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| 727 vs 904 https://www.slantsix.org/forum/viewtopic.php?t=37794 |
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| Author: | Dave95693 [ Wed Nov 04, 2009 10:47 am ] |
| Post subject: | 727 vs 904 |
I have an opportunity to pick up 2 slant 6 727 auto trannies for cheap. Is there any advantage of a 727 over the 904? |
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| Author: | Reed [ Wed Nov 04, 2009 11:21 am ] |
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Durability and strength. But you really need to ask yourself if it is necessary and worth it. 727s are physically much heavier than a 904, and also take more horsepower to turn. I have read estimates (online, so I don;t know if it is true) that a 727 takes over 20 more horsepower to turn than a 904. Unless you are driving a very heavy vehicle or do a LOT of towing, I would recommend using the 904. Plus, I don't think the slant six 727 ever got a lockup torque converter, which is a negative as far as fuel economy goes. Of course, some people think that the 727 is the end-all be-all of Mopar transmissions, so you might get bragging rights in certain circles. |
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| Author: | olafla [ Thu Nov 12, 2009 9:42 pm ] |
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I have a spare /6 with a 727 that came out of a van, and the 727 is much heavier and bigger. I also think I read somewhere that the van/truck 727's came with different gear ratios than the model for cars, with a very low 1.st gear. I cannot remember that I have seen reference to /6&727 been used in cars at all, but I could be wrong! 904 is plenty strong, they used it in the late Duster 360's with no problems, and I understand that many racers use it because of lower rotating mass, and as Reed pointed out; a lot less internal friction. If you use the 727, you should also check that they are the same length as the 904, van/truck trannies can have a different tailhouse. Olaf. |
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| Author: | Reed [ Thu Nov 12, 2009 10:09 pm ] |
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Last week I swapped the 727 in my brother's van for a 904. Different length driveshaft. The 904 weighs MUCH less and there was a very noticeable improvement in the performance of the van. Acceleration was much better and I fully expect fuel economy to increase as well. |
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| Author: | olafla [ Fri Nov 13, 2009 11:48 am ] |
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Hi Reed. Was I right about different gear ratios? I have a /6 from '75/76 with forged crank block/late head combo that I'm planning to squeese to the max, but I'm unsure about the 727 that was bolted to it . I have a 904 from an Aspen I can use. I also dream about winning the lottery and bying me a Gear Vendors overdrive to have a 6-speed auto... |
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| Author: | Reed [ Fri Nov 13, 2009 12:26 pm ] |
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I don't believe the 727s had different gear ratios than the 904s, but I may be wrong. I do know that starting in the early 80s Chrysler introduced the A904T. 904Ts DO have a different first and second gear ratio form the older 904s and 727s. The 904Ts have numerically higher ratios to allow big heavy cars to get moving easier. A cheaper and probably easier alternative to the gearvendors unit would be to get an A500 non electornically controlled transmission and one of the A100 adapter plates that lets you mount a v-8 transmission to a slant six. You get the better gear ratios of the 904T AND an overdrive fourth gear. This would be a slick setup for a truck or van. |
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| Author: | SlantSixDan [ Fri Nov 13, 2009 12:32 pm ] |
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Quote: I also think I read somewhere that the van/truck 727's came with different gear ratios than the model for cars
Nope.1st: 2.45 2nd: 1.45 3rd: 1.00 I think you're thinking of the '81+ A904/A998 with wide-ratio gears (2.74/1.54/1.00). Quote: a lot less internal friction
I have a hard time imagining how/why this would be so.
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| Author: | Reed [ Fri Nov 13, 2009 1:12 pm ] |
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I don't think it is friction. The 727 has more and heavier internal moving parts. What it has more of is inertia. It takes more power to get the guts spinning and to make them spin faster. More rotating mass = more force required to get and keep that mass moving. |
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| Author: | SlantSixDan [ Fri Nov 13, 2009 1:35 pm ] |
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Quote: I don't think it is friction. The 727 has more and heavier internal moving parts. What it has more of is inertia.
That makes sense.
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| Author: | olafla [ Fri Nov 13, 2009 4:54 pm ] |
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Sorry, I always mix up sense and nonsense... The Gear Vendors unit has the advantage that it is easy to move it to another transmission if you want to, as the main gear unit is the same, only the adapters, mounts and yokes are different. It has a hefty price, but is virtually indestructible. The makers claim that ten year old units are sold for 1 - 1,5k$ on eBay. Back to talking sense, I guess I'll stick to my Aspen Wagon with its 904 as long as it drives anyway, we've kind of grown together - that is unless someone suddenly dumps a '62 Lancer Wagon in my lap... |
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| Author: | Reed [ Fri Nov 13, 2009 5:02 pm ] |
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You know, I once owned an 84 Ford van that had a gear vendors unit on the back of a C-6. I was underwhelmed after hearing about how great the gearvendors was and seeing the price tag. THe overdrive wasn't that great. It only dropped highway RPMs by about 500 RPM. Compare that to the Ford AOD transmission that is in my 89 Ford van which drops the highway RPMS about 1000 RPM. I NEVER used the under drive feature, and wouldn't unless I was pulling a house or something. Personally, I think gearvendors units might have been a good idea back before the advent of Fords AOD and Mopars A500 and A518, but I wouldn't spend my money on one now. If I want an overdrive on my transmission, I will just go out and get the factory parts to have one. It is much cheaper than gearvendors and installation would probably be easier or on par. By the way, I ended up selling the van with the gearvendors. I like the stock C-6 in my current 84 and the AOD in my 89 better than the gearvendors unit. |
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| Author: | Dave95693 [ Mon Nov 16, 2009 7:10 am ] |
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Gentlemen, as always you have been most helpful. My hat is off to all of you. You saved me some money and effort and I really appreciate that. Have an excellent week. |
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