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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - MGB final drive gears

Why will the later model MGB final drive gears not work in a T series rear? I have two 72 rears. Just curious. PJ
P S Jennings

I think the answer is no Paul. The earlier "pumpkin" type might. Even if they did the ratio would be way too tall ( 3.9 or more) for your TF.
LaVerne

The crown wheel and pinion (cwp) gears for the TD, the TF, the MGA and all models of the MGB are fully interchangeable. This will give you a choice of final drive ratios of 5.125, 4,875, 4.55, 4.30, 4.1 3.9 and 3.7.

If you have a YA or YB or YT, be careful as only a handfull of Y-types used the TD drive train, otherwise mostly TC, which cannot reasonnably be adapted to the TD/TF. The MGC and the MGB-V8 are not adaptable.

What is NOT interchangeable, are the centre-sections. The TD and TF use a split axle, while most models of the MGB use a 'banjo' or, tube-type axle, and these centre sections cannot be mixed.

Most changes for the TD or TF come from the (standard) MGA 4.3 or when found (rare) the Mark II 4.1. In these cases, if you're adapting these ratios to your TD/TF, the MGA and MGB centre sections will not be useable and the cwp will have to be adapted to your split axle TD/TF centre section.

This requires a mechanic who can machine pinion spacers, as the job is mostly trial-and-error and the assembled centre section may have to be dismantled and rebuilt several times, using different spacers, until the correct and critical clearances and gear-play (backlash), are achieved.

Carl Cederstrand has published an elaborate description of this change, and except for re-calibrating your speedo, is much more straight forward than he describes.

Gord Clark
Rockburn, Qué.

Gordon A Clark

Although I have heard of people changing the whole rear ends from A's and B's...that is not the normal way its done... The gears themselves are pulled out of one and put into the TD/TF rear end housing.... this does mean machining of certain parts, but is such a common swap, many are capable....clubs and individuals....
The booklet from Moss/Cederstrand is about 8 pages of useless information with a page of the actual method...which is written so confusingly it is almost useless..... I believe there is a much better method written out there by one of the clubs (?)
The 4.3 in mine is great, but I would think you could also go 4.1, or 3.9 and the xpag would still handle it....i feel no feeling of bogging down at all....It will mean more downshifting, but what the hell....you will get to use 1st gear again....(I never used it before the swap)
gblawson(gordon- TD27667)

Gordon, then what your saying is the XPEG, with a little more HP, should handle the 3.9 gears with ease? I don't mind down shifting in the hills, kinda goes with the car. Only thing is down shifting to the non synchronized 1st gear would take some practice, like the old trucks. (Double Clutching). PJ
P S Jennings

You certainly wouldn't need to worry about going down into 1st....just treat it normally (use 1st from a standing start).... you would just find shifting down into 3rd on a grade.... Yes, I feel the XPEG (even the XPAG) could handle 3.9....
(I double clutch up 'and' down gears...have since I got the car....saves on that bit of crunch that can happen....)
gblawson(gordon- TD27667)

I disagree, Gordon, only the banjo axle MGB 3.9 ring and pinion gears can be used from the early MGB's, NOT from the the 1968 onward Salisbury axle.

Putting in too small a ratio problems comes not at high speeds but at low speeds, the engine has no power below 2400 RPM, and 25 MPH may not be possible in 3rd or 4th. You wind up shifting down excessively at low soeeds to get enough power even on a level surface.

Our Club's experience suggests that the 4.3 conversion is best for most XPAG 1250 engines, with Stage 2 or better able th handle the 4.1 and the 3.9 should only be used for flatlanders or supertuned XPEG 1500's


Don Harmer

I have the 4:1 in my TD. Originally put it in thinking I would have a Judson SC on the thing. Dont have that anymore but the ratio is ok, except you do find yourself shifting down, especially on hills. The 3:9 would most likely be even worse. My engine is .80 over so a little more power than stock.
Tom Maine (TD8105)

Phillip H Smith gives the HP curves in his book, on the basic T-Series engine. I know that we can fiddle torque curves with a number of things, starting with the cam design.

Assuming that 3500 RPM is a speed most of us will accept as a safe (engine) cruising speed, we can calculate the torque (at 3500) as (HP X 5250) ÷ 3500, or about 60 pounds/feet. In fact, I found that the XPAG HP curve with the factory cam, was a pretty straight line; so that means we’ll continue to get around 60 pound/feet at engine speeds below 4800, and this makes it easy to select the best ratio for our use. This 60 pounds/feet will pull your TD/TF between about 1200 RPM and 4500 RPM. thereafter. it drops off sharply. (I could show the calculations but it would bore most of us).

If you select a ratio too (numerically) low, you’ll not be able to easily get on to the torque curve (“getting on the cam” to use hot rod terminology); similarity, if you select a ratio numerically too high, then the engine runs out of torque as the engine approaches it optimal speed - say, 4,800 RPM which with a TD is about 71 mph.

That’s why from experience, most of us prefer engine flexibility, and it appears that the 4.3 is the best compromise to getting the car up to speed and keeping it there, and to minimize down-shifting on hills. Also fuel economy will be best with this ratio.

I have a friend with a small-block Ford 302 V8 (295 HP)in his MGB with a 3.1 cwp, and he gets significantly better fuel economy with his V8, than he does with his standard 4 cyl. MGB. It all boils down to torque to provide flexibility to keeping the car rolling with minimal HP. Let the torque do the work!

There are some of you that have the 4.1 and even a few with a 3.9 in their T-Series. The 3.9 will probably be good in the flatlands of Alberta, but will not work in the Rockies. It all boils down to torque.

Gord Clark
Rockburn, Qué.
Gordon A Clark

Hello Paul. I think that your origional question was why can't use the ring and pinion from the late model tublar rear axle. The reason is that the distance from the center of rotation of the ring gear to the center of rotation of the pinion is different than the earler ring and pinions. So when put in the TD/TF differential the gear teeth will not mesh correctly.

Butch Taras
VMG
R Taras

Thanks Butch, That's all I wanted to know! PJ
P S Jennings

Hi Guys:

On the subject of flat land driving in Alberta . . .

Has anyone put a 5-speed transmission (20% over-drive in 5th) into a TD TF with a 4.3 diff. It would seem from the discussion that this might be a reasonable installation since the taller gear would only be used at highway speeds leaving the engine with sufficient torque at lower speeds.

Godspeed in Safety Fast
Jc
John Crawley

John Crawley I have a 4.3 CWP installed and a Skyhook Engineering kit with a 5 speed installed. Great, the car has great highway manners. If I sneak up to 4000 revs I am in danger of big black marks on my license. Only occasionally do I have to shift into 3rd for hills. First gear is now usable and has a good synchromesh.

The biggest problem I had was finding someone to recut the carpet over the new transmission tunnel. I even found a guy the reengrave the gearshift knob to show the fifth speed. All-in-all very happy with the whole thing.
Cheers,
Bob
Bob Jeffers

....Bob... would love to see a photo of the gearshift knob, closeup and straight down....?
gblawson(gordon- TD27667)

Speaking of MGB rear ends,

There are two MGB's out in the back shed. One is a 1974 1/2 with steel wheels (Rostyle?) the other is whats left of a 1967 with wire wheels, I found that the '67 has a 3.9 CWP ratio. (stamped into the housing). The other I'm not sure about but is probably the same. The '67 engine does not turn over, but the 74 1/2 ran the last time I started it.

People talk about banjo and tubular rear axles. What is the difference and how do I tell which I've got.
Cheers,
Bob
Bob Jeffers

The early banjo type is a total cast iron unit. The differental can be removed from the front by removing the bolts.

The tube axle is a combo of cast differental housing and ub ends with a tubing axle cover. It has a stamped steel cover on the rear of the housing and requires a case stretcher to remove the differental.
LaVerne

Steve Neal is working on a 5 speed Datsun for me right now which will go with my 4.3. Road test results to be reported after install.

Jim
James Neel TD28423

I posted this on my web-site, but thought it would be useful to repeat here. If I have made any mis-calulations, I trust that those more knowledgable than I will correct my errors.

The MPH and corresponding RPMs with the original TF's differential are: 15.14 mph per each 1,000 rpm in 4th gear. So, at 65 mph the engines RPMs would be about 4,300; at 70 mph the corresponding RPMs would be about 4,625. This is calculated on the original differential gear ration of 4.875.

By installing the gears (crown ring and pinion) of an MGA with a gear ratio of 4.3 the corresponding mph per 1,000 rpm is 17.16. This ratio would then produce the following results: 3,800 rpm at 65 mph, and about 4,000 rpm at 70 mph. These figures were calculated from the data provided by Carl Cederstrand in his manuscript, "Ring and Pinion Interchanges for the MG TD/TF" (p.4).


I provide the following gear ratios for the original mgtf tranny and the Skyhook/Datsun: 1st gear, 3.5 TF/3.513 Datsun; 2nd gear, 2.07 TF/2.17 Datsun; 3rd, 1.385/1.378; 4th, 1:1/1:1; 5th, .846 Datsun.


So, what would be the final results for having both the 4.3 differential ratio and using the Skyhook/Datsun tranny? The first 4 gears being essentially the same for both trannies will produce the RPMs as calculated above. But, when using the 5th gear of the Skyhook/Datsun tranny, then the RPMs at 65 mph would be 3,215. Thus, by incorporating both the 4.3 differential and the Skyhook/Datsun tranny will result in a reduction of engine RPMs (when using 5th gear) from 4,300 to 3,215. Even traveling all day at 65 mph at this rpm will not burn up this engine, which was my goal to start with.

For those of you who are not aware, I have moved my web-site to the following site: mgtf54.blogspot.com

Cheers -- John
John Brickell

John,

Your figures are correct, but only if you had the original tires, the 5.50 X 15 Inch. Most replacement tires are smaller in diameter due to th "80" profile and thus have more turns per mile.

With modern radials, such as the 165R15, commonly used, you get about 4000 RPM at 65 MPH in 1 to 1 gearbox gear with the 4.3 rear
Don Harmer

Good point, Don. I kinda felt I was most likely missing some key element here in my calculations. I am using the 165R15 tires. One more thing: I haven't had the opportunity to actually find out how this system of having the 4.3 combined with the Skyhook tranny will work out in our northwest region, but like James above, I will report on such when this TF is finally "out on the road".

Cheers -- John
John Brickell

I know that we have gone way beyond what Paul was looking for, but I would like to second what Don Harmer says about the 4.3 ratio. I have been driving my stock TD with it for some years now, and I also think that it is the ideal solution for these cars. I can cruise comfortably at 58 mph at 3500 rpms all day, but still have something for the hills. First gear is now actually useable.
I personally feel that 58-60 mph is about as fast I ever want to go in my TD. The car is a virtual deathtrap by todays standards and I work very hard at being defensive and keeping my distance from others. For the kind of back roads cruising around that I enjoy the most, the 4.3 ratio is great. At 40-45 mph the car is as quiet and smooth as can be!
Steven Tobias

As I pointed out in one of the entries (above), it boils down not to speed, but to what engine revs you're happy with if you're planning to run for a couple of hours without stopping.

To wit: Again, it boils down to what RPM you think is comfortable for your engine, and not necessarily road speed.

If you're happy to cruise at 3,800 RPM in 40° heat for 2 hours (I wouldn't), then, do so.

These engines were designed in the 1930s when motorways didn't exist and a typical road speed was 50 MPH. We're asking these engines to do much more by using modern technology, to push the bounds.

Your call. Once you get off the torque curve of the engine, you're stressing it and that's when overheating takes place, and you may not notice 'till its too late, when the damage is done.

Gord Clark
Rockburn, Qué.
Gordon A Clark

Gordon has a great point... what your comfortable with. My engine just hums along at 3200 rpm.. hardly fast, but so comfortable....if I give it a little burst, it is to about 3800....(and I get over the shimmy)...and it is still really smooth.... my highest rev was about 4500 and didn't feel at all comfortable.....
I also think about the little curvy British roads while i'm cruising down the QEW (4 lane) that goes on for mile after mile....certainly not what they were designed for.....
gblawson(gordon- TD27667)

This graph pretty much confirms Gordon's comments about stock torque curve. I'm comfortable running to 5000 rpm between shifts with the blower and cruising at 4800 rpm when needed. I have two MGA rear ends in the shop ( one 4.3 and one 4.1) and a spare TD rear end and may have a stab at transplanting one to the TD in the future.


LaVerne

If some of you are serious, there are several, 5 and 6 speed gearbox options. There are kits for the Datsun 210, the Ford Type 9 and the Toyota T50.

The attached matrix gives you an idea.

Gord Clark
Rockburn,Qué.


Gordon A Clark

... sorry for the poor copy.

Attacched should be better to copy.

Gord Clark


Gordon A Clark

Gord Your first copy came out good on my computer. I looked at the second one and couldn't see any difference.

Laverne I hope I haven't got a tube axle. I don't want to have to get a case strecher to get the gears out.
Of course one of our esteemed informants has said that the gears from a tube axle can't be used in a conversion of a "T" series rear axle. I'm not sure I have heard that before, can we confirm that?

Anyway my TF1500 pulls a 3.9 ratio very nicely. Of course as an avid reader of Hot Rod magazine in the late '40's and early '50's there have been a few upgrades to the engine.

I'll try to get a picture of the gearshift knob tomorrow. My only problem will be it is a new camera and so far I have not succeeded in getting pictures from the camera into the computer for sending by email.

Anybody know if there is a problem getting images from a SDHC chip to work??
Cheers,
Bob
Bob Jeffers

This has been and still is a very interesting post. It has given me many options and changed my way of thinking on the subject. My thanks to all for contributing! There is one thing I'd wish to convey, that is, there's no way I'd ever drive this car at 70 MPH on the freeway in traffic! Amongst other things, that's overdriving the inadequate braking system. Even though I have thought of converting the front to disc brakes, I have a complete set, I think I'll keep it original and orient my self to the car, not the other way around. PJ
P S Jennings

LaVerne and Bob,
As always, we never fail to learn something from each other in this BBS. What the heck is a case stretcher? As a TD owner, I have never read or heard about this particular tool.
TIA
Jim Merz

Gord:

You mentioned that there are 3 kits available for the Ts. Have you by any chance compiled a list of suppliers for the various kits . . .

Jc
John Crawley

John,

The 3 kits are:
· Hi-Gear Engineering using the Ford Type 9
· The Skyhook Engineering using the Datsun 210
· The Dellow kit using the Toyota T50

Gord Clark
Rockburn, Qué.
Gordon A Clark

I've never seen one Jim, but there is a drawing of one in the Bently MG manual. I think most would just fab one up with some all thread or bolts and a flat plate. Some have reported being able to remove the differential without it but others no. Directions say not to deform the cast iron case more than 12 thousandsth so it obviously doesn't take much. Some wonder why but my understanding is that it was done by design to clamp the bearing/spacer assembly in place.
LaVerne

You don't need a case stretcher because the tube/Salisbury axle is the one you cannot use the gears from.
If you did need to take one apart, then you could get the stretcher from any place that does rear axle work, because the "Salisbury" axle is used on many vehicles - Volvo, Jaguar, Triumph and six gazillion American cars - where it is commonly known as the Dana. Salisbury started in Jamestown NY, 60 miles from me, about 1902, and after a few years became part of Dana Corp, along with Spicer, the New Jersey company that first made u-joints as we know them. Salisbury Axle was renamed Spicer Axle Division somewhere around 1980, but it is still all part of Dana. It got really well known in UK as the axles used in the Jeep, which were Dana built Salisburies. The Dana 44 might be the most common axle in the world; the number designates a series by capacity, and none of this means any parts are necessarily interchangeable, though there are reports of people putting Jeep gears in Jaguars etc.
While you can take the diff out without stretching the case, it is very difficult to put back together, since the diff bearing preload is set with shims, which make it too big to go back in a not-stretched case. Stretch it too much and the bearings & gears die from lack of preload, plus the wheels point funny!
These axles have a tin cover on the back with a big (about 1") round depression either side, which is where the stretcher engages.
The "banjo" axle appears to be a BMC produced unique item, in which the guts are mounted in an alloy housing that unbolts from the front and comes out in one piece.

FRM
FR Millmore

PS Jennings wrote:

"there's no way I'd ever drive this car at 70 MPH on the freeway in traffic! Amongst other things, that's overdriving the inadequate braking system"

I drive my car with 4.3:1 gears at 70 (by GPS) on MAJOR URBAN freeways frequently. The brakes are MORE THAN ADEQUATE if set up properly, with arced linings and properly rebuilt AND installed cylinders. Even fully loaded with gear on the rear luggage rack I can stop straight and faster than almost any commercial truck. I do drive defensively, and stay mostly in the right lane.

Remember, these are also fairly long stroke engines with even longer connecting rods, meaning the angle of force on the crank and rod is more favorable. That allows higher piston speeds. My RPM at 70 is a shade over 4200 rpm given my 165R15 tires.

warmly,
dave


Dave Braun

Gordon - doesn't Dellow also offer a Toyota Celica-XPAG bellhousing? Tom
t lange

This thread was discussed between 31/10/2010 and 05/11/2010

MG TD TF 1500 index

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