Postby Workshop Help » 18 Sep 2013 11:50
Here's another recycled topic of conversation. That's okay.
As one who has lived with both gearboxes, the four speed has a slow 1st to 2nd gear synchro. It is far too easy outshift the gears resulting in a gaunch until the synchro catches up. First gear is too high, second gear is a bit too low, third is okay, while fourth, being direct gear, spins 3275 RPM at 60 MPH, which is a bit frantic.
On the plus side, this gearbox does not have an oil pump like the LT77. It uses the traditional splash method of gear lubrication and, as such, lasts forever provided the hot young driver doesn't jam into second gear trying to drag race with Datsun 240's on the Friday night he got the car from his parents as a graduation gift, with the resultant internal explosion as it disintegrates.
Yes, the four speed is about 20 lbs lighter than the LT77. But, that extra weight of the five speed is placed in the best location on the car, right in the center of gravity.
The virtues of the LT77 are a proper gearing spread thru 4th gear, which is direct drive. That wonderful 5th gear overdrive lowers cruising RPM to either .83:1 or .77:1. The negative aspect of the LT77 is the effects of normally occurring metal shavings, called swarf, on the fiber gears of the internal oil pump, and the factories original specification of gear oil. Both of these issues have been solved, thanks to us here on the forum.
The swarf issue is dealt with by regular and frequent flushings of the gearbox and cleaning the magnetic drain plug. This minimizes the collection of swarf around the oil pump intake nozzle. Then, the lubricant is replaced with Pennzoil MTF in the yellow bottle.
Other minor chores for the LT77 are considered maintenance issues such as the deteriorated exterior gear change housing bushes and the replacement of the rear extension main shaft bearing with one that has a shield on the back side to prevent dirt and grit from entering past the oil seal. This rear bearing is the one most subject to replacement and creates a grinding whine when damaged.
The final issue with gearing lies in the differential. The four speed uses the 3.63:1 ratio. This is a very good all around ratio. It provides the virtue of both acceleration and reasonable fuel economy for our four cylinder engines. The factory five speed differentials originally were the 3.90:1 ratio but then changed towards the end to 3.45:1. Those with the 3.45:1 ratio are indeed blessed as the 3.90:1 ratio wastes the advantages of the LT77 gearing spread.
In conclusion, the four speed box may have it's adherents, but this soul lived with it on a daily basis for some 30 years and 125,000 miles. Looking back, it's hard to believe I waited so long to make the conversion to the LT77.
Mildred Hargis
