Project Beater B: Transmission Swap

A few months ago I introduced my latest cheap classic, a 1975 MG B roadster. I have no firm plans as to how long I will own it but thought it might be interesting to others to document what fixes it needs and how I end up using it. First on the priority list was the replacement of the wonky transmission. Follow along as we swap that and discover a few quirks of B ownership.

The first quirk I discovered was before even attempting the transmission swap. I have owned a couple other convertibles including a pair of Triumph Spitfires and a TR8. The tops have been easy and painless to fold up and down. The MG B with the Michelotti top is not nearly as straight forward as one would expect. It can also be damaged by improper folding so I am glad it did not attempt to drop the top right after buying the car. Here is a video of the instructions for those morbidly interested. For everyone else I would recommend buying a Triumph if an easy folding top is a priority for your little British car.

I suspect the gearbox that came in the car had a bad syncro on third gear. This meant one had to double de-clutch to get into third and if one was to let off the gas while in third it would pop out of gear. The seller disclosed this up front and it was reason why the car was priced so cheaply. The drive home was enough to convince me I did not want to live with it as is for the summer. Luckily I was able negotiate the inclusion of a spare transmission with the car purchase. It was untested and filthy however. The MG B is relatively mechanically robust so I felt I could gamble and install it as is. The fall back plan would be rebuilding one or the other in the case that they were both bad.

I did feel it, at least, it needed a bit of a clean first.

First up was removing the hood for ease of access. This is not strictly necessary as one could tie it upright to a garage rafter. Unfortunately my garage does not have any exposed beams. It is not a particularly hard process to remove the hood with only a few easy to reach bolts. It was a little cumbersome to do solo but I managed.


I should probably buy a workshop manual for the car but according to all the online resources the easiest way to remove and install the transmission is as a unit with the engine. After poking my head under the car I can see why. It would near impossible to line up the transmission with the engine and bolt it together. So next up is draining and removal of the radiator.

Obviously well overdue for a coolant change as this is what came out of the radiator.

The fan is looking rather shabby. I cleaned it up and gave it a coat of black paint. I neglected to take an after photo so only this before shot will have to suffice. Please imagine it shiny and black as the end result.

New parts. The previous owner had installed poly bushes last summer in the front suspension.

Here is another quirk of the MG B. The battery is under a panel, behind the passenger seat. It can make for tight clearances and I have heard that sparks can fly when removing the cables or battery. Still this is an improvement on the early Bs which had a dual 6V battery configuration.


We will skip a pile of boring work (disconnect hoses, driveshaft, remove alternator, etc, etc) and get right to taking the engine out. The factory recommended using the two rather small looking rocker cover bolts as the mounting points for lifting the engine. The 1.8L four cylinder is a surprisingly heavy lump of metal and the transmission adds more weight so I wrapped a chain around it instead. The oil cooler and lines ideally should have been removed before pulling but I surmised that I would likely to damage them so they came along with the engine.

With the engine and transmission out, a reasonably spacious engine compartment remains. A previous owner did some odd rewiring of the fuse box (next to the coil). It all appears to work well so I am going to leave it in place until it gives me reason to think otherwise. You can see some of my labeling in the engine compartment. I tend to label everything I can with painter’s tape as it does not leave a sticky residue when removed. I also like to take piles of photos of the original configuration. I find it keeps the inevitable head scratching to a minimum when putting it all back together.

The replacement transmission swapped onto the motor with minimal drama and is ready to be dropped back in.

Luckily my engine crane has a large range of motion as the engine/transmission needs to get fairly high off the ground to go in at an angle. It also helps to have the rear wheels of the car jacked up.

Here is another MG B quirk. The transmission needs to be filled from inside the car. There is a rubber plug behind the center console that needs to be pulled out. Then with a bit of groping around in the dark you find the dipstick for the transmission.

A length of clear hose and a funnel aid in adding oil to the gearbox. Apparently spilling oil all over the passenger side of the your car is a rite of passage for B owners. I only managed to get a drop on the passenger seat which wiped up easily. A significant spill on the carpet would not have had such a happy ending.

Pulling an engine/transmission and reinstalling it is a big job comprised of many, many smaller ones. Some are easy but require attention to detail, reconnecting the spark plugs in the right order, while others are frustrating due to access constraints, re-connecting the drive-shaft where the bolts are tightened a fraction of a turn at a time. I finally got all the details sorted and turned the key for the first time only to be confronted with a no start situation. Jumping into troubleshooting mode I found the engine was getting spark when cranking over and as well as fuel. I knew I had not touched the timing and really any engine should at least run poorly if it is getting fuel and spark.

After some contemplation and perhaps a few four letter expletives I realized that the engine was starting but only very briefly. As soon as the starter was released the engine would cut out. A short while later I located an ignition wire that should have been connected to the coil. Restoring that connection brought the car back to life and running condition. I have heard since that this wire can often be knocked out of place when an oil change is occurring leading to a frustrating no start situation. I seem to be learning a great number of MG B quirks in a short period of time.

The initial drive around the block showed promise. All gears were accessible and appeared to work. I did, however, almost manage to shift from 1st into reverse instead of second at speed. The above shift pattern means one has to be mindful shifting to second. Ironically it can be tough to find reverse when you actually want it.


A longer shakedown run outside the city limits again went very well. A yellow Canola field offers an interesting contrast to the blue paint. As I build trust in the car I will continue to take it farther afield so follow along at a later date to see where the Beater B goes this summer.