401 gearbox

RALPH M · #1 (**permalink**) 25-11-19, 06:36 PM

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

Geoff Dowdle · #2 (**permalink**) 25-11-19, 10:58 PM

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

RALPH M · #3 (**permalink**) 17-02-20, 10:18 PM

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.

RALPH M · #4 (**permalink**) 11-03-20, 09:00 AM

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?

RALPH M · #5 (**permalink**) 12-03-20, 08:40 PM

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.

Geoff Kingston · #6 (**permalink**) 16-03-20, 03:10 PM

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.

RALPH M · #7 (**permalink**) 12-04-20, 11:04 AM

Now I am grounded like us all, I am attending to several tidying up jobs on the Bristol as sick of gardening! I did take the 401 for a brief test drive before lock down with Castrol XXL 40 in the gearbox and overdrive and was very pleased that all the synchro worked and the gears shifted nicely. The change was a bit notchy so I have since slackened off the detent springs slightly but otherwise very pleased. The clutch is also now super smooth so clearly the minute skimming of the flywheel was just what was needed. Such a shame we are missing this weather but we fully support the stay home policy.