UN1 More torque-ing points.!

[CHANGES 577]

As mentioned in the chat section my UN1-027 gave up due to the

excessive torque created in my modified 424 bhp 910 engine... The

failure in this case was the primary shaft at 5th gear, this is the most 

common place for it the shear.. other areas that fail from to much torque

are the 2nd gear dog teeth and the crown wheel and pinion, however these

are more likely to fail from aggressive snap gear changes that create a shock

loading on top of the torque.

Just fitting a replacement box would be a short term fix with the same inevitable

results as before... The solution i have adopted is the GTO racing kit,

The one piece thicker primary shaft with the close ratio 1st 2nd 3rd ...1st being

straight cut should fix the problem allowing me to use the full power without

worrying about failure..

Actually fitting this kit is not complicated at all , as long as you have suitable

pullers and a press..

 

 

I started by laying out the parts and making sure everything was there..I then

stripped down the broken primary shaft using gear/bearing pullers, The retaining

clips were tight and needed good quality circlip pliers..

 

 

 

 

 

Building the primary shaft was a reversal of the strip down with the aid of a press

instead of the pullers.. The 5th gear end of the shaft is done later... the only new parts

fitted other than the shaft itself will be the replacement 5th gear.

 

 

The secondary shaft was stripped to fit the new ratio 1st and 2nd gears. the same

principals applied on strip down using pullers an press tools to remove the old.

When reassembled the bulk rings were slid into position to check the locating action

with the new dog teeth.. The were a little tighter than before but only to be expected.

 

 

 

 

 

You will note in the last pic the straight cut first gear. 

Now the shafts are assembled and checked they can be installed into the casing which

has been cleaned of any remaining shrapnel from before. When fitted making sure all

bearings are positioned correctly , I can go though a sequence of tests to insure a gears

are locating and nothing is out of place..before closing..

 

 

 

I can now install the 5th gear assembly and finally torque up the shafts. Whilst doing this i

noticed the bulk ring on 5th was very tight, so i had to polish the teeth on the new gear until a smooth section action was achieved.. This is unusual but not unheard of. 

 

 

 

Once complete I refitted to the Esprit and took for a test drive.. I have done 200 miles with

it now and all seems good...The tall first gear is fine and the close ratios work well . Its a

little notchy on one and two but selects  well . i expect that to settle in time.  I can down

shift at 35 mph into 1st quite easily and hit 70+ in second without breaking a sweat .. or use

quite sedately in a normal driving manor.  I have had it jump out of 5th a couple of times early

on when casually selecting. however not for the last 100 miles when firmly selecting.. I believe

this could be a slightly bent selector fork from the failure, which on hind sight i should have

renewed .  The straight cut gear whine is not really noticeable at all  inside the car but i have

been told it is quite apparent outside.. As I put it through its paces I will keep you informed of

any developments...  

 

 

 

[CHANGES 577]

Another 200 miles on the new set up now and it is settling down well.

The notchy feel on one and two is much better, and fifth is now behaving

its self.. as the miles go on it gets better and better

The general feel is really nice, I am enjoying the fact that the gear change

is so much quicker, particularly 1st to 2nd... 0 to 60 will be good if i can get

the bloody tyres to grip...

[stugilmour 7]

Thanks for posting Dave.  I will forward the link to Richard.  Did you contact him regarding any issues? 

 

Glad to here you like the ratio change and shift action.  Getting the car out of storage next week and install set for later in May.

 

thx

 

Stu

[Dave Freeman 23]

Good stuff!, I guess a some of us will see gearbox failure at some point, the thought for most would be the horror of unpacking a box. The difficulty is I think identifying the parts that have been slightly damage and the judgement call - do I replace. Would helpful to know a ball park figure of cost.

Dave

A thought, or rather a question, a straight cut gear can transmit more power, presumably as there are little or no lateral forces. But why stop at first gear, should 2,3 be replaced with straight cuts.

Is this cost driven or no significant gains.

Edited April 25, 2013 by Dave Freeman

[sailorbob 170]

Straight cut gears are weaker than the same sized helical gear because helical gears have more teeth in mesh which results in a greater load bearing surface area.

[jonwat 260]

A thought, or rather a question, a straight cut gear can transmit more power, presumably as there are little or no lateral forces. But why stop at first gear, should 2,3 be replaced with straight cuts.

Is this cost driven or no significant gains.

Straight cut gears can handle more power & are cheaper to manufacture than helical cut gears, that's why race cars use them, but are a lot noisier then helical gears, just listen to the noise of a car reversing at speed. Way too loud for road cars.

[sailorbob 170]

For the same gear width straight cut gears are weaker than helical cut gears. Race gearboxes tend to use straight cut gears because it eliminates the side thrust that results from a helical gear and simplifies the bearing support.

[Trevsked 723]

I would imagine that a stright cut gearbox produces fewer losses and is a major reason for use in race cars, and cost of course?

 

Trevor.

[sailorbob 170]

Their efficiency is about the same at 97% - 99%.

[jonwat 260]

Race gearboxes tend to use straight cut gears because it eliminates the side thrust that results from a helical gear and simplifies the bearing support.

You can do that with herringbone gears, even more expensive of course.

[PhillipM 0]

The slight efficiency increase is as much from reducing the lateral thrust loads than the actual torque transfer efficiency itself, but yes, helical gears are actually stronger for a given size/material.

Edited April 29, 2013 by PhillipM

[ramjet 943]

You can do that with herringbone gears, even more expensive of course.

 

Yes, but you can't engage herringbone gears the way a gearbox operates by sliding gearsets along shafts.

[sailorbob 170]

In a synchromesh or dog box it isn't the gears that move to engage them.

[jonwat 260]

Yes, but you can't engage herringbone gears the way a gearbox operates by sliding gearsets along shafts.

 

They don't slide along shafts to engage, they're all constantly engaged (except, of course, reverse), that's why they're called:

 

Constant-mesh and Synchromesh Gears 

[ramjet 943]

Yeah. You're right. I don't know what I was thinking when I said that.

[peteh 0]

Any updates Dave as I am following your threads with much interest.

[DanR 61]

What ratios for 1st and 2nd and 5th did you end up with.

[CHANGES 577]

Hi Dan,

1st  standard is 3.36 and mine is now 2.66

2nd standard is 2.05 and mine is now 1.75

3rd remains the same at 1.38

This gives a close ratio 1-2-3 

On 5th i have the standard V8 ratio even though mine is a 4 pot.

This works well with my increased torque , giving low rpm at cruise and

great mpg on motorway...

With 140+ mph capability in 4th ....I use 5th as an overdrive facility.. (works well)

 

update I have done a few thousand miles with it now and all the notchy newness

has gone and all initial issues with 5th stayed away.. working great now..

My only niggle is my cerametalic paddle clutch is a little juddery in traffic with the tall

first and needs slipping a lot... It will not last long like that... However i have a completely

new clutch design/set up to fit and test this winter.... This should be even smother and

capable of 420 lb ft static...

 

[Mysterae 72 1 Vehicles]

Nice work Dave. Makes me want to get an old gearbox to take apart and play