13 replies to this topic

[cian]

What thou should a straight cut idler gear be? Also endfloat on a straight cut primary gear?

[Cooperman]

End floats should be the same as for helical gears.
If fitting straight cut drop gears, don't forget to buy a few sets of ear plugs for both driver & any passengers(and I'm being serious here).

[cian]

Thanks cooperman! Are these figures in the haynes? I had them in before i tore down the engine and ive heard louder straight cuts than mine which i thought was odd

[The Principal]

As above, if you are fitting the latest Roller Bearing drop gears the idler bearing does not need shimming as per the MED tech pages -

 

A steel top hat then replaces the idler bearing within the transmission housing which encapsulates the ider gear assembly when fitted. There is no need for any shimming as all tolerances are taken up within the gear assembly, this itself can save time and further expense on over/under size shims.

 

The primary gear end float still requires adjustment this may help -

 

http://www.minispare...55-d804159216f3

Edited by The Principal, 29 October 2013 - 06:59 PM.

[cian]

I just have the non roller bearing type, pretty comprehensive that lol

[Cooperman]

I just checked in my original BMC Workshop Manual (the Bible!).

It gives primary gear float as 0.0035" to 0.0065".

The transfer gear float is given as 0.003" to0.008".

I had assumed that you had the non-roller-bearing transfer gear, hence your asking the question  .

 

Personally I wish I had never fitted the SC drop gears, even though it's a rally car. I simply hate the noise and hate having to use ear plugs on the road. Next time the engine is out I shall go back to helical drops, but, of course, keep the SC CR gearbox to enable the engine to stay 'on cam' with the 286 cam.

[cian]

Now that you have brought it up i was going to build a sc cr gearbox with a 3.4 ratio and kent 276 cam, my previous set up was compromised by the standard ratios

Previous set up
1275
Stage 3 head
Sw5 cam
Sc fuel injection
3.4 ratio

[Cooperman]

A 3.4 with SC CR ratios and a 276 works well. With my 286 I use a 3.9:1 FDR and SC CR box with 1:1 drops. It really goes well from rest and at 7000 rpm, just where it is running off the cam it's doing 100 mph. Ideal for a rally car. Cruising on the road sections at 4000 rpm gives about 58 mph.

The SC drops are OK when crash helmets are being worn, but ear plugs are really necessary if not, unless you want to risk getting tinnitus, which is what I suffer from quite badly (it's horrible!).

The only real benefit of SC drops is for racing where the overall drive ratio can be changed between different circuits without taking the engine out to change the crown-wheel & pinion. Otherwise they are just a 'pain in the ears'.

[cian]

I was told that going to close ratios give you more traction off the line as it effectively lowers you fd in first gear is this correct? I was thinkng about putting a quaife lsd in but at 660 its a bit rich for me at the moment and is it ideal in a road car?

[The Principal]

I have a Quaiffe diff in my weekend warrior its great on roundabouts and spirited driving but how often can you realise the benefits before the plod take an interest?

Edited by The Principal, 29 October 2013 - 08:34 PM.

[Cooperman]

I can only speak from personal experience and opinion.

First of all, a SC CR gearbox has a higher 1st, 2nd & 3rd gear ratio to keep the gears 'closer' and help keep the engine 'on the cam' so it has a raised final drive ratio in 1st. That means that if the final drive ratio is too high, 1st gear take offs will require a lot of clutch slipping and hence rapid clutch wear. The acceleration will be poor as well. So, to counter this a lower FDR is used which, of course, reduces the mph/1000 rpm in 4th gear which is still 1:1 ratio. I tried a 3.44:1 with a 286 cam and it was dreadful at pulling away. Lots of clutch slipping. I had to change the clutch after just one rally.

On a road car an LSD is unadvisable. For driving on a public road you are surely not going to be doing sprint starts every time you pull away, are you? In 52 years of driving Minis I still don't like the way an LSD changes the handling and throttle response. I love the way with a standard diff if you come to a corner a bit too fast, or especially if the corner tightens a bit, you just lift off and the Mini will turn-in a bit tighter. With an LSD if you lift off in a corner it just under-steers, and I've tried all sorts of different LSD. They really are for race track or hill-climb use. I would never even use one in a rally car. The first time I drove one on a twisty B-road in the wet it scared me s******s. 

[cian]

Yeah i have heard a few people saying lsd isnt really for a road car, i had to slip the clutch on my previous set up on the standard ratios as it kept spinning the wheels in first, will the close ratios lessen this?

[Cooperman]

What do you use the car for? Is it a competition car?

I think with the 276, a SC CR 'box and 3.44:1 FDR it will drive very well and you will like the gear ratios.

[cian]

Its a road car but i would like to take it on a few track days if the opportunity came up