Neil Palmer

1978 C3 Silver Anniv coupe:
I'm doing body off restoration - also having head read.
Have had problems with chassis due to previous (US) owner's accident.
Chassis is 'presumably' straight now.
Have put engine and gear box back in place in readiness for body refit.
Now the tail of the gear box is out by about 3 inches, ie it is pointing in
the direction of RHS rear wheel.
And now obviously there is no way that the drive shaft will meet with the diff. And even if it could I'm not sure the universals should take that much of an angle.
I understand that the engine was offset by about 2 inches to allow the
driver in the US more leg room (as evidenced by the longer bracket for the engine to mount on to on the LHS).
My conversion to RHS has not touched this area as it is not a mirror
conversion but a cross-shaft or roddy.
My question is:
Should there be some offset or pointing of the tail of the transmission towards
the RHS side rear or should it align directly with the diff ?
It seems odd when one tries to understand it, that on the one hand the engine is over by two inches, and the diff is in the centre of the car, how could they have lined up directly anyway.
So, trying to draw a picture, if was was in the middle of the rear of the
chassis with a straight line towards the front of the car, would the diff uni be directly in line with that of the tail of the gear box ?
My guess is the chassis is still out somewhere.
But obviously - I need help - to convince those in body shop.


[Modified by Neil Palmer, 6:08 PM 12/19/2001]

jdunne

Neil,you need to get some serious measuring done.....there is not a complete alignment of the engine and the diff in both the vertical and the horizontal planes....there is a reason for those uni joints but it seems that yours may be out of alignment......a proper manual or AIM is needed to get the chassis measurements to see if the rails are bent......there are a fair number of adjustments that effect the diff placement.......start with the trailing arms to see if the rear wheels are aligned with the front,if not you will prob have a frame prob.......if you are planning on any mods to the engine such as headers you will find there is zero room on the rt hand side......since my 74R is a mirror conversion,i took the trouble to center the engine and gearbox....you will then find that the floorpan is not symmetrical in the transmission tunnel.....it is lots of fun.....john :chevy

Neil Palmer

Thanks John,
I've had the measurements checked to a 1977 and to a 1979 which are slightly different. Both people who supplied these chassis meaurement pages said my 1978 would be the same.
To correct the chassis problems it was pushed and pulled by an Auotrobot and its been checked over and over. Its been trembler bar checked here and there a number of times. And yet it still is out somewhere.
Corvette expertise here in Australia in this area seems hard to find.
I wonder if anyone has definitive 'plane' views like you mention of the chassis/transmission/diff problem areas or even photos?

wombvette

There is a slight offset but no where near that much. It sounds like the motormount stanchions may be out of line. The offset gets less and less as the driveline moves to the rear untill it is in the center at the rear pinion.
The offset has more to do with the torque of the engine than the big butt drivers in the States.

wombvette

Actually it is easy to tell exactly how much offset that there should be at the transmission mount. Just measure and mark the centerline between the frame rails near the mount. You will see that there is a difference between that and the transmission mounting holes. That is the offset at that point.

Nomad78SA

Neil, I have the body off my 78 if you need me to take some measurements or pics for you. I have a 700R4 transmission in mine and have changed out the mount as far as changes go.
Neil in Tenn

jdunne

Neil,dont assume it is the motor that is out of position.....suggest you measure exactly where the front and back of the diff are in relation to the frame rails......on mine it is dead centre.....there is a 2* variation inthe vertical plane between the end of the 700R4 output and the diff,the variation in the horizontal is less than 1/2 inch which minimizes the stresses on the uni joints but that is after cutting the old engine mounts and centering the engine...the 700R4 is very tight to the left side of the trans tunnell,but there is sufficient airflow around it........also vettes are very "adjustable" as to how the body sits on the chassis,make sure you hve carefully measured that as the diff ultimately bolts to the body and if the body is out of line with the chassis it may explain the diff being out of position....john :chevy

Neil Palmer

Hey Neil, thanks for the offer.
The picture showing where you're up to is just - just unbelieveable.
I should be there!
Looking and drooling over it I've now lost all track of what I was on about!

Neil Palmer

I didn't mean any slight on the BB (big butts) in the US, in fact I think I was more talking about feet.
The mount holes offset to centre of rails sounds like a good idea and I will check that thanks.

Neil Palmer

John, I dont recall anything about the diff bolting to the body. Where does this happen?