Some Objective Data About SMG Motor Replacement

[Stepstools]

I replaced my SMG electric motor a few weeks ago and decided to gather some data to see how much the new motor objectively helped my situation. The code thrown by my SMG every time the cog light illuminated was 56 (0x38) "switching-on time of hydraulic unit" for me. This lead me to believe that a new motor would help in my situation. My conclusion was the same as many others: the old motor had become weak and simply couldn't produce enough force to prime the accumulator in the time allotted by the SMG computer. I performed a little test using INPA to gauge how much the new motor actually helped. Here's the details of my test:

Conditions and Testing Protocol:

• Transmission and SMG Fluid at Ambient Temperature (~70F)
• Accumulator Preload Pressure Previously Measured at 32 Bar
• Old Motor at 154k Miles, New Motor From SMG Society
• Shift Between 1 and 2 Until Pump Motor Turns On (I Got 3 Shifts Each Time)
• Begin Stopwatch When INPA Shows Motor Has Turned On
• Stop Stopwatch When INPA Shows Motor Has Turned Off

My Results:



Conclusions:

• The new motor didn't increase the max charge pressure on these cycles. The motor still shut off when the accumulator reached 63-64 Bar.
• Because the max pressure didn't increase, I still got 3 shifts for each charge cycle.
• Most importantly, the new motor was able to complete the charge cycle 33% faster!
• The new motor is also much quieter, not that it matters when the engine is on.

As far as subjective improvement goes, I haven't had too many opportunities to drive recently, but I have been on a drive very similar to one that set off my cog light on a few occasions. In fact, it was probably hotter and I sat in more traffic too. Zero SMG issues on that drive. Overall, this information isn't really anything new for the SMG community, but I wanted to share some objective data in case others have been on the fence about doing the swap. Obviously there are many different SMG issues out there, but I would highly recommend this fix to anyone suffering from this fairly common problem. 100% worth the money, 99% worth the anguish of actually swapping it.

[TexaZ3]

Cool. But technically, the speed and quickness of the new motor does not translate into anything performance related for the SMG or shift speed, so in real world it makes no difference whatsoever, aside from that fact that its a new motor and will last longer than the old one.

[BubbaTree]

So, if a new motor doesn't translate into anything performance related, why bother changing it unless it fails? If the old motor dies on the road, I see that as a problem; otherwise, is a new motor just peace of mind? My car has no symptoms yet, but it's approaching 100K miles, and I live in the Arizona desert where the summer temps are high!

[oceansize]

So, if a new motor doesn't translate into anything performance related, why bother changing it unless it fails? If the old motor dies on the road, I see that as a problem; otherwise, is a new motor just peace of mind? My car has no symptoms yet, but it's approaching 100K miles, and I live in the Arizona desert where the summer temps are high!

Motor pressurizes the accumulator so there is no point in changing a motor that hasn't failed. It is mechanical so it will fail and it can be an abrupt. I replaced it at 100k miles for piece of mind but many on here have gone much further.

Edit: I relocated my SMG hydraulic unit to the drug bin so the job was super easy.

[Stepstools]

Totally agree with the above responses. A new motor wont make your shifts any quicker or give any kind of performance related benefits. However, replacing an ageing motor can fix some particular SMG issues that can seriously detract from drive-ability. My issue was that factors like ambient temperatures above 70, sitting in traffic, or hard acceleration would sometimes trigger the cog light and force my transmission into neutral. I believe that the code I got (see original post) was triggered because the pump was either not able to prime quick enough to keep up with rapid shifting or just exceeded some kind of ECU limit for how long a prime cycle should take.

As oceansize said it is possible for a motor to fail abruptly, but I think most people's motors just wear out and weaken over time, eventually leading to cog lights and missed shifts. This isn't a performance upgrade by any means, just a fix for a key drive-ability issue that many SMG cars face later in their lives. I would not recommend replacement unless you've started seeing issues that indicate the motor is wearing out. Also as oceansize said, replacing a 100k+ mile motor for peace of mind when the pump is already out is a wise consideration.

[Distinct]

Aged dying motors can have much longer "on time" and after a while, it's just basically always running to build the pressure back up to maximum. My old pump was like this.

[cmstrilchuk]

Hey Stepstools,
Did you replace with a new oem unit?
I recall from M3F days there was a company rebuilding, or selling parts to rebuild the motors......something about the motor getting loaded up with carbon brush debris or something, and the recharge time dropping off.
I swapped out the whole SMG unit (used) some years ago due to faulty accumulator. I've wondered if I should crack open the old motor and maybe clean it up inside as a spare.

[oceansize]

Every individual wear item is replaceable at this point. Motor, pump seals, accumulator, o-rings, solenoids, and sensors all can be individually bought and replaced. However, BMW doesn't sell the motor separately so you would have to buy a motor from a third party like Burkhart. As far as fixing the old motor, from everything I've seen it seems like getting into the motor is a real PITA but I'm sure it is doable and couldn't hurt.

[Stepstools]

Hey Stepstools,
Did you replace with a new oem unit?
I recall from M3F days there was a company rebuilding, or selling parts to rebuild the motors......something about the motor getting loaded up with carbon brush debris or something, and the recharge time dropping off.
I swapped out the whole SMG unit (used) some years ago due to faulty accumulator. I've wondered if I should crack open the old motor and maybe clean it up inside as a spare.

I got my new one from SMG society. Was cheaper than the burkhart one, but I think the fit isn't quite as good. They hand grind the metal rectangular bit that fits into the pump and the body of the motor doesn't seat into the pump without tightening down the screws. Zero affect on the performance of the unit from what I can tell. I was considering taking the old one out, getting it refurbished by a local shop, and then putting it back in. It wouldn't have been much cheaper and would have just been a big hassle. I'm considering opening up my old one just to see what it looked like inside.

[Good]

I got my new one from SMG society. Was cheaper than the burkhart one, but I think the fit isn't quite as good. They hand grind the metal rectangular bit that fits into the pump and the body of the motor doesn't seat into the pump without tightening down the screws. Zero affect on the performance of the unit from what I can tell. I was considering taking the old one out, getting it refurbished by a local shop, and then putting it back in. It wouldn't have been much cheaper and would have just been a big hassle. I'm considering opening up my old one just to see what it looked like inside.

Burkhart's motor is underpowered and uses the incorrect bearing size but includes a sleeve for the bearing to fit the slot. MLReng offers a motor which uses the correct size bearing and matches the stock motors power specifications. The problem with replacing the motor is more than likely your SMG hydraulic unit may have internal leaking causing the motor to activate more often wearing out the motor. I would recommend either purchasing a refurbished unit from MLReng, or rebuilding the unit yourself with new seals. The gearshaft seals on my SMG pump were the worst.

[oceansize]

Burkhart's motor is underpowered...

Hey Good. First I'm hearing of this. How did you come to that conclusion? Plus one for mlreng as I'm currently running their motor but haven't been for long so didn't want to recommend it just yet. I have a burkhart, oe, and the currently installed mlreng.

[JokerElite]

An interesting test. I wonder if the OEM pump motor produced the same numbers when it was new.

I replaced my motor with Burkhart's almost 3 years ago and it's still running great!

[Good]

Hey Good. First I'm hearing of this. How did you come to that conclusion? Plus one for mlreng as I'm currently running their motor but haven't been for long so didn't want to recommend it just yet. I have a burkhart, oe, and the currently installed mlreng.

There was a thread on M3F that specified Burkhart's motor specs as well as BMW's OE motor specs and the Burkhart motor was only 2/3rds of the power of BMW's motor. If you look at your Burkhart motor you'll notice the bearing is undersized with a sleeve around it to allow the bearing to fit snug into the hydraulic unit's block. Robert at Mlreng has the exact specifications of the stock motor.

[oceansize]

There was a thread on M3F that specified Burkhart's motor specs as well as BMW's OE motor specs and the Burkhart motor was only 2/3rds of the power of BMW's motor. If you look at your Burkhart motor you'll notice the bearing is undersized with a sleeve around it to allow the bearing to fit snug into the hydraulic unit's block. Robert at Mlreng has the exact specifications of the stock motor.

Will check out the burkhart. I refurbished my original pump with parts/seals/motor from burkhart and ran it for a few weeks to make sure it was good and then ordered a complete refurbished unit from mlreng (I wanted a backup). I'm running the mlreng unit now. Robert is a great guy and super responsive to emails. I had one issue from mlreng (that he rectified very fast) and it was the o-rings inside the housing where the collet sits. One of them failed and was allowing air into the system, I guess due to age as I don't think he replaces those as a matter of course, but he sent new ones without any fuss.

[Stepstools]

Burkhart's motor is underpowered and uses the incorrect bearing size but includes a sleeve for the bearing to fit the slot. MLReng offers a motor which uses the correct size bearing and matches the stock motors power specifications. The problem with replacing the motor is more than likely your SMG hydraulic unit may have internal leaking causing the motor to activate more often wearing out the motor. I would recommend either purchasing a refurbished unit from MLReng, or rebuilding the unit yourself with new seals. The gearshaft seals on my SMG pump were the worst.

Thanks for the info, didn't even know about MLReng. Looks like their motor is cheaper than the one I got too. Overall their prices seem really good, wish I had known about them sooner! I would love to see some people with the MLReng motor and the Burkhart motor do the same test that I did and share the data.

I'm sure my seals are starting to go from age, but honestly my pump is working great right now with the new motor installed. My accumulator preload pressure is getting near the bottom of the allowable range, so I'll probably rebuild the whole unit when it's time to replace the accumulator. Hopefully in a few years I'll actually have a garage to work in.

Speaking of the accumulator, does anyone know if it's possible to have that refurbished and refilled? I haven't heard of anyone doing it, but I'm willing to bet there's a hydraulics shop somewhere out there that would do it.