Grantura (MkIV) final drive
Discussion
I want a lower final drive ratio for my Grantura. Preferably with a gear ratio between 3,1:1 and 3,5:1. I have been searching the Internet but I cannot find any stock units that are lower than 3,7.
Does anybody know if any aftermarket gear sets with that kind of numbers are available for the MGB banjo axle?
My car has an overdrive gearbox fitted today but as I have a tuned engine (not MGB) I want to replace the OD-box with a stronger unit that is 1:1 on highest gear. Hence the need for a lower final gear.
I assume that one possibility is to convert the car to Salisbury (Jaguar) diff, like Griffith 400. The Salisbury diff are available with gearings like 3,54:1, 3,31:1 and lower. But how much modification of the chassis is needed to install one? Will custom driveshaft have to be made or can the stock ones be modified to fit the Salisbury diff, etc…?
Help and advice is appreciated
//Göran
Does anybody know if any aftermarket gear sets with that kind of numbers are available for the MGB banjo axle?
My car has an overdrive gearbox fitted today but as I have a tuned engine (not MGB) I want to replace the OD-box with a stronger unit that is 1:1 on highest gear. Hence the need for a lower final gear.
I assume that one possibility is to convert the car to Salisbury (Jaguar) diff, like Griffith 400. The Salisbury diff are available with gearings like 3,54:1, 3,31:1 and lower. But how much modification of the chassis is needed to install one? Will custom driveshaft have to be made or can the stock ones be modified to fit the Salisbury diff, etc…?
Help and advice is appreciated
//Göran
What are you doing with the car? what engine are you running?
MGB Banjo type diff can be had in different ratio's, certainly enough early MGB Racers are around in period running the banjo. Do you need a lower ratio to allow for a 5 speed gearbox or just lower revs for more relaxed cruising?
Salisbury can be installed and made to re-use driveshafts with adaptor plates to allow driveshafts to be fitted. But the Jag Diff is very heavy compared to the alloy cased Banjo. You will need to build an H frame to hang the diff in and a lower carrier. 4 brackets need welding into the top framework and the diagonal tubes removed. the lower mount requires brackets welded to the lower chassis rails immediately above where the front pinion shaft exits.
It all depends on what you want from the car.
N.
MGB Banjo type diff can be had in different ratio's, certainly enough early MGB Racers are around in period running the banjo. Do you need a lower ratio to allow for a 5 speed gearbox or just lower revs for more relaxed cruising?
Salisbury can be installed and made to re-use driveshafts with adaptor plates to allow driveshafts to be fitted. But the Jag Diff is very heavy compared to the alloy cased Banjo. You will need to build an H frame to hang the diff in and a lower carrier. 4 brackets need welding into the top framework and the diagonal tubes removed. the lower mount requires brackets welded to the lower chassis rails immediately above where the front pinion shaft exits.
It all depends on what you want from the car.
N.
Thanks for your reply. I guess a little more information is appropriate.
The car is just for track days and road use. So the purpose is to lower revs when cruising but without using an overdrive transmission.
The engine is a Volvo B20 and the gearbox is a Volvo M41. This setup can be found in the Volvo 120, 140 and P1800 series. It was also fitted to the Marcos 1800GT. It is tuned to about 170+ hp with different camshft, bigger valves and dual dellorto 45s. Unfortunately I have not had it to the dyno I don’t have any actual numbers regarding torque and power.
The Volvo drivetrain was installed after the Swedish authorities refused the previous owner to register the vehicle with a Ford 289” engine and transmission. The V8 was already installed and extensively test driven when he found out it was illegal. For some reason the previous owner decided to stick with the MGB diff like the Griff 200. He told be he was sure that it would cope (I was not!).
Anyway, as the original MGB engine was completely worn out he decided to replace it with a local and reliable unit that the authorities could accept. When I took over I simply decided to carry on…
The M40 transmission is a four speed box with a Laycock de normanville J-type overdrive. The OD-is known for having trouble with too much torque and it is also on the limit for the actual gearbox. I would like to switch to a much stronger Volvo M400 (originally fitted to the 6-cylinder Volvo 164 and a few P1800). Outside dimensions are almost exactly the same as the M40 but the M400 is “bullet proof” when it comes to torques. As I already have one with the correct bellhousing to fit my engine it would be a perfect choice. However, the M400 is 1:1 on highest (4th) gear!
There the possibility to install a Getrag transmission from a BMW with modified bellhousing. This is a quite common modification when turbo charging old Volvos (which is very common here
). However I’m afraid they are too big to fit a Grantura and I don’t think they have the right look for a 1960s car.
I have also not yet found out if they are 1:1 or “overdrive” on highest gear.
//Göran
The car is just for track days and road use. So the purpose is to lower revs when cruising but without using an overdrive transmission.
The engine is a Volvo B20 and the gearbox is a Volvo M41. This setup can be found in the Volvo 120, 140 and P1800 series. It was also fitted to the Marcos 1800GT. It is tuned to about 170+ hp with different camshft, bigger valves and dual dellorto 45s. Unfortunately I have not had it to the dyno I don’t have any actual numbers regarding torque and power.
The Volvo drivetrain was installed after the Swedish authorities refused the previous owner to register the vehicle with a Ford 289” engine and transmission. The V8 was already installed and extensively test driven when he found out it was illegal. For some reason the previous owner decided to stick with the MGB diff like the Griff 200. He told be he was sure that it would cope (I was not!).
Anyway, as the original MGB engine was completely worn out he decided to replace it with a local and reliable unit that the authorities could accept. When I took over I simply decided to carry on…
The M40 transmission is a four speed box with a Laycock de normanville J-type overdrive. The OD-is known for having trouble with too much torque and it is also on the limit for the actual gearbox. I would like to switch to a much stronger Volvo M400 (originally fitted to the 6-cylinder Volvo 164 and a few P1800). Outside dimensions are almost exactly the same as the M40 but the M400 is “bullet proof” when it comes to torques. As I already have one with the correct bellhousing to fit my engine it would be a perfect choice. However, the M400 is 1:1 on highest (4th) gear!
There the possibility to install a Getrag transmission from a BMW with modified bellhousing. This is a quite common modification when turbo charging old Volvos (which is very common here
). However I’m afraid they are too big to fit a Grantura and I don’t think they have the right look for a 1960s car. I have also not yet found out if they are 1:1 or “overdrive” on highest gear.
//Göran
Edited by Grantura SWE on Friday 29th August 16:44
Edited by Grantura SWE on Friday 29th August 16:45
Grantura SWE said:
Thanks for your reply. I guess a little more information is appropriate.
The car is just for track days and road use. So the purpose is to lower revs when cruising but without using an overdrive transmission.
The engine is a Volvo B20 and the gearbox is a Volvo M41. This setup can be found in the Volvo 120, 140 and P1800 series. It was also fitted to the Marcos 1800GT. It is tuned to about 170+ hp with different camshft, bigger valves and dual dellorto 45s. Unfortunately I have not had it to the dyno I don’t have any actual numbers regarding torque and power.
The Volvo drivetrain was installed after the Swedish authorities refused the previous owner to register the vehicle with a Ford 289” engine and transmission. The V8 was already installed and extensively test driven when he found out it was illegal. For some reason the previous owner decided to stick with the MGB diff like the Griff 200. He told be he was sure that it would cope (I was not!).
Anyway, as the original MGB engine was completely worn out he decided to replace it with a local and reliable unit that the authorities could accept. When I took over I simply decided to carry on…
The M40 transmission is a four speed box with a Laycock de normanville J-type overdrive. The OD-is known for having trouble with too much torque and it is also on the limit for the actual gearbox. I would like to switch to a much stronger Volvo M400 (originally fitted to the 6-cylinder Volvo 164 and a few P1800). Outside dimensions are almost exactly the same as the M40 but the M400 is “bullet proof” when it comes to torques. As I already have one with the correct bellhousing to fit my engine it would be a perfect choice. However, the M400 is 1:1 on highest (4th) gear!
There the possibility to install a Getrag transmission from a BMW with modified bellhousing. This is a quite common modification when turbo charging old Volvos (which is very common here ). However I’m afraid they are too big to fit a Grantura and I don’t think they have the right look for a 1960s car.
I have also not yet found out if they are 1:1 or “overdrive” on highest gear.
//Göran
I may be wrong but I believe an MGB V8 is 3.07 and MGC 3.31 and I think that these are a straight swap for a 'standard' MGB diff which is 3.9, however I suggest you speak to an MG specialist such as Malcolm at Brown and Gammons to ensure you can just swap. The car is just for track days and road use. So the purpose is to lower revs when cruising but without using an overdrive transmission.
The engine is a Volvo B20 and the gearbox is a Volvo M41. This setup can be found in the Volvo 120, 140 and P1800 series. It was also fitted to the Marcos 1800GT. It is tuned to about 170+ hp with different camshft, bigger valves and dual dellorto 45s. Unfortunately I have not had it to the dyno I don’t have any actual numbers regarding torque and power.
The Volvo drivetrain was installed after the Swedish authorities refused the previous owner to register the vehicle with a Ford 289” engine and transmission. The V8 was already installed and extensively test driven when he found out it was illegal. For some reason the previous owner decided to stick with the MGB diff like the Griff 200. He told be he was sure that it would cope (I was not!).
Anyway, as the original MGB engine was completely worn out he decided to replace it with a local and reliable unit that the authorities could accept. When I took over I simply decided to carry on…
The M40 transmission is a four speed box with a Laycock de normanville J-type overdrive. The OD-is known for having trouble with too much torque and it is also on the limit for the actual gearbox. I would like to switch to a much stronger Volvo M400 (originally fitted to the 6-cylinder Volvo 164 and a few P1800). Outside dimensions are almost exactly the same as the M40 but the M400 is “bullet proof” when it comes to torques. As I already have one with the correct bellhousing to fit my engine it would be a perfect choice. However, the M400 is 1:1 on highest (4th) gear!
There the possibility to install a Getrag transmission from a BMW with modified bellhousing. This is a quite common modification when turbo charging old Volvos (which is very common here
). However I’m afraid they are too big to fit a Grantura and I don’t think they have the right look for a 1960s car. I have also not yet found out if they are 1:1 or “overdrive” on highest gear.
//Göran
Edited by Grantura SWE on Friday 29th August 16:44
Edited by Grantura SWE on Friday 29th August 16:45
As far as I know 3.909 was the only ratio used in an MGB: 4.1 was only in an MGA twin cam and 1600 de luxe: 4.3 was in lots including MGA 1600s, 4.55 in lots including MGA 1500s: 4.875 in a 10cwt van. Lower ratios were only available through special tuning for competition and are now pretty unobtainable, although I'm happy for someone to tell me that an A55, Sherpa or something obscure had a 3.5 or 3.7 as standard. If you do swap bear in mind that they changed from course to fine spline in 1962 with the introduction of the MGB, so the output shafts may differ.
An MGB gearbox is already 1:1 direct drive in 4th and overdrive makes it about 0.8:1. In an MGB on 14" wheels overdrive 4th gives about 22mph per 100 revs. Those of us who race MGBs use competition overdrive units from ORS which may be a way to enable yours to cope with the extra power. They appear to do J type
http://www.overdrive-repairs.co.uk/products.html
HTH
Cheers
Richard
Hi,
My Gilbern runs an MGC back axle with a 3.31 diff.
I would suggest you go to Denis Welch Motorsport and see what they've got in the way of crownwheel/pinion sets.
PM me if you want a 3.31 MGC CWP set - I bought a scrap Gilbern off the Club and robbed the roof off it. The axle is spoken for but the car it's going into has a tired axle with a 3.31 diff that may be going spare.
Cheers
Chris
Hi,
Robbed off the MGB V8 website ... sorry MGC's don't have the Banjo and it looks like you even have to machine a later MGB diff carrier to accept an MGC crownwheel/pinion ..
Chris
Quote
"The 1800 B has used two types of axle. The early cars used a banjo axle, up to GHD3 and GHN3 132923. Later vehicles were fitted with a Salisbury or tube type.
The standard 1800 B tube axle has a ratio of 3.07:1. Unfortunately no suitable ratios have been made up for the banjo axle.
The tube axles fitted to the 1800 and V8 are basically the same except for the crown wheel and pinion, differential cage, pinion oil seal and prop shaft flange.
The MGC used the tube axle in both wire wheel and bolt on (5 stud fixing) forms. These two ratios, 3.3:1 and 3.07, although very similar these axles were fitted with Girling rear brakes instead of Lockheed.
Although V8 crown wheels and pinions are no longer available form Leyland, reproduction items are. The 1800 differential cage can be machined to accept the V8 crown wheel. The settings up of the crown wheel and pinion is rather complex and requires some specialised tools(refer to the MGB workshop manual). A limited slip differential cage can also be obtained for the MGB axle.
Robbed off the MGB V8 website ... sorry MGC's don't have the Banjo and it looks like you even have to machine a later MGB diff carrier to accept an MGC crownwheel/pinion ..
Chris
Quote
"The 1800 B has used two types of axle. The early cars used a banjo axle, up to GHD3 and GHN3 132923. Later vehicles were fitted with a Salisbury or tube type.
The standard 1800 B tube axle has a ratio of 3.07:1. Unfortunately no suitable ratios have been made up for the banjo axle.
The tube axles fitted to the 1800 and V8 are basically the same except for the crown wheel and pinion, differential cage, pinion oil seal and prop shaft flange.
The MGC used the tube axle in both wire wheel and bolt on (5 stud fixing) forms. These two ratios, 3.3:1 and 3.07, although very similar these axles were fitted with Girling rear brakes instead of Lockheed.
Although V8 crown wheels and pinions are no longer available form Leyland, reproduction items are. The 1800 differential cage can be machined to accept the V8 crown wheel. The settings up of the crown wheel and pinion is rather complex and requires some specialised tools(refer to the MGB workshop manual). A limited slip differential cage can also be obtained for the MGB axle.
Hi Chris.
Not sure if machining to accept later CWP is an option. The banjo Diff in a grantura was housed in a TVR Specific casing.
It may be possible but not sure.
Goran. if you want to go to a salisbury set up and need to see how it all fits e-mail me and I will send you some pics of a salsbury 4HU installation in a Grantura Chassis.
N.
Not sure if machining to accept later CWP is an option. The banjo Diff in a grantura was housed in a TVR Specific casing.
It may be possible but not sure.
Goran. if you want to go to a salisbury set up and need to see how it all fits e-mail me and I will send you some pics of a salsbury 4HU installation in a Grantura Chassis.
N.
Edited by heightswitch on Sunday 31st August 20:10
I have checked and V8 and MGC diffs are NOT interchangeable with early banjo axle MGB diffs. The 3.07, 3.31 and 3.7 diffs are all for tube axles, so the lowest available standard ratio for a banjo diff is 3.9 unless you can find a period special tuning racing one (unlikely methinks)
Looks like ORS for an uprated competition overdrive or a complete diff change to Jaguar/Salisbury as per Griffith 400
Cheers
Richard
Looks like ORS for an uprated competition overdrive or a complete diff change to Jaguar/Salisbury as per Griffith 400
Cheers
Richard
Grantura SWE said:
Thanks Richard
I have now recieved photos of hoe to make a Salisbury installation from Neil. It look like a very straight forward operation so it might just be what I'll end up doing.
Cheers
//Göran
Goran some thoughts before you embark on your little fabrication Quest:I have now recieved photos of hoe to make a Salisbury installation from Neil. It look like a very straight forward operation so it might just be what I'll end up doing.
Cheers
//Göran
My original top carrier was made in round tube. using square hollow section approx 40mm x 40mm will be easier to fabricate and allow the 6mm top plate to be welded in a lot easier.
when you weld the top plate into the carrier tubes note that mine has a little arrow facing forward. This denotes that you need to set the top plate nose down approx 4 degrees which in turn sets the pinion flange level. You may like to check your rear gearbox output flange so that you can set your diff flange "In Phase" IE the angle of the rear g/box and pinion shaft should add up to 180 degrees
Another thought is that a 3.6 Cosworth diff may be a lot easier to source than the 3.54 powerlok you will need for your car. you will also see from the cosworth diff that the same principle of mounting can be followed.
If you do still decide to go for a 4HU powerlok it will need to be re-built mainly to alter the ramp angles IE how severe the diff comes in. A grantura / Vixen is a whole lot lighter than the 2 tonne jag it was meant to fit.
your final hurdle will be driveshafts. You will need new ones, triumph one side and jag the other.
The Cosworth install will be lighter and allow Lobro CV type driveshafts.
I can't send you pics of a cosworth installation just yet but will be doing this to my old mans vixen S2 in a couple of weeks.
Just a thought.
Neil.
Edited by heightswitch on Wednesday 3rd September 21:21
Neil,
If you have the possibility to send photos of the Cosworth conversion when it is completed please do.
I certainly appreciate all the help I can get choosing the best solution. Time is not an issue for me anyway. I will not do any major rebuilds to my car until winter.
Silly question perhaps but I assume the Cosworth differential you are referring to is one fitted to the Sierra Cosworth?
Square tubing sections is easier to build but round certainly looks a lot better
How the diff operates is a very important thing and you have a point there. I imagine there are a few diff ratio setups available, but as usual it all comes with a price…
My old RX-7 club race car had a rough working diff so I'm familiar with the problem.. Perfect for the racetrack but terrible when the car was used on the road. In a light weight car I becomes even more apparent.
Thanks again!
If you have the possibility to send photos of the Cosworth conversion when it is completed please do.
I certainly appreciate all the help I can get choosing the best solution. Time is not an issue for me anyway. I will not do any major rebuilds to my car until winter.
Silly question perhaps but I assume the Cosworth differential you are referring to is one fitted to the Sierra Cosworth?
Square tubing sections is easier to build but round certainly looks a lot better
How the diff operates is a very important thing and you have a point there. I imagine there are a few diff ratio setups available, but as usual it all comes with a price…
My old RX-7 club race car had a rough working diff so I'm familiar with the problem.. Perfect for the racetrack but terrible when the car was used on the road. In a light weight car I becomes even more apparent.
Thanks again!
You are so right about LSD,s in light cars. I recently fitted a new Salisbury plate type MGB banjo LSD with perfect 3.9 crownwheel and pinion to my Grantura. It was brilliant if you were driving REALLY hard but at normal road speeds was "interesting".I have taken it out after about 50 miles and rebuilt the original unit which is a lot easier to live with in a road car. Perfect for someone building a race/track car and incredibly rare to fnd a new old stock LSD. With the ramp angles altered it would be more forgiving on the road but that would almost defeat the object
Edited by thegamekeeper on Saturday 6th September 18:46
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