurements and got great readings. Hope this helps.

[phileas_fogg]

I found Karlos' thread to be the most helpful: https://thefactoryfiveforum.com/showthread.php?22594-Driveline-Setup-(aka-Pinion-Angle)

Also, I could never get repeatable measurements using my phone & the Tremec App, so I used a digital angle finder to measure and plugged the numbers into the app.


John

[ggunter]

I also couldnt get repeatable results form my phone either. I used a digital protractor. Worked well.

[cfriedman67]

Can the car be on jack stands when doing the calculations?

[CraigS]

Yes it can. It might even be an advantage. You are comparing diff angle to engine/trans angle so it doesn't matter what angle the car is sitting at. I have done it by just jacking the axle up as high as the jack will go and leaving the front on the ground. (jack stands of course) Reason I say it might be an advantage is that messing around w/ angles that are only a few degrees from zero you can goof up easily by ending up w/ a + 1deg when it was really a - 1deg. If your car is sitting at say 6 degrees, your measurements will be in the 2-10 deg range. It's a lot easier to work on getting your 1-2 deg difference if one is 4 and the other is 6.

[GoDadGo]

Here are a video that will likely help you better understand U-Joint Angles & Phasing:

https://youtu.be/Idk3BVDVHq4

Also, a simple angle finder is all I needed and you can get them nearly anywhere.

[GWL]

Yes it can. It might even be an advantage. You are comparing diff angle to engine/trans angle so it doesn't matter what angle the car is sitting at. I have done it by just jacking the axle up as high as the jack will go and leaving the front on the ground. (jack stands of course) Reason I say it might be an advantage is that messing around w/ angles that are only a few degrees from zero you can goof up easily by ending up w/ a + 1deg when it was really a - 1deg. If your car is sitting at say 6 degrees, your measurements will be in the 2-10 deg range. It's a lot easier to work on getting your 1-2 deg difference if one is 4 and the other is 6.

Now, why didn't I think of that? When doing my pinion angle setup, yes, when close to 0º it was hard to figure if it was + or -.:confused: Great point Craig.:D

George

[efnfast]

I follow the forum link and understand what it says, but I don't understand how to apply it.

My setup is a T5 w/ S10 tailshaft, T5 stock rubber mount and a 5-link suspension. I'm using a digital protractor.

If I measure at the tailshaft (or crank pulley) I get 2.4* down (-2.4).

If I add 0.5'' of shims under the transmission mount I can move the angle to 1.4* down (-1.4). So .1'' of shim = ~0.2* of movement.

In order to achieve a -1* pinion angle this means I need -1.4* on the pinion (-2.4 - -1.4 = -1.0). But because the slope is measured at the rear of the object this means I need the pinion flange to be pointing up 1.4* (since I'm measuring on the pinion flange).

So here's where I'm lost - if the pinion flange points up 1.4* then I'm running negative slope on the pinion (as rear of pinion is pointing down) and it says I want to be running positive slope (pinion flange pointing donw) on the pinion to account for power under acceleration.

If I need positive slope on the pinion that means I need to add ~1'' of spacers to the transmission mount, which I've never heard of anybody doing.

I'm so confused????

[NAZ]

Stop right now and don't overthink this, it's not that difficult of a concept to understand. Start looking online for drawings of what you're trying to achieve and why. All this discussion about angles, negative and positive and which end slopes up or down will do nothing but confuse you. Looking at pictures will help simplify the concept. Here's one site that may help and there are others out there.

https://www.therangerstation.com/tech_library/pinionangles.shtml

[efnfast]

Stop right now and don't overthink this, it's not that difficult of a concept to understand. Start looking online for drawings of what you're trying to achieve and why. All this discussion about angles, negative and positive and which end slopes up or down will do nothing but confuse you. Looking at pictures will help simplify the concept. Here's one site that may help and there are others out there.

https://www.therangerstation.com/tech_library/pinionangles.shtml

I agree - I understand everything in the link you posted but here's my question - if I have a negative -1* pinion angle but it involves the pinion flange pointing up (such that the pinion itself is considered negative slope) is that okay? Some links say this is fine, some say it is not and the pinion must be positive sloped.

[Big Blocker]

The very bottom picture in the link that NAZ provided is the one you should follow . . . you are trying to get to a difference (-2°) between the engine angle and the pinion angle. Doesn't matter if the car is on the ground or standing on it's nose, -2° difference is the spec you are trying to achieve.

FWIW, a lot of builders confuse the pinion flange pointing down as "Down" when in all actuality, that is really "Up". Measure from a known "set" engine part; front crank pulley is very accurate for engine "down angle". Measure the rear end on the pinion flange, another reliable point to get degree readings. As per the referenced image (from NAZ's link), engine "down" -3.5°, Pinion "up" -1.5°, you have your -2° [optimal] difference.

In the image the pinion looks to be pointing up but is really pointing down - Try to think of the rear end as the engine and the pinion flange as the front crank pulley . . .

Doc

[NAZ]

151329
Let’s make this easy – forget all the positive and negative angles, all this is doing is confusing you. Also, for now forget the operating angle and simply concentrate on the pinion shaft relationship to the trans output shaft.


Look at the attached cartoon and pay attention to Centerline A and Centerline C. In the cartoon they appear to be horizontal but they could be vertical and it won’t matter, what’s important is their relationship to each other. Under acceleration you want these two centerlines to be parallel to each other regardless of the angle to the world that they project. But we measure their angles in a static condition when the car is at ride height, not under acceleration.



Under acceleration the axle will rotate some amount due to the flex in the elastomer bushing that attach the rear axle to the chassis. When it rotates it lifts the u-joint end of the pinion shaft. So if these two centerlines were parallel at static ride height, under acceleration Centerline C would diverge from parallel to Centerline A. With me so far?


To compensate for the axle rotation under acceleration we adjust the pinion angle so that the u-joint end of the shaft is 1 to 2 degrees angled down (down in front) from parallel to Centerline A. So on the attached cartoon the projected Centerline C would be angled a couple degrees down in front as compared to Centerline A which is shown as horizontal to the world.

[GoDadGo]

Stop right now and don't overthink this, it's not that difficult of a concept to understand.

https://www.therangerstation.com/tech_library/pinionangles.shtml

Amen Sir Naz, Amen!

[efnfast]

Okay, I finally understand pinion angle! But now I'm on to operating angles! The problem is I can't find a set of parameters that make everything fall within specifications.

If I shim the transmission mount 1/4'', best I can do is -1.7* transmission, +0.3 pinion (i.e., pinion flange faces down, pumpkin faces up) for a -2.0 pinion angle. But driveshaft is +3* (i.e., faces downward, like pinion flange is facing downwards), so my operating angles are 4.7* and 2.7*. Tx operating angle is out of spec (3* max) and difference between operating angles exceeds 1*

If I shim the transmission mount 0.4'', best I can do is -1.5* transmission, +0.3 pinion for -1.8 pinion angle. Driveshaft is +1.3*, so operating angles of 2.8* and 1.0*. Difference between operating angles exceeds 1*.

If I shim the transmission mount 0.75'' best I can do is -1.2* transmission, -0.2* pinion for -1.0 pinion angle. Driveshaft is +0.8*, so operating angles of 2.0* and 1.0*.

So I can set pinion angle between -1* and -2* many dfiferent ways, but the only way I can get proper operating angles is to really shim the transmission. However, adding 3/4'' to the T5 mount feel like too much (at around 1/2'' shim I can no longer push the transmission up by hand anymore, assuming it's unbolted from the transmission frame member).


If I shim it to 0.4'', the most I'm comfortable doing, and my operating angles are all under 3* but the difference between them exceeds 1* (1.8*) is that okay, or will bad things happen?

[egchewy79]

I have a SBF/T5 combo and used 3 Forte shims to get the proper angle.

[CraigS]

From many threads here I have come to realize that it is very common to shim the trans between 1/2 and 3/4 inch on solid axle FFRs. So I think you are fine at your .4 inch. Although I have messed w/ this on a couple of FFRs the only time I have ever actually dealt w/ a problem was on a sedan that had had major body repair and they didn't get the front clip (everything forward of the windshield) right. That car had a vibration on anything more than about 2/3 throttle between 20 and 35 mph. I bring this up just to say that, if you leave it at your .4 inch, the worst that will happen is you may have a slight vibration on accel in a certain speed range. "IF" that happens, then you can work on it more but I doubt it will.

[Jeff Kleiner]

As an FYI, I've never had to use shims to bring a T-5 into range however I have also never had one with an S-10 tail housing. I don't know how that stacks up in comparison to a Mustang tail or if that may be playing into your situation.

Jeff

[efnfast]

So if I only partially shim it up, having an operating angle difference of 1.8* may be not ideal (e.g., faster u-joint wear) but it shouldn't cause any serious issues?

Also, are there any rough guidelines to determine if shimming the transmission up is putting it under too much stress (and could lead to another cracked tail housing)? I'm just making up the rule that, once the transmission support member is installed, if I can still push the engine/transmisison up by hand a little bit (e.g., 1/8'') then that isn't too much stress

[efnfast]

Finally some good progress - I re-adjusted the engine mount and was able to get the measurement into spec -> -1.3* transmission, -0.3* pinion, +0.7* driveshaft (so -1* pinion angle, operating angle A 2*, operating angle B 1*) using a 1/2'' spacer under the transmission.

So I guess this leads me back to my original quandary - using a T5 w/ S10 tailshaft and T5 mustang mount, is shimming the transmission up 1/2'' too hard on the case and could cause me to crack another tailshaft someday?

Am I better perhaps putting 1/4'' washers under the engine mounts to lift the engine up, then use a shorter spacer on the tailshaft so it's not as stressed?

[NAZ]

Nobody is going to guarantee that you won't break a tail housing, you need to make your own decision about the risk. The elastomer mounts generally have a lot of flex but how much misalignment is too much? And how much misalignment can you remove with adjustments, taper shims, fabricated brackets, etc. Don't be afraid to experiment and modify your way out of an issue. Experienced builders of customs do this everyday.

Pull the trans mount, place it in a vice and see for yourself how much flex there is. Then decide based on some actual testing and an educated guess about your application. That's more than you'll likely get here as every build is different and all builders have a different experience base. Some things you just have to learn for yourself.

Remember, if it breaks it needed to be replaced anyway so there's little to lose.

[efnfast]

I built a 917 so I'm not afraid to experiment but I'd also like to not break the tail housing again :)

I'm kinda thinking what broke the first one is I had a -5* pinion, really bad operating angles, and u-joint bind under full suspension hang .... I hit a number of sharp bumps that resulted in a bang around the transmission area, which I assumed was the transmission fin bottoming out (even though I had trimmed it), but now I think the banging was the ujoints binding

[NAZ]

I run a 3-deg misalignment on my 33HR trans mount and don't worry about it. However, I also run solid motor mounts and a 1-deg u-joint operating angle. If the trans mount angle would have come out closer to 5-deg misalignment I would have used misalignment washers to reduce the angle delta. More than 5-deg I would have fabricated a custom trans mount.

If you decide to adjust the misalignment angle, McMaster-Carr carries misalignment washers (leveling washers). https://www.mcmaster.com/91944A450/ You use one set between the trans mounting surface and the trans mount. Then another set between the trans mount and the fastener. There is always a workaround if you're creative.

Good luck, don't give up, and have fun with your build.

[efnfast]

I finished my build 15yrs ago ... I don't like when parts decide to break 15yrs later .... hoping to not break another one 15yrs from now

[efnfast]

Mystery solvedish - I was doing the measurements with my old cracked tailhousing installed. Installed my new tailhouse and measurements are somewhat different (and make more sense - i.e., in need of substantially less shimming). Even though the tailhouse was solid (i.e., it's not like the crack was see-through, just hairline) I guess it was cracked enough to become warped

[efnfast]

After playing around with everything I think I got it - rather than raise the transmission I raised the ride height from the 3'' I had to 4''. Here is where I ended up:
Transmission: -1.7* (transmission snout faces down)
Differential: -0.7* (pinion flange faces up)
Driveshaft angle: +1.2* (side of driveshaft closest to transmission faces down; side closest to differential faces up)

Pinion angle: -1.7 - (-0.7) = -1.0*

Transmission Operating Angle: 1.2 + 1.7 = 2.9*
Differential Operating Angle: 1.2 + 0.7* = 1.9*

Operating angles are under 3* and within 1* of eachother and exceed 0.5*

Good now?!?!?!??!

[ggunter]

If I got what you put down correctly this is very good.151725

[ggunter]

I didnn't see you had a negative drive shaft angle. It still isn't bad till you get over 4000 rpm then itt goes into the yellow marginal column.151728

[efnfast]

I didnn't see you had a negative drive shaft angle. It still isn't bad till you get over 4000 rpm then itt goes into the yellow marginal column.151728

I have a positive driveshaft angle (rear of driveshaft points up) ... it has to, the pinion flange sits above the transmission flange

I've driven it and havn't felt any unusual vibrations or issues.

Of course then my clutch starts sticking so it's time to pull it all apart again *le sigh*

[ggunter]

I understand what you are saying, but on the driveline analyzer anything that points down is a positive angle and anything that points up is a negative angle. If your setup is like the second picture I sent with the driveline pointing up in the rear then it is a negative angle. And it also loooks at the rear facing up angle as positive angle because it doesn't reverse direction. It's only when the angle changes direction that the analyzer calls it negative. Mine is very similar to yours.

[NAZ]

This is where a picture or drawing helps to bridge the divide between the translation of positive and negative angles. Y'all don't want to get wrapped around the axle on terms that are not always used with the same meaning. But everyone can look at a drawing with angles (sans the polarity) and instantly see if the angles will be copacetic. The goal is always to have the imaginary center-lines through the trans output shaft and the pinion shaft parallel under load. Doesn't matter which direction they point, just so they are parallel under load. That's a much easier concept to understand without all the positive and negative angles that not all understand or even share a common meaning of.

[ggunter]

True.

[CraigS]

Naz, that is why I made the comment way back about doing the measuring by just jacking up the car by the rear axle. I discovered that by accident one day. I had been doing it on stands but it was 4 stands so the car was near level. Also at that time my angle measurer had a flat only on one side so I measured the engine/trans looking at it from the left side of the car. Then I measured the diff looking from the right side of the car. What a mess that was. A couple of days later I wanted to go back and verify a measurement and I was lazy so just jacked the rear axle. Suddenly all the crap trying to deal w/ #s hovering within a couple degrees of zero went away.

[GoDadGo]

Craig & Naz,

Being a Corvette Enthusiast and former C4 Owner, understanding U-Joint Phasing and driveshaft angles just seemed to be common knowledge.
It amazes me how this same topic (Pinion Angles & Drive Shaft Phasing) just keeps popping up.
Set the angle to the dangle & you are pretty much done.

Steve