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MG MGA - Gearbox conversion

Hi All, I am thinking of changing the 1500 engine and gearbox for an 1800 engine and overdrive gearbox. The engine swop should be easy but the overdrive gearbox swop might be more of a challange.Comments and tips please.I will also want to upgrade to MGB discs.
Many thanks for any help.
s page

I have recently fitted a 3 bearing early B engine in my 1500. Later engines get slightly more complicated.

The only incompatibly I found, as discussed in an earlier thread and now on Barney's site at: -

http://mgaguru.com/mgtech/cooling/cool_108e.htm

was the water pump requiring radiator spacing slightly forward. You also need B pulley.

I believe fitting overdrive is quite difficult and most say go for easy 5 speed conversion instead. I am still on standard gearbox and A clutch.

Paul
Paul Dean

I did this many years ago and used an MGB differential. I did however have to greatly modify the rear cross member. You have to cut out the MGA one and fabricate one to fit the OD unit.
Combine the larger engine/OD gearbox/MGB rear end and 15" wire wheels made for an 75 MPH cruiser.
You might have trouble with the exhaust manifold as it will be close to the steering columb on LH drive cars.
Wish you much enjoyment as did I.
Sandy
ss sanders

I ran out of time this morning so didn't comment on brakes. I attach below a summary of how I see the situation taken from a thread back in May. As I see it there is no point in fitting MGB discs as the parts are once again available to fit MGA 1600 brakes, Also neither of the B conversions (Moss or MGOC) I investigated are entirely satisfactory hence if I was going disc (I am not) I would go A 1600. Since my comments below I have had another conversation with Bob West where he once again reiterated his comments in 3 below. (I presume you know Bob's status in MGA circles.) Do the change if you want but you don't need to.

Paul

___________________________________
P M Dean, Fife, United Kingdom
Paul

I have a 1500 and have considered and extensively researched this twice. The last in the autumn 2013 but I can't find it in the archive. Some times it is difficult to search as I might have added on to an existing thread that has wandered a long way from its title.

There are at least 4 options:-

1) There is the Moss kit As it says in their catalogue if you are on bolt on wheels you will have to obtain 1600 hubs that are only available secondhand. The other issue that I was told about by one of Bob West's assistants is that these kits are very difficult to set up correctly due to what I understand is the holes in the special plates being slightly oversize (a metric not imperial size I think). I also know someone local who had a problem with one fitted by a professional and was it taking back for fine tuning. Obviously once fitted correctly this is no longer a problem.

2)There is the MGOC approach that was around a couple of years ago that may be what they still list. This involves a rebuild of much of the front suspension/steering with MGB components at least one of which is not available new. Seemingly this approach can upset front geometry. I suspect it was the first approach but is now well past its sell by date.

3) I discussed the above 2 approaches with Bob West a couple of years ago. His view was then that while option 1 was useful when new A calipers weren't available, and all you could do was use B calipers, they were no longer the best approach. This was because A calipers were now available and you might as well get the bits and just convert to standard 1600 set up. Assuming you can locate all the bits the only remaining issue is that you have to weld a new support for the brake pipe/hose join. I nearly did this option, but he also added that it is a lot of effort for minimal if any advntage.

4)Stay with drums. Having discussed my plans with several very experienced A expert there is widely held view that is 'stay with drums'. The experts include one who owns 3 As that between them have with all 3 front brake variants, one guys who has as an ex works rally 1500 that he still rallies in major international events, and a couple of well established restorers. The view is that there are 2 reasons quoted for changing. Firstly 'drums fade', well people who have rallied Alpine passes say they don't. Secondly drums can pull, this can be true but this can be solved by careful set up. Thirdly they all say that the A drum set up is excellent and also drums have a nicer progressive feel. To be fair if you read original roadtests of which I have several they all seemed to like the move from drums to discs although the test figures only show marginally better braking, (Of course this move had to be done in late 1950s as any credible sports car had to have new fangled discs)

A general conclusion I came to is that if you are going to upgrade a 1500 bolt on wheeled car to discs, and if you have any interests in wires, you might as well go to wires at the same time as both jobs require a hub change.

I hope this isn't confusing but there are at least 3 real options (1, 3 and 4) all of which have issues. I am still on drums and just about to give them their annual set up check to avoid any pulling.

By the way I have no idea about the master cylinder extender question.

Good luck, I think this is about all I know on the subject.

Paul
Paul Dean

Why are you considering a 1800 and overdrive change for your 1500 MGA ? Just buy a MGB as you will end up with a modified MGA special neither one thing or the other....I can understand the change when there is no alternative available... the time is fast approaching when nobody will know just what a standard MGA had in original trim....For more performance fit a supercharger and really enjoy yourself.......
Cheers Rex
Rex Thompson

Simon

Is this a road car, or another race car project?
Dave O'Neill 2

"Just buy an MGB" and have a car that doesn't have the looks or attract the attention that an MGA does. People have been modifying older cars for years and years because they love the looks of the old but prefer the performance of the new...why should MG's be any different? They're not rare or exotic, just fun.
Gene Gillam

Hi All. Many thanks for your comments. Dave its a road car. I understand the sentiment to keep the cars as they came out of the factory. However I want some thing that I can use for long distances. Any modifications I do would be able to be taken off and returned to standard. I also want to keep the spirit of the car which is why I prefer the MGB box rather than Sierra In my mind the MGA is so much pretty than an MGB so thats why I want an up dated A.

Thanks again. I will probabley be back for more help in the future.
s page

Having done the engine change last winter all I can say is that it has transformed driving pleasure whether you want to drive hard or lazily. I got to the point of feeling the 1500 was gutless when I got it out each Spring but wow it is so different now. The impact of the improved torque is what I didn't anticipate. Firstly it really plugs the ratio gap between 2nd and 3rd when pushing it. Secondly when in traffic or getting tired you can just change gear less often. In terms of originality as well as looking the same it is effectively only a bored out A hence is almost what could have been done in period (I know this is a bit simplified)

On the gearbox I have stayed original which is fine for me as I do very little motorway driving, mainly going 'up north' from Central Scotland. My son in law though thinks I should change the rear axle ratio. On the originality bit my question is 'you wouldn't dream of fitting a Sierra engine so why would you fit the Sierra gearbox just because it is out of sight'. There again in a different situation I may have swallowed my pride and fitted one!

Paul
Paul Dean

I have a 18v and a 4sync.owerdrive box in my Mga 1500
and it goes werry fine. Dont forget the Mgb dif.

We did Denmark-- Dover--Scotland and back this summer no problems

Harry
HL Lagoni

The OD gearbox change is documented here.
http://clancy.ch/MGB_Overdrive.html


I know someone who tried a slightly different approach and switched back. But that was an installation without cutting the MGA frame, and resulted in the propshaft having a very sharp angle and the back of the engine being raised a bit to reduce this as much as possible.
dominic clancy

As you are in the U.K., whatever the engine, go for a Hi-Gear five speed conversion; if using an 1800 cc engine then install a 3.9 banjo from an early MGB
David Werblow

Dominic-

A conversion such as you describe could very likely be successful, with the use of a custom driveshaft with a double cardan (aka CV) joint up front, and a regular single joint in the rear. It would also require alignment wedges at the spring perches, to adjust the rear axle pinion angle properly (pinion flange surface needs to be exactly perpendicular to driveshaft).

This type of shaft is very common in vehicles that have been modified for off-road use with taller suspensions. Those modifications can sometimes result in excessive driveline angles, so extreme measures such as the CV shaft described above become necessary to prevent destructive vibrations. A good driveline shop should be able to build such a shaft.

-Del
D Rawlins

Del

I am sure you are correct, but the simple approach to avoid all of that is to modify the chassis by cutting off the gearbox Mount and bolt or weld the business part of a MGB mount into place, that would be cheaper, and avoids the more complex and expensive CV joint altogether, and then you also avoid realignment requirements for the axle.

That it has been tried without cutting the chassis and without the mods you mention is not surprising, but it didn't work very well.

I looked at doing the MGB mod, but in the end went with the much better Ford five speed from peter gamble
dominic clancy

The simple approach is to accept the MGA for what it is. Failing that, I prefer modifications that are non-permanent in nature, even if they require more effort. The arrangement I described above is not something I would ever do to an MGA, but better that than hacking on the frame, such that the car is unlikely to ever be put right again.

-Del
D Rawlins

S

I have an 1850cc 3 bearing MGB engine fitted to my MGA as well as a Ford 5-speed box and a standard 4.3 diff.

It is a great combination, the uprated engine is superbly torquey and gives great lazy pulling power from low revs. I only ever use 1st gear to start off and occasionally on really steep mountain hairpin bends. The MGB engine looks identical to the 1600 engine and the ford gearbox looks quite like the MG box too.

We have just returned from a traverse of the Pyrenees on the borders of France and Spain, a journey of 2000 miles. We travelled for up to 350 miles per day on the run down to our start point on the Mediterranean coast and the 5th gear really helps to keep the revs down on those long stages, 3500 rpm = 70mph.
On the journey over the Pyrenees we crossed all the high passes, many of them up to 7000ft and most of that involved constantly changing up and down between 2nd and 3rd gears.
If the car had an MGB 3.9 diff I think that most of the climbing would have been done in 2nd gear only, it would have made 3rd gear too high to be useful.
The best diff for the mountains would be a 4.55 to 1, it would make third gear perfect for the long climbs but would make the engine rev "as if it was stuck in 3rd gear" on the motorways.

I suppose the ideal would be to have a 3.9 diff fitted for the long motorway sections and then swap to a 4.55 diff for the mountains. But no one I know would want to go to that much trouble for a fun run over the mountains.

So if you go for a 5 speed box I would keep with a std 4.3 diff, it is probably the best compromise.

On the subject of drum brakes, a few of our group of 9 MGAs who made this trip were driving 1500s and their brakes proved to be fine on the long descents. The trick is to use the gears to help control the speed and that way the brakes never become over stressed.

If anyone is concerned about the modifications on my car, I have reserved a 1600 MGA engine and gearbox for it so that the next owner can convert it back to standard in a few hours if they prefer. But I love it as it is!

Colyn

PS. If anyone is interested in reading about our recent trip to the Pyrenees, I have published a blog about it. It is a day by day account of the journey down and then the run across the Pyrenees. It includes lots of pictures and some YouTube video clips of us driving the MGA. The pictures can be double clicked on to enlarge them.
It is still a work in progress but I am almost up to date with it now.
If you enter mgachallenge.wordpress.com
on your search engine it should be there.
c firth

Having driven a couple of cars with the 1800 & Ford combo I can highly recommend it.

If you can afford a Moss Supercharger on top, that would definitely be the way to go if permitted by local regulations.

Unfortunately neither route is allowed here, so the Judson rules supreme!
dominic clancy

This thread was discussed between 07/09/2014 and 10/09/2014

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