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MGA Speaking of 5 gear Transmissions and MGAs

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ronzet

ronzet

Jedi Knight
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LBC Guruss,

I have been looking lustfully at the 5-speed converstion from Moss for my A. Being the tightwad that I be.....the $3K price tag is a bit more than I want to spend for one more gear...

Does anyone have a suggestion for a tranny and bellhousing conversion that might be a less $$$ investment for my 1500???

Thanks....
 
Early MGB OD trans.
 
You may want to look at another option which will be way less expensive, require no modification and give you a highway gear.
Put in an early mgb diff (pumkin) and change your gear ratio from the mga stock 4.3 to the mgb 3.9. You will also need to change the half shafts to the early mgb.
I did it in my mga and its been great and the next best thing to fifth gear.

Liam
57 mga
 
While the higher ratio will work, it will also hurt the acceleration of a 1500, especially at higher speeds. I agree with Bill and that's exactly what I plan to do with my A at some point. I already have the D-Type OD module waiting. A hidden switch will give you two extra gears and the feel of the gearbox will remain unchanged from stock. If you WANT a modern-feeling gearbox then that's another matter.
 
Steve - wire the OD to the foglight switch on the dash - F= 'faster' :thumbsup:
 
Steve,
Hurting the acceleration of the 1500 at higher speeds?

<span style="font-weight: bold">Well after putting 2000 miles on my mga with the 3.9 that hasn't been my experience.</span> If anything acceleration is improved. The only draw back I have encountered is that I can't start off in 2nd gear any more. And of course I need to down shift more when hill climbing.

And yes an overdrive unit would be great but so would finding that needle in a haystack.

Liam
57 mga
 
ronzet,

You may want to check the mga guru site which goes over the pro's and con's of the 5 speed swap, the mgb over drive swaps and even a nissan 240 5 speed swap.

The main question you need to ask yourself is:
Do you mind chopping up the under carriage and trans tunnel of your mga? If the answer is "No I don't mind" than the mgb overdrive transmission option or the nissan 240 5 speed may be for you.
If the answer is "Yes I mind " chopping up my mga than you really have two options at this present time.
Pay the $3000 to moss and buy the kit before it goes up in price any more.
or
swap in the early mgb rear end.
Also, sorry to hear about your accident.

Liam
57 mga
 
It entirely depends on what speeds and RPMs we're talking about. It's pure mathematics. A certain amount of torque is required to accelerate a given mass. A low gear will give greater mechanical advantage than a higher one, therefore a vehicle can accelerate faster in a lower gear than in a higher gear. This is why race cars typically run lower gear ratios than street cars (not in all applications of course!).

It is possible for a vehicle to see a higher 0-60 time by increasing the rear end for a few reasons, one of them being that one less shift is required. At certain speeds, a higher ratio will give an advantage because your engine will be within a better part of the power band, but of course this is true for a lower gear ratio as well.

Power band aside, a vehicle will always accelerate faster with a lower gear than a higher one!

I increased the rear gearing in my TC for touring, and while I lose a bit of hill climbing ability, I gain more usable gearing in many situations. No , it doesn't accelerate quite as fast but it is quicker overall some of the time.

By the way, I also have a 3.9 in my MGA but I run an 1800 bore to overcome it.
 
Gentlemen,

Thank you for all of the comments and recommendations. :thumbsup:

SInce I am of the mind not to cut up the A to put a B+OD tranny in the A (Or anything else that requires cutting and chopping), the 3.9 seems to be a very viable solution to the issue of freeway driving RPMs....and well below the $3K for a five speed....

My A is deffinately a cruiser; so the downside performance impact is of little concern, while the lower RPMs at hiway speeds is desirable...and in SoCal there is a LOT of freeway driving...

I have added the differential gear to my list of things to be done...<span style="font-style: italic">And removed the 5 speed tranny</span> from the list...

Ya' add one and you take one away...sort of a god complex :devilgrin:

Thanks again...
 
Changing the rear end gearing is the easiest and least expensive way to reduce highway RPMS. If nothing else, it's worth a try just to see if you like it. If not, you just sell the 3.9 rear end and all you're out is your labor, a gasket and some gear oil.

Be sure you have the proper spider gears in the diff before assembly!
 
Gentlemen,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Put in an early mgb diff (pumkin) and change your gear ratio from the mga stock 4.3 to the mgb 3.9. You will also need to change the half shafts to the early mgb.
[/QUOTE]

Just to be sure.... I should get the differential from an early (3 main?) MGB 1964-1965 (?) that has a pumpkin housing. Is there a way to easily tell if it is the correct ratio when I purchase the diff, as in a stamped number or??? I would hate to buy one off eBay or elsewhere that ends up being the 4.3 ratio...

I also understand that the axles from the B pumpkin should be used as part of the replacement.

Correct-o-mundo??
 
Any diff from 62-67 MGB will be a 3.9 and will fit the MGA axle. Other than the brake plates I can't think of any major difference in the axle assembly from MGA through Mark I MGB.

Unless I'm missing something, you should be able to transfer your current spider gears from your MGA diff into the MGB diff and use the same axles. This is the same thing you do when converting from a wire wheel axle to steel wheel axle (or vice versa) when you want to retain your old diff.
 
Famous Steve.....

I have not yet crawled under my '66 B to check for differences...

Although I think my B has a banjo rear since it is one of the last MK-Is out of Abingdon....

Would it be easier to find a complete rear axle assembly from a MK I B (as long as it has a pumpkin with spokes vs. banjo rear) and replace the entire assembly into the A's springs???
 
I would want to open up an unknown axle anyway, so in my opinion it's easier to just drop the diff from your current axle rather than pull the entire axle from the car. You will also retain the MGA brakes by doing it this way, which would make the modification invisible.
 
Steve,

Thanks. I had not thought of the brake issue....which is a recuring problem with me lately... :rolleyes:
 
the surest way to check ratio is to count the teeth on the pinion and ring gear.

thqdwew banjo rear had lots and lots of ratios available
 
Pierce Manifolds in Gilroy Ca. handles the 5 speed gearbox also. They might be cheaper than Moss.
 
You can spot a 3.9, its got 11 teeth on the pinion.

My 1500 A is too short geared, the syncro is knackered on 2nd gear so I needed to swap the gearbox.

I decided the best sourse of action was to rebuild an 1800 and fit a 5 speed box.

I bought a old 1800 motor, rebuilt it with new shells and oil pump and rings, new valves and guides, new cam, new lifters, new....and so it goes on.

Have bought the 5 speed conversion and the gearbox itself.

I also bought a rough 3.9 diff, replaced all four bearings and the pinion seal.

I bought a whole car for the gearbox, got most of the money back when I scrapped it.

I have a little bit of work to do on the cylinder head.

Hopefully next week I'll do the big swap out and fit new diff, prop, gearbox and engine, I reckon I can do it in 3 days. We'll see.

I'll keep you posted.
 
burgundyben,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]knackered[/QUOTE] :wink:

AS Sir Winston once said.. ' the only difference between the US and the UK is that we speak a differnet language...

Anyway.... Sounds as if you have the problem well in hand.. I look forward to hearing of the successful completion of the project....

As for me... since I just finished rebuilding the 1500 and the attached tranny, the 3.9:1 diff seems to be the biggest 'bang for the buck' right now... or would it be 'biggest bang for the pound'..?? :cheers:
 
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