TC 5 speed box

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jddevel
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TC 5 speed box

Post by jddevel » Mon Jun 22, 2020 7:20 am

So this is the situation. Satisfied with the 5 speed box in my TF and in the process of a rebuild of a `48TC (body off car been off the road since 1956) I`m trying to decide the way to go. On the one part I`m informed that the TC box is robust and reliable and on the other I`ve never been able to drive the car to know it`s condition. Add to that my knowledge of gearbox wear is very very limited. So do I go for the 5 speed box from Hi-Gear (as stated fitted one in my TF and satisfied and happy with the work involved) or strip open the existing box to try and understand the possible hidden faults. The car is for pleasure use but will involve a certain amount of motorway driving.

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Steve Simmons
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Re: TC 5 speed box

Post by Steve Simmons » Mon Jun 22, 2020 8:43 am

Having driven both, my personal preference is for the TC box. The 5-speed does have its advantages, the biggest obviously being an extra gear on the highway. But it feels completely different and even the synchromesh first gear bothers me a little bit since it takes away from the vintage driving experience. The TC box is indeed very robust and has a great feel to it. In my opinion, a much better feel than five-speed does. And even if your original needs are rebuild, it will be far cheaper than a 5-speed kit.
1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507
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ROGER FURNEAUX
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Re: TC 5 speed box

Post by ROGER FURNEAUX » Mon Jun 22, 2020 10:06 am

I don't know what the percentages are, but my guess is that more people go for a higher back axle ratio than fit a Ford gearbox: it is certainly cheaper to change the diff. ratio than the gearbox!

You are in a catch-22 situation, but if the car was only on the road for 12 years, the 'box should be a good condition - but you never know! There must have been a reason that the car was taken off the road, so you really have to dismantle the engine, gearbox & diff - or at the very least give them a very careful inspection. It would be a blow to get the car built up, and then discover a problem...I can rebuild the diff. for you with a higher ratio, and know somebody to do the gearbox.

The good news is that all the parts are available for the engine & diff and I am presently looking at have some 3rd. gears re-made as they most often have missing teeth.

'46 TC0978
'47 TC2365
roger.46tc@gmail.com

jddevel
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Re: TC 5 speed box

Post by jddevel » Mon Jun 22, 2020 11:27 am

Roger , Have emailed you. I`m not adverse to the acquistion of a change in diff and ungrade of shafts. Regarding the engine and its rebuild that holds no real concern for me having done so in the past. It`s my relationship with the TC gearbox that lacks experience but always interested to learn and extend my knowledge.

Tom Lange, MGT Repair
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Re: TC 5 speed box

Post by Tom Lange, MGT Repair » Mon Jun 22, 2020 1:43 pm

In my experience, 92% of all TC boxes are just fine; I have probably stripped a dozen, and 10 of them needed nothing - NOTHING. The needles all were in spec, the gears were all fine, and the box needed only a good clean and re-assemble.

A 5-speed does indeed change the feel of the car, but I think it is safe to say that it all depends on your style and type of driving. I have little interest in being in a TC on an A-motorway going 75mph, but prefer to keep revs down on normal country roads. I agree that a modified Morris Minor pumpkin is the easiest and least expensive way to accomplish that. You can re-use your TC spider gears and keep the TC axles, or go to one of our Canadian brethren for axles with MM splines on the inboard and TC hub splines on the outboard end. And adding a bit of power to a stock engine is always a good thing.

You can dismantle a TC gearbox in under an hour, examine it, clean everything, and have it back together in a total of 4.5 hours. They are EXTREMELY simple, and EXTREMELY robust, which is why TD and TF racers installed TC boxes. As long as you reinforce the rear gearbox mounts! If one breaks the entire rear of the gearbox and engine drop; you then break the shift tower, which is an expensive circumstance.

Tom Lange
MGT Repair

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Steve Simmons
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Re: TC 5 speed box

Post by Steve Simmons » Mon Jun 22, 2020 2:02 pm

Using a Morris pumpkin may end up the cheapest but I'm not sure it's the easiest. Machining is required on the pumpkin housing. Likely easier to simply put higher gearing in the existing TC pumpkin. A stock TC can easily run 4.875 and a hopped-up engine can do well with 4.625.
1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507
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Duncan M
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Re: TC 5 speed box

Post by Duncan M » Tue Jun 23, 2020 12:42 am

Except for the gear cut and synchros and neat sounds, the 5 spd box is meant to run a stock differential ratio. 1st, 2nd, 3rd and 4th of the 5spd duplicate the ratios of the original transmission, but 5th is then a bonus overdrive. Problem with the pumpkin ratio mods is you then must have an engine that can rev much higher, unless you want to be left in the dust by stock TC's. When the XPAG engine is limited to 4,000 RPM's it is amazing how the problems of tappet wear and cam wear and valve seat recession and broken crankshafts become nearly non-existent. All the power is made by 4,000, and the only reason to rev higher in a stock setup is to hit high top end speeds. Running Model A tires (30" diameter) with a stock 5.125 gives you about a 4.8 effective ratio which means you can easily get going 65mph on a flat road without ever exceeding the 4,000 rev limit. The destructive harmonic inherent to the XPAG starts somewhat over 4,000 rpm.

If JD's car has limited mileage (like 20K or 30K miles) and never had any engine work done, then it was probably taken off the road due to overheating from burnt exhaust valves or a faulty head gasket that allowed high temp exhaust gasses into the coolant. Typical symptom of that is much climbing temps going up hills that then (temp) drops quickly when going downhill or on the level. Loss of coolant without any visible leaks can also confirm a bad head gasket. Another reason could be the quickly disintegrating original brass caged pinion carrier bearing in the diff.

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Steve Simmons
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Re: TC 5 speed box

Post by Steve Simmons » Tue Jun 23, 2020 9:59 am

The pumpkin mod on the Morris unit actually raises the ratio, so you rev LOWER than stock at a given speed, not higher. Or maybe I misunderstood the previous post.

Max HP on a stock engine is at 5200 RPM, but max torque is much lower. Of course this data goes out the window if running a non-stock cam, which I'm sure most TCs are these days.
1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507
http://www.mgnuts.com

Duncan M
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Re: TC 5 speed box

Post by Duncan M » Tue Jun 23, 2020 11:06 am

No, I do not misunderstand anything about gear ratio's. Quite simply, if you have two identical cars, except one has the stock 5.125 diff ratio and the other has a "lower number" ratio like 4.6 and you start both cars from a stop and accelerate up to say 60mph, the 5.125 ratio car will get there quicker, unless the 4.6 car is spinning the engine much faster.

Of course I realize a "lower number" ratio will provide lower RPM's at top end, as is indicated in my post. Why do you think I have 30" tires instead of 27"? As stated, it is to allow sustained driving at 65mph without wrecking the engine--by giving lower engine revs at 65mph than what I would have with standard 27" tires. About 400 RPM lower. Since using larger dia tires gives "in effect" a 4.8:1 final drive ratio, the car will accelerate a bit slower-- for the reasons I have described.

I did mis-speak when I said "all" power by 4,000 RPM and should have said "most all" power by 4,000 rpm. If someone wants to rev their engine over 4,000 or even to 5,200 rpm to (maybe) extract those last very few bits of power then go ahead and wear out your engine at a dramatically increased rate. Fine with me.

Overall, from a mechanical and performance perspective, the 5 spd conversion makes far more sense than the changing of differential ratio. As has already been mentioned, by doing so you do loose a very fine TC transmission, along with the neat, sporty & vintage feel and sound that goes with it. My solution to the whole problem has been to live in an area where I can enjoy the local backroads without ever going on the freeway.

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Steve Simmons
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Re: TC 5 speed box

Post by Steve Simmons » Tue Jun 23, 2020 1:20 pm

No, you didn't mis-speak. As noted I suspected it was a misunderstanding of words, and it was. What you're meaning to say is that with a higher ratio, one must accelerate with more gusto than an equivalent TC using lower gearing. I was reading it as requiring higher RPMs to keep pace at a given speed, which would obviously be backwards. Just a different way of saying the same thing... I think!

Even though my TC will safely rev to about 6500, I top out at around 4500 max during hard acceleration, and when cruising on the highway usually keep it at around 4000-4200. The guys in Europe often poke fun at us Americans and say "The TC doesn't even start to make power until 5000!" Well, I'm not that brave. :)

I can get pretty much anywhere I need to without going on major freeways or Interstates, but sometimes I just want to get there faster or I'm running late. In those cases I'm usually in the right two lanes passing a few here and there but for the most part holding 60-65. My rear is a 4.875 with original style tires.
1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507
http://www.mgnuts.com

lindi
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Re: TC 5 speed box

Post by lindi » Fri Jun 26, 2020 8:21 am

Since some weeks our supercharged TC has a Morris Minor Pumpkin. In our region there are many mountains and I did some calculations before I fitted a 4.22 version. The TC has also a bit greater tyres. As expected the setup is fantastic. Hills can be easily climbed one gear lower with very good performance.
The work was not too hard to do, there are 2,8 mm to be cut away from the pumpkin housing and some other rectifications. We used MM axles which were cut at the outer sides and MG splines were cut in. We also Applied a thread, so that the whole thing is not only pressed together, axle and hub.
The best: the feeling of the fine gearbox is still present.

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