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switching the 4th gear in a 4-speed?

795 Views 5 Replies 4 Participants Last post by  BernieFrank
I want better gas mileage and i also want a manual trans. (i have a C4) a friend of mine told me it might be cheaper to buy a rebuilt 4-speed and swap out the 4th gear and put in a 5th gear to get better gas mileage on the freeway as opposed to finding a rebuilt T-5. does anyone know if this is possible and if so how much it would cost?

1968 Mustang Coupe - Daily driver
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Never heard of putting a "5th" in a toploader.. It is posible to put an OD 4th in a toploader but requires much work and some fabracation. I have changed a 66 from a c-4 to a Tremec and made a *Sweet* driver.

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Ford made a toploader in the 70's where 4th was an overdrive. These were put behind lopo 302's in Granada's and probably other models.

You should be able to buy one of these cheap since nobody wants them. To rebuild a good toploader into one of these things sounds expensive and useless :)

1965 Mustang 2+2
1989 Mustang GT Convertible
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Discussion Starter · #4 ·
The late 70's 4sp overdrive tranny ford sold came two ways. One had a bunch of aluminum
showing when you looked at it under a car. That one is a light duty thing not much good for
anything anymore.
The other tranny is a toploader. Ford made THIRD gear an overdrive gear and flipped
the 3-4 shift arm upside down on the case so the shift pattern would make sense.
There are many people who bad mouth this tranny I am not one of them. For some people
with vintage mustangs is is an economical and dependable solution to both mileage and
rear end gear issues. Sure it's not a close ratio t-loader. But everybody here is not
looking for that 13 second quarter.
(I am though)

M.C.A.# 50000

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22,553 Posts
You'd be better off with a good used T5. Yes there are toploader O.D. 4 spds. 1st, you cannot make a regular 4 spd toploader into an O.D. toploader, the case is different to make room for the larger dia. of the cluster gear. You can find the O.D. toploaders is pass. cars but they have a rail type shift linkage that might present problems with fitting into early Mustangs.

The O.D. toploader 4spd. you want to look for, is out of a pick-up or van. They use the conventional linkage like a regular toploader and have bigger bearings and are a much stronger transmission than the car version O.D. unit. On a final note, on the truck unit, the shift lever is upside down for 3rd-4th. gear compared to 3rd and 4th gear lever on a regular toploader 4 spd. This may cause problems if use the Mustang shifter on the O.D. unit if you flip the lever to work.

BTW, I have one of these toploaders out of a 77 van at home!

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I have one of those "real" top loader overdrive units too. It looks just like a regular top loader except that the cast iron tailshaft has slightly different mounting hole positions for the shifter. It seems like this transmission would make a lot of sense in certain situations, like a substitute for a 3 spd. Since I have a close ratio toploader for the 66, I'll probably take it to Ford Carlisle and see if anyone wants to buy it.

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