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  #1  
Old 09-15-2016, 05:48 PM
adamdrives adamdrives is offline
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Question m46 vs ZF

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.
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Old 09-16-2016, 10:25 AM
ngoma ngoma is offline
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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.
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  #3  
Old 09-16-2016, 04:37 PM
adamdrives adamdrives is offline
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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.
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Old 09-16-2016, 05:07 PM
Goteborg Vapenfabrik Goteborg Vapenfabrik is offline
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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.
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Old 09-16-2016, 05:36 PM
adamdrives adamdrives is offline
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I believe mine may have been swapped as well, as apparently it has the automatic throttle spool. I plan to drain and refill.
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Old 09-16-2016, 10:15 PM
adamdrives adamdrives is offline
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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.
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  #7  
Old 09-17-2016, 12:04 PM
RedArrow RedArrow is offline
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Default Transmission fluid in m46 manual transmission of the d24t 740

I'm sorry for this off topic question guys.
I have the m46 laycock pushbutton `5speed` in the 740 and I experience similar abnormalities:

1.
sometimes (not always) it is hard(-er than normal) to move shifter into 1st gear. I usually just move it down to 2nd gear then back to 1. Double clutch helps too, I guess.

It did not happen suddenly, it is something that has always been there and not developing into getting worse.

2.
getting into reverse, I can hear a squeak (squeek?) like clutch wasn't good, but it is. Not always but like 1/3 of the time. It is not something that came suddenly either, it was always like that since almost five yrs ago when I got the car.

I was wondering if this can be caused by having lower than suggested level of tranny fluid?
I DO NOT have any tranny leaks at the m46. I will try adjusting and/or lubricating the clutch cable I think. I should have done it much earlier but I learnt to live with this problem. Otherwise the tranny has NO issues in any gear, no leaks, no sounds, no knocks whatsoever.
I`m 100 percent sure that my clutch is ok and I never abuse the car at all.

3.
About the m46 fluid itself.
Is it suggested to bother with it every `x` years; or is it better not to try fixing something that operates okay.
IF I realize that a small amount of fluid is needed, then Is it suggested to simply top it up ONLY,
or is it highly suggested to flush AND fully replace?

People say different things here. Especially those who don't own (or never owned rwd Volvos).

4.
What is the exact product to use when/if m46 transmission fluid top-up / replacement is needed?

Please share your idea about it. It is best to hear it all from the diesel Volvo and volvo people who know it the most.


Thanks for sharing your opinions on this matter.
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  #8  
Old 09-17-2016, 01:51 PM
Goteborg Vapenfabrik Goteborg Vapenfabrik is offline
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I have an M47 in a 240 that exhibits similar behavior in first and second occasionally, seems the car must nearly be at a stop to down shift into first, going into second then first really seems to help. The transmission has been this way for 150,000 miles and isn't getting any worse. Otherwise it functions perfectly. I have always kept it over filled, nearly two quarts. I am using Amsoil 5w-30 manual transmission lubricant. The M46 in the 740TD wants to grind every now and then going into reverse, something I associate with a worn clutch due to long spin down time. No issues downshifting into first or from first to second. This M46 has Redline manual transmission lubricant installed. I wouldn't hesitate to drain and refill an M47 or M46 with a synthetic manual transmission lubricant.
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  #9  
Old 09-17-2016, 06:39 PM
adamdrives adamdrives is offline
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Can anyone confirm their speed in 4th gear at 2000 or 3000 rpm? My rear axle has no markings on it and I'd like to confirm it is incorrect reduction before I refurbish the spare or spring for a new (used).
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  #10  
Old 09-17-2016, 06:42 PM
adamdrives adamdrives is offline
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Can anyone confirm their speed in 4th gear at 2000 or 3000 rpm? My rear axle has no markings on it and I'd like to confirm it is incorrect reduction before I refurbish the spare or spring for a new (used).

While look at the rear for any stickers or markings I noticed the PO hadn't tightened the bolt for the upper torque bushing. Also, one bolt on the driveshaft to axle was loose, another two were only barely snug
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