Opinions wanted: Close ratio or overdrive gear box?

J

Johan

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I need to buy a new gearbox since it is getting more and more difficult to get it in 1st and 2nd gear.

So, should I get a close ration box or one with overdrive?

I have the overdrive one now and it is sweet on the motorway as it gives 800 rpms less than the close ration and it is nice to cruise at 160kph without going deaf.
But it is no fun on winding roads and in town as I often seem to find myself in the "wrong" gear. And I am not too fond of the gears having different "lengths".

My driving is quite mixed which I doesn't make the decision any easier. I live in Switzerland right now which means there are very nice mountain roads but also a lot of motorway driving.

I should add I have done a full 3.5L Motronic conversion with a trim cam so I have a bit more torque and HP than a standard CSi.

So I wonder what your experiences/ thoughts are?
How is the close ratio to drive ? Is there a difference in quality etc?


Any input is appreciated.

/Johan
 
Johan,
Several options, but you need to be able use the speedometer cable. Most of the modern BMW boxes do not have this facility. (post 1990?)
However a 5 speed box out of an E28 does have the cable port, though it maybe plugged.

I have an E28 (1986 M535) with a "dog-leg" 5 speed box. The ratios are great for the 3.5 litre engine, though the change pattern needs a bit of getting used to, especially after driving a car with a "normal" 5-speed pattern.

It does have a port for a cable (I haven't investigated further) so that's a bonus. You may have to change the propshaft and the way the gearlever is mounted to the box, however you may be able to "mix and match" parts from the original box and any 5 speed you get.

Hope this helps
Malc
 
Johan,

I have gone from a cr back to an overdrive. As far as swaping them the mechanicals are the same and so is the lenth so it is straight forward from that perspective.

As far as driving... It's a blast for performance and if all you were doing was just racing around or going to the track it's great. I live in the big city and so racing around isnt always an option. (Unless one wants to lose their drivers permit.) Also it makes driving the car on the hiway for any stretch of time a lot less fun.

I had an overdrive at first. Then went to a cr. I am now back to the overdrive. You may want to look at changing your rear diff ratio thats what I did. I now have a 3.64 with the overdrive box and I'm pretty happy with that setup.

Good Luck
Steve
 
cr vs od

Generally, the e9 is not an acceleration, stop light-to-stoplight, type of vehicle. The BMW factory usually mated a cr 5spd with a tall 3:07 diff. Anything shorter than a 3:07 will enhance acceleration but at the cost of a higher rpm at any given speed. Some have even used an 5spd OD with a 3:07 mated to a 3.5 liter but that seems a bit underdriven. I would not use a cr with anything numerically higher (lower geared) than a 3:07.
 
Redline MTL for Gear box

Loss of synchros is a great excuse to change, but have you tried Redline MTL in your gearbox? Makes a lot of difference.
 
tranny choice

Johan:
I have both set-ups-
3.0 cs with OD tranny and 3.64 diff
3.5csi with CR tranny and 3.07 lsd diff.

A major factor will be the diff. Because you have the added power of a 3.5 I suggest you go for the CR set up. Around town the CR is more fun to drive. It's not bad on the freeway either. There's a great web-site that can show you the speeds at different RPM's...I think it's metric mechanic...
 
I have a CR box in my csi with a 3.24 lsd , I have a 3.2 motor with @ 240 bhp , she gets up and goes very nicely. No complaints
 
You don't say what final drive ratio you are running. My e12 has a similar engine to yours, and I have a 3.64:1 final drive behind the OD 5 speed. I have no problem with approprate ratios for the twisties or the open road.

I'm not really a fan of the CR box/3.07 with an M30. The torque of the big six comes on in strong in the middle rev range, so running a tall final drive seriously hurts off-the-line acceleration.

I had a 3.91:1 final drive with an OD 5 speed in my e21 323i. That was short enough to hurt cruising RPM a little, but it gave that M20 some serious off-the-line punch. It surprised a lot of other drivers.
 
Heh, thanks guys.

Lots of different opinions as expected, we can all agree on which car to drive but not exactly how to configure it ;)

Just to answer two questions first:
- I have tried Redline and it made a very small difference
- I do not know which diff I have, should be the original. The car is a -74 CSi. I should know that....

And I know about the speedo cable issue but I understand it is fairly easy to add that if the box doesn't support it?

The plan was to buy a restored on from Sima or W&N and they have the speedo connection anyways.


The main goal is not the stop light to stop light driving, I just keep finding I need to shift up and down a lot "unnecessarily" to be in the right gear and I was imagining it would be easier with the CR. I'm always going betweeen 2nd and 3rd when I'm driving.

I would really have to find one to testdrive and see.

thanks again!

/J
 
steve said:
Are there 3.9 lsd availible for the e9?
Click to expand...

I do not think so. The highest non-custom diff ratio I have seen is 3.64. I have no doubt that you could send a diff to Diffsonline or Metric Mechanic and they could whip up a LSD with whatever ratio you wanted, although it would not be cheap.
 
The main goal is not the stop light to stop light driving, I just keep finding I need to shift up and down a lot "unnecessarily" to be in the right gear and I was imagining it would be easier with the CR. I'm always going betweeen 2nd and 3rd when I'm driving.
Click to expand...

That's interesting. I was driving over a very twisty hill road earlier this week. I find with the torque of my 3.5, I use 3rd for moderate corners and have plenty of power coming out, plus enough range to run the straights without shifting, and use 2nd only in the sharpest of corners. On my local track, I use 3rd for all but one corner, a hairpin that takes second. I never use 5th because the longest straight can be completed in 4th. My car pulls strongly from 1500 rpm to redline in 3rd, which equates to 20 to 90 mph.

Seems like with the narrower ratios of the CR box, you'll shift more, not less. As I understand it, the whole purpose of the close ratio box is to give you more ratios so you can keep the revs in the power band. But -- the power band for a reasonably stock M30 is a mile wide, so more ratios are redundant. If you had a built race engine with a cam biased toward high end power, headers, low restiction or no restriction exhaust, a high rear end ratio for more top speed, etc., then a close ratio box would be helpful. Otherwise -- just more shifting, not more benefit.
 
Tony,
Thats interesting my M535 with 3.5 engine and dog-leg box has enough grunt even in top gear to pull out of corners at respectable turn of speed, plus potter about in traffic if needs be.
However if I need to hussle then I drop a cog or two.....
Malc
 
Enough already!

You really need to find out what diff. ratio it has now and do the math as to the overall ratio in 2nd and 3rd. For a stock or lightly warmed 3.5 a 3.07 with CR or 3.25 with OD would be ideal. My stock CSi has the 3.25 and is just right with the 4 speed (or CR 5 speed), and a 3.45 would be plenty short if I went with the OD. The gearbox ratios are on the Metric Mechanic website if you don't have them.
 
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... :roll: 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.
 
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