Getrag gearbox/prop-shaft

[EXCEL V8]

The Getrag gearbox has several kilogram of lead bolted to the rear of it.  Given the Lotus weight ethos why would they do this?  Does it have to do with vibration control?  Where might all this vibration be coming from on a notoriously good gearbox?  I think it's the prop-shaft - it is oddly designed (I think) - it has a u/j at one end and a CV at the other.  This means that variations in the speed of the prop-shaft main tube caused by the u/j at the front are then carried into the rest of the drive train because they are not cancelled out by a second u/j at the tail of the prop.  Does this make sense?  What I'm getting at is that a "normal" prop with either u/js or CVs at both ends would make the lead weights superfluous, surely?  What do you think guys?

Pete

[Angus553]

Its a very good question. I dont know the answer but if it isnt vibration/noise suppression/absorption it maybe weight distribution/altering or lowering the centre of gravity or could it be the legendary ground effects for the road cars!! Wouldnt it be good if it was.

[mikeeech]

I have ujs on both ends of my prop shaft and no weights on the gearbox. Several kilo grams sounds like a big bit of lead. Do you have photos since the fixing point doesn't seem that big!

[Tony D]

Mike : Do you have the getrag box though or the original series 1 Maxi based box? 

Like yours, my series 1 Elite has UJ's both ends, the maxi box and no lead weights. I've never seen one with a mixture. 

Maybe the lead is some sort of handicap system🤔

Tony 

[pbharcourt]

I removed the lead weight from my Getrag gearbox and found no difference at all.

Probably cancelled out high speed vibration but as mine only gets to potter around with a few high speed blats I don't think it matters too much.

[mikeeech]

1 hour ago, Tony D said:

Mike : Do you have the getrag box though or the original series 1 Maxi based box? 

Like yours, my series 1 Elite has UJ's both ends, the maxi box and no lead weights. I've never seen one with a mixture. 

Maybe the lead is some sort of handicap system🤔

Tony 

No I fitted a getrag with all the bits coming from lotus bits ( prop shaft, clutch plate, chassis support and sppedo drive). Luckily I swapped to a S2 chassis as well so had the mounting points for the gearbox.

[EXCEL V8]

There were two different props fitted to the Getrag-equipped cars.  The early type had a u/j at the front and a plunging CV at the rear, and the last cars had two u/js which were "phased" (no information about the actual phasing).  Both are tube-in-tube types, with rubber bonding (as with the Series 1 Lotus-'boxed cars and the Excel).  I'm going to see if Mike Taylor has a later type to analyse the phasing - since I may be putting 250lb.ft through it I may want to get a stronger one made with similar phasing.

I'll get some photos over the weekend.

Mike - if yours has never had the weights have you ever thought it had any vibration/resonance problems?  You must have one of the later propshafts if it has two u/js.

Paul - do you know which joints you have on your propshaft?

Cheers

Pete

[mikeeech]

To be fair I've never driven it. When I noticed that there seemed to be something missing from the bottom and posted on here about it a few years ago Paul mentioned that his didn't have the weight so I have not worried too much about it. I have plenty of lead and making one wouldn't be too hard if I knew the dimensions but I'll cross that bridge at some point in the future as access is easy. If anyone has the dimensions of the weight that would be useful as a reference.

If it really is a couple of kilos then the size of the mounting point would mean it would be quite deep and would be vulnerable to speed humps. 

[Clive59]

Mine's an early S2 Elite, and soon to pull out engine and gearbox, will take photos and measurements. Interesting bit of info.

[EXCEL V8]

So in theory Clive, yours should have the weights and the prop with the CV at the rear.

Pete

[soldave]

Good discussion and reminds me of a thread on here about my propshaft cv joint. Mine is a '79 523 Eclat and has a u-joint at the front (which I need to grease - good reminder here!) and a CV joint at the back.

 

[EXCEL V8]

Here are the weights:   They are made by forming a welded-up shape in mild steel and then filled with lead.  The saddle-shaped piece sits on top of the 'box and also acts as a support for the gear lever assembly via the Metalastic bobbin.  This bit weighs 3.4kg + bolts.  The rectangular bit weighs 4.0kg + bolts and fixes under the tail-end of the 'box.

Pete

[mikeeech]

I had no idea the brown rusty thing on the back of my gearbox was a weight!



I'm only missing the one underneath (the rectangular one). Could you post the dimensions of the rectangular one?

 

Edited July 12, 2020 by mikeeech

[Clive59]

You left the gear knob on Mike. Was there any clearance issue with leaving it on? Seems like a big fiddle to remove if no need.

[EXCEL V8]

Mike - what  combination of joints do you have on your propshaft?  

I'm looking at trying to make it easier to fit the gearbox without the gear lever attached - I can see that being a pain when I come to fit the engine/'box.  My gear lever's rubber damping material is very soft and I'm not keen on the sensation of a bendy gear lever so I may delete the rubber all together and fabricate a removable upper section.  I know that will transmit a little more noise but it will probably be worth it.  The whole assembly is already rubber mounted to the 'box.

Pete

[mikeeech]

17 hours ago, Clive59 said:

You left the gear knob on Mike. Was there any clearance issue with leaving it on? Seems like a big fiddle to remove if no need.

The gear knob just unscrews. It's similar to the S1 knob but with a different gate pattern. With the getrag box though the gearstick stays on when the engine goes in as its impossible to attach the gear lever once in the car. 

Second or forth gets it through the hole in the body but it does need a load leveler and the front end of the car needs to be as high as possible

8 hours ago, EXCEL V8 said:

Mike - what  combination of joints do you have on your propshaft?  

I'm looking at trying to make it easier to fit the gearbox without the gear lever attached - I can see that being a pain when I come to fit the engine/'box.  My gear lever's rubber damping material is very soft and I'm not keen on the sensation of a bendy gear lever so I may delete the rubber all together and fabricate a removable upper section.  I know that will transmit a little more noise but it will probably be worth it.  The whole assembly is already rubber mounted to the 'box.

Pete

Pete,

Is yours a getrag box. I didn't really examine the mechanism on mine so I'm not familiar with the rubber damping material. It's all coming out again soon so I'll take another look.

[EXCEL V8]

Yes - I have done what you have done and replaced the Lotus box with the Getrag.

The lower weight measures 140mm x 75mm x 40mm.  The M10 holes are at 95mm centres.  The little triangular cut-out is 40mm x 20mm and 7mm deep.  The 45 degree chamfer on the block is 15mm x 15mm.

Pete

[mikeeech]

Thats really useful and will make it easy to make up a new one if needed.