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MG TD TF 1500 - Differential Conversion

I read about converting my differential to a 4.3:1 ratio on Bud's superb Ttalk website (http://www.ttalk.info/ClarkConversion.html). I understand that the benefits include a useable first gear, and reduced engine speeds (and related noise and vibration). I would imagine that the car would have poorer acceleration and climbing ability. A local British car shop owner also told me that it would increase the likelihood of failing the TD's "weak" crankshaft if the car is routinely accelerated hard from zero speed.

I'd like to hear some opinions regarding the benefits/drawbacks from the conversion from those who have accomplished it.
Corey Pedersen

Corey, I can't think of a single negative about my experience with the 4.3 conversion. All of the gears are more useable, not just first. What I may have lost in top gear in hill country I have more than compensated for by my longer third gear. Bud
Bud Krueger

Thanks Bud. My thoughts were that since the TD was designed for driving conditions in the UK in the late '40's, the designers probably envisioned use at typical speeds of 30-35 MPH, and rare use at over 45 MPH. Modern traffic requires higher speeds. Even here in Connecticut with ideal TD driving opportunities, one needs a comfortable 50-55 MPH on secondary roads.

Anyone else with opinions?
Corey Pedersen

Correy,

Acceleration improved when I put in my 4.3:1 (well, actually, I sent it to John Twist) but I also rebuilt the engine so I can't completely assign the improvement to the rear axle. But now first gear is usuable and I am able to accelerate in first before changing to second. I can also tool around in third on local roads with no concern. Finally I have no problems holding speed on all but the steepest and longest hills, but that was present before the change.

Although the original 5.125:1 rear end allowed about 14.4 mph per 1000 engine RPM, and you would expect the new rear end would allow 17.2 mph per 1000 RPM, the actual figure with my radials is about 16.7 mph per 1000 rpm.

warmly,
dave
Dave Braun

corey, i did mine 5 years ago..NO regrets. my experience mirrors that of the other posters here. the one thing i would say is it seems harder to find the MGA 4.3 pumpkins now. i do not understand the shops idea about the lower rear end being harder on the crank...the lower RPM's at speed would reduce the wear on the crank..and if you drive your standard transmission in a way that lugs the engine you can do that with any ratio rear end. regards, tom
tom peterson

Gents, I assume a speedometer change would be required with this modification. Suggestions?
Corey Pedersen

Never heard that the crank on the TD was weak; when TF 1500 first come out they did have trouble with the cranks. But in the 1250 cc. engine it's fine.
David Werblow

Hello Corey. I did mine back in 1977. I would never go back. For mine, I had the help of Carl Cederstrands tooling. I decided to do the change when coming back from an overnight trip with our club and I was having to run at 5000 rpm to keep up with the TC's. I did have to change the carrier bearings about 15 years later after about 100,000 miles. then I got into doing the ring and pinion changes. I've done almost 100, just finished another one. As for the speedometer, you can have it recalibrated or fit a conversion adapter to the gearbox. To get anywhere in a reasonable amount of time you need to take the freeways. The slow lanes here in Los Angeles are running 65 except during rush hour. I have no problem keeping up.

Butch Taras
VMG
TD, Y, MGBGT
R Taras

I went to 4.55 some time back and wish I had gone 4.3. Huge difference, and I use first gear now! David, TD cranks are just fine until they just snap in half between the #1 main/rod or at the opposite end 3 main/4 rod journal. I have a couple two parters in my attic. The one from my own car had about 10K miles on it since magnaflux when it broke. If you rap the big piece with a hammer, it gives a dull thunk, meaning there is at least one more serious crack elsewhere. My other one is the later "better steel" crank, snapped same place. When we had the crank from my friend's TF 1500 magnafluxed in the late 80s, it had at least 5 serious cracks in it. Inconsistent quality steel, no harmonic balancer, worn bearings, and likely metal fatigue from age and all of the above, in my opinion cause the failures. So knock on wood quickly! George
George Butz

david, the original 1250cc cranks have a history of cracking. i believe in the area of the number 1 main. the repop forged cranks appear to be bullet proof. regards, tom
tom peterson

OK, I'm convinced. One more task added to the restoration list!
Corey Pedersen

While on this topic, does anyone have any familiarity with "Ken's MG Machining," Fall River, MA? As well as other work, he does "rear end gear conversion exchanges."

I spoke with Ken Silvia on the phone earlier this year. At that time he had a 4.3:1 rear end that was fully configured, including drums and brake lines and was offering it at a very good price.

I am considering Ken for a rear end exchange to 4.3:1 gearing for my wire wheel 1952 mg td.

If anyone wants contact information for Ken, please send me email. If anyone has experience with his work, I would appreciate receiving this information.

Thanks.

Larry
Larry Shoer

Corey,
There are so many options and combinations available in today's market place it is difficult to make comparisons. I put in a 5 speed from Skyhook and I have a Judson supercharger. It's a great combination.

I just received a 4.55 from Dave Clark to replace my 5.125 and I will put it in next month. I selected the 4.55 to fit my combination of components and how and where I drive. There are many ratios available.

You should think carefully about any changes you might contemplate in the future and select the best combination of components.
The modifications that we all make give us great performance improvements. Not only in speed and power but in handling, comfort and just plain fun.
Decisions, Decisions,Decisions.
Good luck,
Mort
Mort (50 TD "Mobius")

Mort, sounds like you've built a hot rod! With my planned use I think a stock setup with nice sedate 4.3 gears should work well.
Corey Pedersen

Corey,
Much less of a hot rod than it sounds. The Judson came with it when I purchased it. I added the 5 speed primarily for the sort of overdrive it gives me on the Hwy. The comfort in the lower gears is a great bonus.
I'm adding the 4.55 just to reduce the RPM and thus strain on the engine at Hwy. speeds.
It's difficult to get around in this area without hitting the turnpike or an interstate.
I'm sure you'll be happy with the 4.3.
Mort
Mort (50 TD "Mobius")

Agree with the change, just not sure of which is the best. I have 4.55 in mine and find starting in first a bit doggy (That is, takes a bit more power to get it going). This ratio makes freeway driving ok, but still pushes the revs when you get to 65.

Bruce Cunha

Cory, I also took the route that Mort did; I run an MGA 4:55 rear end with a 5-speed [Ford Sierra Type 9] and a supercharger. I run larger wheels and tires [185-16] so in fifth gear on the highway I run 3500 rpm at 70 MPH. It makes for a car that I really can run at freeway speeds without any drama. You'll be happy you made the switch.

Dave
Dave Jorgensen

I guess I'm a milk-toast; I feel 70 MPH or above in a T-type is SCARY.

P.S.
Don't run over the dog the first time you back it up with the new gearing-it'll fly.
David Werblow

You ought to try over 95 in my TF 1500 as a passenger with my Son-in-Law, Scott Sewell driving.
There are my finger prints in the crash handle.

My TF has a 4.1 rear end and is Stage 3 Tuned (9.5 compression ratio).
70 MPH at 3900 RPM. 75 HP at 5000 RPM on the Dyno

It can outrun an MGB in the mountains

At 4.1 it still is easy to drive at 35 MPH around town. No matter what you still have to run at least 2000 RPM to have any power. Too tall gearing makes 25 -45 MPH a downshifting problem
Don Harmer

This thread was discussed between 25/09/2012 and 26/09/2012

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