Opinions on 4 speed with OD
As in, "when MINE broke, I was....."
1) one time, with deep 3.55s, I was banging thru the gears and in the excitement, I forgot which box was under the stick, and Zing od was history. see below.
2) one time, It was winter and I had my stock, low-compression 318 (allbeit with a TQ and the TTIs,) with a different od box, NOT acting crazy, but .... zing, od was gone.
3) one time, the 360 zinged off all the teeth of the input gear.
Now; there are TWO different tooth-counts of these boxes;
>one of them has a .71overdrive which it does with an 18tooth mainshaft gear. When the cluster engages this mini gear, it pretty much engages just one of those 18 teeth, atta time.
>The other has a .73overdrive, which IIRC has 21teeth, and has a bit more contact area.
NONE, I repeat, NONE of the gears between these two boxes will interchange, they have to be used as a set.
> that tooth-count difference is worth ~100rpm, so of course, I was trying desperately to use it. lol.
The 18 tooth gear, in my experience, cannot take much torque or abuse. The 21tooth seems to be a lil more robust.
As for the alloy box I was using at the time; I had a machine-shop machine out the front cluster pin-hole, and install a steel bushing, with a light press-fit to the pin. Just enough to not leak oil. BTW, The overdrive gear is AT THE BACK of the box, so any error on their part would NOT affect the od gear.
Currently I run a Commando gearset in a Passon Performance alloy box, with the GVod behind it. No more problems. In the beginning I had a bit of elusive to diagnose vibration, that I traced to THREE sources and fixed them one by one. The first was the cruising pinion-angle, the Second was the short driveshaft. The third was the Diaphragm clutch with it's centrifugal flyweights, the take-away here is to not try and cruise at too-low an rpm because the flyweights may not all park in the same place at the same time. There is no solution to this, even at 65=2240rpm. My best solution is to, once cruising, clutch it and blip the throttle. Sometimes it takes a few tries.
Here's the thing;
if you run a street gear like a 3.55, then 5500 in "third gear" will be about 124 mph, and it is hardy likely that you would ever power-shift into overdrive. AND, because of the H-pattern shifter, it is impossible to powershift from Second into "Fourth". So for most guys, that 23tooth gear is relatively safe.
And the other thing is this;
With 3.55s again, 65mph is ~4800 in 1.67ratio/Second. This is just past peak torque with "a bit of a cam".. Since this is the speed limit up here in Manitoba, it was all too easy for me to skip Direct/Third, and go straight into Fourth/overdrive. Well with a CF-II disc and a factory heavy-flywheel, and the rpm forced to drop to 2040, you HAVE TO WAIT FOR THE RPM TO COME DOWN! else the inertia in the flywheel will rip the teeth right off. :(
SO;
if you promise to be kind to overdrive, then you should be fine.
But did you catch that 65=4800 in that 1.67 ratio? That is about where the factory 318 cam makes peak power. So at 4800 you are a good 300 to 500 below the powerpeak of a typical street cam and a good 500 to 800 below it's shift rpm. So I donno why the heck you would run 3.55s.
To hit 65 at say 5500, on the backside of the power curve of a "bit of a cam" would require a road gear of 6.795, and 6.795/1.67=4.07, so the right gear to run, is gonna be about 4.10s for 65=5540 with 27" tires. And that make 65=2420 a very nice place to be. But when you hit redline in Second, do yourself a favor and shift into THIRD
NOT OVERDRIVE!
, lol.
Cuz when it goes ZING, you better have a rev-limiter.....
If you do Strip off a gear, clutch it, and STOP THE CAR!
You have no control of where those pieces are gonna go. If they end up between teeth of another ratio, they will take the rest of the box out. But before they do, they could lock-up the rear wheels, and if/when that happens at 65mph, NOTHING GOOD will come of it. Tow the car home and drop the trans. After a good clean out, you can still drive it as a 3-speed until your new gears come in. But I gotta tell ya, I highly recommend having a spare one in the garage.