# Transmission question



## TheSeeker (Mar 19, 2008)

My '85 318i started having major transmission issues, and it was cheaper and faster to replace the car with a newer POS than to get the transmission rebuilt.

So, my question is, can a transmission for a different car be put in place of the old transmission? That would make it easier for the conversion, since I could buy a kit that includes an adapter plate and not have to worry about custom fabrication there... it would also mean not having to hunt down a working mid-80s BMW transmission.

I'm starting to get comfortable with the electronics side of the conversion process, but I'm still really dumb on the mechanical side. <not a car person>


----------



## lazzer408 (May 18, 2008)

TheSeeker said:


> My '85 318i started having major transmission issues, and it was cheaper and faster to replace the car with a newer POS than to get the transmission rebuilt.
> 
> So, my question is, can a transmission for a different car be put in place of the old transmission? That would make it easier for the conversion, since I could buy a kit that includes an adapter plate and not have to worry about custom fabrication there... it would also mean not having to hunt down a working mid-80s BMW transmission.
> 
> I'm starting to get comfortable with the electronics side of the conversion process, but I'm still really dumb on the mechanical side. <not a car person>


It would not be a bolt-in situation. You would likely need to have custom half-shafts made if it's front wheel drive. If it's rear wheel drive you would likely need a custom drive shaft. The trans mounts themselfs are fairly easy if you have some metal working skills and a welder.

Is this it?
http://cgi.ebay.com/ebaymotors/87-B...trksidZp3286Q2em20Q2el1116QQitemZ170224586219

Looks like their all over ebay. Hit up some bmw forums. I'm sure you can find one.


----------



## TheSeeker (Mar 19, 2008)

lazzer408 said:


> It would not be a bolt-in situation. You would likely need to have custom half-shafts made if it's front wheel drive. If it's rear wheel drive you would likely need a custom drive shaft. The trans mounts themselves are fairly easy if you have some metal working skills and a welder.
> 
> Is this it?
> http://cgi.ebay.com/ebaymotors/87-B...trksidZp3286Q2em20Q2el1116QQitemZ170224586219
> ...


No metal working skills nor a welder.  Car is RWD, so I guess the issue is getting splines to match up?I'd have to look up part numbers I guess, almost have enough of the engine taken apart to get at the transmission, will probably get it out by next weekend.

Depending on the costs of replacing/fixing the transmission, I might think about getting a more powerful motor and just go 'direct drive' either with the motor in the front hooked to a drive shaft, or by installing the motor where the back seat is mated directly to the differential.


----------



## Toby B (Aug 10, 2008)

BMW uses a unique system to connect their driveshaft to the diff.
(well, Mercedes uses a similar, but dimensionally different, system...)

However, an e30 318 will have a '6- bolt guibo' that's going to be common
to later 320's (e21) and possibly later (e36) 318's. Since you're not
worried about exactly how long the transmission is, you can probably use
any gearbox that has a small 3- bolt flange for output. 

Annoyingly, 325s with the same body style have a different (bigger) transmission. 

Honestly, it'd make your life easier to just find another 318 tranny- 
goodness knows there are enough OTHER things to adapt on a conversion.

Oh, BTW, your engine is the same from the 1968 2002 through the
last 318 (1984?) E30, so if you find an adaptor plate for any of those cars, it'll work. 
The 1991 318i had a different motor, and thus, different trans.

hth,
t


----------



## HDS (Aug 11, 2008)

Has anyone heard of the use of CVT's or a simple torque converter like the ones found on snow mobiles for increasing the efficiency of their electric motors?


----------



## TX_Dj (Jul 25, 2008)

Electrics produce max torque at or near 0 rpm... there's no need to "convert" that torque, it's just instantly available.


----------



## mark1030 (Jul 28, 2008)

Another question about transmissions from a non-mechanical guy: Will a transmission last longer or wear better if you shift less because the electric motor doesn't need to use different gears as often as the ICE?


----------



## TheSeeker (Mar 19, 2008)

TX_Dj said:


> Electrics produce max torque at or near 0 rpm... there's no need to "convert" that torque, it's just instantly available.


From what I've been hearing, the reason for converting the tourque (using a transmission) is because it takes a lot of energy to take 1.5 tons at rest and make it start moving... without a transmission, that means a huge number of amps, which can stress components and lower range due to Peukert's Law.

By requiring less torque you allow the motor to turn at closer to its optimal RPM sooner and use less energy overall as a result... My first thoughts were that a CVT would be perfect for an electric car, allowing the motor to run at a nearly constant efficient RPM. Then I learned about how the torque stresses the components and how CVTs tend to rip themselves apart in electric applications... :/

Am I way off base here?


----------



## MalcolmB (Jun 10, 2008)

HDS said:


> Has anyone heard of the use of CVT's or a simple torque converter like the ones found on snow mobiles for increasing the efficiency of their electric motors?


I know a little about EVs but not a lot about transmissions. Even though EVs develop maximum torque from zero rpm, unless you have an oversized motor and Zillaesque converter (or very low gearing) it may be difficult to get moving with a single gear ratio and the motor and controller are likely to be pushed close to their limits.

The idea of using a lockable torque converter occurred to me as well, to reduce start-up torque and improve efficiency at low rpm. I know torque converters are lossy, so you may not actually improve system efficiency, but it could improve tractability and usability at low speeds. What I'd like to know is if it is even possible to use a torque converter on its own – is the fluid system self-contained or is it usually connected to the rest of the transmission?


----------



## TX_Dj (Jul 25, 2008)

@TheSeeker - right - but there's no reason to use a CVT to feed the manual transmission, which is what I seem to recall the original question pertaining to.

One or the other, adding more just adds more loss points in the drivetrain.


----------



## Qer (May 7, 2008)

TheSeeker said:


> From what I've been hearing, the reason for converting the tourque (using a transmission) is because it takes a lot of energy to take 1.5 tons at rest and make it start moving... without a transmission, that means a huge number of amps, which can stress components and lower range due to Peukert's Law.
> 
> [...]
> 
> Am I way off base here?


Just slightly. 0 RPM means that the motor is close to short circuited, so while it means LOTS of amps the voltage is low and thus the effect consumed is not that high (high enough, but still). This means that the controller will work hard since it will feel the full current, but the controller is (a bit simplified theoretical here) in essence a power converter that converts watts from one form of voltage*amperes to another form of voltage*amperes.

Now, lets say you have a battery pack of 150 Volts and the motor at 0 RPM only runs at 30 Volts @ 500 Ampere, that means that the motor chews 15 kW which, in the battery end, means "only" 100 Ampere (I'm happily assuming 100% efficiency of the controller now since I'm just rambling theoretical numbers anyway ).

So even if the motor is burning amps like crazy to generate a brutal torque, the Peukert's might actually not be worse than it is at ordinary cruising. The controller, however, takes a serious blow when it has to switch those 500 Amps on and off, so that stress is very real and odds are that if you're ever gonna blow your controller you'll do it when you start from a stand still.

The batteries will have it's really rotten moment the day you stomp the accelerator and peaks the current while already moving. Let's say you're cruising at 40 MPH and decide to pass that sunday driver and floor the accelerator, that means that the voltage over the motor will be much higher (the higher rpm, the higher voltage over the motor) and even at a much lower current the total power will exceed those 15 kW and thus the batteries will be hit by much more than 100 Ampere. That's when your Peukert's really gonna ruin your range.


----------



## TheSeeker (Mar 19, 2008)

TX_Dj said:


> @TheSeeker - right - but there's no reason to use a CVT to feed the manual transmission, which is what I seem to recall the original question pertaining to.
> 
> One or the other, adding more just adds more loss points in the drivetrain.


I figured he meant CVT or Torque Converter _instead_ of a manual transmission... Want to help us out, HDS, and clarify the question?


----------

