Fitting BWM complete rear axle

[curbo165]

Hi, I'm looking into fitting a BMW E30 complete rear axle on to my mk2 2000 estate, I've seen some general information on the monarch web site and quick search of Google. What I am trying to find is some more indepth technical information regarding exactly what work is required to fit the BWM rear to the triumph.

[Alan Chatterton]

Google for Monarch Stags. They do a kit for the stag which can be adapted to fit the 2000.

[curbo165]

Thanks Alan, as I said in the original post I’ve looked on monarch stag site. But of course he doesn’t give any of the technical information away, well not without me parting with £1650, which unfortunately I don’t have to give away. What I was trying to find was some information from people that may have undertaken the conversion who would share some of their experience/knowledge. Before I pull the axles off the BMW@2000 and start to figure it out myself.

[leesellars]

Hello Andy

What's wrong with the triumph set up?

Lee

[tony]

Hello Andy

What's wrong with the triumph set up?

Lee

With Datsun half shafts.....?
Tony.

[djw113uk]

I have just finished fitting the BMW diff conversion into my mk2 saloon.. even more involved than I expected due to the closer spacing of the diff mounts on a mk2 saloon!

I have seen the complete BMW rear end conversion (DIY copy) on a stag and it revealed a few problems:

1. no holes in BMW subframe for exhaust to pass through. - the exhaust has to be brought "low" or the subframe modified to make it high
enough to pass the exhaust via the normal position,

2. BMW track is far wider. The stag I viewed had cut and shut shafts to make track correct - even with wheel spacers to make BMW stud PCD back to triumph. With monarch kit you either need new wheels with special offset or flared arches!

3. BMW diff nose is shorter so you need a longer prop. Due to extended length of a 2000 over a stag a 1 piece prop is not possible so you need a 2 piece and to find somewhere to place a centre mount.

The BMW diff in Triumph subframe is a nice setup - but you are left with triumph driveshaft and rear hubs - which I have recently been told to swap out due to failure such as seen on Tony Harts race car.

The final hurdle I found was that stag handbrake cables pass through the subframe at a higher level - I have therefore drilled another hole(s) to suit saloon - now needs sleeving to stop cables chaffing away!

[curbo165]

Hello Andy

What's wrong with the triumph set up?

Lee

I've fitted the Rover V8 engine and GM180 auto box from an SD1 into the car and have been advised to upgrade the rear axle to handle the extra power. I was going to fit a stag rear axle but I don’t think there would be much benefit over the 2000 axle? Hence the thought of using the BMW axle.

[Alec]

Hello Andy,

unless your V8 is highly uprated, the Triumph rear will handle it OK particularly with an automatic gearbox. I take the point that the Hart Racing Stag had different hubs but that is racing, road use is a different kettle of fish. I'd leave it as standard, it will save you a huge amount of work.

Alec

[djw113uk]

I had got about 30,000 miles from the original 3.45:1 PI diff on my car.(over 3 years) Admittedly the car is usually on LPG so (slightly) down on power, but the previous owner ripped a BMW 4 speed autobox apart, and sheered the prop, yet the diff survived! Both as an auto and as a manual it was a lot of fun, and would shift when it needed to. The number of cars that thought they would nip past at lights and were shocked when they couldn't is endless!

I have only changed to BMW diff as there is no need for the rover v8 to be doing 3000rpm at 75mph! When I thought it had finally died, I decided to fit the BMW diff before I realised it was only the pinion bearing. 2700rpm at 70 is far more comfortable, and 3.07 is the standard SD1 diff ratio anyway. To be honest the car seems quicker, not slower, even with the taller diff ratio.

I don't know much about the GM auto box, but can thoroughly recommend the zf4HP22 auto. Torque lockup gives overdrive style cruising, and it bolts straight onto the rover engine using rangerover bellhousing. With the original diff and 4HP22 autobox 3000rpm was 90mph, when I swapped to the LT77 manual box I was horrified to find 3000rpm was now only 75mph. I might put the autobox back in, but will see how the economy has reacted with the new diff first.

The BMW complete rear end is a complicated thing to fit, even if using the monarch kit. I would enjoy it with the original diff, and if, or when, it breaks then your hand has been forced!

The p6 diff can also be fitted - Ken in Perth, and Roger Keys have gone this route, but I chickened out. The advantage of the BMW route is a massive choice of diff ratios and cheap Limited slip options. If I was doing it again I would still buy the 'halfway house' and stick with triumph subframes and BMW diff. On the estate it will be a piece of cake!

[andyborris]

£1650 buys a lot of re-conditioned Triumph diffs........!