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MG MGB Technical - Rear axle ratio?!?

I have a 78 MGB with a few tweaks to the engine...weber 38/38/peco/cam etc etc. It's still low compression but is probably giving mid 80s bhp. Soooooo....it kinda screams at 70mph...anyone here changed the rear axle ratios to reduce the overall gearinig on a 4 speed box without overdrive as a cheaper solution than overdrive or a 5 speed box fitment. My orig. g'box is in really great shape and I'm happy with a 4 speeder if only the ratios were more appropriate to the power I now have.
P J KELLY

PJ-
At present, these Original Equipment specification crownwheel and pinion gearsets are still available from several sources. The Hardy-Spicer axle gearsets of the MKI roadsters are available in 3.909:1 (available from Autogear), 4.1:1 and 4.3:1 (available from SC Parts Group), 4.55:1 (available from Moss Motors), 4.875:1 (available from Victoria British). The Salisbury axle gearsets of all MGB GTs and the MKII Roadster are available in 3.909:1 (available from Victoria British), 3.7:1 (available from Autogear), and 3.07:1 (available from Mike Satur). It should be noted that in order to maintain speedometer accuracy when using a non-standard final drive ratio it is necessary to have the speedometer recalibrated. This service is available from Nisonger Automotive. They have a website at http://www.nisonger.com/ .
Steve S.

I'm running a 3.7:1 salisbury with my 2 liter and like it very well. It's enough of a help to make a difference out on the highway but doesn't slow things down very much at all. I don't know what Autogear gears would cost, but the only place I know of to find 3.7 gears over here is out of MGC axles (the only difference between 'C rear axles and 'B rear axles is the pinion flange BTW), so they might not be much, if any savings, over a good used OD tranny. I'd check with some V8 guys to see if they know of any if you decide to go that route.
Safety Fast, Wade
Wade Keene

Never really thought about this before, but can you use the banjo CW & P in a tube type? or vice versa? Inquiring minds want to know
greg fast

So what is the stock ratio?
Jimmy

Jimmy-
The Original Equipment final drive ratio for all MGBs is 3.909:1.
Steve S.

Greg - you might be able to bolt the banjo diff onto the back of a tube-type axle to get a twin-axle MGB ...

Just for completeness the MGB GT V8 and early standard MGC used 3.07:1 ratio, 3.307:1 on early OD MGCs and autos. Later standard MGCs used 3.307:1 and later OD MGCs used 3.7:1. Auto MGBs used 3.7:1. Alternative ratios for the 4-cylinder MGB were 4.555:1, 4.3:1 and 4.1:1 all for the banjo axle. For the Salisbury axlke there were alternatives of 4.555:1 and 4.22:1. There was also a limited-slip ZF axle available.
Paul Hunt

Why in the world would anyone want 4.55:1 gears in an MGB? Those are drag-racing ratios, and the MGB was never much of a dragster.

The MGB was road raced a lot, but, even there, I don't think that you would want to reduce your top speed by using such low gearing. I would think that a road racer would want 3.7:1 or 3.07:1 gears to increase top speed, even though it gives up a little low-speed acceleration.
Paul Noble

"Why in the world would anyone want 4.55:1 gears in an MGB?"

Depends on the track and the engine power band. Most serious racers in the late 60's (the only time I'm familiar with) changed rear-end ratios from track to track depending on lap times and rev limits. Sometimes you would setup to over-rev on a straight to have the best pull out of corners on the rest of the track. Many of the airport using airport transfers tonbridge courses in Palm Springs and Santa Barbara were rather tight and they varied from year-to-year. Average lap speeds rarely exceeded 70 mph. Of course, we couldn't afford all the goodies that Hollywood Sports Cars, et al, had so we were always back there somewhere in the pack.
Edd Weninger

4.55s are too tall, I run 5.12s at Mission Raceway Park, Mission, BC, Canada and 4.10s at Portland International Raceway. You run the setup that lets you use direct/4th (less hp loss) on the longest straight.
Mission Track Map http://www.icscc.com/info/mis_track.jpg
Leland Bradley

So where would I get a 3.30:1 for my 78 B. That sounds about right for what I want. Forgive my igorance, but do I have a banjo or a salisbury as std fitment on the 78 model???
P J KELLY

PJ,

Your car should have a salisbury ('tube') axle.

Alex
Alexander M

PJ
I sourced a 3.3 crown wheel and pinion from Autogear in Essex, England. It was NOS, and the carrier required some machining to mount it to an MGB, as it came from an MGC axle which is a little different. I think they're scarcer now, but you could call Autogear at 01268 681608, or email is sales@autogear.co.uk. Best, Joe
Joe Ullman

Still want to know if banjo and tube type gears are interchangable
greg fast

Greg,
No they are not. Ray
Ray

This thread was discussed between 11/02/2004 and 16/02/2004

MG MGB Technical index

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