Fitting BWM complete rear axle

[djw113uk]

For £1650 you still have to source and supply the raw materials! Monarch then chop, trim and fabricate, while you recon your diff, brakes etc, and then you get to fit it all into your car.
You could spend a lot of money on Triumph diffs and still not get one as quiet as a used bmw one tho!

[leesellars]

I had mine built by TREnterprizes with a LSD in and you can't hear a thing. Also there is no sound deadening in the back as the rear seat has been taken out aswell.

Lee

[e.p.j.]

I have a rumble in my rear end. I renewed the hub bearings, new drive shafts, new and balanced propshaft. new bearing in the subframe and also new bearings in the differential.

So when I read about an BMW diff in the saloon I am curious about it. Do you have some pictures?.

Did you do the whole conversion or did you stick with the original subframe and drum brakes?

[djw113uk]

If you have a mk1 saloon or any estate the job is simple. On a mk2 saloon Triumph used a narrower diff mounting. This is not wide enough to easily fit the fatter BMW diff and insulate it with any form of rubber.

I have chopped off the old mounts, removed the fuel tank, and installed new diff mounting pins at the wider centres as found on estates. I bought the bmw diff conversion (NOT complete bmw rear end) from monarch, and have therefore retained the triumph rear shocks, rear hubs, rear brakes and driveshafts. If you look at Monarch's site there is a picture of the BMW Diff setup - basically a BMW central carrier welded into two triumph rear subframe arms.

I already had (new) Stag rear brakes and uprated shocks and springs, plus I wanted to feel I was paying for parts, and not just to have some bits chopped, welded and sent back to me.

With the complete BMW rear end you have to provide all the parts. Your money just gets the modifications done to the BMW subframe which you have to provide. You need to supply the diff, rear brakes, driveshafts etc. I understand that BMW mini wheels have the right offset, but the wider track of the BMW complete rear end can leave you buying some VERY expensive wheels, then you have to play with the front to match too!

With either 'kit' you fit it and then advise the propshaft length, which monarch will then provide. Of course they expect the simple 1 piece prop, but I spoke to a couple of driveshaft suppliers who advised that at 57" a one piece prop could not exceed 4000rpm without 'whipping' itself to bits
Bearing in mind I already have an LT77 (or 4 spd auto box) both of which are shorter than the triumph overdrive unit anyway I decided to get a 3 series BMW prop shortened, so I have a nice light 2 piece prop and no vibrations or 'tramp' when pulling away. The BMW flange matches the diff nicely too! I still owe monarch the "exchange" subframe arms, and he owes me a prop.

I don't have a host site to refer to pictures so have never managed to upload pictures, but if you provide an email address I will send you some.

I think I could have made the outfit myself for a reduced cost, but I hope it will pay for itself in fuel improved economy and all the driveshaft spacers etc mean it would be very easy to end up with more vibrations than you cure. If my estate plans come to fruition I might go down the same route again!

Talking to someone a few weeks ago I was told how much an LSD benefits competition use. Considering a BMW LSD is available in many ratios for less than £300 and could be swapped in about an hour I am happy with what I now have!

[andyborris]

Slightly off topic, but does anyone know how power (and torque) the Triumph diff can cope with (assuming it's the weak point)?

If it's not the weak point, what is (the weak point) and how much etc.!

Andy

[curbo165]

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!

I would like to fit the zf4HP22 auto but I'm a bit unsure of what parts I would need, I believe a gear box from a Jaguar then Bell housing and other parts from a Range rover V8? So I imagine having to buy two complete boxes one from a Jag and one from Range rover to build one that suits with all the correct parts? Also do they have a speedo cable output to drive the speedo?