What do you guys think of the lock up trans for a slant? For my 69 Dart gas miser project,I have recently been considering using on of the low gear/lock up trans for better highway economy. WHat do you guys think of these transmissions? Is it a good system,known problems? Or should I avoid it?

1969 Dart 4 door
225 1bb aluminum intakel 1945
Head shaved for a true 9-1 comp
ported stock exhaust manifold
Heated and ram/cool air intake
HEI
7 1/4 with 3.23 open.
195/70/14 tires
Mercedes clutch fan
2 1/4 exhaust

Jared

Well, I did not have any problems with mine... I think it is ok, as long as you are not trying to put big power thru it.

Just my opinion, based on my limited experience with it.

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I have no idea what I am talking about.

Thanks RC. Deff not going big on the power side. I dont think I will see more than 160 with a 1bbl and the mods I suggested above. Maybe a small cam upgrade in the distant future.Plus I plan on being gentle on the drivetrain,trying to get the best economy here,and sticking with the 7 1/4,I dont want to break anything

Jared

You'll gain about 5% highway mileage with the lockup converter. If you use a wide-ratio trans, you can then use a taller (numerically lower) rear axle ratio for additional (and larger) mileage benefits, without spoiling the car's ability to get out of its own way and scoot acceptably quickly when the lights turn green around town. If you are looking for highway mileage, 3.23s are not where it's at; pick 2.76s.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

My 66 Dart "tow car" station wagon has one of these transmissions and it works OK.
These "later" transmissions are set-up to shift real soft and early so it took a bit of shift kit work to get the shifts "firmed-up".

From the factory, the lock-up function happens to early for me (35-40 mph) so getting a stiffer spring for that valve is a good move, I like to get lock-up at 45 to 50 mph. (TransGo TF-TC kit)
DD

Dan-

What kind of RPM drop will I see with the L/U converter? I have been doing some searching and have seen responces from 400-600 rpm. I wonder what my RPM would be with the L/U converter,24 inch tire,and 2.76's at 65?




Jared

400-600 rpm sounds about right when the torque converter locks.

Engine RPM at any given road speed can be calculated:

Tire diameter × π = tire circumference

(63360 ÷ tire circumference) × (rear axle ratio) = engine rpm @ 60 mph in direct gear (that's third gear in an automatic). This number will be accurate for a locked torque converter; it will be a few hundred RPM understated with an unlocked converter.

Multiply either result by 0.83 to get engine RPM @ 50 mph, by 1.17 for 70 mph, by 1.33 for 80 mph, by 1.5 for 90 mph, and by (n ÷ 60) for n mph.

(63360 ÷ tire circumference) × (rear axle ratio) × 1.45 = engine rpm @ 60 mph in 2nd "passing" gear with a regular Torqueflite, or replace 1.45 by 1.54 for a wide-ratio Torqueflite. It's worth doing this calculation; with a near-stock engine and a numerically-high rear axle it's easy (and annoying) to run out of revs at the top of 2nd gear for passing at highway speeds.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for the math formula Dan

In your opinion,if you were after getting the best economy with a 69 Dart daily driver,would you use a L/U trans?

For best economy, a stick will be better, but for an auto, LU will be best. Actually, I think a LU 904 would be better than what I have in my '68 Dart (A500 4spd OD auto) because there's less wt and drag in the 904.

I picked up a bunch of MPG (10% at least) going from non-LU 904 to T5 5spd.

Lou

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Home of Slant6-powered fun machines since 1988

I would love to go with a 5 speed,but its cost that kills me. I can pick up a L/U trans for 50-100 bux,im thinking a 5 speed swap would be close to 1k. Which is twice as much as I spent on the car

LU sounds like the way to go. Parts can add up fast. I bought my '66 Valiant racecar chassis/body for $300 and spent more than that on the road race fuel cell to get it on track...

Lou

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Home of Slant6-powered fun machines since 1988

I know,even after finding "deals" I have almost spent as much as I have paid for the car on carpet,leaf springs,scarebird disc parts etc...But I have also sold un-needed parts from the car for almost 300 bux and still have a few small things I can sell. When all is said and done I hope to have about 1000 into the car on the road.

Doc-

I just saw your reply. By "works OK" what do you mean by that? Anything you are not happy with,besides the early engagement of the L/U function? Does the Transgo / Superior TF-TC kit come with the stiffer spring you are talking about?
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Answer:
I have been into this trans 4 times, working to get it "just right" and to be honest, I will likely be into it again, to get the 2 to 3 shift point a bit higher.
When I first installed it, the shifts were 'total mush' but with knowledge & effort... it shifts pretty good now.

We did have some LU 'shudder' when the lock-up was happening @ 35 mph but the TF-TC kit fixed that. (it now locks at 45 mph)
Yes, the Superior TF-TC kit has the stiffer spring.
Expect to put a shift kit and some work into one of these units.
DD

raPom, I totally agree with Doc, I have a lock-up 904, and it is definitely saving gas, but lock-up is too early.

Take a look at this thread, where bigslant6fan describes the lock-up mechanism for different years. It seems getting a '80->up 904 with lock-up is better.

If you don't want a full shift kit, there is a Superior TF-TC shift correction kit from Oregon Transmission that also does the trick.

If you look past the joy of working on your car, the numbers are always there: How much gas do you get for the price of a transmission and parts?

Olaf.

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Aspenized

Olaf thanks for the link. This has given me much to think about...I might just stick with the stock trans for now,and worry about an upgrade later.