m46 vs ZF

[adamdrives]

Anyone not happy with their m46 d24t?. This is the first m46 car i've driven, but the gearing seems very short, especially with the diesels high low end torque and lower rev limit. Under moderate throttle, the car feels like it runs out of gear very quickly. I try to avoid moderate to hard throttle after first starting the car, but is an issue in my hilly area with lots of intersections where I need to merge with traffic. Often times, I shift through the gears in a matter of seconds before reaching OD and coasting at what seems acceptable rpms. Also, it revs very high at cruising highway speeds, higher than l would expect from a diesel. It seems to me like a lot of efficiency and drivability could be gained by having taller gears, especially since the car makes easy power down low. Anyone have similar thoughts? I've heard good things about the ZF transmission, I'm curious how they drive in comparison to the m46.

[ngoma]

M46 1st gear, at 4.03:1, is granny gear low. 4th is 1:1, and OD is a pretty good 0.79:1 OD reduction. The M46 cars came with the 3.31 rearends, the highest (lowest numerical) available. Didn't you say your car has a much lower-geared rearend? That would affect the driveability, making it great for towing at lower speeds but too busy on the highway. Probably don't even have to use 1st, could start out in 2nd. The 3.31 rearend would make it more useable but 1st is still a stump puller. Larger diameter rear tires would also help. The 740s came with 185/70x14, which are maginally sized for these large cars. I had better results running 195/70x14, and more recently 195/65x15 (even better).

The ZF is seemingly better suited to the D24T, strong, with good ratios, logic, and smooth shifting. 1st is 2.48:1, 4th is a healthy 0.73:1 OD, lockup occurs at ~57 mph. It had a known defect that would destroy itself if revved in neutral or park after having been in gear. TSB retrofit solved this problem, otherwise do not rev in neutral or park, or if necessary turn off the engine and restart, then can rev in P or N *before* placing it in gear. There is another common failure mode with the governor in the tailshaft that causes it to hang in 1st gear too long first start off in the morning. I think the ZF cars came with the 3.46 rearend.

I have one of each, and personally prefer the M46, simply because I have always preferred manual over automatic, but would really prefer a real 5-speed over the kludgy OD, and with better ratios. Too bad the M90s are so hard to come by here in the US.

[adamdrives]

Thanks for sharing. The rear end was changed, the PO said it was an identical unit, but my feeling is that it's not. I still have to record rpms and gps speed (since speedo reads too high, which is another clue that it is wrong rear axle) to calculate rear reduction. My research shows that the 3.31 came in the b28s, I didn't realize it was in the d24s as well. Either way, seems like I may be hard to find one. The car came with the original rear end, but the PO said he hit a curb (??) and thought it was bad, I'll have to look into checking that out for damage. I have 195/60s in the back, I don't think it's made much of a difference but that may have close rolling diameter to the 185/70s.

The m46 is also clunky between 1st and second (intermittently) and has a little crunch going into reverse (more often than not). Not sure if this is indicative of wear, or linkages can/need to be adjusted. The PO put a new clutch in, not sure if improper installation could result in car sometimes being hard to put into gear. Clutch grabs nice and high.

[Goteborg Vapenfabrik]

My 740TD left the factory with a ZF, swapped to an M46 by the PO. He left the rear axle in, the ratio is 3.91, factory M46 cars got a 3.55. Swapping in a ZF wouldn't be a picnic, but I have one, along with the brake pedal assembly and swifter, I don't have a cross member for it or the drive shaft. The ZF 4HP22 was used by quite a variety of manufacturers including Jaguar and BMW. Sounds like your M46 has seen better days. I would check the oil level.

[adamdrives]

I believe mine may have been swapped as well, as apparently it has the automatic throttle spool. I plan to drain and refill.

[adamdrives]

Did some quick math using GPS speed and looks like my final drive ratio is close to 4. I actually got 4.3-4.5 but I assume that's some noise in the data. Probably explains why I have to shift from 1st to 4th just to get moving, and why my girlfriend can't stand this car. If anyone is in the tri-state area with a 3.31, please message me.