The Ford Barn

bunnyc · 08-30-2015, 05:11 PM

Have my '29 Tudor up on jacks. Wheels and tires are not mounted.
Running the engine @1290 +/- 10 RPM in 3rd gear.
I have a laser tachometer I like to play with. The right drum turns at 334 RPM, the left at 133 RPM.
Brake drag doesn't seem to be a factor, I have the rods disconnected and the adjusting wedge backed out. Both drums read 84 deg after 5 minutes running, which is the present OAT.

Does the difference in RPM sound normal? I admit to ignorance. You can't hurt my feelings.

Blessyouboys · 08-30-2015, 05:16 PM

If it were mine, I would reassemble and adjust the brake linkages Then I'd put the car on the ground and drive it.

You don't have a locked differential. The rear axles will spin at different rpms.

bunnyc · 08-30-2015, 05:23 PM

Quote:

Originally Posted by Blessyouboys

If it were mine, I would reassemble and adjust the brake linkages Then I'd put the car on the ground and drive it.

You don't have a locked differential. The rear axles will spin at different rpms.

Thanks. I learned something from you.

Dollar Bill · 08-30-2015, 05:45 PM

With an open differential, bearings could be tighter on one side than the other allowing them to spin at different rpm as BYB indicated.

PC/SR · 08-30-2015, 05:49 PM

I would not worry about that if you do not hear any strange noise. Turn by hand and listen as well, and see if you can feel any difference.

bunnyc · 08-30-2015, 06:16 PM

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Quote:

Originally Posted by PC/SR

I would not worry about that if you do not hear any strange noise. Turn by hand and listen as well, and see if you can feel any difference.

No, I don't hear any strange noises. Just the wonderful sound of my engine at the tail pipe!

Y-Blockhead · 08-30-2015, 06:27 PM

Quote:

Originally Posted by Blessyouboys

...You don't have a locked differential.

Boy wouldn't THAT be fun trying to go around corners with the tires turn the same speed...

1955cj5 · 08-30-2015, 06:54 PM

I am no master mechanic but simple differentials are designed so the power from the engine is sent to only one wheel at a time. The other just turns do to internal friction.

When you go around a corner the outside wheel has to travel a greater distance, so the wheels must be more or less independent of each other, yet designed so that either wheel can be the driven wheel. The driven wheel is usually the one that has the least resistance.

Hope that helps a little..

bunnyc · 08-30-2015, 07:12 PM

Quote:

Originally Posted by Y-Blockhead

Boy wouldn't THAT be fun trying to go around corners with the tires turn the same speed...

Yeah, you're right.

Tom Endy · 08-30-2015, 08:08 PM

Power from the engine rotates the drive shaft that rotates the pinion gear attached to the end of the drive shaft. The pinion gear drives the ring gear that is attached to the carrier assembly. Inside the carrier assembly are the gear ends of the two axles in mesh with the three spider gears.

When you are going straight down the road the pressure from the tires holds the two axles evenly to the spider gears and hence to the carrier. Both wheels are then driven evenly. When you go around a corner in either direction, the pressure on the tires changes and it allows the spider gears to drive each axle at a different speed. The guy that invented it had to be a genius.

I have taken a number of rear axle assemblies apart where some kid with a duck-tail haircut back in the 1950's spot welded the three spider gears to their hubs so that it locked the two axle together permanently. This was known as a poor man's posit-traction. It made it easy to lay a strip of rubber out in front of the high school to impress all the girls. The only problem was that when you went around a corner the outboard tire chirped.

Tom Endy

bunnyc · 08-30-2015, 08:14 PM

Thanks Tom.

Mike V. Florida · 08-30-2015, 10:27 PM

This has been posted here before but this will save you a search;

How a differential works

Idaho Brett · 08-30-2015, 11:08 PM

Quote:

Originally Posted by Mike V. Florida

This has been posted here before but this will save you a search;

How a differential works

OR......... You could watch the movie "My Cousin Vinny" which explains it all. Those of you that have seen the movie know what I'm talking about.
I still laugh after seeing it a thousand times.

Minn-Tex Lee · 08-31-2015, 10:57 AM

I believe the differential was first used in China in building the "South pointing chariot". That was over 3000 years ago. Those guys were smart.
Lee

SSsssteamer · 08-31-2015, 11:15 AM

For years, I have noticed on most all of my cars, that the right rear wheel will break traction before the left rear wheel will. Also while running on jack stands, the right rear wheel will spin faster than the left rear wheel. I have accepted this phenomenon as normal. I think why the right rear wheel will break traction first is because of the lift that is given to it from the direction of twist from the drive shaft? While on jack stands, the reason why the right rear wheel spins faster than the left needs to be thought out. Drag is the only thing that comes to mind to give different spin speeds.

CT AV8 · 08-31-2015, 01:21 PM

Quote:

Originally Posted by Idaho Brett

OR......... You could watch the movie "My Cousin Vinny" which explains it all. Those of you that have seen the movie know what I'm talking about.
I still laugh after seeing it a thousand times.

Ha, ha...yeah....lovely Marisa explains Positraction

bunnyc · 08-31-2015, 02:46 PM

Here's the clip from the movie where she explains it:
https://www.youtube.com/watch?v=6qgREMBTE28

08-30-2015, 05:11 PM	#1
bunnyc Senior Member Join Date: Apr 2015 Location: KY Posts: 296	Rear wheels turn different RPM Have my '29 Tudor up on jacks. Wheels and tires are not mounted. Running the engine @1290 +/- 10 RPM in 3rd gear. I have a laser tachometer I like to play with. The right drum turns at 334 RPM, the left at 133 RPM. Brake drag doesn't seem to be a factor, I have the rods disconnected and the adjusting wedge backed out. Both drums read 84 deg after 5 minutes running, which is the present OAT. Does the difference in RPM sound normal? I admit to ignorance. You can't hurt my feelings.

08-30-2015, 05:16 PM	#2
Blessyouboys Senior Member Join Date: May 2010 Location: Blissful Posts: 298	Re: Rear wheels turn different RPM If it were mine, I would reassemble and adjust the brake linkages Then I'd put the car on the ground and drive it. You don't have a locked differential. The rear axles will spin at different rpms.

08-30-2015, 05:45 PM	#4
Dollar Bill Senior Member Join Date: Oct 2014 Location: Keystone Heights, FL Posts: 647	Re: Rear wheels turn different RPM With an open differential, bearings could be tighter on one side than the other allowing them to spin at different rpm as BYB indicated. __________________ I Love Anything That Turns Money Into Noise

08-30-2015, 05:49 PM	#5
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,279	Re: Rear wheels turn different RPM I would not worry about that if you do not hear any strange noise. Turn by hand and listen as well, and see if you can feel any difference.

08-30-2015, 06:54 PM	#8
1955cj5 Senior Member Join Date: Apr 2015 Location: Boise, Idaho Posts: 1,578	Re: Rear wheels turn different RPM I am no master mechanic but simple differentials are designed so the power from the engine is sent to only one wheel at a time. The other just turns do to internal friction. When you go around a corner the outside wheel has to travel a greater distance, so the wheels must be more or less independent of each other, yet designed so that either wheel can be the driven wheel. The driven wheel is usually the one that has the least resistance. Hope that helps a little.. __________________ Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62

08-30-2015, 08:08 PM	#10
Tom Endy Senior Member Join Date: May 2010 Location: Southern California Posts: 3,131	Re: Rear wheels turn different RPM Power from the engine rotates the drive shaft that rotates the pinion gear attached to the end of the drive shaft. The pinion gear drives the ring gear that is attached to the carrier assembly. Inside the carrier assembly are the gear ends of the two axles in mesh with the three spider gears. When you are going straight down the road the pressure from the tires holds the two axles evenly to the spider gears and hence to the carrier. Both wheels are then driven evenly. When you go around a corner in either direction, the pressure on the tires changes and it allows the spider gears to drive each axle at a different speed. The guy that invented it had to be a genius. I have taken a number of rear axle assemblies apart where some kid with a duck-tail haircut back in the 1950's spot welded the three spider gears to their hubs so that it locked the two axle together permanently. This was known as a poor man's posit-traction. It made it easy to lay a strip of rubber out in front of the high school to impress all the girls. The only problem was that when you went around a corner the outboard tire chirped. Tom Endy

08-30-2015, 08:14 PM	#11
bunnyc Senior Member Join Date: Apr 2015 Location: KY Posts: 296	Re: Rear wheels turn different RPM Thanks Tom.

08-30-2015, 10:27 PM	#12
Mike V. Florida Senior Member Join Date: May 2010 Location: South Florida Posts: 14,054	Re: Rear wheels turn different RPM This has been posted here before but this will save you a search; How a differential works __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

08-31-2015, 10:57 AM	#14
Minn-Tex Lee Senior Member Join Date: May 2010 Location: Stewrtvl MN-Fredbrg TX Posts: 192	Re: Rear wheels turn different RPM I believe the differential was first used in China in building the "South pointing chariot". That was over 3000 years ago. Those guys were smart. Lee

08-31-2015, 11:15 AM	#15
SSsssteamer Senior Member Join Date: Nov 2010 Location: Sedro-Woolley, WA Posts: 1,023	Re: Rear wheels turn different RPM For years, I have noticed on most all of my cars, that the right rear wheel will break traction before the left rear wheel will. Also while running on jack stands, the right rear wheel will spin faster than the left rear wheel. I have accepted this phenomenon as normal. I think why the right rear wheel will break traction first is because of the lift that is given to it from the direction of twist from the drive shaft? While on jack stands, the reason why the right rear wheel spins faster than the left needs to be thought out. Drag is the only thing that comes to mind to give different spin speeds. Last edited by SSsssteamer; 08-31-2015 at 11:23 AM.

08-31-2015, 02:46 PM	#17
bunnyc Senior Member Join Date: Apr 2015 Location: KY Posts: 296	Re: Rear wheels turn different RPM Here's the clip from the movie where she explains it: https://www.youtube.com/watch?v=6qgREMBTE28