# Drive shaft angle.



## gojo (Feb 1, 2011)

My 83 RX7 makes a rubbing grinding noise as I come out of a left hand turn when accelerating from a stop. 

One possibility I have ran across is the angle of the drive shaft. I have read where just lower the springs can change the drive shaft angle, and cause a similar type of noise. 

I hadn’t really concerned myself with drive shaft angle when I did my conversion. When compared to my S10 pickup the RX7 has a sharper angle coming out of the transmission. I could raise the motor a couple of inches, and cut down on the angle were the drive shaft meets the transmission. This may put less stress on the U joints, but it would angle up my motor, and I would seem like that would put stress on the motor bearings. 

Just wondering if others have concerned themselves with drive shaft angles. Also affecting the angle of the drive shaft is the heavy duty springs I installed to support the batteries in the rear. They may have lifted the rear an inch or so higher then stock.


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## o0o (Jun 29, 2011)

hmm the car should shake on higher speeds too on a bad angle from my experience^^

btw u say its when u turn left from a stop, could the front wheels scrub on the arches?
or do u have a welded diff?

there are so many reasons...make a vid


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## EV-propulsion.com (Jun 1, 2009)

The important thing about driveshafts is to be sure the angle of the output shaft of the transmission is parallel to the pinion shaft of the differential. Raisng or lowering the car should not change this parallelism, just that the shaft itself will have a larger or smaller arc of the u-joints. The rear axle is constantly changing heights while you drive over bumps (but does not rotate on its mounts), but the trans and pinion shaft angles remain parallel (not necessarily in a straight line). Often overlooked, but when you converted to electric, you should have tried to maintain the same engine/trans angle (that was originally there) when you installed the electric motor. If they are different, the front and rear u joints will actually rotate at different arcs and speeds increasing wear and causing inbalance/vibration.
Mike
www.EV-propulsion.com


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## welder4u (Nov 30, 2010)

Here's some good info on drive angles.

http://www.markwilliams.com/driveshafttech.aspx


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## EV-propulsion.com (Jun 1, 2009)

good link. That was the drawing I needed to go with my explanation!


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## gojo (Feb 1, 2011)

o0o said:


> hmm the car should shake on higher speeds too on a bad angle from my experience^^
> 
> btw u say its when u turn left from a stop, could the front wheels scrub on the arches?
> or do u have a welded diff?
> ...


Sometimes the car will make the same sound going straight if there is a dip in the road. 

I don't know what a welded diff is, but I don't think I have one. I do have a limited slip diff, and I have replaced the lube with limited slip differential oil.


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## gojo (Feb 1, 2011)

EV-propulsion.com said:


> The important thing about driveshafts is to be sure the angle of the output shaft of the transmission is parallel to the pinion shaft of the differential. Raisng or lowering the car should not change this parallelism, just that the shaft itself will have a larger or smaller arc of the u-joints. The rear axle is constantly changing heights while you drive over bumps (but does not rotate on its mounts), but the trans and pinion shaft angles remain parallel (not necessarily in a straight line). Often overlooked, but when you converted to electric, you should have tried to maintain the same engine/trans angle (that was originally there) when you installed the electric motor. If they are different, the front and rear u joints will actually rotate at different arcs and speeds increasing wear and causing inbalance/vibration.
> Mike
> www.EV-propulsion.com


Just visually the angle coming out of the transmission appears to be more the the angle coming out of the differential. I purchased a protractor today in order to compare the angles.

I think raising the rear end would have different outcomes on different cars. On RX7's because of the kind suspension, it, according to what I have read on the RX7 forms, does change the angle of the diff, but in my case, I think the angle coming out of my transmission is the main problem. 

My motor is held in place by the original motor mounts, and I could shim it up an inch or two in order to decrease the angle coming out of the transmission. This would have the motor running at a slight angle, and I am concerned about stress on the bearings. Are you aware of any problems mounting the motor at a slight angle would cause, other then maybe aesthetics?


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## gojo (Feb 1, 2011)

welder4u said:


> Here's some good info on drive angles.
> 
> http://www.markwilliams.com/driveshafttech.aspx


The engineering involved in cars is fascinating. 

I purchased a protractor today, and plan on comparing the angles, and maybe shimming up my motor a little if needed to bring them more into harmony. 

If nothing else it will save drive shaft wear and tear.


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## EV-propulsion.com (Jun 1, 2009)

I don't see a problem with having the motor at the correct angle needed. This should only be @ 3 degrees, many similar motors are actually used upright in a 90* verticle angle (walk behind forklifts and such).
As far as the noise, while you are under the car checking angles, I would look for any wear points of any revolving parts hitting something else like tires, wheels, shafts, springs,etc
Mike
www.EV-propulsion.com


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## madderscience (Jun 28, 2008)

Sure it isn't a tire rubbing against the wheel well? If the car has been lowered, or it has too large tires on it, this can happen. My MR2 has that issue because I put one size too large tires on it. (only happens in the tightest left turns though, so not a major problem in my case)


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## gojo (Feb 1, 2011)

madderscience said:


> Sure it isn't a tire rubbing against the wheel well? If the car has been lowered, or it has too large tires on it, this can happen. My MR2 has that issue because I put one size too large tires on it. (only happens in the tightest left turns though, so not a major problem in my case)


I don't think it is tire rub. I have had tire rub before, and this doesn't sound like tire rub. It is more of a binding sound. It mainly happens when there is some torque going on, and usually coming out of a left turn when accelerating from a complete stop. I can feel the vibrations through the floor, and it sounds to be coming from the right rear. 

I have a limited slip differential, and there could be something going on there.


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## mizlplix (May 1, 2011)

GoJo: Here in the USA, right turns are sharp and lefts are a wider sweeping turn.

With a limited slip diff, a tight right hand/sharp turn has the diff unlock-turn re-lock. A lefty unlocks, (then due to the gradual turn) stays open, then tries to find a speed where it can re-lock and eventually does. 

The later(exit) part of the turn is where the clutches are attempting to re-lock. They all need a friction modifier to allow them to slip/slide a little before re-locking. 

If your noise-vibration happens during the later part of a left turn, I would add some posi additive to the diff lube. Dont be too surprised if it works. It is a common problem. BTW: dont trust any lube alone. get the additive too.


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## gojo (Feb 1, 2011)

mizlplix said:


> GoJo: Here in the USA, right turns are sharp and lefts are a wider sweeping turn.
> 
> With a limited slip diff, a tight right hand/sharp turn has the diff unlock-turn re-lock. A lefty unlocks, (then due to the gradual turn) stays open, then tries to find a speed where it can re-lock and eventually does.
> 
> ...


I am amazed at the information this site has. It has to be one of the best. 

I have added limited slip, and replaced the oil in the differential about a week ago. Not knowing the mechanics involving limited slip, I just thought it would be worth a try. I have driven the car about 50 miles with the new additive, and I am still getting binding sound, but maybe it will take awhile to loosen up. 

The way you have described the limited slip fits the scenario. I can go around and around in a circle, and there is no noise until I start to come out of the turn, but only if I continue to accelerate. To avoid the sound now, I just don't accelerate as I come out of my left hand turns. 

I will occasionally get a slight noise when rolling over a dip in the road going perfectly straight. I can see how coming up out of a dip with my 175 pound springs could cause the wheel to become air born for a brief second and possibly involve the friction modifier for a fraction of a second. 

I will have to research the friction modifier some. If it needs to be replaced, I think I would try to find a non limited slip and put that in instead. It is for a 1983 Mazda RX7, and I think both options fit in the same rear end, or maybe just leave things the way they are, and drive accordingly to avoid the noise. 

I was told the rear end would make a clatter if it wasn't working properly and this is more of a binding noise that vibrates the entire car, so I had ruled out the diff, but it occurs mainly coming out of a left turn if I continue to accelerate just as you have described it. 

Thanks for the info. I think you may have nailed it.


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## mizlplix (May 1, 2011)

Heh....a FORD clutch posi will grind /vibrate and sound like a brake gone metal to metal if you do not use their friction modifyer. It smells evil. But it smooths them out like magic.

Invest in a bottle from ford. It is 10 oz. Or so. It takes 25 miles or so to mix and start working.

Mazda is a division of ford you know....

Miz


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## gojo (Feb 1, 2011)

mizlplix said:


> Heh....a FORD clutch posi will grind /vibrate and sound like a brake gone metal to metal if you do not use their friction modifyer. It smells evil. But it smooths them out like magic.
> 
> Invest in a bottle from ford. It is 10 oz. Or so. It takes 25 miles or so to mix and start working.
> 
> ...


Good to know it takes a few miles for the additive to work. I am now thinking it is the LSD. The original information I had was that LSD made a clattering sound, the sound I am getting is more what you describe. 

I did figure 8's for about 10 minutes in a church parking lot last night, and I haven't heard the noise since. I have gotten a number of concoctions that different people have had success with and I will keep yours in mind if the noise comes back. 

This has all been good. I have learned I need to adjust my drive shaft angle, and I took my rear sway bar off which is giving me a smoother ride.

Happy trails........Don


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