rear end problem

1980convertible · 02-12-2002, 01:04 AM

Hey guys I have a 7.75 inch rear end with 3:45 in my 1979....I am currently rebuilding the engine....upgrades as it stands are basic and include...4 barrel intake and Edelbrock 600 carb, Competition Cam setup with an E303 I think, a 42 psi edelbrock fuel pump, Fllow master headers and H-pipe...under drive pullies and a new alt are coming...I know this doesn't sound all that wonderful compared to some of your setups but I was wondering if my 3:45 will hold up to whatever power the engine puts out?

dmorley12 · 02-12-2002, 06:43 PM

Sounds like 3.45 gears would be a decent ratio for your setup, if it will be for street use that is. You will still have decent gas mileage and top speed while gaining acceleration on the low end.

Unit 5302 · 02-12-2002, 08:33 PM

7.75 or 7.5? I thought there was a 6.75 and a 7.5?

The 6.75 will get trashed. The 7.5 might hold 250hp or so.

Bob · 02-12-2002, 08:39 PM

The 7.5 should hold up fine on the street, with street tires, but if you go to the track and put on some drag radials or slicks and use high rpm launches you'll have problems. I ran my 7.5 with the 3.45's in it for a long time.

02-12-2002, 01:04 AM	#1
1980convertible THE Member..hehe Join Date: Mar 1999 Posts: 24	rear end problem Hey guys I have a 7.75 inch rear end with 3:45 in my 1979....I am currently rebuilding the engine....upgrades as it stands are basic and include...4 barrel intake and Edelbrock 600 carb, Competition Cam setup with an E303 I think, a 42 psi edelbrock fuel pump, Fllow master headers and H-pipe...under drive pullies and a new alt are coming...I know this doesn't sound all that wonderful compared to some of your setups but I was wondering if my 3:45 will hold up to whatever power the engine puts out?

02-12-2002, 08:39 PM	#4
Bob "Old School Gearhead" Join Date: Oct 1998 Location: Peru, Illinois Posts: 617	The 7.5 should hold up fine on the street, with street tires, but if you go to the track and put on some drag radials or slicks and use high rpm launches you'll have problems. I ran my 7.5 with the 3.45's in it for a long time. __________________ 1985 Mustang GT '85 GT "Red302" 12.96@107.1 N/A ... Sprayin' for the 11's 2003 Torch Red Mach1 '68 Fastback ...331 Stroker "Restomod"

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02-12-2002, 06:43 PM	#2
dmorley12 Registered Member Join Date: Feb 2002 Location: Fort Worth, TX Posts: 2	Sounds like 3.45 gears would be a decent ratio for your setup, if it will be for street use that is. You will still have decent gas mileage and top speed while gaining acceleration on the low end.

02-12-2002, 08:33 PM	#3
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	7.75 or 7.5? I thought there was a 6.75 and a 7.5? The 6.75 will get trashed. The 7.5 might hold 250hp or so.