LCA and Pinion Angles...
10-04-2011, 09:23 AM
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LCA and Pinion Angles... Ok, so I've read several threads on the pinion angle adjustment, and I thought I had it sorted out, but I'm getting vibration under very light load (just enough throttle so that the torque converter doesn't disengage on the highway) and heavy load. All of my measurements were taken with the car level. However, I did not have weight in the driver's seat, but could that really make such a drastic difference. I'm only 195lb...
I have read different methods of measurement. One involves measuring the angle of the yoke coming out of the transmission and the angle of the yoke on the rear end. Another method says you can use the angle of the driveshaft itself and the flat part of the tq arm mount (this is the method I used most recently). The DS is set at -1.5 degrees sloping down towards the rear, and the rear is set at -.5 degrees sloping down towards the front of the car. Feel free to mock my microsoft paint diagram of my current set up.
Also, I read a thread on here about LCA angles but now I can't find it
In the thread it said that for optimal weight transfer you actually want about -1 or -2 degrees in your LCAs so that they slope down towards the rear. I have larger tires than stock and mine currently slop up towards the rear at +3.6... I'm guessing I need the LCA relocation brackets? Would just adjustable torque arms work, or do I need both? Thanks for any useful help.
I have read different methods of measurement. One involves measuring the angle of the yoke coming out of the transmission and the angle of the yoke on the rear end. Another method says you can use the angle of the driveshaft itself and the flat part of the tq arm mount (this is the method I used most recently). The DS is set at -1.5 degrees sloping down towards the rear, and the rear is set at -.5 degrees sloping down towards the front of the car. Feel free to mock my microsoft paint diagram of my current set up.
Also, I read a thread on here about LCA angles but now I can't find it
In the thread it said that for optimal weight transfer you actually want about -1 or -2 degrees in your LCAs so that they slope down towards the rear. I have larger tires than stock and mine currently slop up towards the rear at +3.6... I'm guessing I need the LCA relocation brackets? Would just adjustable torque arms work, or do I need both? Thanks for any useful help. 
10-04-2011, 08:08 PM
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You should really look at the stickies( in yellow on thread list) it has good descriptions and explanations.for lca position you want it pointing down towards the rear, lca relocation brackets would work great especially when lowered. Adjustable ta will cure the pinion angle. I know bmr' s web site has some videos of installs, check em out, and nice parts.
10-05-2011, 12:00 PM
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You should really look at the stickies( in yellow on thread list) it has good descriptions and explanations.for lca position you want it pointing down towards the rear, lca relocation brackets would work great especially when lowered. Adjustable ta will cure the pinion angle. I know bmr' s web site has some videos of installs, check em out, and nice parts.
Well, I guess it's time for me to order those LCA relocation brakects. Too bad I don't have a welder
I'll have to decide if if I need/want to spend the extra $$$ for the adjustable LCAs. I mean, you can never have too much shiny stuff under the car.
10-10-2011, 07:45 AM
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Ok, still have the stupid vibration... If it's the DS itself, at high mph wouldn't it have vibration under all throttle conditions, and not just light deceleration? I've tried a combination of "pinion angles," and none of them alleviate the issue. The rear u-joint is brand new (**** cost ~$30 b/c it's a conversion joint), but I'm not sure how old the front u-joint is. I didn't notice this problem before the rear-end swap.
If the DS is a 1/2" too long, could that cause the issue? Or could it be my torque converter acting funky (like it wants to disengage, but there's just enough throttle to prevent it from disengaging)? Thanks again everyone
If the DS is a 1/2" too long, could that cause the issue? Or could it be my torque converter acting funky (like it wants to disengage, but there's just enough throttle to prevent it from disengaging)? Thanks again everyone
10-10-2011, 12:04 PM
#7
Torque converter could always be an issue. Did the problem just develop or did it start after a tranny install, tc replacement, etc? I had a tc give me some vibration issues once, took it back to the guys that installed it and they unbolted it from the flexplater and turned it one set of holes and bolted it back in and the vibration was gone. Just something to do with how the tc and flexplate was balanced.
I had chased a seperate vibration issue on the same car for a long time. I had taked the ds to drivetrain specialist, with the front and rear yoke, and new u-joints and gotten their "race balance" (absolute bullshit) and it never went away. Finally I bought a new one from summit and the problem was gone.
If the ds is too long I would imagine you would have a horrile binding issue under hard acceleration. I've had that issue as well and I pretty much stripped all the splines on the front yoke. And that was under bolt on power with an LT1.
I'd say check the length, get new u-joints front and rear, and take the whole assembly (ds, u-joints and both yokes) to a ds shop and have them balanced. Tell them what you have going on and see if they have any advice.
One last thing, all 3 of my factory ds have had what looks like dampner on the front of them. I'm not sure the technical term for the piece but I notice there is a rubber seal that is always cracked out on them. I have replaced the front yokes with solid ones that dont require the dampner and it seems to be a better way to go.
I had chased a seperate vibration issue on the same car for a long time. I had taked the ds to drivetrain specialist, with the front and rear yoke, and new u-joints and gotten their "race balance" (absolute bullshit) and it never went away. Finally I bought a new one from summit and the problem was gone.
If the ds is too long I would imagine you would have a horrile binding issue under hard acceleration. I've had that issue as well and I pretty much stripped all the splines on the front yoke. And that was under bolt on power with an LT1.
I'd say check the length, get new u-joints front and rear, and take the whole assembly (ds, u-joints and both yokes) to a ds shop and have them balanced. Tell them what you have going on and see if they have any advice.
One last thing, all 3 of my factory ds have had what looks like dampner on the front of them. I'm not sure the technical term for the piece but I notice there is a rubber seal that is always cracked out on them. I have replaced the front yokes with solid ones that dont require the dampner and it seems to be a better way to go.
