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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #1  
Old 12th September 2022, 08:50
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Default Considering an automatic gearbox swap

Oh my. This place hasn’t changed a bit… ��

As title. I have an m20b25 engine & a getrag 5 speed manual box at the moment. I’m thinking of swapping to an auto. Don’t laugh, but over the past 5ish years I’ve managed to pick up a condition that really doesn’t give the strength I once had in my legs anymore - so driving Vikki for any length of time leaves me aching and shattered from the heavy clutch on her.

What I need to know (if anyone knows) is what’s entailed bar the new box & torque converter. I think I’d need a new ecu. And probably a kick down switch on the throttle?

Thanks

Jason

(Still around, now over 50, not willing to part with Vikki just yet)
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  #2  
Old 13th September 2022, 09:48
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Default Welcome back!

Hi Jason,
welcome back to the forum although things are a lot quieter here these days as there are fewer of us left. So sorry to hear about your condition and I hope you can still get out about in your Sportster.
Retrofitting an auto box is an intriguing project but quit a major project. My biggest concern (which you may have already checked?) is whether the BMW auto box will fit in the steel tunnel. Mike Garner might know if anyone has fitted an auto to a Cabrio which I think has the same dimensions as the Sportster chassis.
Maybe an alternative idea would be to fit a servo to the clutch hydraulics. From a bit of googling I found this is a not uncommon upgrade on MGB's to make the clutch pedal lighter. People seem to use a standard remote brake servo. Maybe you could fit one high up in the passenger footwell as I doubt there is enough space under your bonnet.

all the best,
Peter
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  #3  
Old 13th September 2022, 13:13
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Thanks Peter - I’ll take a look. I’ll also drop Mike a PM.
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Old 14th September 2022, 15:55
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Hi Jason

Nice to see you back on here, though sorry to hear of your health issue.

Your question raises several intriguing questions. As Patrick has questioned, the first is Will it physically fit? The Cabrio does have the same transmission tunnel as the Sportster, and I know there have been auto Cabrios built, and even retro fitted (for similar reasons to your own).
I cannot offer any direct experience with auto gearboxes other than to raise pertinent questions:
You will need an auto flywheel and bolts to accept the auto box - it might be best to buy an auto donor to get everything you need and swap you engine to the flywheel gearbox, and all the engine and gearbox electrical harness?
A new prop shaft
A new rear gearbox mount
The gear selector mechanism

Just a thought - if you are going to the trouble of changing gearbox, why not change engine as well and go much more modern to get a dual clutch auto box? This would do away with any kick down mechanism.
The M20’s autobox is very lazy - you will miss the acceleration you currently get from your manual, and pretty thirsty too!


Patrick’s idea of a servo assist is interesting if reducing pedal pressure will resolve your health issue, and will be much easier to install.
Peter Edwards (built a Sportster around your time) is building a Royale Sabre and has incorporated an (MG) remote servo in the brake circuit, so would be a good person to have a chat with.

One last thought: my clutch pedal was really heavy with my first design - so I changed the fulcrum position and pedal length which made it mechanically much easier to depress. It made the pedal travel a little longer, but is now so much easier to live with.
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  #5  
Old 17th September 2022, 14:53
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Hi Jason
There also clutch electrification kits available. I was reading about one the other other day fitted to a motorhome. Basically a button on the gearstick which you press which operates tge clutch via some sort of servo.
Cheers Robin
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  #6  
Old 18th September 2022, 04:17
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I think a big part of the heavy clutch is the pedal box design, mine doesn't disengage until quite far down with considerable pressure, and I just changed everything for new parts last month (https://www.msportster.co.uk/2022/08/07/clutch-hosed/)

Years back I tried using a wilwood pedal and master (two different bore sizes), I did manage to get lighter pedal but the travel was so far it wasn't pleasant to use.

I think I'd try the servo assit next as Peter suggested.

Last edited by Patrick; 27th September 2022 at 07:47.. Reason: typo
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  #7  
Old 26th September 2022, 08:57
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I spent most of Sunday taking the pedal box out. I found that for some inexplicable reason I’d mounted the master at an angle that didn’t allow parallel travel of the rod…

It can’t have helped with the pedal feel. I’ve now aligned it so the stroke is all in line with the barrel of the master.

It’s back in Vikki, but I need to put the column back in and then bleed the clutch before I can say if it’s made any difference
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Old 26th September 2022, 22:16
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I bled the clutch tonight, and all I can say is it’s lighter than it was - how I’ll fair with it remains to be seen. But I think if I need any more adjustment I’ll add a servo as suggested. I think I’d be able to squeeze one in on the passenger side of the engine bay.
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  #9  
Old 28th September 2022, 17:03
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So far so good. I’ve gone as far as getting her taxed, MOTd and insured as it seems to be a lot more comfortable. Just in time for some autumnal blasts
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Old 1st October 2022, 12:36
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Excellent
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