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MG MGB GT V8 Factory Originals Technical - Original 3.07 gears in a 3.9 Carrier

Gentleman,
I am in possession of an original NOS 3.07 (43/13) ring and pinion gear set. I wish to install this in a MGB 3.9 carrier. I have searched the archives for information and have only found one referece to the necessity to machine .200 from the carrier. I know that the carrier for the original MGB V8 3.07 gearset was different than the carrier for the 3.9 axle, or at least they have different part numbers.
Does any one know exactly what is necessary to make this swap--What machining might be necessary--How much and to what component?????
Thank you for any assistance.
James Johanski

Its a shame you didnt post this question earlier, a NOS MGB GT V8 carrier just went on eBay for 10 bucks.
Jake

James,
I'm taking a guess that no machining is required. But, to find out for real, email and ask John Webb at Autogear in the U.K. He's at hologothic@msn.com, or tele: 1256 681608.
Joe Ullman

James,

Machining is definitely required because the pinion is a larger diameter compared to the 3.9:1; .200 needs to be removed from the carrier face where the crownwheel (ring) is attached. The bolts will also probably require extra washers to prevent the shank of the bolt fouling the threads in the crownwheel. The carrier bearing preload and the CW&P backlash (the correct backlash should be stamped on the crownwheel) is adjusted with the bearing spacers and these will almost certainly require machining unless you are very lucky. New ones are available in various thicknesses but I had mine machined and ground to size.

By the way despite what it says in the workshop manuals the diff housing does not need to be stretched to remove the carrier – but it is a tight fit and may require levering. Mine needed a little pressure with a couple of tyre levers but I do mean a little pressure, extreme force was not required.

Geoff
Geoff King

James,

Before you go too far with this project, you should know that the 43/13 ring & pinion is a 3.307 not a 3.07. The 3.07 is 43/14. The 3.307 is still probably not a bad choice for a V8 with a typical overdrive or 5 speed trans.

Good luck.
Allan
Allan

Gentleman,
Updates:
To Allan--You are correct. I actually have a 43/14. Sorry about the mistake.
To Jake--That carrier on e-bay actually had an opening bid of 9.95 with a reserve. The reserve was not met on two attempts to auction it off.
To all--Thank you for your help and comments. Here is what I have found out:
The V8 carrier is a different casting from the standard 3.9. I believe that if you machine off .2 inches from the mounting surface of the standard carrier, the carrier will be weakened to the point of unreliability. The 3.07 carrier casting maintains the same thickness of metal to attach the ring gear as the 3.9 carrier. This is achieved by a change that essentially moves the ring gear outboard.
I have just contacted the seller of the V8 carrier that was on E-bay and he has agreed to sell me the carrier at his reserve price which is less than the machining would cost.
I am curious to know from Geoff, as to his experieces with the machining and how his rear differential is holding up--this is, of course, assuming that he has had this modification done.
I have set up differentials before (both MG and other) and will set this one up with a complete refurbishment of the rear axle assembly and report on the results.
I am presently using a T5 transmission with a 2.95 first gear and a .63 overdrive. I may have to switch to a lower ratio overdrive (.73 I believe) but will try the setup as is first. I am using 15 inch wheels with Goodyear Eagle 195-65 tires. The car should have extremely "long legs".
James Johanski

Geoff,

I just took my rear end apart to start conversion to 3.07-1 gears. Who was your supplier of the crown wheel and pignon.
There is also a spacer on the pignon wheel to adjust the hight of the pignon against the crownwheel, did jou change that too? I assume that your CW&P set is a reprodution, do repro's also have CW&P backlash-setting stamped on it.
If you have any other tip's ore good advice , I'm very interrested.

kind regards,

Arno
Arno

James,

Machining .2 off the carrier does not remove so much material to make the axle unreliable. I machined the carrier and rebuilt the axle last year but only used it for about 450 miles before changing to an independent rear suspension - not because there was anything wrong with the diff. I sold the axle, which is being fitted to another V8 B, and I have every confidence that it will provide many years of reliable service.

Arno

Clive Weatley supplied my crownwheel and pinion (and the carrier was machined as recommended by Clive). The gears are good quality and the axle was quiet but the backlash was not marked. I used the original pinion spacer.

Geoff

Geoff King

I have the 3.07 gears in a MGB with a V8. These gears are so loud I have never installed a Radio. On a trip I wear ear plugs.
Leroy Cook

I have the 3.07 gears in a MGB with a V8. These gears are so loud I have never installed a Radio. On a trip I wear ear plugs.
Could it be that "ANDY" did not set it up correctly ? I have over 13,000 miles on it so far. When the temp warms up here I am looking to just convert to a Ford rear end. Has anyone else had this condition?
Leroy Cook

It's terrible to hear of the noise Leroy ... I have a lot of wind noise in my GT (obviously, with those gutters hangin' out into the breeze) but that's about it ... I would strongly suspect that your gearset is set up incorrectly if it's noticeably noisy.

Perhaps the easiest thing is just to get an MGC axle with 3.07 gears. That's what I have, and it's dead quiet.
Ted

This thread was discussed between 07/02/2003 and 11/02/2003

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