I am thinking of getting the GM service manual for my car,what I would like to know is how detailed is it.I have the assembly manual and a haynes manual ,but I would like to have something a little more detailed.What I was wondering if someone has one can I have your opinon on it please.

For the '75, you'll need two manual sets. The '74, AND the '75 "supplement". The FSM is the ONLY one that will cover the complete car, in detail. The Hayne's, Chilton's, and others cover multiple years, so the info doesn't get very specific.
You'll want to get both the Service(overhaul) manual, and the Chassis manual, to have complete coverage. The Service manual will cover all of the overhaul, repair, replacement stuff, and the chassis manual covers a lot of the electrical, body, and suspension stuff. I would absolutely recommend the FSM to ANYONE that owns a Corvette...it's a must have, imho.
Adams' Apple2010-07-03 20:02:49

The whole 3 book set is still available new from the original publisher GM uses. $75

http://www.helminc.com/helm/product2.asp?session=1BD4F7423ACD46A09CF74829272968D7&Make=CHV&Model=CVET&Year=1975&Category=&class_2=CHV&mk=Chevrolet+%26+Geo&yr=1975&md=Corvette&dt=&module=&from=result&Style=helm&Sku=ST32975K&itemtype=K

That's a hel l of a deal right there!! Thanks for the link, Philip!!
Most of the time, you can find the manuals used for about $40 each....getting NEW ones, and a complete set, for $75 is a steal!

(1) ST32975 - 1975 Passenger Car Shop Manual

(2) ST32974 - 1974 Passenger Car Shop Manual

(3) ST33374 - 1974 Passenger Cars And Light Duty Trucks Overhaul

The '75 part of the set covers all of the stuff that is different from the '74, including the exhaust(cat converter), and the electronic stuff, such as the HEI ignition, and the electric gauge cluster.

That's a great find on the manuals! I'll have to bookmark that one!