Driveline setup 302 T56 and IRS

[Blue Viking]

I am working on my driveline angles. With one spacer from Forte i get 2 degrees down on the transmission, 1.5 down on the driveshaft and 1 down on the rear end pinion. This gives me an operating angle of 0.5 on both joints, which is perfect. However, the transmission and rear end are 1 degree off from parallel. Will this be OK? Will the IRS have the same tendency to rotate under load as a straight axle, thus tilting the pinion slightly upward and bringing the tranny and rear closer to parallel? Raising the rear of the transmission won't fix it, the operating angles become way too large. If this needs to be fixed, the only solution I can think of is trying to lower the engine mounts somehow, as i don't see a way to alter the mounted angle of the rear diff.

[1932]

The trans and IRS are fixed and will not change.

[NAZ]

The trans and IRS are fixed and will not change.

Isn't the IRS mounted in rubber bushings? If so, these will tend to give when the axle is under load and allow the pinion angle to change like the Mustang solid axle. I have no idea how much but if the IRS is mounted with elastomer bushings the same laws of physics will apply, it's just a matter to what degree rotation will be constrained. Of course it will be less than the solid axle as there will be no pinion angle change during squat from unequal length control arms.

[Hoooper]

Isn't the IRS mounted in rubber bushings? If so, these will tend to give when the axle is under load and allow the pinion angle to change like the Mustang solid axle. I have no idea how much but if the IRS is mounted with elastomer bushings the same laws of physics will apply, it's just a matter to what degree rotation will be constrained. Of course it will be less than the solid axle as there will be no pinion angle change during squat from unequal length control arms.

Yeah the pinion will still rise on the IRS. See this video taken in a mustang, @ 0:26. The FFR bushings are stiffer than the stock mustang bushings but unless you go solid bushings the pinion will still rise somewhat


https://www.youtube.com/watch?v=dA0kzu4Ukzk

[Blue Viking]

Isn't the IRS mounted in rubber bushings? If so, these will tend to give when the axle is under load and allow the pinion angle to change like the Mustang solid axle. I have no idea how much but if the IRS is mounted with elastomer bushings the same laws of physics will apply, it's just a matter to what degree rotation will be constrained. Of course it will be less than the solid axle as there will be no pinion angle change during squat from unequal length control arms.

Yes it's mounted with bushings, Polyurethane i believe, so it will flex a little, but I think less than a solid axle. So if it rotates 1 degree, the centerline of the transmission and rear end should be perfectly parallel. But will it rotate that much? And how about during light cruise, will have vibrations then due to the 1 degree off from parallel? That's what I'm trying to figure out.

[Hoooper]

I posted an embedded video, which for some reason requires moderator approval before it posts? Anyhow, it is a video of the stock mustang diff rotation during a launch. It rotates quite a bit with the stock bushings, which of course is going to be reduced some with poly bushings but it still moves quite a bit. Even with the solid aluminum bushings there is some movement but that is probably all from the subframe bushings moving. Link to the comparison is below

https://www.youtube.com/watch?v=jEF_47B0K3Y

[NAZ]

There you go Oystein, use the aluminum bushings like in the video and set your pinion same as the trans output shaft and call it good. No way to tell from the video how much rotation to expect but you can clearly see there is some. Perhaps not enough to be an issue with higher durometer poly bushing.

Now as for pinion angle at cruise -- that's generally not a worry. The vibration (if any) will be worse under the heavy load of acceleration. But you can set-up your pinion angle to a best guess and do some on-road testing to see what the actual rotation you get with YOUR rear end with your car's configuration. You just need a way to capture the rotation under WOT acceleration from a stop in 1st gear on good pavement. Doesn't need to be an elaborate piece of electronic test equipment. Most folks would be surprised how well a piece of welding rod, o-rings, and some simple fabricated brackets can work for tests like this. Just takes imagination.

[Hoooper]

My kit shows up in the next few days so I havent seen the bushings up close, but from what I have seen in pictures the 2015 IRS setup doesnt use mustang bushings, or at least doesnt use 2015 mustang diff bushings. Sourcing bushings may be a bit tougher than just going to the mustang catalog, but they are pretty basic bushings so just taking measurements and getting a bushing made shouldnt be too hard. I do think the FFR mounting setup will be much stiffer than the poly mustang setup since the bushings are much smaller, much less poly between the sleeve and frame to move around.

[Blue Viking]

There you go Oystein, use the aluminum bushings like in the video and set your pinion same as the trans output shaft and call it good. No way to tell from the video how much rotation to expect but you can clearly see there is some. Perhaps not enough to be an issue with higher durometer poly bushing.

Now as for pinion angle at cruise -- that's generally not a worry. The vibration (if any) will be worse under the heavy load of acceleration. But you can set-up your pinion angle to a best guess and do some on-road testing to see what the actual rotation you get with YOUR rear end with your car's configuration. You just need a way to capture the rotation under WOT acceleration from a stop in 1st gear on good pavement. Doesn't need to be an elaborate piece of electronic test equipment. Most folks would be surprised how well a piece of welding rod, o-rings, and some simple fabricated brackets can work for tests like this. Just takes imagination.

you know, I was actually thinking of how to measure rotation under load, and thought of a contraption much like you are suggesting. I may just leave the angles where they are now, and see when I start driving if there are any issues with vibration. Maybe the engine even settles a bit in the engine mounts which will help a little towards paralleling the transmission and rear diff.

[CraigS]

You will be fine as is. The bushings FFR uses to mount the diff are many times stronger than stock Mustang pieces. The FFRs are small pieces of solid poly vs the OE that are huge maybe 2.5-3 inches in diameter made of soft rubber w/ large hollow areas.

[phileas_fogg]

If you want aluminum bushings for the 8.8 T-bird differential Mike Forte sells them. On my car, I had to put 1/4" spacers under them to get all the angles to work out.


John

https://live.staticflickr.com/4292/36123036102_8f3ee54e8a_4k.jpg (https://flic.kr/p/X3518h)IMG_2968 (https://flic.kr/p/X3518h) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

[Blue Viking]

Don't think I want to use aluminum bushings in the rear, poly is plenty stiff for me. Now, my main concern is wether or not I should address the 1 degree difference in the transmission and diff centerline, as i don't really se an easy way to accomplish that. There is no adjustability in the rear, and i would need to somehow modify the engine mounts to adjust the angle of the engine.

[rich grsc]

Don't think I want to use aluminum bushings in the rear, poly is plenty stiff for me. Now, my main concern is wether or not I should address the 1 degree difference in the transmission and diff centerline, as i don't really se an easy way to accomplish that. There is no adjustability in the rear, and i would need to somehow modify the engine mounts to adjust the angle of the engine.
NO, leave it as is. Why are you even worried about it? There is absolutely no set up that doesn't run with differing angles, you DO NOT want 0*. The u-joints must have some offset to keep lubricated, I wouldn't even worry if they had 3 or 4 degree difference. Good lord.:eek:

[CraigS]

You are looking at this in side view right? Whatever you do don't look at it in top view! I have only had experience w/ two cars w/ a drive line vibration. They had both been wrecked and the body hadn't been straightened properly. And in both, you could feel a vibration between 15 and 30 mph when accelerating. The harder acceleration, the more obvious the vibration. Both cars could have lived for many years as they were. In your car, the T-56 is the only somewhat out of the ordinary component. And since it's an IRS car, that extra length compared to a T5 really doesn't matter. You will be fine.

[Mark TX]

Oystein, I am struggling with the same issue (T56 Magnum, IRS, 8" drive shaft), except my angles are not quite as good as yours. Transmission vs pinion are 1.2 degrees apart from each other, and although my Operating Angles are each safely under 3 degrees, they are 1.2 degrees apart (above the "1 degree" rule). I have also concluded that my only remaining adjustment is to lower the engine, but... that looks hard to do (thin down the spacers in the motor mounts?), and it may drop my Coyote into the steering rod or push my oil filter too close to the frame. So... Right now I am hoping for a bit of IRS bushing flex (0.2 degrees) under load to make everything perfect, and hoping that without load, breaking the 1 degree rules (both of them, by 20% each) will not create vibration. If it does vibrate, then I will need to figure out how to lower the engine as much as possible without bumping into other stuff. It will be a lot harder to mess with motor mounts once the car is put together. I would be happy with your numbers!

[Blue Viking]

Oystein, I am struggling with the same issue (T56 Magnum, IRS, 8" drive shaft), except my angles are not quite as good as yours. Transmission vs pinion are 1.2 degrees apart from each other, and although my Operating Angles are each safely under 3 degrees, they are 1.2 degrees apart (above the "1 degree" rule). I have also concluded that my only remaining adjustment is to lower the engine, but... that looks hard to do (thin down the spacers in the motor mounts?), and it may drop my Coyote into the steering rod or push my oil filter too close to the frame. So... Right now I am hoping for a bit of IRS bushing flex (0.2 degrees) under load to make everything perfect, and hoping that without load, breaking the 1 degree rules (both of them, by 20% each) will not create vibration. If it does vibrate, then I will need to figure out how to lower the engine as much as possible without bumping into other stuff. It will be a lot harder to mess with motor mounts once the car is put together. I would be happy with your numbers!

I'm not too worried about the operating angle. My concern is with the offset from parallel between the transmission and diff. I will leave as is for now though, I suspect it will be fine anyway. Hopefully the engine will settle a little in the mounts, which should improve the geometry a bit.