Optimum gearing ideas

[Jeff Balazs]

Now that I have begun to use my truck on a daily basis I am starting to think about how I might go about optimizing the gearing. My truck has a 54 230 truck engine with a fluid drive 4 speed and a Grand Cherokee 3.55 ratio rear axle. I feel like the 3.55 ratio is a little too tall for the power and gearing I have available at the moment. It is probably fine at freeway speeds but it feels a little tall for most of my stop and go commuting. With the power I have on tap and this final gearing I do not think OD is anything that would be useful.

 

The existing 4 speed ratios are 1st) 6.4    2nd) 3.09    3rd) 1.69    and 4th) 1.0

There is no synchro in 1st and 2nd. Not fond of that on a daily basis.

 

First gear is pretty much useless and I almost always use 2nd gear for takeoff. I could be wrong about this but I feel the combination of the 3.09 2nd gear and the 3.55 final drive ratio is a bit too high for maximum clutch life. At any rate I think something a bit lower would work better. Maybe 3.5 not sure. The truck is heavy at a little over 4000#. An automatic with the right gearing might make it much nicer to drive in the conditions I have to face daily.

 

I am not sure how to proceed with this. If any of you would like to share ideas for a workable solution I would appreciate your thoughts. About all I know is that this sort of conversion would require a bell housing swap and mods to the driveshaft and parking brakes. I removed the parking brake provision from the Grand Cherokee rear axle but that wouldn't be too hard to rebuild.

 

Thanks in advance,

Jeff

 

 

[Don Coatney]

You mentioned clutch wear. With the fluid drive unit I would think there would be minimal to no clutch wear. No need to "ride" the clutch for initial startups from a dead stop. Let the fluid coupling do the slippage work.

[Merle Coggins]

Maybe a T5, or similar, 5 speed trans swap would give you usable gear ratio splits for your application. It would still likely require a bell housing change, as I don't believe it could be made to work with your FD. And if you do find an input shaft that would work with the FD I'd be interested in hearing about it.

 

Merle

[Frank Elder]

Maybe a T5, or similar, 5 speed trans swap would give you usable gear ratio splits for your application. It would still likely require a bell housing change, as I don't believe it could be made to work with your FD. And if you do find an input shaft that would work with the FD I'd be interested in hearing about it.

 

Merle

I know you really like your fluid drive Merle....to me it was a novelty that soon wore thin....it really does help in certain areas but it robs so much power when we have so little to apply in the first place. I pulled mine and replaced it with a standard 3 spd and the difference is amazing...to my feeble mind anyway. But now due to having a bum leg I am considering the 904 option, surely it doesn't leech HP as badly as a FD.

[Jeff Balazs]

Yes I am not really sure how useful the fluid drive really is either. You can use it sometimes but often in stop and go conditions you don't really get the chance. You do have to use the clutch every time you shift and it seems like I often just have time to roll to a stop and then it is time to go again. With no synchro in 2nd the process get a bit busy. If the fluid drive does rob power I could certainly live without the occaisional benefit. It has some other negatives that I could live without too.

 

What I think would be really nice would be to have a 3 or 4 speed automatic with ratios something like 1st) 3.5 /3.3     2nd) 1.9/ 1.8    3rd) 1.4/1.3   and 4th 1.0  I don't know if anything like this could be found that would fit? I don't really have any experience with transmission swaps of this sort but if I go to this much trouble it needs to be very close to perfect.

 

Jeff

[John-T-53]

It's critical to consider the final drive ratio when changing the gearing. These flat six engines need something in the 13:1 range for efficiently taking off from a standing start.

 

When I installed a five speed, I opted to keep the gearing on the "low" side for better performance, but not too low that 1st gear would be useless. I kept the original 4:10 rear end and chose a gear set that would work with that ratio. I have found this to work perfectly with the motor I have and feel it's a good balance on the scale of performance to economy.

 

1st 3.35, 2nd 1.99, 3rd 1.34, 4th 1.00 and 5th 0.72

 

Final drive ratio:

 

1st 13.73, 2nd 8.16, 3rd 5.49, 4th 4.10 and 5th 2.95

 

At 65 mph, the motor is just a little over 2,000 rpm.

[55 Fargo]

It's critical to consider the final drive ratio when changing the gearing. These flat six engines need something in the 13:1 range for efficiently taking off from a standing start.

 

When I installed a five speed, I opted to keep the gearing on the "low" side for better performance, but not too low that 1st gear would be useless. I kept the original 4:10 rear end and chose a gear set that would work with that ratio. I have found this to work perfectly with the motor I have and feel it's a good balance on the scale of performance to economy.

 

1st 3.35, 2nd 1.99, 3rd 1.34, 4th 1.00 and 5th 0.72

 

Final drive ratio:

 

1st 13.73, 2nd 8.16, 3rd 5.49, 4th 4.10 and 5th 2.95

 

At 65 mph, the motor is just a little over 2,000 rpm.

I couldn't agree more John, I have 3.23 gears in my diff, not always optimal, but nice after 45-50 mph.

I have no problem starting off in 2nd gear, and no revving or clutch wearing either, I do find a problem on the highway, when trying for max acceleration to highway speeds. If I am bucking a head wind, and once I shift from 3rd to 4th, it can be doggy until I get to at least 50 mph, which is around 1800 rpm or so.

With your current set-up, if you shift into 5th at 45-50 mph, how is your acceleration and power after that?

When dealing with an approximate 100 hp, for most of us, we need all the help we can get. Even gaining 30 to 40 hp with some engine add-ons would make a difference....good thread Jeff

 

T 98 Acme 4 spd trans

 

1st 6.40

2nd 3.09

3rd 1.68

4th 1.0

 

Final drive with 3.23 gears

 

1st 20.67

2nd 9.98

3rd 5.42

4th 3.23

 

Final Drive 4.10 gears

 

1st 26.24

2nd 12.66

3rd 6.92

4th 4.10

Edited December 7, 2015 by Fargos-Go-Far

[55 Fargo]

Here are the Chrysler A833 4 spd gear spreads,

 

A-833 Transmission Gear Ratios 1st 2nd 3rd 4th 6-cyl (also 64-65 273, 74-75 318) 3.09 1.92 1.40 1.00

Fine-spline V8 (most pre-1971) 2.66 1.91 1.39 1.00 Coarse-spline V8 (1966-70) 2.65 1.93 1.39 1.00

Coarse-spline V8 (1971-74) 2.44 1.77 1.34 1.00

Road Race T/A; most 1971-74 fine spline 2.47 1.77 1.34 1.00

Overdrive (mid-1970s and newer) 3.09 1.67 1.00 0.73

 

OD A833 with 4.10 gears

 

1st 12.66

2nd 6.84

3rd 4.10

4th 2.99

The A833 trans would or may likely have a more suitable gear spread in this application..

Edited December 7, 2015 by Fargos-Go-Far

[Jeff Balazs]

Thanks for your input Guy's. There is a lot to consider when making these types of mods. I do know I would like to simply retain the Grand Cherokee rear axle. The 3.55 ratio without an OD transmission should be fine at speed. The more I think about this the more I am convinced that I need to concentrate on finding an automatic with an acceptable set of ratios that will fit in this truck. Not sure what the options are there? Putting another stick in even if it is a modern one is never going to be great in the crap traffic here. Just so we are clear the truck is drive able the way it is.....I just think it could be better.

 

I did look at the 833 trans but lowest 1st is the same as my second is now.....and it feels a little too high with the 3.55 rear. Also I don't know about how it might fit into a truck. If anyone has used one in a truck it would be useful to hear about it.

 

We all know a bit more power would not be an awful thing either. I am considering this as well.

 

Jeff

[jeffsunzeri]

Install a Powerflite.

 

Install a Torqueflite.

 

Or, if you want to break down more often and generally beat yourself up, put a GM automatic in with a trans adapter.

Edited December 7, 2015 by jeffsunzeri

[55 Fargo]

I think if Jeff, seriously wants to go auto trans route, he needs to speak with Gary aka Wayfarer.

This will be a somewhat intensive project, but has been done, and it may give you want you need for your driving environment...

[Jeff Balazs]

I looked a bit at the torqueflite. It doesn't seem to have the sort of ratios I think this truck needs but I could be wrong. Has anyone put one of these mated to a flathead in a truck?

Fred yes ideally I would want an automatic. I am going to have to look very hard at what is involved though. I would have to have some confidence that once I tear into this it can be accomplished over perhaps a long weekend. Right now I would say there are too many tasks involved for this to happen.

 

What I may do is start gathering the bits needed to give this engine a little boost in power first. I think what I want to do is find a 2 bbl manifold, get some headers and shave the head a bit. If I could pick up 15 to 20 HP this way it might just do the trick. As I said the truck is drive able the way it is. The other thing i am wondering about is the lack of synchro in 2nd on the existing transmission. I don't know if this is something that could be modified during a major overhaul on the transmission?

.....but if it could it would make it much nicer in traffic.

 

Jeff

[55 Fargo]

I looked a bit at the torqueflite. It doesn't seem to have the sort of ratios I think this truck needs but I could be wrong. Has anyone put one of these mated to a flathead in a truck?

Fred yes ideally I would want an automatic. I am going to have to look very hard at what is involved though. I would have to have some confidence that once I tear into this it can be accomplished over perhaps a long weekend. Right now I would say there are too many tasks involved for this to happen.

 

What I may do is start gathering the bits needed to give this engine a little boost in power first. I think what I want to do is find a 2 bbl manifold, get some headers and shave the head a bit. If I could pick up 15 to 20 HP this way it might just do the trick. As I said the truck is drive able the way it is. The other thing i am wondering about is the lack of synchro in 2nd on the existing transmission. I don't know if this is something that could be modified during a major overhaul on the transmission?

.....but if it could it would make it much nicer in traffic.

 

Jeff

I do know that Wayfarer stated it is not a simple swap, some fabbing rear trans mount, as you will no longer have th fluid drive/clutch housing, shifter install, driveshaft cut and matched, throttle cable kickdown (Lokar possibly),external trans cooler and lines, starter motor. I am not sure whats involved in bolting the flexplate to the trans crank, possibly comes with trans adapter.

With all of this, and the cost, it has been said a 318/360 might be no more work, and most likely cheaper.

[JBNeal]

The fluid drive was an early attempt at an automatic transmission that was replaced by fully automatic transmissions with integrated park lock pawl that was developed in conjunction with the slant 6 and V8 engines.  The literature I have read about the fluid drive was that some of its benefits were to reduce stress on engines and improve tire wear (harder to initiate wheel spin).  As far as I know, Dodge Truck did not offer an automatic transmission with the flatheads like Dodge Cars did, and it may have been because the flathead/auto combo did not have enough power for truck applications.  I think Merle's 3.73 rear axle ratio is the best setup for modern use as it still falls within the flathead's torque curve for good power delivery.  The 3.55, while good for cruising on the highway, is a little tricky at low speeds, because this setup is right at the edge of the flathead's torque curve, which is why it was never offered from the factory. Powertrain development is a balancing act that employs entire divisions of engineers by manufacturers.  Engine torque curves are established, axle ratios are chosen, and the transmission is designed to fit in between to operate within a set of parameters for shifting (manual or automatic).  You may improve the flathead torque curve by a few percentage points with some engine modifications, but there was a reason Chrysler developed the slant 6 engine family, and it probably was that the flathead's limitations had been reached; any major improvements in power and economy could only be made with a new design.  I think you are approaching the limit to the flathead powertrain you have installed, as any changes you make now will not be a quantum leap in performance.

 

I know how ya need to shift through the gears quickly for fear of some yahoo smoothing ya over from a red light, which amplifies the lack of 2nd gear synchronizer.  The Outback has a 5 speed, and many a time there has been somebody who nearly rams me after a light change when I shift to second and they are still stomped on the gas.  This of course leads the offender to blow by me at their soonest opportunity to hand-signal that I am super #1, to which I exclaim in my Floyd Lawson voice "ohhhhhhh such a nice man"

[Jeff Balazs]

The fluid drive was an early attempt at an automatic transmission that was replaced by fully automatic transmissions with integrated park lock pawl that was developed in conjunction with the slant 6 and V8 engines.  The literature I have read about the fluid drive was that some of its benefits were to reduce stress on engines and improve tire wear (harder to initiate wheel spin).  As far as I know, Dodge Truck did not offer an automatic transmission with the flatheads like Dodge Cars did, and it may have been because the flathead/auto combo did not have enough power for truck applications.  I think Merle's 3.73 rear axle ratio is the best setup for modern use as it still falls within the flathead's torque curve for good power delivery.  The 3.55, while good for cruising on the highway, is a little tricky at low speeds, because this setup is right at the edge of the flathead's torque curve, which is why it was never offered from the factory. Powertrain development is a balancing act that employs entire divisions of engineers by manufacturers.  Engine torque curves are established, axle ratios are chosen, and the transmission is designed to fit in between to operate within a set of parameters for shifting (manual or automatic).  You may improve the flathead torque curve by a few percentage points with some engine modifications, but there was a reason Chrysler developed the slant 6 engine family, and it probably was that the flathead's limitations had been reached; any major improvements in power and economy could only be made with a new design.  I think you are approaching the limit to the flathead powertrain you have installed, as any changes you make now will not be a quantum leap in performance.

 

I know how ya need to shift through the gears quickly for fear of some yahoo smoothing ya over from a red light, which amplifies the lack of 2nd gear synchronizer.  The Outback has a 5 speed, and many a time there has been somebody who nearly rams me after a light change when I shift to second and they are still stomped on the gas.  This of course leads the offender to blow by me at their soonest opportunity to hand-signal that I am super #1, to which I exclaim in my Floyd Lawson voice "ohhhhhhh such a nice man"

FloydLawson.jpg

You are probably correct about this. One thought I have had about this situation is to do what is reasonable to boost the power first. Then if that isn't enough I can always swap the gearing set in the axle to 3.73. Wouldn't be cheap but I could retain the brakes etc....that I already have into it. At least I have a pretty solid 230 T342 in this truck.......the 3.55 might have been way too much for a smaller version of this engine.

 

Jeff

[Plymouthy Adams]

not sure if this will ease your mind but my 54 Plymouth is stock 230 with Powerflite transmission and a 3.73 rear axle..the combination will bark a tire if you wish...first gears runs to 50+ before shifting into high just by holding down the accelerator...for the period of vehicle it is representing, I feel it quite capable car..that speaks volumes as many here think I V power everything...LOL    

[55 Fargo]

A short video just made, this shows the old Fargo accelerating, 4 spd regular clutch 3.23 rear gears.

[John-T-53]

Wilcap makes trans adapters for the flat six, unfortunately only for GM turbo-hydros though: http://www.wilcap.com/chryslerfh.html

 

As suggested by others I would prefer a Torqueflite 727 as well, if going the auto route.

 

"Keep your Mopar all Mopar"

 

I think changing your rear end to a 3:73 would be your easiest move at this point, for better drivability.

[55 Fargo]

Wilcap makes trans adapters for the flat six, unfortunately only for GM turbo-hydros though: http://www.wilcap.com/chryslerfh.html

 

As suggested by others I would prefer a Torqueflite 727 as well, if going the auto route.

 

"Keep your Mopar all Mopar"

 

I think changing your rear end to a 3:73 would be your easiest move at this point, for better drivability.

904 would have less parasitic loss, less HP loss and is shorter and lighter. The 904 is plenty stout enough for a flathead 6 truck...

 

http://www.qualityengineeredcomponents.com/?page_id=616

Edited December 8, 2015 by Fargos-Go-Far

[Jeff Balazs]

So has anyone actually put an automatic into a flathead powered truck? I have looked but have not found any examples other than the Truck-O-Matics.

It definitely looks like a pretty big job.....more than I think I want to get into at this point without more confidence in the outcome..

 

Has anyone put an 833 transmission in a truck? Again have not seen or heard of one.

 

What about mods to the existing 4 speed non spur gear box? Anyone know if it would be possible to have synchro added to 2nd gear. Or do any gearing mods?

In one sense I wouldn't mind throwing some money at this gearbox as there would be no other mods required. It probably could stand to be overhauled and repaired anyway. It is a little noisy in 3rd and the shifter mechanism feels a bit worn.

 

Jeff

[jeffsunzeri]

We've installed at least 2 Powerflites into 39-48 Dodge pickups, and 2 A-833's, all with 218/230/251/265 flatheads. We did these decades ago and unfortunately don't have any photos for DIY'ers, The Powerflite is an easy installation and works quite well, and requires no cooling lines as the later Torqueflites do. The biggest deal is the rear transmission mount, which varies depending on the chassis, otherwise it's pretty straightforward with all factory parts.

The A-833 requires a plate to accommodate the different bellhousing bolt patterns, and fabricating a shifter assembly to work with the cab configuration. Now that adapter plates are being made, this avoids the custom fitups we did 25 years ago (we just did 2 custom plates at the time using borrowed equipment).

The A-833 also requires some modification to a frame crossmember on some chassis, and it also requires that something be done for the emergency/parking brake. Solutions we used were driveline disc brakes and hydraulic valve parking brakes. The A-833 also requires a change in clutch plate to a later spline configuration, but otherwise allows you to keep the flathead starter, bellhousing, and clutch/brake setup. The overdrive 4th and all-syncro made this a great setup. I plan on doing it again for my '47 1/2 ton and probably for the '42 WD-21.

[52b3b Joe]

I have a 3.55 rear end with a strong 230 and a standard 3 speed. After getting some miles put on the truck, I really wish I had a 3.73 ratio. The 3.55 has too slow of acceleration and not much power for a truck where you need it. It is sluggish in the wind and going up grades. The cruising engine speed is nice, but you don't have any power when you need it. I have rode in Merle's truck, and that is the setup to have with the 3.73. Great acceleration and good cruising capitally. 

[Jeff Balazs]

Thanks for your input. Jeff on these conversions you did a while back did you just use the stock ratio rear axle? I kinda think my 3.55 set up would be too tall for the gearing in a Powerflite. The other thing I wonder about is that my truck is a fluid drive.......and I am not certain what all would be involved in making it compatible for a swap. I know the bell housing is different but I am not at all certain what else might have to be changed or modified?

 

One scenerio I was considering is the 833.......just not the OD version. According one source there was an early 6 cylinder version that had gearing that might work OK with my 3.55 final ratio. At least it would give me 4 usable ratios to work with instead of 3. As I recall the ratios of 2nd and 3rd straddle my current 3rd gear ratio.

 

Jeff

[jeffsunzeri]

Stock rear ends in all cases. One one of the PowerFlite installations I recall we had a 3.23 rear end and it cruised real well, but was a dog off the line. Because you could hold it in first or second as long as you want, it was a nice setup. The customer used his truck for farm work and the automatic made getting out of the mud much easier than with the standard 4-speed granny.

 

One of the A-833's was installed with the 4.1:1 rear end and the overdrive gave her an easy 60 MPH cruise and the lower gears worked real well around town.

 

The blessing of the flathead six is it's ability to make power from around 1,000 to 2,000 RPM so it's pretty much impossible to lug it too much. The opposite problem is that it is a horsepower dog. No 2 ways about it. Going from a flat six to a slant six feels like a hop up, and the slant 6 is a pooch which makes the 2 BBL 318 look like a monster!

 

Sometimes livin and drivin in the 40's - 50's has it's good points and bad points.

[Jeff Balazs]

Thanks for the additional info Jeff. And you are so right about the good and bad points. Honestly I am not looking for a speed wagon here. Just want to make it as good to drive as possible. In general I am very happy with this truck. It has taken me a little while to feel comfortable in it......but then I had never even driven one until I put this back on the road. I wasn't at all sure of what to expect from it. Now that It and I are starting to feel settled in I know it is going to do just fine. It has it's little quirks but has been reliable on a daily basis.

 

This gearing thing is just a wish right now. I will probably drive it this way for a while and then maybe see if I can get a few more ponies out of it. Nothing radical but even a 10 HP boost could make a significant difference. It is OK as it is on flat ground or even better than OK downhill.

 

Jeff