Can it be done? Yes. Should it be done? Absolutely not. The manual transmissions available for the F750 from Eaton Fuller and Spicer were synchromesh transmissions - nothing like the unsynchronized twin countershaft transmissions found in Class 8 trucks. Trying to float this box could destroy the synchronizers and ultimately cause the transmission to have to be rebuilt or replaced.
The F750 was not in production in 1990.
The F750 was not in production in 1965.
The F750 was not in production in 1993.
If the 750 is unladen, yes. The tare weight of the F750 is well within the towing limit of the F350.
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The Ford F750 has a higher Gross Vehicle Weight Rating, and more powerful engine options available.
one
Many websites will have Ford F750 parts. Autozone is a popular and reliable website to look for these. One other which is an option is called Partstrain.
Depends entirely on which transmission you have with it.
36 to 40 oz
According to the Ford Website, the GVWR for the Ford F750 is either 30,000 or 33,000 lbs depending on how the truck was configured. http://www.commtruck.ford.com/ctw/default.asp
Depends on what your transmission is. If it's a manual, it may simply not be broken in quite yet, and you should double clutch, rather than float. It could also be possible that you're hitting the gears wrong.