Anything and everything GT6.

Section : Overdrive

Overdrive

Posted By : Dom Weaver, 28-Jul-2003, 07:02pm

OK, here's another lovely Overdrive query...

The overdrive is working a treat - now the electrics are sorted out. However, once the car has done a few miles and cruising on the motorway, the overdrive will firstly go in and slip back out. Then on further attempts I get that "half-way" feeling and finally nothing whatsoever.

It generally seems to occur when sitting at around 3000 rpm in non-overdrive fourth. If i reduce the speed, say to 2000 rpm and then try the overdrive again its fine. Goes in and out no problem. It's as though it's oil pressure related - any ideas?

Oh, and while i'm on the subject, does anyone have any advice, best practice or techniques on using overdrive? i.e. Should the throttle be released completely before engaging overdrive etc etc.

And another thing I was pondering on the M3 yesterday, do you racers make use of overdrive much, or is it taken out?

ta-ta

Followups :

Overdrive

Posted By : David Thompson, 29-Jul-2003, 08:49am

Dom,

Using an overdrive in a racer seems to be a matter of personal preference

Fors;
You can run a much higher diff without compromising your speed.

Against;
Extra weight
More to go wrong

Andy Stark in the USA runs one and on some of the longer USA circuits he regularly sees 120mph but still has the acceleration from a 4.11 diff. running at a rev limit of 7,000rpm.

I don't think that Clive Gimson uses one but I believe that Karl Dandridge was at first - not sure if he is now.

On a circuit like Snetterton it would be a big advantage as you run out of revs very quickly, somewhere like Mallory it would be a waste of time.

Cheers

Dave
- Overdrive
  
  Posted By : Nigel Gibbins, 29-Jul-2003, 12:08pm
  
  In the 1300 Spitfire (small journal) I don't think they're worth it as you can rev any good version of this engine to 8,000 and that 120mph with a 4.11 diff.
  
  I think the only circuit I would worry about running out of revs is Thruxton, but I would expect to hit the rev limiter a Snetterton too, but more likely a the end of the straight.
  
  If you run a 1500 engine then it's probaby worth it.
  
  Another point against the O/D in racecar is that it will take a few extra BHP away from your roads wheels - and we all claim to try to squeeze the last ounce out of our engines...
  
  NiG
  http://www.niginthecar.net
Overdrive

Posted By : Nigel Gibbins, 29-Jul-2003, 12:01pm

This is the same problem I've been having and I'm going to make/fit some ducting to draw cold air into the transmission tunnel as per Laurences suggestion - you have to admit he is a clever chappie

NiG
http://www.niginthecar.net
Overdrive

Posted By : Graham Reeks, 30-Jul-2003, 11:19am

Try the Canley Classics O/d page - it has some useful diagnoses and tips. A friend recently did this and then purchased a new clutch for his o/d box as a result of the tests suggested. It solved the problem which was basically the same as yours.
nb: overdrive repair company in sheffield are the cheapest for spares!
- Overdrive
  
  Posted By : Dom Weaver, 30-Jul-2003, 12:27pm
  
  Yeah, I had a look on Canleys site a few weeks ago while I was waiting for my new engine (and clutch)
  
  After what Laurence an Nigel have mentioned, I think Ii'm gonna follow the overheating route first...
  
  Thanks