Jump to content
Greta

adding O/D on 2nd - on an early Spitfire

Recommended Posts

I feel I'm chickening out by taking my MKIV Spitfire on 10CR and not my MKII.
Back in the day the Rallying Spitfires did The Alpine and Monte etc and I'm chickening out of taking the Alpine passes in my 1147cc. Problem is - she has a fast road cam ( comes in at c. 3200rpm ) and a 3:89 Diff - therefore ... great for cruising the long miles to the Alps - but not so good for pulling up the hills -  she struggles to pull 3rd as the revs drop... The thought of grinding and buzzing away from lacet to lacet in 2nd doesn't really appeal. 

Logically a gear in the long gap between 2nd & 3rd seems the obvious answer. The simplest solution I've heard seems to be just to completely bypass the inhibitor switch by joining both wires ... but this solves one problem and creates two ... a) risk of trashing o/d by reversing with o/d engaged & b) would require me to simultaneously drop O/D as I changed up from O/D 2nd to 3rd.

Now I'm not that technical - it takes Janet & John type explanations before I even begin to comprehend many issues ... but I guess what I'm asking is:  can anyone provide a step by step guide to adding O/D 2nd to to my options? Better still, point me in the direction of an affordable workshop experienced in achieving this mod without sacrificing any long-term reliability.

Share this post


Link to post
Share on other sites

 feel I'm chickening out by taking my MKIV Spitfire on 10CR and not my MKII.
Back in the day the Rallying Spitfires did The Alpine and Monte etc and I'm chickening out of taking the Alpine passes in my 1147cc. Problem is - she has a fast road cam ( comes in at c. 3200rpm ) and a 3:89 Diff - therefore ... great for cruising the long miles to the Alps - but not so good for pulling up the hills -  she struggles to pull 3rd as the revs drop... The thought of grinding and buzzing away from lacet to lacet in 2nd doesn't really appeal. 

Logically a gear in the long gap between 2nd & 3rd seems the obvious answer. The simplest solution I've heard seems to be just to completely bypass the inhibitor switch by joining both wires ... but this solves one problem and creates two ... a) risk of trashing o/d by reversing with o/d engaged & b) would require me to simultaneously drop O/D as I changed up from O/D 2nd to 3rd.

Now I'm not that technical - it takes Janet & John type explanations before I even begin to comprehend many issues ... but I guess what I'm asking is:  can anyone provide a step by step guide to adding O/D 2nd to to my options? Better still, point me in the direction of an affordable workshop experienced in achieving this mod without sacrificing any long-term reliability.

https://rimmerbros.com/Item--i-158072UR - could the replacement actuator be adapted to work on 2nd too? Has anyone done this?

An old post on Triumph Experience suggests:

"My calculations show the 2-over would be a very middle position between 2 and 3. 
Second is 2.16 
2-Over I think would be 2.16 x 0.797 = 1.72, and 
Third is 1.39 
"

... so I think I've talked myself through the theory and that by machining a correctly shaped actuator - understand perhaps how it can be achieved ... I just really need someone with the engineering competence, experience and workshop facilities to make it happen ... anyone?

( PS ... is there no way on here that one can edit ones original post? )

Share this post


Link to post
Share on other sites

I think you are right with your gearing calculations,  Certainly Roger finds his useful and I don't think the gear ratios are very different between Mk2 and 1500.

Don't think you'd break a D-type with an 1147, even in second gear.

Having trouble getting my head around how you'd make inhibitor switches work on a 3 rail box to give you OD in 2nd, 3rd and 4th but not 1st and especially not reverse.  Might need a switch in the box cover rather than external ones on the remote?

Share this post


Link to post
Share on other sites

You could bypass the  switches that enable the OD on 3 and 4th and then use a relay feed off the reversing light switch on the gearbox to inhibit the OD when reverse is engaged.
That would mean that it would be impossible for the OD to work when in reverse.
I could draw a simple circuit for you if that would help?

That would let you use OD on all the gears, not ideal but as Nick said it shouldn't break the OD and a simple way of doing it. Don't know what would happen if you started in first with OD engaged I guess it would come in gradually as the oil pressure increased as the shaft speed increased.. Probably better to remember to disengage it when in first :)

regards

mike

Edited by mpbarrett

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...