Modena's progress update

[Tenrocca]

Originally Posted by Modena

Pilot bearing was suggested to me thanks Andrew. However it is the right one, there's only two sizes and it would be very hard to get wrong. I installed the bearing myself so I'm confident it is correct. How did you get it wrong?

Rookie error. One of the few parts not interchangeable between the 5.7 and 6 litre blocks. As a rule, 5.7 blocks use the small pilot bearing. 6l+ blocks the big one.

[SVO 050]

I have been changing the reverse switch in my Tremek and looked at the Mal Wood site for info on the box.
I read in the Tremek installation info that you should not try to shift gears above 6400 rpm??
Anyone seen this detail and can explain why?
Cheers
SVO

[Aussie Mike]

Originally Posted by SVO 050

I have been changing the reverse switch in my Tremek and looked at the Mal Wood site for info on the box.
I read in the Tremek installation info that you should not try to shift gears above 6400 rpm??
Anyone seen this detail and can explain why?
Cheers
SVO

The job of a synchro in the gearbox is to match speeds between gears so that when the next gear is selected it will slot in easily. It means us ham-fisted drivers can easily select a gear without having to double clutch and spin the box up to match gear speeds.

The synchro is a kind of conical clutch between each gear where one cone is forced inside another cone. They were once brass on steel but now they have organic facings like a Kevlar and carbon fiber. The issue is these clutches like any clutch can only transmit so much power. The can only cope up to a point with the loads to spin gears up and down from high RPMs.

6400RPM is probably the manufacturers recommendation for the limit of what the synchros can cope with.

Interesting fact: The cone clutch design was used as the main clutch in many early automobiles. Clutches were faced with leather or cork. Often the clutch pedal had to be pushed down to force the cone into it's socket and transmit engine power to the trans.

Racing gearboxes like in V8 supercars or F1 don't have synchros. They have dog rings on the gears. These are rings with a hard step on them. As the gear is moved across on it's shaft the edges of the steps on the dog rings collide with a bang, the gears speeds are matched instantly and the gear slots in. Very harsh and only works when shifting hard. Gear speeds need to be matched carefully on downshifts (double clutching etc). Not much good for driving down to the shops but they cope with big HP and high RPM shifting.

Cheers

[Jaydee]

And to add to that, they are usually straight cut gears. That's why they whine so much.
JD

[Aussie Mike]

Originally Posted by Jaydee

And to add to that, they are usually straight cut gears. That's why they whine so much.
JD

You are correct. Actually I think they have to be straight cut for the dog rings to work.

Update looks like I was wrong, there are helical cut dog engagements. Found an interesting article about straight cut vs helical cut gears and the reason whey straight cut are used in race boxes. It's down to the side loads a helical cut gear exerts on the case. Straight cut don't exert any side loads so the gear case doesn't need to be as beefy for the same power level.

http://automotivethinker.com/transmi...rs-vs-helical/

Cheers