Automotive differential gears

Putting aside the steering and motor rotation issues, it should work just fine. They all run backwards when we are in reverse.

There a lot of "ifs" in your question. If you are using a similar engine and vehicle weight, you should be fine for the first 150,000 miles. If you are using a higher powered engine, or a heavier vehicle, your differential life may be shorter. The pinion bearings will be under load in the opposite vehicle direction from the factory design. That will leave the smaller pinion bearing under load in forward. I still believe you should be alright though. When the factories put axles in their 4wd trucks, the axles did not get any upgrades. Good luck.

Thanks. You hit on the issue i was interested in, that the pinion bearings would be seeing opposite loads. I'm not looking at big HP, actually looking at building a three wheel front drive electric...

I would contact the manufacturer of the differential, but dont see a problem with the reverse rotation. Its not like the gear teeth are treated on one side 'hardened' to take more pressure say when moving forwards and burning out and a reverse burn out would chew up a softer surface side of the teeth. Kind of confused trying to picture a rear differential used on a front wheel drive 'car' which normally has direct linked axles to the transmission, where as the differential is a part of the transmission assembly. The only 'cars' that had front differentials that could be toyed with between front and rear pumpkins that I am aware of was the 4 wheel drive AMC Eagle. What type of vehicle are you modifying or building?

Back in the 1930's Buckminster Fuller did exactly that: he took a conventional drive train and turned it around so the engine was in the rear of the car with a drive shaft traveling under the 11 seat passenger compartment forward to a live axle, that was flipped upside down.

The car was a "Trike" with only one steering wheel in the back operated by chains and sprockets. The rear wheel could turn 90 degrees and with that, the car would pull nose first into a spot and then the rear would turn in, all in a space just a few feet longer than the car which was 20 feet long and fully streamlined.

I had a chance recently to examine the actual car while on display recently at the Whitney Museum in New York City. Accompanying the machine were Fuller's original pen and ink drawings which show the power train in detail. I continue to view his accomplishments with awe. There is no question in my mind: he was generations ahead of his time. You would do well to get copies of his patent drawings from the US patent office.

BTW: There is no need to reverse the direction of rotation of the ring and pinion set. The act of turning the differential and aiming it towards the back of the car and then flipping it upside down will accomplish your intent. However, if the design is of a hypoid type, which is very likely, the pinion shaft and it's gear will likely be ABOVE the hypoid gear oil. You can't simply overfill the oil level to compensate as it would likely vent.

What puzzles me is why you don't simply use the differential from a front wheel drive car in the first place?

L.J.

Sorry,

"flipping it upside down will accomplish", nothing.

Would you care to explain why not? As a reference, years ago I know of fellows who took VW transaxles and turned them around to use in midengine applications (SCCA Formula Vee). In doing so they had to switch the ring gear to the opposite side of the pinion (which could be done in the older VW transaxles) to reverse the rotation. I believe my intent is the same.

Not to mention all of the SCORE off-road applications in classes 1,2, 4, 5 and 12. All were with reversed transaxles/ veedub gearboxes. Then there was the "2000" modification of the Pinto/German 2.0 litre 4 cyl. Most modifications were made by plugging existing fill and vent orfices and creating new. Any help?

This site used to be a help, but now looks like just a summation. More research required if you are interested.

r/s

re "flipping it upside down will accomplish", ...

This WILL reverse the direction of wheel rotation. (for the same direction of rotation of the drive shaft). So it would achieve the desired result. The comments about iol levels & where the vent in the dif housing is located ARE valid.

i.e. if you turn a diff housing over (upside down) so thet the right wheel is now on the left with the drive shaft still facing forward, you will reverse the direction of drive at the wheels.

It's driven with an electric motor that can turn either way. Why torture yourselves by turning the differential upside down?

I wasn't planning to turn it upside down, that was suggested by one of the respondents. My original question was regarding the effect on the gear set as turning the pinion gear in the opposite direction for the primary drive direction is counter to the general application in a RWD car. This aspect was addressed in the response by GLB yesterday.

"This aspect was addressed in the response by GLB yesterday"

And in my response #1.

Thanks for the feedback. I'll have to look into the Fuller drawings although I am planning on front steering. I agree that i could invert the differential to preserve the rotational direction but was also concerned about the lubrication issue that you mention. As far as using the differential from a front wheel drive car, everyone that I have seen is built intergral with a transmission which I do not need as I am looking at electric motor power.

Put a pipe plug in the original vent and relocate it as desired

Not so fast here:

If your were to examine earlier 4WD powertrains, I'm sure you would find a multiplicity of options. One that comes to immediate mind is the 1962 'Scout which had an independent front suspension option. I sold this little critter to a gold panner in Auburn, California in 1998. I broke the rear axle at the Auburn Airport in the snow storm of 1988. I drove that vehicle on and off road for two years with only the front engaged and the rear drive shaft removed. A bit 'odd' on close right hand turns, but otherwise un-remarkable.

" I'll have to look into the Fuller drawings although I am planning on front steering."

Now that we know that you plan on powering the car with a motor, I'm inclined to discourage the use of anything in the drive train that causes power losses.

Driving and steering through the same wheels will require four constant velocity joints, two per axle.

The friction losses in such devices are not high but they are there. Furthermore, they add some unsprung weight to the suspension which does have an adverse effect on handling, not to mention the extra cost and complexity.

In engineering as in everything else, KISS is the philosophy to keep in mind, especially when attempting to develop something new. Keep the number of variables as low as possible.

Good luck

L.J.

I have a friend that ran one of the larger transmission transmission shops in Ft Lauderdale. One day he called me to stop there after work. It seems he had a customer that had installed a rear end from a rear disc brake Firebird into a V8 Monza. When the transmission was reinstalled, it would not shift, Took out the valve body and went through it again, with the same results. At this point they took a 350 off the shelf, and installed it. Same results. When they went to back it into a spot in the yard, it shifted.

When I got there, we put it on a lift and sure enough, the rear was inverted. Then the shop that had put the rear end in had to tell the owner the cause of the transmission problem.

I do not think that there were any significant differences to the Dana 30, 44, or 60s that were used in front drive service.

GLB wrote: "Shaping the gear faces for a PREDOMINATE direction, allows a greater surface area for the transmission of the applied torque."

Before Detroit was able to lower the floor of the car, they had to lower the drive shaft. Before they could lower the drive shaft, they had to lower the pinion gear on the ring gear and create the "Hypoid" gear set. Before they could do that, the oil companies had to invent a lubricant capable of protecting the gear set from the wiping action common to that environment.

What you wrote GLB, is absolutely correct. However, our host has announced that he wishes to drive the car with an electric motor. That changes things a bit.

It strikes me as being inefficient to be loosing friction horsepower in a hypoid gear set for a feature which is of no benefit to him.

The environment that drove the creation of hypoid gears sets is no longer present. If he wishes to use a differential to turn the power 90 degrees, he'll get better mileage per charge with a spiral bevel gear set, than a hypoid. Given the relative inefficiencies of current battery technology, he'll need every extra foot of distance he can get.

Spiral gears sets are every bit as quiet as hypoids so he won't be giving up anything.

L.J.

Hi L.J.

Yep, there are a large number of alternative gear-set drives out there. Actually, my favorite was an Italian double-involute (essentially two worm gears) that we explored in the mid '70's for driving 60 ft., C-Band communication dishes in a more traditional EL-over-AZ configuration.

The exact design we all seem to be refering to is shown in the below link (needless plug, I worked here in the late '90's/early '00's):

http://www.lektro.com/default.asp

These are various sized electric tugs, depending on the GTW (Gross Take-off Weight) of the aircraft to be towed.

The use of the a standard Dana differential was based on commonly available spare parts. Efficiency studies for these electric vehicles provided no significant gain for alternative gearing schemes WHEN COMPARED TO the availabilty of spare parts in the field, hence, total cost of operation. MTBF and MTTR times were the guiding critera. Maintenance regimes were not shifted from current equipment and (please believe me on this one) one could rebuild a failed unit in a snowstorm at the hangar with standard tool sets. The fact that the customer was dragging a skidded S-280 Shelter across the tarmac and broke half of the ring teeth in the process actually speaks well for the utility of the tug. It was a 'Dr. Phil' moment... ... you had to be there!

r/s

GLB

Remove the axle tubes and rotate the differential 180° then reattach axle tubes.

If you flip the differential 180 degrees (turn it upside down) you will have the design rotation. In a hypoid gear-set, lubrication will be a problem. The easiest solution is to use a 'climbing' lube additive such a 'Lucas'. I have built race cars with reverse rotation engines and we simply flipped over the Ford 9" pumpkin to achieve correct rotation. With the proper additive, the gear-set survived insane HP.

Why not just save all the trouble and use the front differential and axle assembly from a small truck like a chevy blazer 4x4? Or if the electric vehicle is really lightweight use one out of an ATV - KZ, Honda, Yamaha etc. all make 4x4 atv's with front drive assemlies and independent front suspension.

TURN IT UPSIDE DOWN!!!!!!!!!!!!!!!!!!!!!!!!!! WORKS FINE. IF YOU WANT TO GO ALL THE WAY, MAKE SURE YOU WELD IN A NEW DRAIN PLUG AND FILLER PLUG.