I'm going to swap my old tired 300 six in my '94 F150 with a 351 from a '95 F250; months before my truck's engine died, I had changed the fluid in the Mazda gearbox and it wasn't discolored nor did I find anything metallic in the old fluid. I even added a quart of Lucas automatic transmission additive which made shifting gears even smoother.

So here's my question...I just want to get my truck running again and I've heard horror stories of how the Mazda gearbox will grenade behind the 351 because of the huge torque difference and that I'd be better off finding a ZF 5 speed. Now I'm a very conservative driver and I don't plan on doing any hard launches from a dead stop or even pull a fifth wheel trailer. If I do pull anything, it might be my little 4x6 trailer with my 2000 Vmax. So what do you guys think?

 

Transmission will be fine.. good luck with your swap.

 

Good!! Thanks Paul, plus I was also under the impression that the ZF gearbox was more of a 4 speed with a granny first gear....

 

Yes, if you have any kind of decent rear axle gear ratio skipping 1st isn't uncommon with the ZF.

 

No, it's a 3 speed with a granny low and an OD fifth gear. Your Mazda transmission is a 4 speed with a 5th OD. Just make sure you keep the oil level full. They tend to leak oil from the plugs up top at the shifter housing. If it every starts to get excessive gear noise, drain it and replace the ATF with straight 40 weight motor oil. That'll buy it more time before it needs to be rebuilt. You'll need the correct 28 oz flywheel for the 351, the six flywheel is neutral balanced.

 

Yup, I've got the 28 oz flywheel; I had an old Honda CRX with an Integra swap and the gearbox required 10w-40 motor oil. I was thinking of using 10w-40 Mobil 1 and Lucas oil additive in mine...what do you think??

 

Stick with ATF.

 

That is needlessly complicating things when Ford used so many manual transmissions over the years with so many different combination of ratios, 5 forward gears = 5 speed to me doesn't matter what the ratios are.

 

Your call. I did this with the Mazda 5 speed in my 89 Ranger. At some point I had to reseal the tailhousing's joint to the main case. Not sure if this leak developed due to age or the change in oil. Motor oil's been used in several heavy truck transmissions in the past. The real reason for the switch to ATF by the factories was due to having to meet ever stringent EPA mileage mandates, same as the switch to lighter weight engine oils. It's not because of anything special about ATF.

 

Yea, but when the 1st gear's ratio is so far in numbers from the other ratio spreads, that's when it's called a granny low, a gear that's seldom used. Same with an OD last gear, only it being an overdrive ratio delineating it from the others.

 

Back in 1982 or '83, before Ford installed the T5 gearbox in the Mustang GT, Ford used a 4 speed...it was a 3 speed, with an overdrive 4th and I remember all the car magazines criticized the gearbox calling it a "5 speed missing a 4th gear" because all the gear ratios were there for acceleration, 1st to 2nd, 2nd to 3rd, and then a huge bog on the 3rd to 4th shift...

 

Yea, they were famous for doing crap like that. That was the SROD. And the "performance" ratio rearend was 3.08

 

I had the iron version of that trans. 3rd to 4th was fine. 2nd to 3rd was the Grand Canyon.

 

The SROD was worse, 1st gear 3.07, 2nd 1.72, 3rd 1.00, 4th .70. The iron version was the OD Toploader 4 speed.

 

Ford finally got the Mustang right in 1985...T5 gearbox, 4bbl carb and dual exhaust...