More close ratio questions

[steve]

Started a new thread to get it back up top.

I really seem to flip flop on the subject. When I had my cr in I had 3.45 gears in the rear and I really wanted to try some different ratios. I had talked with the metric mech about building a 3.18 but didnt want to spend the money and not be sure if that would satisfy me.

Now that I put the od unit in with 3.64 ratio I'm thinking that it could still use a taller ratio maybe a 3.9? I dunno. Maybe if theres a way to fit a 6 speed... Oh just falling off the deep end here...

One issue I have and have had with every od unit I have gotten my hands on (been thru a couple of them). Is the bearing rattle while idling. Is it just the trannys that I have had the good fortune of getting or is this just the way they are? My cr tranny didnt make any noise at all and it is smooth as butter. The problem I have with the cr is a leak from the shift shaft. I have tried replacing the seal several times and it still leaks. So maybe the shaft is worn?

The jury is still out for me. If I get the leak fixed maybe I will try the cr again and have the custom diff built.

 

[Malc]

Steve,
It is difficult to give advice as the choice is up to you depending on the terrain you drive in, how you drive, and what you expect from the car.

Having just met Dave today with his tidy Csi with a 5-speed OD box and 3.3 engine that suits him, where he is and what he uses the car for.

I'm toying with the idea of putting my e28 dog-leg box in with the 3.0 engine that is blue printed. Rear diff staying the same.

Yes, you could get a 6 speed in, you could even get a 6 speed sequential box in, and that's a real one not one of these "toy" ones which are often touted (basically an automatic box with flappy paddle change) but a BMW unit as used in Touring car races etc will not leave you much change from £60,000 (about $100,000). A cheaper option is to use a standard BMW casing and fit the gearsets you want, different ratios, straight cut gears etc. In the UK companies like Hewland will make you a set. I am sure there are companies in Germany that specialise in them too
However all modifications like this, unless your prepared to do the work your self will empty your wallet faster than a Range Rover doing 90 mph.

On the technical side:
The main input bearing on nearly all BMW 5 speed boxes are known to rumble with age. It's pretty much standard practice to change these if the box comes out for any reason. Its not difficult However if you can live with it they will rumble for years before failing. This also applies to the 5 speed dog-leg box too.

From what I know most of the internal components of the rear differential are basically the same from the E9 through to the E34, and maybe even later. Thus a choice of final drive ratios are available. However a diff taken apart needs to be set up correctly otherwise it will eat it'self for lunch in no short order.

Malc

 

[dp]

Bearings that are known to rumble are the reason Metric Mechanic and Jim Blanton convert these trannies to roller bearings. ReGARDless of which trans you select, have one of those guys rebuild it for you....and you will NOT have to worry about noise or breakage. I guarantee it!