# Direct Drive Diff Problems ! HELP !



## Ruben (Dec 1, 2008)

Hi Guys,

I hope there are some clever people out there that can give me a hand with this.

I have completed my EV conversion but have a problem with the drive shaft making noise when I am rolling / coasting. The motor is connect directly to the drive shaft and the rear wheels, there is about 2 meters between diff and motor.

When I release the throttle the drive shaft is loose, because the electric motor has very little resistance when not powered up. 

The diff appears to have almost a 1/4 turn of slack, so when standing still with the handbrake on I can move the drive shaft almost 1/4 turn, and it makes a small clunk noise at the either end.

The time you hear is most if when stop/starting at very low speeds as then then pressure/throttle is release from the motor and the drive shaft bounces back and forth a few times (clunk clunk clunk).

This is no good for my certification and it will not pass while I have this issue.

I have tried opening the diff and adding extra spacers to the pinions but the problem persisted.

Any assistance would be most appreciated.

Thanks very much,
Ruben


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## EVfun (Mar 14, 2010)

Unless the play in the final drive (and/or u-joints) is in excess of what the manufacture allows why would it be a certification problem? You will hear a lot of noises in an EV that you didn't hear before, mostly because the car is quieter. If those parts are out of spec I guess they need a rebuild. (I'm honestly a little confused, that buggy in my avatar didn't require an inspection where I'm located.)

The only other thing I can think of is some method of applying a small amount of power to the motor when the throttle is released. It seems less safe to me, but if the amount is strictly limited it should apply a slight preload without making the car likely to roll away when the brake is released (the creeping force should only be a fraction of the creep in an automatic transmission ICE car.) Perhaps just 20 or 30 amps would do the trick and be low enough to not overheat the brushes or commutator. I had thought about this for racing purposes, to remove slack from the driveline while waiting for the green light. Hammering hundreds of ft-lb of torque very suddenly into a little driveline slack is quite the impact hammer. I've never thought of this as an issue for normal street cars.


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## TomA (Mar 26, 2009)

Of course, you'll get a lot more help if people know something about your equipment, like specifically:

Motor
Coupler
U-Joints
Rear Axle Type
What it came out of
Rear axle ratio
Posi or open gears
Age/mileage on the axle and gears

Adding spacers to the pinions? I don't know what that means exactly, either. Have you looked for broken gears, debris in the diff case, and checked the wear pattern on the R&P? 

Have you removed and inspected the U-Joints on the driveshaft? Has the driveshaft been shortened and/or balanced? 

Are the motor mounts and coupler good and solid?

The only thing I can say at this point is that, depending on the rear axle and differential, 1/4 rotation free play is not necessarily the problem.

TomA


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## casey.mynott (Sep 29, 2011)

Hey Ruben!

Sounds like your diff has issues. A 1/4 turn is WAY too much. Some good info here:

http://www.ehow.com/how_2159877_set-up-differential.html



Casey


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## Ruben (Dec 1, 2008)

Thanks guys,

Yes the first thing I did was replace the diff with another standard one but the problem was the same. So this is the way it is standard.

Sorry I dont know the details of the diff modification as a mechanic did it for me but he said he put some spacers in the cogwheels, that axles are connected to, to move the them closer together. This made the diff tight to turn but did not reduce the noise (just changed it a bit).

The details of my conversion are:
1996 Subaru Legacy
Standard rear axle (type?)
Standard diff 4.1.1:1 (posi/open gears?)
Warp 9 (mounted where the gear box was)
Shaft shortened and balanced (by a engine reconditioner)
Coupling made (by a gear manufacturer)
There are two U joints before it reaches the motor to allow for off centre rotation

Motor/mounts/couplings are all very tight. The only movement (when standing still) is the drive shaft that can twist about 1/4 turn. At the end of each quarter turn there is a small clunk. This clunking can be heard when driving without giving any acceleration.

Im pretty sure the problem is that the drive shaft is quite long and when coasting has nothing holding on the other end so it flaps around a bit.

The options I have been thinking off are applying a small amount of power, emulating automatic. Or adding a break, like a rubber block.

Either option is not ideal.

Thanks again guys,

Ruben


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## Coley (Jul 26, 2007)

"Im pretty sure the problem is that the drive shaft is quite long and when coasting has nothing holding on the other end so it flaps around a bit."

This part is confusing. Why is it not supported on each end securely?


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## Ruben (Dec 1, 2008)

Sorry for the confusion: The drive shaft is attached securely on the one end to the motor via a custom hardened steel coupling, secured on the other via the standard 4 bolts to the diff (and even supported in the middle with the standard bracket and bearing).

However when there is no power being given the motor can turn freely, because there is no resistance from the motor end.

Do you guys want some pictures/diagrams to assist?

The diff end has a bit of slack in it, 1/4 turn, so when coasting (being rotated only from the wheels) the drive shaft rattles a bit. This isnt a huge issue.

The biggest is when stop starting and you release the pedal, the drive shaft springs back goes clunk clunk clunk a few times quite loudly. This happens every time you release the 'gas'.

Thanks so much for your help guys, I've been banging my head against this one for months.

Kind regards,
Ruben


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## DavidDymaxion (Dec 1, 2008)

My RWD car does regularly clunk its rear end a bit when transitioning to power on and power it. It'll sometimes do multiple clunks if you are in an in-between state, such as letting off the gas slowly. I've been told this is normal for a solid axle rear wheel drive car. My truck does not clunk that I can hear, but that rear axle is way back there and not under the passenger area like in the car. 

I just ran out and twisted both driveshafts with the transmission in neutral. The truck turned freely maybe 10 degrees, and has only about 25k miles. The car had barely perceptible free play, probably under 1 degree (BTW the car has 215k miles, but is on its 3rd set of rear axle bearings). 

A 1/4 turn sounds like way too much free play. In my gasser the lash looks to be difficult to adjust, but it is possible to do.


Ruben said:


> Sorry for the confusion: The drive shaft is attached securely on the one end to the motor via a custom hardened steel coupling, secured on the other via the standard 4 bolts to the diff (and even supported in the middle with the standard bracket and bearing).
> 
> However when there is no power being given the motor can turn freely, because there is no resistance from the motor end.
> 
> ...


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## casey.mynott (Sep 29, 2011)

Interesting.....on the race truck that we built (http://www.dssev.ca) the drivehaft is over 69" long. VERY long. We are using a Netgain Traswarp 11 running to a Ford 9". The truck is smooth! Everything is pretty brand new with about 8 thou backlash on the ring and pinion. If your diff has 1/4 turn slop this seems like the issue. The question in my hea,d does the Subaru use a typical hypoid gear setup? Are you able to check out another Subaru to see if 1/4 turn slop is typical? Again, seems like this is way too much slop. 

Casey


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## Ruben (Dec 1, 2008)

I have had another look and it is less than 1/4 turn, maybe 10-15deg.

I have also met a new neighbour with a similar legacy and the movement is about the same. But no clunk.

The clunk is coming from the Warp9 end. I guess usually there are a whole lot of gears and oil absorbing at that end but now there is only an electric motor.

Do any of your motors make noise when you turn the axle back and forth manually?


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## DavidDymaxion (Dec 1, 2008)

Is it a spline fit to the motor with some lash? That could potentially clunk back and forth. Another trick is wiggle the driveshaft back and forth and put your hand on the U-joint near the electric motor and wiggle opposite to feel for play in the U-joint. If you put your hand right on the U-joint it'll be easier to feel.

Of course this is with motor off, fuse pulled, wheels in the air, chocks, etc.


Ruben said:


> I have had another look and it is less than 1/4 turn, maybe 10-15deg.
> 
> I have also met a new neighbour with a similar legacy and the movement is about the same. But no clunk.
> 
> ...


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## dougingraham (Jul 26, 2011)

Ruben said:


> I have had another look and it is less than 1/4 turn, maybe 10-15deg.
> 
> I have also met a new neighbour with a similar legacy and the movement is about the same. But no clunk.
> 
> ...


Hmmm, there really isn't anything in the motor that can make noise when the shaft is loaded and unloaded. This sounds like the coupler or front U joint. If the hardened key is a poor fit I could see the coupler/key/shaft bouncing at the motor. You might check the coupler to make sure that isn't slipping and allowing the key to bounce around.

If a motor mount was broken that could make a clunking noise. I am assuming you used the factory mount so there is some isolation. If not every noise in the drive train will be clearly heard. I just re-read your earlier note where you said the motor is mounted where the gearbox was. How did you isolate it from the body/frame? There was probably a rear rubber isolated transmission mount that could have worked if you used it but that is probably too far back. If you just welded the motor mounts to the firewall and body then you will hear everything.


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## rwaudio (May 22, 2008)

I'm using the transmission from a 944 Turbo in my 944HV and there is some "slack" in the drive line that I can feel, its more noticeable when crawling up the slight incline into my garage since the tendency to roll back introduces that "slack" every time I let off the throttle. Mine doesn't make any bad noises other than a soft clunk as the slack is taken up. The only thing that would worry me about this is if I try to take off REALLY hard fro a complete stop without taking up the slack first. That could apply much higher forces than it was designed to handle. 

As for the rubber block solution that would just apply drag that would reduce the efficiency of your EV, an option might be to take it to a race shop that deals with Subaru's since they would probably know the diff inside and out and know how to make them bullet proof for racing.


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## EVfun (Mar 14, 2010)

Is there an appeals process for certification disputes? It seems that if your factory parts are within specs it isn't fair to fail the vehicle. You will hear driveline play more because ICE engines are quite loud, even when we think they are being quiet. I'm sure a box full of oil helped quiet the noise too. 

My guess for the location of the noise would be the sliding element (the slip splines) in your driveline. These can't be that tight. I suppose you could go with a ball and trunion front joint, but good luck finding one of those that you can adapt into the driveshaft ('50's and '60's Mopar cars are the main use I know about.) If you are using the fine splines typical of a transmission output shaft perhaps you could go to coarser splines from a driveline slip joint (these are typical in 2 piece drive shafts used in larger Pickups or the front of 4wd Pickups.) I'm not sure the typical transmission output shaft splines are designed to be used without an outer support bearing. I have thought about doing a direct drive street conversion and I know I would use a fixed yoke at each end and a drive shaft with a slip joint.


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## Ruben (Dec 1, 2008)

DougingGraham, you might be onto something here.

I have made a custom mount that attach's the motor where the gearbox was http://www.evkapiti.co.nz/img/motor in mount.JPG.

I put some rubber spacers on the inside bolts (closest to the motor), but not on the outside ones. Here is the motor mounted but not connected to the drive shaft yet http://www.evkapiti.co.nz/img/motor in car.JPG.

The noise is really coming from the entire motor area and sounds worse in the car than outside.

I will check out those U joints and coupling again as soon as I get home tonight.

Thanks again guys, your responses have been overwhelming and I really appreciate the help.

Kind regards,
Ruben


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## Ruben (Dec 1, 2008)

Hi guys,

I have checked all the U-joints and there is no noticeable movement in any of them.

I have also checked the coupling but this is tight as a rock. I can see the axle moving on both sides of the motor simultaneously so this is also fine.

I will try adding some extra 'padding' under the motor mount to hopefully absorb some more noise. Im just still not seeing where its coming from.

Thanks again everyone for your assistance, Ill keep you posted.

Regards,
Ruben


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## poprock (Apr 29, 2010)

Hi; Have been down your road and had similar issues with transmitted noise. As the pics show, I mounted my Electro Dynamic 9"; 8" in front of the diff in my 89 L series Suby. I used a short jack shaft with 2 uni's. Performance was underwhelming because the motor was 36v basic and only 12" long. Much smaller than yours. 30 mph and many melted battery posts ( contactors, no controller).See pics. A much better result was the last pic with Suby motor removed and elec to gearbox ( no clutch ). Same top speed but reasonable acceleration and no burnt posts. The noise was reduced in the direct drive mode by conveyor belting between floor and mount plate.


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## TomA (Mar 26, 2009)

Sounds like you have isolated the play, and clunk, into the rear axle housing. Good start.

You might take a look in there for damaged bits, and you might even want to take a whack at adjusting the lash on the R&P, but if a good used replacement has basically the same amount of slop (and clunk,) then you're probably just bumping up against the inherent design problem of having the motor's rotating mass fixed to the pinion gear. 

You have a couple of things working against you: 

Firstly, every time you go over a bump, that motor's rotational mass is banging hard on your diff gearset, probably far harder over, say, a broken up railroad crossing under braking where you chirp the rear tires, than at any time you're accelerating. That's making the free play worse, and a bad sign for the longevity of your diff. Might be OK, but its out of design spec. 

In stock configuration, there's either a torque converter or the spring packs in the clutch disc to damp this clunking, as well as the transfer case gears and clutches. Moreover, the Subaru rear axle isn't the primary vehicle drive as designed, and probably only gets 1/3 of the drive torque at any time in operation. You're putting tons more driveline shock into that diff than it was designed to handle. There's really nothing you can do about that, short of putting the center section of a clutch with the circumferential springs into your coupler. Even then, it won't dampen the shock as well as a stock clutch disc, and your forces are extreme. Just kind of something you'll have to live with...

Secondly, as you note, every time you cut the throttle in and out you're banging on the free play in the diff with the power. 

You need some way to very softly apply the throttle for the first 1/10 of a second or so just to take up that 10-14 degrees of rotational slack. I don't know if a Soliton or Zilla is programmable that way, but maybe someone here can help you figure out how to add a circuit that could give you that very short, very soft start throttle dip-in function with your existing controller. It would seem many EV conversions could use something like that, too.

That's the only real cure I can think of. Everything else is sort of a bandaid...


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## StanSimmons (Sep 3, 2011)

TomA said:


> You need some way to very softly apply the throttle for the first 1/10 of a second or so just to take up that 10-14 degrees of rotational slack. I don't know if a Soliton or Zilla is programmable that way, but maybe someone here can help you figure out how to add a circuit that could give you that very short, very soft start throttle dip-in function with your existing controller. It would seem many EV conversions could use something like that, too.
> 
> That's the only real cure I can think of. Everything else is sort of a bandaid...


A softer start can be defined by the "Slew Rate" as shown on page 22 of the Soliton manual, v1.4. I don't know about other controllers.

http://www.evnetics.com/downloads/Soliton_Manual_1v4_rev2.pdf


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## TomA (Mar 26, 2009)

StanSimmons said:


> A softer start can be defined by the "Slew Rate" as shown on page 22 of the Soliton manual, v1.4. I don't know about other controllers.
> 
> http://www.evnetics.com/downloads/Soliton_Manual_1v4_rev2.pdf


Yes, slew rate is the handy Soliton feature that would be used to enable the function I described.

This stock Soliton slew rate is a global rate that operates continuously, and is the rate at which the controller ramps up power to match the throttle position. Other controllers also have this feature. Operationally, we wouldn't want to change those parameters for the soft dip-in function.

What I've described is an additional, very slow slew rate (the 100A/sec Soliton base rate may be gentle enough,) that operates only for a very short period of time after the throttle position goes from zero to anything. That would gently take up the slack in the driveline every time you put your foot on the throttle from when it was completely released. Call it the "clunk stopper."

You probably wouldn't need more than a fraction of a second to take up this slack without clunking the components, so as a practical matter, you wouldn't even feel it driving the car. In fact, if you felt it working, it _wouldn't_ be working right.

Would make a nice feature for the Soliton line, but I'm guessing it could also be done with a stand alone circuit for a controller that doesn't have adjustable slew rate. 

Anyway, yes, it isn't rocket science, and in the Soliton it might be as simple a matter of just taking up the feature request and coding it. All the inputs and commands seem to already be there...


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## Dougnutz (Aug 22, 2011)

Ruben said:


> Hi Guys,
> 
> I hope there are some clever people out there that can give me a hand with this.
> 
> ...


Driveshaft movement is a function of backlash which is adjusted by shimmin the carrier bearings in the rear end. Normally the diff with have some backlash. It varies with the differential but if you put a dial indicator on the ring gear and hold the pinion still you will probably see .005 to .025 in. slack or backlash. .025 is pretty high for most applications but I have seen a lot of jeeps (dana) rear ends running that much without issue or noise. 

Adding shims to the pinion generally has little affect on the backlash but a great deal of affect on pinion depth and gear contact pattern. 

Setting up differentials is sort of a lost art with most mechanics. Though there are quite a few racers that still understand it. My recommendation would be to restore the original pinion shims and concentrate on shimming the carrier to remove backlash. It's also worth mentioning that this doesn't just happen. It is usually a result of bearing wear, so take a close look at pinnion and carrier bearings for wear and or pitting. Spin them and listen for any roughness. Also make very, very sure you get the pinion preload set correctly. usually 20-25 in-lbs for new bearings and half that for used bearings. If this is too low you will quickly wear through the surface hardening on the gears and soon be replacing them.


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## tinkeringgreg (Mar 27, 2008)

do you have a u-joint at the motor or is it solidly coupled? Also check the drive line angles. universal joints don't like excessive angles and if all u-joints are not working at about the same angle then they will cause the output end (motor while coasting) to oscillate instead of turning smoothly..


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## coulombKid (Jan 10, 2009)

Ruben said:


> I have had another look and it is less than 1/4 turn, maybe 10-15deg.
> 
> I have also met a new neighbour with a similar legacy and the movement is about the same. But no clunk.
> 
> ...


Things your mechanic should be checking are: 1) pinion bearing pre-load. With an inch-pounds torque wrench one can read the torque required to spin the pinion during its slack angle. With new bearings one would expect something like 20 in-lbs. if there is none then the pinion can actually traveling fore and aft during the wind-up. With out pinion bearing pre-load set correctly the back-lash checks of the ring gear with the pinion locked are meaningless. 2) If the differential carrier bearings don't also have a pre-load then once again all bets are off. One would expect a dial indicator to show about .005" of case stretch when the carrier pre-load is about right. Always check the factory manual for exact specs. Old grey-beards can do a Ford 9" with out checking the books but newer smaller/lighter cars will tend to have even tighter tolerances. If the pinion bearing pre-load was absent for any amount of time then the pinion spline/yoke spline may be shot requiring replacement of both.


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## coulombKid (Jan 10, 2009)

Ruben said:


> I have had another look and it is less than 1/4 turn, maybe 10-15deg.
> 
> I have also met a new neighbour with a similar legacy and the movement is about the same. But no clunk.
> 
> ...


Things your mechanic should be checking are: 1) pinion bearing pre-load. With an inch-pounds torque wrench one can read the torque required to spin the pinion during its slack angle. With new bearings one would expect something like 20 in-lbs. if there is none then the pinion can actually traveling fore and aft during the wind-up. With out pinion bearing pre-load set correctly the back-lash checks of the ring gear with the pinion locked are meaningless. 2) If the differential carrier bearings don't also have a pre-load then once again all bets are off. One would expect a dial indicator to show about .005" of case stretch when the carrier pre-load is about right. Always check the factory manual for exact specs. Old grey-beards can do a Ford 9" with out checking the books but newer smaller/lighter cars will tend to have even tighter tolerances. If the pinion bearing pre-load was absent for any amount of time then the pinion spline/yoke spline may be shot requiring replacement of both.


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## mizlplix (May 1, 2011)

What you are hearing is drivetrane wind-up. It is being transmitted to the car by your rather solid mounts on the motor. 

The small roller clearances in the u-joints, the small slack in the mid shaft slip splines, the small ring/pinion oil clearance (many times called backlash), and the slop in the axle splines where they go into the diff side "pinion" gears are all adding to the sound. 

Jack up the car. Set the emergency brake. At the front end of the drive-shaft at the motor coupler....By hand-turn it all you can one way. mark it. turn back until it stops. That is your "wind up". It is in most vehicles. Just not heard. 

It is less in front wheel drive cars, but still there. 

Isolate your motor mounting as best you can. That will reduce the noise some.

You can set the ring gear to the minimum clearance allowed by the spec. On a typical Ford that could be .008" as measured at the ring gear outer tooth with a dial indicator. (Too tight and a street car will make a howling noise and have a short life). Pull an axle and inspect the splines....We used to lightly peen the splines on the axles when they were worn, making them drive-in tight. 

In a drag racer, we would set the pinion gear engagment deeper as engine HP went up because the pinion gear would try to climb the ring gear. A heavier retaining plate helps, but strange things happen when you get above the 1000 HP level. 

Among other things, I worked for a Racing School for 10 years. We had 140 cars and changed out the rear gears 3 times. (just 4 of us mechanics). It gives a good idea of what works and what does not......LOL


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## BlueSkyStu (Feb 1, 2012)

Mate, my diff is perfect and I'm having EXACTLY the same problem. You're right - the noise is coming from the Warp 9 and is caused by the backlash from your diff having no resistance on over-run (and/or coast) to stop it floating and creating a knock/rumble which in turn gets amplified by your motor. You will hear it in some vehicles and not others for a number of reasons. Brake regen would fix it, but as you probably know, not a good idea for Warp 9's. I'm going to experiment with a few ideas, one being to mount a 12V alternator via belt drive off the front shaft that switches on under light or closed throttle and powers up the house battery - maybe that'll help provide enough load to move past the backlash and provide at least some sort of useful regen too.


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