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What wheel is the drive wheel?

Posted by ThoRGilbert

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What wheel is the drive wheel? #1
ThoRGilbert Thomas Gilbert Greensboro, NC, USA 1971 MG MGB	Posted: June 10, 2012 01:10PM Registered: 4 years ago Posts: 81

Ok this may go into the dumb question log, but my B is on jack stands and while running yesterday it was knocked into gear. I noticed that the back left wheel was spinning, but the back right was trying to spin. It acted as though it was stuck and would turn slightly and stop and repeat the process. So what is going on and is it bad?

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Re: What wheel is the drive wheel? #2
aeropaul Paul Collado Wichita, USA 1978 MG MGB "Attention-whore" 2011 Suzuki Grand Vitara XV6 "Suzi"	Posted: June 10, 2012 01:36PM Registered: 1 year ago Posts: 72

Google "Open Differential." You are seeing the normal effects of an open differential seeing different levels of traction at the two rear wheels. To answer the question in the topic title, both rear wheels are the drive wheels, seeing the power split 50/50 between the two under normal ideal conditions. Researching the operation of an open differential will provide the rest of the explanation.

The reason I say "google it" is not because I mean to be curt. Just that there are many websites that will provide a more in-depth and eloquent explanation of the operation than I am willing to type, and its been explained before, so I'd rather not retype it. Have fun!

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Re: What wheel is the drive wheel? #3
ErnieY Ernie Y Nr Cahors, France 1970 MG MGB 1976 MG MGB GT 1978 MG MGB	Posted: June 10, 2012 01:56PM Registered: 1 year ago Posts: 2,885

Could be a very slightly rubbing right rear brake, it won't take much to allow the differential to drive the other wheel.

Is it bad, no, not really. The fact that it's moving means that any rubbing is minimal. You could if you wanted take say 1 flat of the adjuster but I doubt I'd bother.

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Re: What wheel is the drive wheel? #4
JohnTF John F Northeastern Ohio, USA 1970 MG MGB 1970 MG MGB	Posted: June 10, 2012 04:29PM Registered: 1 year ago Posts: 843

If you think about it, the differential allows you to go around corners, the outside wheel has to turn more RPM, it has further to go. If you raise one rear wheel, and put car in gear, the one up should turn, though I don't recommend experimenting too much, ;-)

When my rear brakes were frozen (was pushing car with dead fuel pump into garage and used e-brake to stop, and left it on all winter) I got the car running, jacked up one rear wheel, put it in gear and the motor was able to brake the rears loose, one at a time so I could get the car moving to where I could work on it.

If you do take a good look at your rear brakes, make sure the e-brake linkage is free, including the parts in the linkage on the vacuum plate under the drums.

It took me a lot of elbow grease and lubriplate to free up the left rears, the linkage was so rusted, the shoes could not engage, so the right side would lock up.

Regards, John

ps-- in many cars, the torque of the motor and drive shaft slightly lifts the right rear so if you peel out, the right rear spins first, becoming the "drive wheel", if you are stuck in snow, reversing alters this, and it is one of the reasons if you are careful you can "rock" your car out of snow, etc.

"Special" differentials, limited slip, etc. act differently.

Edited 1 time(s). Last edit at 06/10/2012 04:33PM by JohnTF.

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Re: What wheel is the drive wheel? #5
TR8todd Todd Kishbach Mass, USA 1978 Triumph TR8 1980 Triumph TR8 1980 Triumph TR8 1980 Triumph TR8 1980 Triumph TR8 ~ For Sale ! ~	Posted: June 10, 2012 05:48PM Registered: 12 months ago Posts: 74

With an open diff, whichever wheel has the least rolling resistance is going to spin easiest. One on pavement- one in the mud. The one in the mud is going to spin and fling mud at whoever is trying to push you out. Reminds me of an incident once up at the British Invasion in Stowe Vt. A rainy previous day left the field very muddy. I was talking to a couple of friends when a Rolls Royce got stuck in the mud right in front of us. Everybody but me rushed to push the guy out. When I didn't budge my buddies gave me the business and all lined up in back of the Rolls. I quipped back, If he has enough money to buy a Rolls, one of his equally rich buddies in a Range Rover can pull him out. No sooner did I say that did the Rolls start rolling. The driver gunned the gas and showered everybody in mud. He kept gunning it all the way out of the field. Never looked back, never even waved an acknowledgement to the mud covered do gooders. Don't get me wrong, I love helping people, I'm just not dumb enough to stand behind a car stuck in the mud.

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Re: What wheel is the drive wheel? #6
ThoRGilbert Thomas Gilbert Greensboro, NC, USA 1971 MG MGB	Posted: June 11, 2012 08:50AM Registered: 4 years ago Posts: 81

Okay feeling a lot better after reading responses...Thanks.

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Re: What wheel is the drive wheel? #7
Retro Fit Tony Zito Los Angeles, USA	Posted: June 11, 2012 12:10PM Registered: 1 year ago Posts: 503

The rear left is the one that primarily puts the power to the ground. This is why, when the rear springs droop, it is mostly the left side drooping.

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Re: What wheel is the drive wheel? #8
GeeMoo Greg M City, Ontario, Canada 1970 MG MGB 1972 MG MGB GT	Posted: June 11, 2012 12:28PM Registered: 6 years ago Posts: 2,585

This is my favourite answer to that question.
Check this one out. Oldie but a goodie.

__________________________
1970 MGB Black Label OD, APTVP12, Fidanza Flywheel, Flowspeed Head, Hilton AUD405 HS4 SU's, Schlemmerized Distributor, Pertronix Ignition, Saturn Alternator, 15" Dayton Wire Wheels, Falken ZE 912's, Falcon Big Bore
1972 MGB GT Blue Label OD, HIF SU's, 123 Distributor, Peco Exaust, APTVP14, Fidanza Flywheel, Flowspeed Head

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Re: What wheel is the drive wheel? #9
JohnTF John F Northeastern Ohio, USA 1970 MG MGB 1970 MG MGB	Posted: June 11, 2012 12:30PM Registered: 1 year ago Posts: 843

Tony, do MG motors turn the same direction as US cars? (I am thinking yes) If so, then the torque lifts the right rear slightly when accelerating forward. That would tend to make the right rear break free first when we are peeling out, as all of us do, I am sure. ;-)

That torque and my too big rear is enough to make the spring sag over there on the left, maybe that is why in England they put the driver on the other side. ;-)

I hear the motors turn the opposite direction "Down Under", which should reverse all of this, allowing for Coriolis force deflecting the opposite direction. drinking smiley

Moving my car's spare to the right side this PM.

Regards, John

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Re: What wheel is the drive wheel? #10
Retro Fit Tony Zito Los Angeles, USA	Posted: June 11, 2012 01:14PM Registered: 1 year ago Posts: 503

Quote: I hear the motors turn the opposite direction "Down Under", which should reverse all of this,

John, I believe it is just toilets and sink water that go in the opposite direction there.... smiling smiley

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Re: What wheel is the drive wheel? #11
JohnTF John F Northeastern Ohio, USA 1970 MG MGB 1970 MG MGB	Posted: June 11, 2012 01:30PM Registered: 1 year ago Posts: 843

In reply to # 2091018 by Retro Fit

Quote: I hear the motors turn the opposite direction "Down Under", which should reverse all of this,

John, I believe it is just toilets and sink water that go in the opposite direction there.... smiling smiley

Which seems to be where my money goes on cars. spinning smiley sticking its tongue out

John

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