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Automatic transmission options for a 65 Dart
https://slantsix.org/forum/viewtopic.php?t=46556		 Page 1 of 1
Author:  ppsi [ Wed Oct 05, 2011 6:20 pm ]
Post subject:  Automatic transmission options for a 65 Dart
My 65 Dart has a super six, 8 1/4 rear and a 1976 block with the original transmission. It really revs high at highway speed and I'm wondering if there is a good option for a trans upgrade/change. I have another 904 laying around but it is out of a 72 duster so I will have linkage issues but I expect just about anything I do will mean doing away with the cable shift anyway.
Any input is welcome and appreciated. I am putting together a wish lilst to make a restomod for this car. I've already done disk/15" wheels and a load of other stuff but it was done 10 years ago and I want to do a lot over again and give it to my son next year for graduation.
I plan on a complete instrument cluster upgrade and interior work plus smooth out a lot of the exterior lines.
Thanks
Howard
Author:  Charrlie_S [ Thu Oct 06, 2011 5:03 am ]
Post subject: 
Is an auto a requirement, or is a manual a consideration?
Auto" Adapt in an "A500" trans, which does require cutting and welding floor and cross member, and finding a adapter plate.
Quicktime is making a modular bell housing for the slant, and might have the piece that goes with it, to adapt one of the small GM 4 speed auto od transmissions (they were talking about doing this).
Also a separet planitary gear box (Ger Venders) mounted on the rear of the later 904.
Do a search on the site. There has been a lot of discussion.
Easiest way: put on taller tires.
Author:  ppsi [ Wed Oct 12, 2011 4:06 pm ]
Post subject: 
Thanks- I already have put 15" wheels/tires on this Dart and they come very close to rubbing now. If I go any taller they will rub and not give me any better high speed rpm to speak of.
Author:  SlantSixDan [ Wed Oct 12, 2011 4:09 pm ]
Post subject: 
Wait, whoah. Before we start talking about sheetmetal surgery to fit (even) bigger tires or undercar modifications to hack in a different type of transmission, let's see if we can figure out what's causing the problem you're experiencing. What do you mean, exactly, by "really revs high" and "highway speeds"? What is the gear ratio in your 8¼" rear axle, and what size tire are you running? With that info we can calculate what the engine RPMs should be, and from there we can narrow in on the problem.
Author:  ppsi [ Fri Oct 14, 2011 5:22 am ]
Post subject: 
Ok-I should have included details. The rear ratio I honestly don't know but it is my understanding that the 8 1/4 peg leg only came with 2ratios-both being in the low 300's. If I had to take a stab I would say a 3.23? The tires are 225/70/15. The car has the original cable shift 904 and there are 65k miles on the transmission. Prior to putting in the 8-1/4" rear it had a 7-3/4 sure grip and I was hoping the new rear &tires would lower the hwy. RPM but that is not the case. I think I measured the RPM at 60 mph at 3600 but even if I'm off on this I can say that my auditory tachometer senses an RPM that would make a trip of 100 miles hard on my anxiety.level
Author:  wjajr [ Fri Oct 14, 2011 7:16 am ]
Post subject: 
Something is fishy here. Using your info, and this gismo, I get a rear end ratio of 4.89 assuming tire diameter is 27.4 inches ( I looked up BF Goodrich 225/70/15 to use as typical dia for that size tire).

By the way, tire used for this example provides 758 revolutions per mile.

Is your tachometer on four cylinder setting? If so, I think six cylinder reading would be .66 of 3600 = 2399 rpm. This info run through calculator yields rear axel ratio of 3.26:1 which is real close to factory ratio of 3.21:1.

My 2 cents
Bill
Author:  SlantSixDan [ Fri Oct 14, 2011 10:08 am ]
Post subject: 
Quote:
Ok-I should have included details. The rear ratio I honestly don't know but it is my understanding that the 8 1/4 peg leg only came with 2ratios-both being in the low 300's.
Not correct. Available ratios included 2.47, 2.71, 2.94, 3.21, 3.54, 3.91…
Quote:
If I had to take a stab I would say a 3.23?
Don't take a stab. Find out for sure! Do it this way.
Quote:
The tires are 225/70/15.
That's a big 27.4" diameter.

Your engine RPM at 60 mph with these tires would be as follows per axle ratio:

With 2.47: 1818 rpm
With 2.71: 1995 rpm
With 2.94: 2164 rpm
With 3.21: 2363 rpm
With 3.54: 2605 rpm
With 3.91: 2878 rpm

All of these are very low engine speeds at highway road speed.

However, if your transmission were to fail to shift into 3rd gear, then your RPM at 60 mph would be:

With 2.47: 2636 rpm
With 2.71: 2893 rpm
With 2.94: 3138 rpm
With 3.21: 3426 rpm
With 3.54: 3777 rpm
With 3.91: 4173 rpm

So my guess is you need some transmission repair. Could be as simple as a shift cable adjustment (shifter in "D", transmission control valve actually in "2"). Another possibility would be a (badly!) slipping torque converter, but I think you'd be reporting nonexistent acceleration, too, if that were the case.
Author:  olafla [ Fri Oct 14, 2011 3:52 pm ]
Post subject: 
Quote:
Don't take a stab. Find out for sure! Do it this way.
That is also a great way to find out for sure if you have a sure-grip differential, because then the wheel will not turn, or only turn with extreme effort.

Olaf.
Author:  ppsi [ Sat Oct 15, 2011 1:34 pm ]
Post subject: 
Thanks Dan. 3.21 sounds familiar but I will check. I can feel the transmission shift through 3 gears so I will need to look at the whole thing thoroughly and perhaps have a transmission shop take a look
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