help with this pinion angle vibration.
help with this pinion angle vibration. First, I've done a search and adjusted the angle at least a dozen times to range between 0 and -3 for my M6. The vibration is horrible above 80mph. Now after reading 4x4 forums I may have found the problem. I have the bmr trans crossmount and stock new mount. I think the crossmount allows the tranny to sit at a lower angle than 0. Actually my tranny points down about 1.5 degrees.. So here lies the problem, I think. My current set up is figure one. The only way I can get and equal but opposite angle would be if I oriented the trans like figure 2. However, Im not sure if that's possible. Maybe with some shims. The other option would be to adjust the torque arm to make the rear face upward 1.5 degrees to be equal but opposite the tranny. However I'm scared that making a positive pinion angle of 1.5 to 2 will actually result in me breaking something on launch. Please take a real look at the figure and give advice. Again, I've adjusted this angle multiple times. and I'm familiar with BMR's video. I think the tranny hanging low has been the problem all the time.
Your transmission should be pointing down towards the rear of the car. Your pinion angle is just the comparison between the driveline angle and the actual pinion measurement. See this diagram for clarification:
My 4L80 trans crossmember with a poly mount is at +2.5* so idk how yours is angled down. My rear diff is around -2.5* unfortunately short of shimming down my crossmember i have no way to lower the engine/driveline angle. I've heard from a few people that the best way to get the engine/trans angle is from the balancer itself since it's easier to get an accurate measurement. My car is lowered also. I keep adjusting mine too to get it better. It's a minor vibration in mine cruising at 70 but the car has always been stiff with subframe connectors, a bunch of BMR stuff in the car, big wheels, lowered, poly trans mount. It's somewhat normal but i've had mine around 90 mph since i did my trans and it doesn't get any worse from what i can tell
Joined: Aug 2007
Posts: 24,241
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From: Turnin' Wrenches Infractions: 005
My trans was pointing down 3 degrees with the BMR crossmember. You cannot shim that out, it's too much angle. I aimed the rearend up 3 degrees so the angles matched and my high speed vibes went away.
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I think the biggest problem is people confusing terminology. Most people say that their trans is pointing down, and think this is a problem because the pinion is pointing up. As the diagram I posted above shows, even when this is the case, they are still on a matching plane, and both angle upwards towards the front of the car. Another issue we see a lot is people will use their angle finder on the tailshaft of the trans and get a measurement, then spin the the angle finder around to measure the pinion flange. Then they end up with a positive measurement and a negative measurement. The angle MUST be measured from the same side, with the angle finder facing the same direction to accurately compare angles. I normally recommend to measure from the crank pulley while reading from the passenger side of the car, then move directly back and measure the rear u-joint yoke on the rear end. This way you will end up with measurements that are accurately related to each other.
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Joined: Jul 2007
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From: Central,NJ
It doesn't matter which side of the car the reading is taken from. What's important is that both of your readings are taken from the same side.
Most of the angle tools available are so inaccurate the numbers basically mean nothing. How you use the tool determines your success.
Eric posted some very good info. I say throw away all the -+ and visualize it/ draw it out on paper. What you want is phased joints and you can get it two ways...it looks like this:
Most of the angle tools available are so inaccurate the numbers basically mean nothing. How you use the tool determines your success.
Eric posted some very good info. I say throw away all the -+ and visualize it/ draw it out on paper. What you want is phased joints and you can get it two ways...it looks like this:
So when you go under load how much does the pinion move and does it try to angle up or does it push down? Idk why this **** is so confusing lol. Right now my trans would technically be facing down about 2.5° then since I was thinking of it by what I was reading on the gauge. So when I angle my pinion down I'm moving it in the wrong direction I actually want to to go up so that they are in equal but opposite directions. That means my pinion angle may be too far angled down. Since my car has a fairly easily adjustable torque arm mount on the crossmember I may slowly adjust up until it feels tolerable or perfect. Right now my BMR crossmember has the torque arm set to the 2nd lowest spot on the xmembers plate.
Last edited by Cole Train; Jun 3, 2014 at 12:01 AM.
So when you go under load how much does the pinion move and does it try to angle up or does it push down? Idk why this **** is so confusing lol. Right now my trans would technically be facing down about 2.5° then since I was thinking of it by what I was reading on the gauge. So when I angle my pinion down I'm moving it in the wrong direction I actually want to to go up so that they are in equal but opposite directions. That means my pinion angle may be too far angled down. Since my car has a fairly easily adjustable torque arm mount on the crossmember I may slowly adjust up until it feels tolerable or perfect. Right now my BMR crossmember has the torque arm set to the 2nd lowest spot on the xmembers plate.
Kevin97ss posted a good representation of what you should be looking for. Ideally, you want your u-joints to be bent an equal amount in opposite directions
Honestly, it does not matter which side you measure from, as long as you measure both from the same side. I just normally recommend the passenger side because the angle finders that we offer, as well as most other suppliers, has a flat measuring surface on the left side making it easier to get a good reading
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
It doesn't matter which side of the car the reading is taken from. What's important is that both of your readings are taken from the same side.
Most of the angle tools available are so inaccurate the numbers basically mean nothing. How you use the tool determines your success.
Eric posted some very good info. I say throw away all the -+ and visualize it/ draw it out on paper. What you want is phased joints and you can get it two ways...it looks like this:
Most of the angle tools available are so inaccurate the numbers basically mean nothing. How you use the tool determines your success.
Eric posted some very good info. I say throw away all the -+ and visualize it/ draw it out on paper. What you want is phased joints and you can get it two ways...it looks like this:
So do we want the angles to look like that picture when its under load or just resting? Because it would seem that it would be a different angle on the pinion end when's under load if you make them the same when they are just at rest. And by that I mean under load you would have the front at say 2° and the rear at 0° if you did them both at 2 while in the air. Also under load means when you're driving and not just meaning the cars on the ground and on all 4 tires correct?
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
The car drives at rest more or less. It only squats under heavy acceleration so that's the only time pinion angle changes. And even then its not a ton. If you have vibes, get rid of them, then see how far negative you can go before they return. Most say you want about -2 with stock suspensions stuff (rubber) and -1 if its all poly or rod ended stuff.
