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MG MGB GT V8 Factory Originals Technical - Has anyone broken the stock gearbox?

Hi All,

I'm considering buying a 3.9 short block to replace my comprehesively knackered P6 unit.

My conversion uses the original gearbox and I'm concened that it may not be up to the task.

Is anone running the original box behind anything other than a stock motor?

Or does anyone know how much toque the original gearbox can take?

The V8 conversion book strongly recommends using the SD1 box but that will more than double the cost. (And I simply can't afford it.)

Best regards,

Nick

Nick Wilson

I have a 1973 factory GTV8 which I have owned from new.

I broke two gearboxes behind the factory low compression engine whilst the car was under warantee - incidentally the only gearboxes I have ever broken in many years of road, rally & race driving.

The third gearbox lasted OK for 60K miles, and was replaced with a new late Range Rover 5 speed when I installed a John Eales 220 bhp engine.

The Rover box seems very robust and I have had no problems in the nearly 4 years since it was fitted despite heavy use in rallies in the Alps and Basque country.

If you can't afford it continue with the standard box, take it very easy, and save for the Rover 5 speed.

Safety Fast

Nigel
Nigel Steward

Nigel,

That's pretty bad news! Unfortunately, I can't change the box that easily. My conversion uses an adapter plate to allow the MGB box to fit behind the Rover. This requires cutting a bit off the Rover block, which prevents the subsequent use of the SD1 gearbox.

Incidentally, did you perform other modifications when you installed the JE motor? I'm wondering about the rear suspension's ability to deal with the torque.

Thanks,

Nick
Nick Wilson

Nick,
If you want to enjoy all the benifits of your new engine, a stronger box is a must. If you're into fiddling about and cut very carefully, the starter ring could-possibly be welded back on later. I wouldn't bother! Save up-sell the kids and the drum kit-borrow the money from your rich cousin-shop around, but don't cut your block. If you're going to keep the car for a while, you'll have to convert sometime! It's time. Good hunting!

Angus Davies

Nick

I am running the JE engine in frint of the RR 5 speed box, and a standard GT V8 axle.

I did fit a purpose built uprated propellor (drive) shaft as the standard item is allegedly not up to the task, but some people ignore this!

The axle had to be rebuilt at 100k miles due to my ignorance in not fitting a cotter pin into the differential spider gear roll pin.

Paul Kile will, sensibily, recommend that you install a "lifesaver" nut installed on the unused stud on the air filter plenum, to prevent the stud from working loose and causing disastrous effects when ingested.

Safety Fast

Nigel
Nigel Steward

I believe the PO of my factory car broke it - stock motor.

PaulH.
Paul Hunt

What is a spider gear? What is a roll pin? My MGC rear end/diff is off the car as I had one of those Quaife units installed ... in fact the cover is even off ... should I be fixing this before I put it back on? I don't particularly want to blow it up. What on earth does this roll pin cotter accomplish?
Niles

Niles,

I spoke to Clive Wheatley about this last year and he explained it well. Call him on 01902 330 489. Any 3:08 modified diff he sells has the required mods so he'll probably tell you straight away what you need to do.

Nick,

I broke the standard box behind a four banger and I wasn't even thrashing it. Cracked the synchro ring on second gear which although cost ten quid to fix took me about a hundred hours. With the V8 I'm going for a stronger box from the start I'm afraid. If you're short of cash the standard box won't explode when you drive it normally, just don't give it a gutfull.

Stainzy
Stainzy

Thanks folks

The message really seems to be that the "right" thing to do is go for a Rover 5 speed. I really don't feel up to cutting the transmission tunnel and welding a bit in, or getting the engine in and out half-a-dozen times while I modify the gearbox cross member. It's my wife's car and she can't stand it when it's broken. (Broken is off the road for any reason, to her.) I'm probably going to stick with the MG 'box and rely on Samantha not to thrash it.

Cheers, Nick







Nick Wilson

What ever happened to the Costello 5-speed gearbox? It was supposed to be a direct bolt-in to replace the MG unit. Did Costello ever get the funding to put it into full production?

BTW, when I was restoring my 1974 CB GT V-8, I found a tiny date on the gearbox that said 1975. I guess some PO busted the original box!

Cheers,
Paul Kile
Paul Kile

Hi

I've just emailed autogear (who do a kit that allows you to use a Ford 'box in an MGB) to see if their conversion will work on my car (with the adaptor plate that the MG 'box is mounted to). I'll post the reply to ensure that it makes it's way to the archives.

Nick

Nick Wilson

Nick,

Being in the UK you donít have access to the video from Glenn Towery. In it he explains how to use a hammer to modify the tunnel rather than cutting and welding to fit the Rover 5 speed. Use a hammer to pound the tunnel from underneath so it no longer dips between the shifter opening and the engine compartment (bay). That canít be any more work than cutting the starter mount off the block.

Itís not surprising that you want to use the MG transmission to simplify the conversion. For the price of the adaptor plate you save changing the drive shaft (prop shaft), speedometer cable and clutch slave cylinder. Not to mention you donít need to purchase a transmission, unless it brakes and then it wonít be too hard to find a replacement. I hope you at least have overdrive and take it easy on that unit particularly for third gear (MG modified production models so they only had overdrive in fourth gear because of breakage).
George Champion

Nick, if you follow the excellent information available from david Vale at V8 Conversions, you can very simply modify the gearbox crossmember. There's no need to worry about hauling the motor in and out - mine went in perfectly first time of asking. All I did was follow the instructions. You really must go for the 5 speed 'box, because you will use the power (otherwise, why bother with a 3.9?).
David Daw

My car is a factory V8 with stock engine and gearbox. Recently, I've had some clicking when the car is cold which sounds as if its coming from the gearbox and increases in speed as the car goes faster. When the car has gone a few miles though, and has warmed up, it all but disappears. Anyone know what this might be ? I have no trouble selecting and finding a gear.

Thanks,

Colin
Colin Hoad

Hi All,

In the interests of completeness, Autogear say their 5 speed conversion is not suitable for a V8.

Nick
Nick Wilson

I am very interested in Colin's clicking problem, because I too have that on my Factory V-8. I have only driven the car less than a week since its total restoration, the trans was rebuilt with new synchros, bearings, layshaft, etc.

Anyone have any ideas?

Cheers,
Paul Kile
Teal Blue 889G, back on the road!
Paul Kile

Paul,

Congratulations! Have you got any pictures??

Nick
Nick Wilson

Congrats, Paul, on getting your car completed.

I too have the clicking from cold, I've ignored it for the past 55k miles.

PaulH.
Paul Hunt

Could it be worn engine mounts making the engine rub against the steering column ? If so, why would the sound go away when the car warms up ? Bit of guesswork here.
Colin Hoad

Colin,
I don't think it can be worn mounts, because mine are brand new, and I have the requisite number of packing spacers under the RH mount to clear the column. It sounds almost like the speedometer cable has a slight kink in it, but the speedo reading is steady and a kinked cable wouldn't straighten out as it warmed up. Whatever the noise is, it was not affected by a complete trans rebuild (along with everything else).

Cheers,
Paul Kile
In the middle of a nerve-wracking shakedown period
Paul Kile

Colin,
Are you sure the clicking noise is from the gearbox, the front disks on my MGB V8 conversion make a clicking sound, I thought it was a wheel bearing but even after replacement the sound remained. It turned out to be the pads not fully disengaging, it is very annoying though at parking lot speeds.
Michael S. Domanowski

On mine the column is definitely clear, and I can feel the clicking through the lever.

PaulH.
Paul Hunt

I would lay odds on the noise coming from the speedo drive. Enough to generate the noise when cold but not actually dragging to any degree that shows in a needle flicker on the speedo.

For the Costello gearbox, people interested may want to speak with Tim Fenna of Frontline Spridgets based near Bath.

Rog
Roger Parker

This thread was discussed between 24/04/2001 and 10/05/2001

MG MGB GT V8 Factory Originals Technical index

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