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6 cyl Bristol cars Type 400 to Type 406

401 gearbox

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Old 16-11-19, 08:15 AM
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Location: Westward Ho, Devon
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Default 401 gearbox

I have to deal with the clutch so have all the floors out ready to remove the gearbox. It has an overdrive and wondered is it best to lift the gearbox/overdrive out as a unit or remove the overdrive first. Also whilst it is out, as she has been jumping out of 3rd on the overrun, I will find someone to attend to this. Any recommendations?
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Old 16-11-19, 09:01 AM
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Default Gearbox 401

Hi,
I had a similar problem with my 1952 401. I used Mike Robinson in Manchester (Mob 0775 3609 222) and he stripped and rebuilt my gearbox 3 years ago and fitted an overdrive + a remote gear lever for me.
It is now great, with smooth slick changes, no rattles and no play!
(after 60 + years in the car, many of my gearbox drive components were simply worn out!

Gearbox and overdrive come out and fit back together, but you need 2 strong men. ( My wife was not quite up to helping with the lifting out of the unit!)

Mike also supplied all new floor panel bolts for me to reassemble the floor panels, I applied copper grease to all bolts to make future removal easy.

He also supplied a 300mm longer speedo drive cable to the overdrive, as it was a bit tight in its route, speedo needle was prone to fluctuation and swings, and the cable was very close to the hot mild steel exhaust.
I re-routed the cable into smoother, gentle radius and wrapped the cable where passed over the exhaust with some heat insulation wrap.

I have had no issues with gearbox or overdrive since and now motorways at 60ish is a pleasure,

......although my original click- out trafficators refuse to pop out (or go back in) at these speeds ( wind pressure, I guess ) so I retro-fitted flashing indicators, front and rear, for my peace of mind.
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Old 25-11-19, 05:36 PM
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I have now removed the overdrive and gearbox as a single until with JUST enough clearance at the rear tunnel end once the prop drive flange is off. I am hoping to improve the synchro on second and also occasional jumping out of 3rd gear on the overrun. Any suggestions for shopping around for gearbox parts?

The main reason for removing the box is to access the clutch and sort the judder. First glance tells me the release bearing has cooked a bit, still I will know more once I have removed the clutch (an MG Diaphragm type). I will also get the flywheel skimmed anyway just in case. Fingers crossed.

Mike
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Old 25-11-19, 09:58 PM
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Mike ,
I have been told it is not recommended to remove the rear flange on an overdrive, as to refit the flange with too much force can damage the internals.
Get some advice before refitting the flange .
Splitting the overdrive from gearbox would have been the better option

Geoff
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Old 17-02-20, 09:18 PM
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Default Slow But Steady Progress

Just an update if anybody is interested. Once the gearbox was out, I took off the clutch and flywheel, the latter having now been skimmed and refitted. A complete new MGB clutch is in a box awaiting fitment. I decided that although the main reason for removing the box was to fix the clutch judder that I might as well improve the second gear synchro and a tendency to jump out of third on the overrun. This is where everything seemed to go into SLOW MO...... but last week some progress was made. Fitted proper thickness circlips to prevent the shaft moving axially, obtained a new old stock complete 2nd gear synchro hub with second gear from Bristol Cars, BUT it seems I also need the first gear freewheel hub as mine does not fit so again Bristol Cars are sending me a NOS one. Fingers crossed this one is a good fit! I did get a quote from a local precision engineering company to 3D scan to splines and do something called spark reduction on the existing splines which is very high tech but it seems eye wateringly expensive.
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Old 11-03-20, 08:00 AM
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Default Gearbox oil

Refitting my 401 gearbox this week at long last. It is the early type and what is the advice regarding oil grade and type of oil? I also have a Laycock overdrive so again any advice on best oil choice?
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Old 12-03-20, 07:40 PM
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Default Lubrication

Well a bit disappointed at not receiving any views on oil grades so have done my own research and will be using Castro’s XXL which is straight40 grade in the gearbox and overdrive which shares the same oil anyway. I managed to get the box back in today with the help of my son in law and tomorrow will be bolting everything together. Looking forward to synchronised gear changes and smooth take offs. We shall see.
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Old 16-03-20, 02:10 PM
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The 405 handbook suggests a an SAE30 for the gearbox and overdrive, I asked Brian at BCL what was best for my non overdrive box in the 401 and he suggested the same 20/50 oil we are using in the engine.
Castrol XXL is one of the oils recommended for the gearbox in the late 401's and 403's so I would have thought should be ok.
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