Feel like an idiot but, do I have a three speed 722.1?

[Phil_F_NM]

I've owned my '78 300D since the last week in August and have been steadily working on the car every weekend and on weekdays that i have the free time to do so.

Anyway, I have no problem doing 70mph on the freeway but I don't really like to, even in gasser cars. I'm a 55mph kind of guy, and I love stretching the limits of fuel efficiency just because I can. So last night I was talking with a friend of mine (a forum member here) about gear ratios and I figured that I have a 3 speed automatic. I know the car starts off in second but if I am at a dead stop and floor it, it will accellerate in first, second and third but there is no shift up past about 45mph if I'm doing a hard accelleration. Under normal driving, it can shift into third below 40mph if I'm really being easy on the pedal.

The tranny was just serviced by a local (Albuquerque, NM) indy who has been working on MB's for decades and is very trusted according to the MB owners here I've asked. Indy said that the only issue is the torque converter seal is leaking but otherwise the tranny is good to go. I'm assuming that if I had a 4 speed and one of the gears was completely missing, they would have told me.

I don't have a problem with a 3 speed automatic but I'm taking a 1400 mile drive in a week and I'm wanting to make absolutely sure that the car is good to go. It's going to be a great drive up to Vancouver, Washington where I'm moving.

So, considering all this, would it be probable that I have a 3 speed 722.1?

EDIT: Can I get a mod to change the thread title to reflect the proper tranny designation, "722.1"? I hit the wrong key.

Thanks all!
Phil Forrest

[kerry]

I'd say the probability is approaching zero. Have you manually shifted into first then gone up thru the gears? I'm guessing your kickdown switch is bad.

[Phil_F_NM]

Kickdown switch under the pedal works great. I've also manually shifted into 1st then shifted into drive. In a nutshell, the last shift I get is well before 55mph.

I have a parts and technical breakdown for the 722.1 and it appears the 3 speed does in fact exist. (I titled the thread wrong with the wrong tranny designation. Hit the wrong key and just went on typing.)

Phil Forrest

[kerry]

The 4 spd shifts into 4th well before 55 mph typically. I say approaching zero because I've been on this forum for 10 yrs and never heard of a 3 spd auto in a 123 diesel. It's far more likely that you are either missing first gear for some reason. (can you tell the difference between the gear it usually starts in and the gear it starts in when you shift it into 1st?--the difference should be substantial) or you are getting stacked shifts and it's doing 3rd and 4th together.

[Phil_F_NM]

I never shift it into 1st manually because I simply don't need that gear. I'll use S on the rural roads around here with speed limits below 40mph. When I shift into D, I have one more gear available to me. So maybe it's the case that I simply don't notice the lowest gear due to the transmission actually working like it should and starting off in 2nd.

I don't think I'm getting stacked shifts from 2-3 or 3-4 because the accelleration is good. So it could just be the case that I have a shorter ring gear and the engine feels like it starts to wind out at 70mph? I still have power to go faster but I don't want to push it since this is my only car and I just need it to work. 60mph for my personal top speed getting 30mpg is perfectly fine for me.

I'm usually pretty gentle on the pedal so this could definitely be the case. If I wanted a car that was fast off the line, I wouldn't have bought a diesel!

Phil Forrest

[kerry]

Originally Posted by Phil_F_NM

I never shift it into 1st manually because I simply don't need that gear.D

Phil Forrest

Well, at this point I'd say you don't know if you've started in 1st gear. Start out in drive and go for 30 yds. Come to a stop and put it in L or 1st gear and start again. You should feel a substantial difference in the gearing. 70mph will seem like a lot of rpm's in an NA 617 even with a 4 spd.
The way the 4 spd was designed to function on the early NA 617's was that it never shifts into 1st or starts in 1st unless specifically commanded to. It was designed to be commanded either by the kickdown switch or the shift selector. The way the selector works is that if at a stop you shift it into L and then back to D without moving the car, it should start in L and go up thru 4 gears.

[Phil_F_NM]

Originally Posted by kerry

The way the selector works is that if at a stop you shift it into L and then back to D without moving the car, it should start in L and go up thru 4 gears.

Aha! I'll test it out today, thanks!

Phil Forrest

[sleepstar]

that "L" gear should be very noticeable, i mean it seems like that gear is made for towing things at like 5mph. also, my transmission shifts into 4th at like... 25-30mph.

[Phil_F_NM]

I drove out and tested it from a dead stop. Stopping the car, shifting to L then back to D and then accellerating. It went through 3 shifts firmly yet smoothly so it's definitely a 4 speed. I guess I was always mistaking the 2nd gear start for first.

Thanks all for helping me clear that up. Now to figure out my differential ratio so I can estimate my RPM.

Phil Forrest

[vstech]

the car SHOULD start in 1st if you FLOOR IT from a dead stop, and the pedal downshift switch is working. my 79 wagon was like this, VERY quick off the line, but poor speed above 15mph, pulls strong from 15 to 35, then bangs into 3rd from 35 to around 60 IF YOU HOLD THE PEDAL TO THE FLOOR! and it'll drop into 4th hard, and hold 4th until you are scared to go any faster from the noise! the car will literally hit 95 and the motor will sound like it's going to tear itself to bits if you hold much longer.
however, if you are above 50 and you try to floor it, you're in for a LOOOOOOOOOOONG wait for any higher speeds... it's REALLY hard to drive this car with hills on the highway if there is traffic that forces you to slow between 65 and 50 there is just very little power in the car.

[MBeige]

You probably have 2nd gear start. If so, taking off normally will give 2 shifts. 2 to 3, 3 to 4.

If you want to check this, manually shift to L to select 1st, then shift back to D while stepping on the brake the whole time. When you take off now, it should shift 3 times. 1 to 2, 2 to 3 and 3 to 4.

[Govert]

Originally Posted by Phil_F_NM

So it could just be the case that I have a shorter ring gear and the engine feels like it starts to wind out at 70mph? I still have power to go faster but I don't want to push it since this is my only car and I just need it to work. 60mph for my personal top speed getting 30mpg is perfectly fine for me.

The 1978 300D should have a top speed of around 88 mph, on the speedometer it usually is a bit higher. Before the Vmax, it will start to lose power, as the governor starts to take back the rack.

You can check whether the lever of the IP reaches the full-load stop if you press the accelerator (an assistent will come in handy, or use a brick, do this with the engine off). If not, adjust the linkage according to the FSM.

Three-speed automatics were only used on the V8s back in the days.

[Skippy]

Originally Posted by Phil_F_NM

Now to figure out my differential ratio so I can estimate my RPM.

Phil Forrest

For a 5-cylinder NA it should be 3.46:1.

[Phil_F_NM]

Originally Posted by Skippy

For a 5-cylinder NA it should be 3.46:1.

Thanks!

Phil Forrest

[Doktor Bert]

722.1 idles in 2nd speed range at a stop light to reduce the car's tendency to pull against the brakes.

My 722.120 in my 1978 300SD makes an immediate downshift to compound low (1st speed range) the minute I release the brake.

There is a control unit under the passenger';s side kick panel that controls this function via a solenoid on the transmission....