Grantura MKIII 1800S gearbox

[grantura1800s]

Hi,
I have some questions.
I want to fit in a 4 synchro MGB gearbox on my MKIII 1800S instead of a 3 synchro MGB gearbox. Is this possible?
Does anyone have maybe pictures or details of the original gearbox support?
Must the gearleaver be replaced regarding to the MGB gearleaver position?


Thanks,
Serge

[Old Git]

Serge

I have a MGB powered 1967 Vixen S1 which I think has an identical chassis. The car had an 18GB 1850cc engine with a three synchro non-overdrive gearbox and sixteen years ago I fitted an 18GG engine with a four synchro overdrive box. As far as I can remember the engine/box dropped straight in and I was able to use the original engine and gearbox mounts. I did have to slightly grind away half the thickness of one of the smaller near vertical small diameter chassis tubes adjacent to the new starter motor to clear the solenoid. The splines on the prop shaft had sufficient movement to accommodate any slight differences in length of the box. As you intend to keep your original engine I don't know if there is anything to prevent a 4 synchro box being used with an older engine, I suggest you email some MGB specialists.

The gear lever did move back about six inches but I cut the lever and welded it together cranked forwards so the top only moved back an inch or so relative to the old lever position. I then fitted a Triumph gear knob with the built in overdrive switch. The speedo needed recalibrating and other than that the conversion was very straightforward luckily 'cos I don't know what I would have done if it hadn't fitted!

My memory is a bit vague now but feel free to ask any other questions.

Clive

[grantura1800s]

Thanks for your info. The problem is that the original mounts are replaced on my car, because in the past they fitted a fiat engine and gearbox. The engine mounts are still in but in a different place. I can see the remnants were they were be welded original. I have now a complete new engine (modified MGB engine, to 1950 cc and X-flow head, etc.) and i wanted to fit to this a 4-synchro gearbox. So your info is very usefull. The gearbox mount im still looking for a picture or drawing. I think the original gearbox mount they used is TVR and not MGB. Or im a wrong?

Serge

[heightswitch]

Hi serge.
From what you are saying It may be a better idea to re-instate your chassis mounts back to original and then mount your engine and box from there. Why not post some pics of your set up so we can see the differences then we can give you the dimensions of what should be there.

neil.

[thegamekeeper]

Hi Serge, hope you are well. What you are trying to do is possible but NOT straightforward. The Grantura Mk3 chassis is significantly different to 1800S chassis and is narrower at the rear of engine bay. The engine plate you need to fit 4 syncro box is too wide to fit in chassis. You will also need to fit pre engaged starter which means using upside down oil filter with cannister filter. This means you need side entry distributor cap which means you need to change from dynamo to alternator. This means some rewiring. Every time you do oil change you need to remove alternator and one weber to access oil filter which means you have to rebalance carbs. To do this you need to remove pedal box to get carb balancer on rear carb.

Are you fitting overdrive gearbox? If you do the overdrive unit goes where existing handbrake mrchanism is so you will need to relocate the handbrake. Of course you will need a new propshaft. The MBG clutch slave cylinder is a very tight fit.

The good news is that you can move the gearlever forward by fitting gearlever from Sherpa van, the bad news is they are getting hard to find. sTeVeR

[thegamekeeper]

If it is going into an 1800S then the problem with the engine plate is solved because the chassis is wider than a Grantura Mk3

[thegamekeeper]

Hi Serge, ignore everything I said. Of course your car is an 1800S, I always get your car confused with Rob de Vos's car. Luckily my treatment for senility starts in the new year. sTeVeR

[grantura1800s]

Anyway thanks for help. I wasn't aware that MK3 chassis was different to the 1800S chassis.

[thegamekeeper]

Hi Serge been trying to send some emails to registry website but thet keep being returned as "bad destination email address". Have you changed email address or do you have another one I can try sTeVeR

[grantura1800s]

My e-mail is [e-mail] Must be working, because i still receive e-mails.

Serge

[grantura1800s]

Steve,

Thanks for your info about those 2 grannies. I shall try to add them the comming weekend.

Serge

[thegamekeeper]

Thanks Serge. I tried to send the details some time ago but for some reason it kept retuning it as spam. I sent it through another email server and it went no problem. I must get round to sending details of JCU 701 for the register but believe it or not I dont have any photos of the car sTeVeR