727 Lower Gear Set for street/highway use

[4spdragtop]

Thanks for the math, im running 323 and would like to stick with those.

I ran some numbers as well. Using 2.94 gears, 65MPH @about 2500 RPM as you stated above. Overall gear ratio at start with a 904 trans would be 8.1 which seems to be ok for spinning tires (above 8 is usually ok, so I have read). Overall torque to the road at start would be around 4000 (includes torque converter multiplier at start of 1.8) with an engine torque of 300, reasonably possible on a small block. Should be able to get more. 3.23 gears makes it easier to spin the tires with a 9.0 starting gear ratio, RPM at 65 MPH is 2700. I think its really between 2.94 and 3.23 when using the 904 lower gear set.

 

[abodyjoe]

Any idea where to get the 904 low gear set? Currently rebuilding our 904 and may need a new set of planetaires.

got mine from A&A transmission Low-Gear Sets - A&A Transmissions

 

[4spdragtop]

Thanks, ouch! Them pricey! Are those a direct drop in? No extra machining required ?

got mine from A&A transmission Low-Gear Sets - A&A Transmissions

 

[abodyjoe]

Thanks for the math, im running 323 and would like to stick with those.

i had 3.23 gear, low gear set 904 in our dart last year for our rt 66 trip. my tires are about 25.5" tall. according to the calculator i was turning about 3k at 70mph. for our smokies trip i put 2.76 gears in it. calculator says now it should be about 82mph at 3k. i know it cruises at 75 like nothing now and I'd say at 80mph it feels like it did at 70 before. either way the car could easily cruise across the country. the difference is when it goes over that 3k mark it really starts using gas. the 2.76 is still fun as hell cruising and can boil the tires. i think this year i may go with 2.94 gears. i really like those. calculator says 77mph at 3k. i think they would be a nice all around gear for our car.

 

[abodyjoe]

Thanks, ouch! Them pricey! Are those a direct drop in? No extra machining required ?

yes.

i went that direction because in my area the 999 trans is getting hard to find and i was on a soft deadline. i went with the reinforced set up. figured id be beating on it.

 

[BT67Dart]

A999,s have been hard to find when I looked, but I did spot a few when I was locking at lock up transmissions..... I'll take another look when I'm ready for the trans

 

[junkyardhero]

I ran some numbers as well. Using 2.94 gears, 65MPH @about 2500 RPM as you stated above. Overall gear ratio at start with a 904 trans would be 8.1 which seems to be ok for spinning tires (above 8 is usually ok, so I have read). Overall torque to the road at start would be around 4000 (includes torque converter multiplier at start of 1.8) with an engine torque of 300, reasonably possible on a small block. Should be able to get more. 3.23 gears makes it easier to spin the tires with a 9.0 starting gear ratio, RPM at 65 MPH is 2700. I think its really between 2.94 and 3.23 when using the 904 lower gear set.

because of your application i don't think there's really a "wrong" option here; it just comes down to whether you want to have something that's a little more itchy out of the hole and you're okay with spending that money, or just keeping the 727 and bumping up a gear ratio.

 

[BT67Dart]

I hear you....I like the a999 option....if I can find one...the lower first gear would be more fun for me....

 

[mopowers]

That's the beauty or the 904/998/999 Low gear sets are stock in the 998/999... So 82 &l ater model L & M body cars, Most junk yards as well as most transmission shops should be able to provide what you need...

Diplomat/Gran Fury as well as the Chrysler 5th Avenue models are what your looking for

And for a O/P something you should consider too... No reason to pay big $$$ for a low gear set for a 727, the combo you're planning would be fine with a 998/999

Avoid the L/U models, easily spotted by the input shaft, non Lock up has splines to the end of the shaft

View attachment 1716496148

Didn't the low gear sets only come in the lock-up transmissions?

 

[1WildRT]

Didn't the low gear sets only come in the lock-up transmissions?

Nope...Lock-up convertors prior to using electronic control (which showed up the same time as O/D) was clunky at best... Chrysler had lots of complaints so they dropped it around 84... But even when they were using it, it was spotty... But as long as they were using the super high geared (2.45) axles for fuel economy... they used the low gear sets to help acceleration..

 

[4spdragtop]

Sorry to sidetrack/hijack, im currently in teardown mode of our 67 904 and looks like some hard parts. I have this spare trans #4130972, a lockup I believe. Would this spare trans have the lower gear set?
Thanks
Steve

 

[1WildRT]

Info on the net is all the place, some say all low gear 998/999 are LU, others say not the case...
I worked in a Dodge dealer 82-84, Lock-ups were the absolute bane of the tranny guy...

https://www.moparts.org/Tech/Archive/auto/22.html

 

[mopowers]

Nope...Lock-up convertors prior to using electronic control (which showed up the same time as O/D) was clunky at best... Chrysler had lots of complaints so they dropped it around 84... But even when they were using it, it was spotty... But as long as they were using the super high geared (2.45) axles for fuel economy... they used the low gear sets to help acceleration..

Thanks. I was confused by this thread: How to identify a non lockup A999 transmission with pics!

 

[1WildRT]

Sorry to sidetrack/hijack, im currently in teardown mode of our 67 904 and looks like some hard parts. I have this spare trans #4130972, a lockup I believe. Would this spare trans have the lower gear set?
Thanks
Steve

View attachment 1716496418

View attachment 1716496419

View attachment 1716496420

Nope.... To early..

 

[mopowers]

Info on the net is all the place, some say all low gear 998/999 are LU, others say not the case...
I worked in a Dodge dealer 82-84, Lock-ups were the absolute bane of the tranny guy...

https://www.moparts.org/Tech/Archive/auto/22.html

Thank you. Yeah, there seems to be a lot of conflicting info out there. Too bad there's not an easy way to identify these transmissions without deciphering the pk number or taking them apart.

 

[1WildRT]

Thank you. Yeah, there seems to be a lot of conflicting info out there. Too bad there's not an easy way to identify these transmissions without deciphering the pk number or taking them apart.

Yup... Mopar never made anything easy... Personally I'd probably grab one out of a late 80's Diplomat cop car... They had the 360 (cop motor) so they have the 999 with the HD planetaries & I don't remember any cop cars ever having a L/U trans..

 

[RustyRatRod]

Those low gearsets were made for the heavy and underpowered cars like the 5th Avenues and such. I've seen where some people did not like the low gearsets in A bodys, because it was too much low gear. What I would do is try to find someone with a low gearset transmission and see if you can drive it. That'd be a lot of money and trouble to go to to find out it wasn't for you. Remember, A bodies are light and it doesn't take much to get them moving. Sometimes too much is indeed too much.

 

[71Demon540]

I just put an A&A 2.74 low gear set in a 727 transmission for a customer. 4 pinion billet steel carrier machined for torrington bearings. The new front planetaries machined for torrington bearings actually come as straight cuts. Not cheap.

 

[mderoy340]

I run a LU 84 Diplomat with a low gearset. LU circuit is plugged, Turbo Action 10" tight 3400 convertor slot drive hub, A&A 4.2 lever, billet double seal front band apply, A&A front drum multi spring kit, 1 3/8" kevlar band.
Rest of trans is stock 5 clutches front and 4 rear, 4 steel planetaries. Trans is bullet proof running 11.3 1/4 mile driven 50 miles to the track with a GV/4.10 gear/26" tire/3200 rpm @ 75 mph. The myth that a LU input shaft wont hold is BS in my experience.

 

[BT67Dart]

Those low gearsets were made for the heavy and underpowered cars like the 5th Avenues and such. I've seen where some people did not like the low gearsets in A bodys, because it was too much low gear. What I would do is try to find someone with a low gearset transmission and see if you can drive it. That'd be a lot of money and trouble to go to to find out it wasn't for you. Remember, A bodies are light and it doesn't take much to get them moving. Sometimes too much is indeed too much.

Last car I had was a 68 Barracuda with an 833 OD gearset and 3.55:1 rear gear which gave me a starting gear ratio of 11:1 for the street. It had P235/60R15 tires on the back. With a 340 engine at 460 ft lbs of torque, it would burn the tires in first, second, and start to grab in third. Honestly, the gear ratio was too low for that combination, but it was fun. That's why I am looking for a lower starting gear this time around while trying to keep the highway RPM's somewhat reasonable. The A999 seems like it might work, but they are harder to find and the parts may not be cheap as you say. Might need to talk to my local trans guy and get his input.

I run a LU 84 Diplomat with a low gearset. LU circuit is plugged, Turbo Action 10" tight 3400 convertor slot drive hub, A&A 4.2 lever, billet double seal front band apply, A&A front drum multi spring kit, 1 3/8" kevlar band.
Rest of trans is stock 5 clutches front and 4 rear, 4 steel planetaries. Trans is bullet proof running 11.3 1/4 mile driven 50 miles to the track with a GV/4.10 gear/26" tire/3200 rpm @ 75 mph. The myth that a LU input shaft wont hold is BS in my experience.

That's great you were able to make that work, sounds like it can take a beating.