I know you didn't but I'm asking you to because I don't understand how the pinion flange runout is even remotely related to pinion angle. Are you talking about radial or lateral runout?
Last edited:
The IRS Tech Article
- Thread starter Snake Eyes
- Start date
93SVTCobra said:
Not sure what the proper term is. But the Pinion flange itself is never perfectly round and will always be just slightly off. Finding that peak point where the flange is highest from the pinion itself is where the d/s needs to be indexed.
This is unrelated to pinion angle as a whole.
Why did my pinion angle change when I swapped gears? No clue.
Indexing a driveshaft has absolutely no bearing on your driveline angles. You also need to find the "low" spot on the driveshaft and you'd ideally want to place the high spot on the pinion flange as close to the low point on the driveshaft as possible.
If your pinion angle changed when you changed gears then you really screwed something up or something isn't tightened down.
There is another reason that this statement doesn't make any sense. If you change the front height of the Pumpkin as you have stated above you're actually causing the whole pumpkin to be put in a bind condition because the rear cover is attachment by two bolts that you've done nothing with. So by changing the front mounting height as you've indicated above you've actually put the pumpkin in a bind condition regardless of any taper in the bushings.
SO I'll ask again. Why would you EVER change the rear IRS pinion angle?
If your pinion angle changed when you changed gears then you really screwed something up or something isn't tightened down.
Stitch said:
There is another reason that this statement doesn't make any sense. If you change the front height of the Pumpkin as you have stated above you're actually causing the whole pumpkin to be put in a bind condition because the rear cover is attachment by two bolts that you've done nothing with. So by changing the front mounting height as you've indicated above you've actually put the pumpkin in a bind condition regardless of any taper in the bushings.
SO I'll ask again. Why would you EVER change the rear IRS pinion angle?
93SVTCobra said:
Uh Mark,
That is partially incorrect (or partially true... half empty, half full. Well you know what I mean). Yes the cover is attached with two bolts but this in turn is attached by only one large bolt back to the IRS cradle. That large bolt goes through a rubber bushing and it acts as a pivot. This allows the pumpking to kick up and down when torque is applied..... Thus 90% of the wheel hop problems. I know it for a fact since I replaced that bushing earlier this year with a urethane piece. All in all the carrier is held in place by two vertical bolts in front and a horizontal one in the back. If it weren't for that design aspect, people would not be able to change the pinion angle.
Last edited by a moderator:
93SVTCobra said:
Well if you change your trans say from a T-45 to a T-56 the longer trans will affect your drive shaft angle (along with length), or you swap the rubber IRS bushings and you need to get your pinion angle back to where it's supposed to be, or just to get it perfect (which Ford doesn't do, they do good enough). Now if you are asking why would you need to change it, you don't. Once you have it set properly you don't need to change it but getting it set right requires adjustment of the differential pumpkin at the ears. It's like corner weighting a car (with coil overs) you don't need to do it but some want to go all out.
Changing the length of the transmission would not change the relationship between the two driveline angles. The physical numbers might change (but they would change at BOTH ends) but the actual difference between the two angles would not. How if the relative height of the transmission was different then you might have an issue but you can just shim the transmission mount to compensate for that.
Swapping out the front diff bushings shouldn't affect your pinion angle unless you don't replace it with a bushing , either urethane or aluminum, that is the same size.
Eric - You are correct. I forgot about the single mount on the back because we changed the rear mounting on my car to get rid of that excess weight.
This is what we did for the rear mount:
Doesn't look like much but on a road racing car you don't need all of the extra support that you would on a drag racing car.
Swapping out the front diff bushings shouldn't affect your pinion angle unless you don't replace it with a bushing , either urethane or aluminum, that is the same size.
Eric - You are correct. I forgot about the single mount on the back because we changed the rear mounting on my car to get rid of that excess weight.
This is what we did for the rear mount:
Doesn't look like much but on a road racing car you don't need all of the extra support that you would on a drag racing car.
93SVTCobra said:This is what we did for the rear mount:
Doesn't look like much but on a road racing car you don't need all of the extra support that you would on a drag racing car.
Me like. What I really want is that KB modified cradle. But at $700 plus shipping it's a little stout.
Last edited by a moderator:
serpentnoir said:
But definitely worth it! :rockon:
93SVTCobra said:Changing the length of the transmission would not change the relationship between the two driveline angles. The physical numbers might change (but they would change at BOTH ends) but the actual difference between the two angles would not. How if the relative height of the transmission was different then you might have an issue but you can just shim the transmission mount to compensate for that.
Swapping out the front diff bushings shouldn't affect your pinion angle unless you don't replace it with a bushing , either urethane or aluminum, that is the same size.
Eric - You are correct. I forgot about the single mount on the back because we changed the rear mounting on my car to get rid of that excess weight.
This is what we did for the rear mount:
Doesn't look like much but on a road racing car you don't need all of the extra support that you would on a drag racing car.
A longer transmission will change the angle at the transmission to d/s point. therefore possibly causing unwanted vibrations.
I did not measure the pinion angle before the gear swap. What I can tell you is that the pumpkin is set at 90* now. The pumpkin is full secure. I'm not sure if the rubber bushings somehow collapsed but after replacing them with the kb aluminum pieces, pinion angle has to be set. As snake eyes pointed out, the rear mount of the diff cover is attached to the IRS frame via a rubber mount and a single bolt representing a pivot point. Normally I would say the pinion angle should be set at factory specs before and after install.
***Pinion flange runout has nothing to do with pinion angle so please stop saying I said that.***
Last edited:
Stitch said:
You are half right here. Both driveline angles (front and rear) will change and the net change will be zero.
If you're pumpkin is set at 90* then you DEFINITELY have a problem.
This is what you said:
Stitch said:
Changing gears has NO effect on the pinion flange runout OR the pinion angle.
The pinion flange is the pinion flange and it's runout could be determined with it sitting on a table 100 miles away from your car. You then bring it back to your car and install it and it the pinion flange runout will not change.
93SVTCobra said:
That was a two part sentence. And yes, ask any mechanic who does rear end changes. Pinion flange runout will change once you tear apart a differential. That little yellow mark that the factory makes will no longer be the peak runout point.
What is your pinion angle set to? When I say 90* I am referencing the Pinion flange being 90* vertical. Most IRS cars I assume will be like this from the factory but could vary. Remember the goal is to have zero difference in angle for the pinion flange and the crank. If my Crankshaft is 88*, I want my pinion flange to also be 88*, difference is zero.
Without having rubber or MM's front differential mounts, you will not be able to change the pinion angle. KB's kit since its aluminum allow for no flex or angle change at the differential ears. Therefore all you can acheive is a 90* pinion angle measured at the flange.
Again, I do not know what the pinion angle is on a factory IRS car.
Last edited:
Stitch said:
Please explain HOW the pinion runout changes when you change a differential. I have explained why it won't change and so I'd like to hear you explain why it would as I still don't see it.
You're also forgetting that you can change the crankshaft degree as well.
Come to think of it if you are changing the pinion flange by 1 or 2 degrees how much stress do you really think that is going to put on the snout?
serpentnoir said:
Once the IRS is setup properly it really hauls ass!
This will sound like a cop out but I'm not at liberty to say what our pinion angle is at but I can tell you that the difference from the front to rear angles is less than 1 degree.
So if you can change your crankshaft angle why do you need to change your pinion angle?
So if you can change your crankshaft angle why do you need to change your pinion angle?
93SVTCobra said:
Honestly, I'm no expert nor a mechanic. I've done alot of research and only have experience with my problems.
I don't know why the pinion angle changed, all I know is it was way off afterwards and I had a nasty vibration over 70mph. After raising the pinion angle to 90 (before adjusting the tranny) the vibrations diminished. That told me and my mechanic that we were getting warmer. After doing more researching and figuring out that the pinion angle/crankshaft angle needed to be less then 1*, we settled on raising the tranny some to compensate since the bushings from KB weren't getting me anywhere above 90* for above stated reasons.
I'm not sure how high the tranny can be raised nor do I want to go extreme either way. I'd rather raise both a little then one a lot. My vibrations are still there but much less then before. I'd say but 85% less. Without tearing down the rear end again, I have no other information as to what could be causing the vibration or why the pinion angle was wrong after the install.
Sounds like you need to index your driveshaft.
There are actually 16 (theoretically a bunch more but 16 to keep it simple and that's usually all you need to get it close enough) because you would also index the transmission side of the driveshaft as well.
Users who are viewing this thread
