1991 300sl...first gear start
 

Any one know if it is possible to get it to start in first gear WITHOUT putting the shift lever in "2" once the vehicle has stopped?? Thanks, Dan

www.bergwerks.com

Sixto
95 S420
87 300SDL

I put a clone of this in my car, and I really like it. My opinion, this is the best $ value improvement in performance (not HP, but "feel") that you can get. It will, however, hurt gas mileage a bit. I can't say if this is because of the first gear start or that I enjoy going fast more with it, and my foot gets "heavier". I can easily turn mine off - but because I drive only in dry warmish weather, I never do.

I asked them about this and they replied to me that it wasn't for the 6 cyl. Too bad because the 1st gear start would really help the car.

More info on the 'clone' ???
Thank you in advance

I imagine you have a 722.4XX transmission. Bergwerks has a page on their site for a valve body modification. Unfortunately, I've waited a long time for this page to be completed.

I do believe that the change is a simple mod to the valve body. Maybe as simple as moving one spring. I've never been able to find the details.

I did run across a place on the net that does this mod. I don't remember who it was but it was unreasonably expensive, about $200-$300 if you sent your valve body in for the simple mod.

Please keep us posted on your progress.

I looked at Bergwerks' website, and figured out what their first gear start was doing - basically, looking at the speedometer pulses and energizing/deeneergizing the transmission solenoid depending on the speed (this is what you do when you go to "B" on the shifter). I thought it would be neat to build one similar in function to it, so I did. Slightly tricky aspects are cleaning up the speedometer pulses (the voltage is not computer compatible) and designing a switch that can handle the solenoid current, about an amp (I was conservative, and I used a relay). I considered making a "production" unit (I actually did this, using a more common and less expensive processor) and selling it but I think that there are too many liability factors for me to want to get involved with it. The Bergwerks unit is fairly priced, considering what it does.

I know the basics ...All I want to figure out is what kind of decoder I can use to tranfer pulses/frequency to voltage so I can control the kickdown solenoid.
I do not mind buying the 1st start kit from Bergwerks,It's just the electronics is my hobby and I'll enjoy doing it myself.

With due respect to the Bergwerks folks, the thing to consider is offering it as a kit and/or for off-road use only. You probably don't expect to retire off this idea so there's no profit motive. It's water under the bridge now that you've documented your concern but the key thing most folks can't figure out for themselves is the speed trigger. Someone with your knowledge and skills might offer a settable speed trigger circuit to lock the doors, turn on DRLs, turn up stereo volume or something innocuous like that. That it can be used to disengage the kickdown or first gear start solenoid is a curious side-effect. Imagine that :)

Sixto
95 S420
87 300SDL

Strife?...Did you use an LM2907?

The 2907 is a frequency to voltage converter IC that will turn-on an output when the input signal meets or exceeds a threshold which you configure with a resistor and capacitor combination. Look here. If you download the datasheet, you will see that it is fairly simple and has many automotive applications.

I have a master's degree in electrical engineering but have remarkably little knowledge of electronics. But this hasn't stopped me form thinking of building my own circuit to give me first gear starts like the Bergwerks. Besides using the LM2907 I considered inputing the speed signal into a counter IC and having an oscillator reset the count periodically -- say for example, every second. This circuit would to some degree of accuracy be taking a measurement of the vehicle speed and outputing it as a binary-coded value for simple, easy processing.

By the way, in my initial experiments I find it is really easy to tap into the speed signal on an R129 at the Combination Module at the back of the fuse box. The signal is on pin #5 of the module's 6-pin connector, and it was really simple to just shove a wire into the rear of the connector and make contact with #5.

Actually, I have a degree in English !

The use of a F/V converter is an interesting idea, but the frequency you get from the pulses is rather low at low speeds, and I think that the accuracy of the F/V conversion will not be good. I used a Ubicom microprocessor, roughly equivalent to the PIC I'm fairly sure that Bergwerks uses. I simply count the number of "downward" pulse transitions withing a given window of time, that roughly translated to MPH. Using a micro allows for features and capabilities that you can't get from analog or discrete digital logic circuitry, like in-field modification via firmware upgrades, etc.

Although I did write code that emulates the Bergwerks, with upshift/downshift speeds (which are apparently settable into the PIC's EEPROM in the Bergwerks unit), the algorithm that worked very well for me and my driving style (not crazy) was quite simplistic:

loop
Detect no pulses for X seconds: arm but do not engage solenoid (x may have been a second or so)
If Detect a pulse and is armed:
engage solenoid immediately.
Wait 0.7 seconds here, then disengage solenoid and disarm
end if
endloop

So, I don't really START in first gear, but the engagement happens very quickly and probably reduces the tire spinning potential (you get rolling just a bit first, maybe 1/20 of a tire circumference). This algorithm is also somewhat foolproof - I was conservative because I didn't know what the long term effect on the tranny would be. I've driven about 6000 miles (mostly urban driving) with no problems.

Changing a valve body (722.3 and 722.4) from second gear start to first gear start is just a matter of spring location.

Insert the spring before the "governer pressure boost valve" and the trans will start off in first gear.

Install the valve before the spring and the trans will start off in second gear.

Hope this helps.

David

Thanks.

Does that "governer pressure boost valve" simply come out of the side of the valve body like it looks in the photo? Appears that it could be done without even removing the valve body, if so.

You will have to remove the valve body in order to remove the retainer pin (from the top). Then the valve can be removed from the side.

It wouldn't hurt to have a set of valve body gaskets on hand if you plan on doing this.


David

I'm hesitant to just relocate the spring in the valve block. Someone else posted the diagram that David shows here in another thread and Stummala -- he modifies valve blocks for 1st gear starts -- commented that "[the] diagram doesn't mention any modification to the check balls, nor enlarging the bore on one of the passages, etc. So while just relocating the spring may work, that comment makes me wonder if further modification that ought to be done.

I have a question. Does anyone know the reason why the electronic method used by Bergwerks and Strife of pulsing the kickdown switch can't be used with the 5-speed automatic?