View Full Version : Driveline Angle needing 1.3" of spacers - IRS
Dropped in my 351W / TKO 600 from BluePrint this week and found to have 2 degrees of driveline angle i need to raise the transmission by 1.3 inches. That seems like a lot compared to others on the forum needs 1/4 to 1/2 inch.
Roaster is an IRS setup and engine mounts are torqued. Lastly, the A frame is installed on the top.
So, is 1.3 inches of spacers to much?
ggunter
04-16-2021, 03:05 PM
2 degrees is not bad, as long as your pinion angle ends up close to the same within a degree. Mine was 3.4 to start and I put a 1" spacer under the trans mount which took it to 1.8. My pinion angle is also 1.8 so it's golden. Drive shaft angle was -2.2 Pretty much as long as they are all within one degree of each other you shoudn't have any issue.
ggunter
04-16-2021, 03:06 PM
Are you measuring the engine angle off the front crank pulley?
I measure off the front crank pulley and I get 1.9 degrees when the transmission is lifted 1.3 inches. When it's not lifted I get 3.8. My Diff is also at 1.9 so I assume if I get a 1.3 inch spacer then we are good.
Gordon Levy
04-16-2021, 03:25 PM
I have a set of lowering engine mounts that will cure your issues.
I had to use three spacers.
https://thefactoryfiveforum.com/attachment.php?attachmentid=136335&d=1602727372
CraigS
04-19-2021, 07:14 AM
When I did my IRS retrofit I never even measured angle. I shimmed it so the driveshaft was a reasonably straight shot diff to trans and that was it. Never a problem. I don't remember the exact thickness but your 1.3" wouldn't worry me at all.
rich grsc
04-19-2021, 07:21 AM
When I did my IRS retrofit I never even measured angle. I shimmed it so the driveshaft was a reasonably straight shot diff to trans and that was it. Never a problem. I don't remember the exact thickness but your 1.3" wouldn't worry me at all.
Exactly. This is an IRS rear end , the drive line angles are only really important on a solid axle where they are changing as the suspension move. Leave as it is.
Hoooper
04-19-2021, 11:35 AM
The driveline angle problems that cause vibrations on a live axle are the same on an IRS, if the angles arent right you are still going to get vibrations, they just arent going to get significantly better and worse as the diff moves around. So yeah put the 1.3" in if thats what you measured.
Update: I've added spacers as well as the driveshaft then remeasured. My measurements seem good except the driveshaft angle is very high now.
Engine/trans - 1.7 degrees
Driveshaft - 10 degrees
Diff - 1.3 degrees
I assume the driveshaft angle is fine as long and the engine/trans and Diff angles are within 2 degrees. Thoughts?
Update: I've added spacers as well as the driveshaft then remeasured. My measurements seem good except the driveshaft angle is very high now.
Engine/trans - 1.7 degrees
Driveshaft - 10 degrees
Diff - 1.3 degrees
I assume the driveshaft angle is fine as long and the engine/trans and Diff angles are within 2 degrees. Thoughts?
You assume wrong. Take the link and gain some knowledge on a subject that is often misunderstood. Pay attention to driveshaft operating angles and their affect on critical speed. https://www.therangerstation.com/tech_library/pinionangles.shtml
BTW, Gordon informed us all that he has bolt-on cure for this problem. Seems strange to me that nobody jumped on that as a solution.
BradCraig
05-15-2021, 08:01 PM
You assume wrong. Take the link and gain some knowledge on a subject that is often misunderstood. Pay attention to driveshaft operating angles and their affect on critical speed. https://www.therangerstation.com/tech_library/pinionangles.shtml
BTW, Gordon informed us all that he has bolt-on cure for this problem. Seems strange to me that nobody jumped on that as a solution.
Exactly....all about operating angles. I just put a new Moser 12-bolt in my ‘67 Camaro with 4-link and had to take a crash course in driveline angles. Tremec has a good iphone app that you can use to calculate the operating angles.
rich grsc
05-16-2021, 07:31 AM
As I said in my previous post, IRS drive angles aren't as big a deal as a live axle. The angles don't change, as the IRS differential is fixed it the frame., the pinion angle doesn't rotate up or down under load.
147894
As Braid says, it's about operating angles, they need be close to parallel.
Rich, agree that IRS does not have the same pinion angle change through wheel travel as a solid rear axle. Solid rear axles on cars and trucks that use unequal length upper and lower control arms do experience pinion angle change throughout their travel, some significantly. However, IRS like the stock Mustang that is mounted in elastomer bushings will rotate and that rotation should be accounted for in the initial drive train alignment.
So, does FFR use a more solid IRS mount that prevents or minimizes rotation under acceleration?
https://www.youtube.com/watch?v=dA0kzu4Ukzk In this video it very clearly shows how much flex the OEM bushings that mount the rear end to the sub-frame allow the rear end to rotate, very much like elastomer bushings on solid axle control arms allow the axle to rotate under acceleration. Harder durometer polymer bushings may reduce this, possibly to a point of insignificance but not totally eliminate it. So something to consider when setting up an IRS.
edwardb
05-16-2021, 09:21 AM
So, does FFR use a more solid IRS mount that prevents or minimizes rotation under acceleration?
The Factory Five 2015+ IRS installation uses hard polyurethane bushings with steel sleeves. None of the stock Mustang bushings. Based on the hardness of the bushings and how tight the installation is (ask anyone that's done it) there's little/no movement of the differential. Certainly not enough to affect the drive train alignment.
rich grsc
05-16-2021, 09:52 AM
My IRS has 0 deflection. It's the older T-bird/Lincoln, and I use the recommended solid aluminum bushing, and as edwardb say's, the new style has very little movement also.
BradCraig
05-16-2021, 11:16 AM
As I said in my previous post, IRS drive angles aren't as big a deal as a live axle. The angles don't change, as the IRS differential is fixed it the frame., the pinion angle doesn't rotate up or down under load.
147894
As Braid says, it's about operating angles, they need be close to parallel.
Based on my understanding, perfect inline is not optimal either. The universals need some angle for proper lubrication.
rich grsc
05-16-2021, 11:46 AM
Yes that's true, but these cars have the drive line offset to the side slightly, and that's enough for lubrication.
phileas_fogg
05-17-2021, 01:46 PM
MVTV: Can you please post some picture of the engine mounts, the transmission mount with spacers, & the drive shaft?
We're all missing something here. There's nothing "off the reservation" about the 351W / TKO 600 combination. Why does MVTV require close to double the usual amount of spacers to get to a driveline angle 3x the spec?
John