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Rear End Gears

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76MGB

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Here is some food for thought. I was wondering if anyone ever thought of putting lower gears in the rear end to get a better top speed. I know this would effect my acceleration. Has this been done? What cars could have swapable rear ends or gears? I was think of fabricating a driveshaft for a lower geared rear end from another car?

Quentin
 
Pick a rear end...from Chevy's to Fords to old Jeep US Mail Trucks! With modifications, the $$$'s the limit!
 
Well, If you were really interested in making a hot car, a Dana type rear end would be excellent (although also heavy). They came in Jeeps, Internationals, and (I believe) GM cars as well -- I'm sure others too. They have a wide range of gears and offer limited slips and lockers ... although they cost bucks, they are still manufactured for virtually everything (assuming you already have the axle) because of their widespread availability.

If not, I'd say the additional weight is a big negative. I know midgets had a variety of rears, so perhaps B's do too (that I don't know). This could be used with minimal cost if it is the case. Also, I know there are a variety of BL/BMC rears and you could probably find one that'd bolt right in from another BMC product (that's only speculation, however).
 
Not to be picking nits, but don't you mean higher? The lower the rear end, the better the acceleration. If you want higher speed, you need a higher rear end.

It is confusing - the higher the number, the lower the rear end
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<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Mickey Richaud:
Not to be picking nits, but don't you mean higher? The lower the rear end, the better the acceleration. If you want higher speed, you need a higher rear end.

It is confusing - the higher the number, the lower the rear end
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<hr></blockquote>

The lower the numbers are the higher the gear is. The number represents the number of turns the input shaft of the rear end makes for every revolution of the wheels.
Changing the ring and pinion gears are a precise thing and hard to get right. There are shims or thrust washers that adjust the position of the pinion gear and have to be perfect to avoid gear whine. Also, unless you have a press, you will be running down to the machine shop everytime you want to try another size of thrust washer or shim. So the average mechanic would do better to find a complete rear end with the gear he wants already installed.

An overdrive transmission might be a better choice since you get the benifit of a higher gear and the ability to stay in the present gear. So you could have the better cruising ability without sacrificing the acceleration.
Bob
 
Hello 76MGB,

the idea of an overdrive is a good one, but bear in mind that a higher ratio may actually reduce top speed as the engine probably will not have enough power to pull it.
Very often overdrive cars are faster in fourth than overdrive fourth.

Alec
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Interesting point, Piman. OD is used to get lower revs not higher speed.
 
Exactly. Theoretically you would get a higher top speed, but only if you had the power in the RPM range the engine would be in when high gear is used. Ask any Corvette owner whether 6th gear is where he get's top speed.

I was, however, reading an article in an old issue of British Car, and it discussed choosing transmissiin gear ratios for the Ford Sierra 5spd conversion. Apparently there are numerous ratios available. If you did that, you could keep your acceleration off the line by not messing with (or getting even better) ratios in gears 1 through 3 or 4, and getting a higher ration 5th. Sure it's expensive, but if you are switching rear ends, that ain't cheap either.

[ 04-15-2004: Message edited by: lawguy ]</p>
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by piman:
Hello 76MGB,

the idea of an overdrive is a good one, but bear in mind that a higher ratio may actually reduce top speed as the engine probably will not have enough power to pull it.
Very often overdrive cars are faster in fourth than overdrive fourth.

Alec
cheers.gif
<hr></blockquote>

I wasn't talking about top speed. OD is good for ecconomical cruising and the stock OD is designed for the MG. If top speed is what you want, then the standard 3.91 ratio would probably be better which with the OD will be there with the OD off.
Bob
 
I have found that I can actually mainain a higher speed (about 90) on a flat road in fourth gear WITHOUT the overdrive enganged but with the overdrive engaged, I can only keep her going a little less than 85 for too long...to accelerate at that speed, I need to disengage the OD.

Of ocurse, downhill speeds increase with the overdrive slighty, indicating to me that the stock engine does not have sufficient power to pull the overdrive at top speed on the level road...err, race track I mean...yea, that's the ticket.

But she is 30 years old! LOL

Bruce
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