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MG TD TF 1500 - TD Higher gearing

Quite a few years ago I installed a 4.3 ex MGA CWP into my 1951 TD. This Winter as a project and because of gearbox problems I decided to fit a Hi Gear Engineering conversion for a type 9 Ford 5 speed g/box which I am currently evaluating.

This installation is coupled to a rebuilt and overbored 1350c engine which I am currently running in.

My first impressions are that the gearing is too high especially for the hills of Wales. To date I have covered some 250 miles of the running in process and with an extra passenger plus luggage my fear is that for a tour the engine would be labouring.

It has been suggested that the 5th gear be used as an overdrive but my initial impression is to convert back to a 4.875 CWP which I still have.

Has anyone got a similar setup that they could give their opinions of.

Thanks in anticipation,

David.



David Tinker

Hi David,

I converted my former TD with a higher ratio back axle and I know the new owner had trouble with hills in the Lake District even with a four speed box. I have fitted a Ford Type 9 into my TF 1250 using parts from Andy King. The car does have a Mangoletsi stage 2 engine and in fourth it pulls up hills like a steam train. Your bored engine probably has similar power to mine and I think the standard rear end with a 5speed box makes a superb drive able car.

Jan T
J Targosz

Hi David,
A friend with a TD has the Type 9 box on the standard axle ratio. I have a TF with a 3.9 axle ratio and standard box. This gives us both around 20mph/1000 revs. His ratios handle North Wales climbs better than mine but we stay together OK.Before I fitted the 3.9 1st gear was redundant except for stump pulling :-)
Ray TF 2884
Ray Lee

I have the Datsun 5 speed behind the supercharged 1250. A couple of years ago I swapped the rear end to a 4.3. That make the final drive in 5th around 3.9 I put the 4.875 in the TD I sold recently. I wish I had kept the 4.875. If I had the original 4 speed in the car I believe the 4.3 would be a good choice but with the 5 speed it puts the blower in boost mode nearly all the time to pull 5th gear at my elevation. I also don't care for the larger steps between gears, particularly on the mountain passes. I'd like to try a 4.55 but if given a choice between a 4.875 and a 4.3 with the 5 speed...I'd go with a 4.875

Just my two cents.
MG LaVerne

Just thought I'd mention that if the fifth gear is 0.82:1, then the overall ratio is 0.82 x 4.3 = 3.526, giving approx 21mph/1000rpm. If the fifth gear is 0.85:1, then the overall ratio is 0.85 x 4.3 = 3.655, giving approx 20.2mph/1000rpm. Both are very low (highly geared) for XPAG or XPEG engines. 1250cc seems to work best at about 4.3, whatever the combination, and 1350cc or 1466cc can cope with about 4.0, whatever the combination. A higher state of tune wil help regain acceleration.
R A WILSON

LaVerne - I've got a couple of good 4.875 R/P sets here if you need/want one.

Tom Lange
MGT Repair
t lange

I also live high in the Rocky Mountains (9800') even higher that LaVerne. After doing extensive research over the years on this site and others, I've decided a 5 speed with the standard rear end is what I need to get up these hills! No MGA rear end for me. Now all I have to do is convince my wife!
Ed
efh Haskell

I would like to know, for a 1952 TD, the installed height of a new, 120# valve spring set.

Cheers...Barry
C B Ryley

Thanks Tom, I'll keep that in mind....gonna be busy for a while now with the B.
MG LaVerne

Elevation is critical. At 4500 feet you're loosing 15% of your power. We've also found the supercharger does not make up for the elevation loss because it's most effective in the higher rpms. Engine condition, tuning, and drag (TD vs TF) are also factors.

La Verne, I sometimes get excellent 4.875 cores in. If you have time I could give you one in an exchange for another core. I also have excellent gears and I'd gladly give you a set along with all the other parts if you have a core to build up. It would be a shame to rework your 4.3.

Dave
Dave Clark Arizona

4.875 in my 1250 TF with a Marshal and a 5 speed. I can get up most hills in 5th so its a perfect combination in my opinion.

Rod Brayshaw

I have a Stage 3 tuned TF 1500 with an MGA 4.1 conversion rear end.
This gives me in 4th about the same overall ratio as the 5-speed in
overdrive (5th). ( Note that I have 75 HP at 5000 RPM instead of 45 HP)

I too have little trouble in the mountains but some of our North Georgia mountains have grades exceeding 25% and the turns are so tight that you can't run at 50 MPH but a 25~30, well off the power curve.
For these I shift down to 3rd to keep the RPM above 2500..

And 1st is no longer just a stump puller with the 4.1 rear end!

But my observations of our many Club members is to do one or the other, NOT BOTH!
Most of our members do well with the 4.3 and use the gear box for what it as intended for: shift down when needed,
you don't need to run in the top gear for all situations!

We don't need to shift into 2nd or 3rd to run at 25 MPH as too much low gearing will cause. (eg: 5 speed plus 4.3 or 4.1)

Don Harmer

I don't see changing out the 4.3 in this case Dave. I have maybe 5000 miles on it with no issues. I'd like to get hooked up with someone wants you to do a 4.3...send them this one and have you do a 4.55 for me.

I have the complete rear end I took out of the TD still here....all new bearings, seals and thrust washers sitting here that could be used. Probably less that 300 miles on it. No rush but just my thoughts.

I agree with the elevation power change. In some of my trips to closer to sea level the power difference is quite noticeable. Something I did not expect with the blower.
MG LaVerne

I'm closing in on leaving AZ for WA for the Summer.I do want to get you where you want to be but we should move the logistics off this thread. Give me a call or email.
360-317-4775
Dave
Dave Clark Arizona

Email sent Dave
MG LaVerne

Thanks everyone for your input. I have decided to remove the 4.3 and revert to the 4.875.

Cheers,

David
David Tinker

Ford type 9 gearbox has fifth gear at 0.82:1. Thus the overall ratio will be 4.875 x 0.82 = 3.9975. This is effectively 4:1, approx 18.5mph/1000rpm, so 1350cc with some tuning should go reasonably well.
R A WILSON

Hi everyone,
Following the general consensus on this board I decided to revert to the 4.875 CWP a job I finished today and a 30mile test drive confirmed it was the correct choice. Thanks again for all the advice.

The installation was a straight swop with 4.875 I took out some years ago so no spacer adjustment necessary. I also have a 5.125 and was surprised to note that the 2 spacers with that set were identical in length to the 4.875 which was taken from a TF some 3 years younger than the 51TD. Both pinions had a Zero etched into the head. Good to see that accurate machining was in evidence then.

David.
David Tinker

For the record, there are 7 optional ratios available to be fit into the TD/TF axle housing ..

Gord Clark
Rockburn, Qué.

Gord Clark

Hi Gord,

Did you include crown wheel and pinions from the Hindustan cars? They built clones of 1950s and 60s BMC cars which continued in production for many years. Initially they were mechanically exactly the same as UK cars but later they used Japanese engines. Is it possible the rear end ratio was changed to suit these?

Jan T
J Targosz

David,
Just saw your post. My 2 cents.

1950 TD 1250cc XPAG
Datsun 5 speed
Moss supercharger
4.55 rear

I have no problems with this combination. Flat out on the highway or up in the mountains. (East coast mountains do not compare with LaVerne in Colorado).

I thought the 4.55 rear would be a good fit for my drive train and it is. I got the rear from Dave Clark.

Mort
Mort 50 TD

This thread was discussed between 25/03/2015 and 03/04/2015

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