CMQuickcoupe

Ya id like to know the difference also lol,are there any differences in trans cases through the years? i have umi 2" lowering on front and rear of my car,if i top the trans out in the tunnel and put my degree finder on the block pan rail it is about 1.5 degrees down.

Toddoky

Yes there are case differences, but nothing that will cause the issue you are experiencing. The earliest design of the case was designed for use behind SB/BB Chevy engines and so doesn't have the LS compatible hole in the bellhousing at the 12 o'clock position. The only other major change to the exterior of the case was in moving the return cooler line to the rear of the case from the front.

If you are measuring a 1.5 degree engine inclination angle relative to the bottom of the frame that is bizarre, but good news for you in regards to be able to obtain optimized U-joint operating angles. At this point I would install a driveshaft so you can measure/calculate your U-joint angles before deciding your good-to-go with your stock crossmember.

You need to know your engine inclination angle, driveshaft tube angle and your rear pinion angle in order to be able to calculate your U-joint operating angles, knowing only your engine inclination angle and rear pinion angle will not get you there.

CMQuickcoupe

Im not sure what the frame angle is i will check today after work. Thanks for all the information

Toddoky

the frame angle is not super important, it's merely a consistent reference point that won't change relative to the other angles you have to measure if you change your ride height or rake.

The only critical angular characteristic is what your U-joint working angles end up at.

CMQuickcoupe

Ok, so if i top the trans out in the tunnel and then lower it a bit to give it clearance to not rub what engine degree should i hope for? I have adjustable upper arms in the rear so i can change the pinion angle also and i will take my driveshaft down to be shortened and balanced.

Toddoky

Your discrete engine inclination angle will only matter in as much as it affects your U-joint working angles. This is where you need to understand that you can have equal/opposite engine inclination and pinion angles (a good thing) and still have excessive U-joint working angles that come about from a large disparity between the trans output shaft height and the pinion height. This is an scenario that's easy to end up with in an A-body due to their low floor height, which limits the ability to raise the trans tail shaft to compensate for lowering the rear of the car much past 1".

Project GatTagO

iTrader: (7)

Any chance of getting the camera close to the frame stands and taking some pictures of the engine mounts? It actually looks like the engine is sitting a little high at the front. It is possible to bolt the 4th gen f-body engine mounts upside down, which I believe will change the installed height.

Also keep in mind that driveline angles will be effected with changes in rear ride height. The lower you go, the worse things get.

Andrew

CMQuickcoupe

CMQuickcoupe

I think the engine sits about right,dont think it will go much lower without hitting the crossmember with the pan. I can set the trans angle at about 2-2.5 degrees down and that will keep it from touching the top of the tunnel then i measured from the ground to center of the output shaft and ground to center of pinion and its about 1/8" from being a straight line.I have adjustable uppers in the rear and my pinion is down about 1-1.5 degrees now,i can go down a couple degrees more and under acceleration the drive shaft should be alomst in a straight line what do yall think?

Toddoky

Is your car sitting at its intended final ride height now? If so, your next step is to get a driveshaft in there so you can take some angle measurements.

CMQuickcoupe

Yes its at its intended ride height,im just trying to get an idea if i will be close before i spend a few hundred bux to get a trans yoke and get my driveshaft shortened and balanced again id hate to spend that money for somethin i wont be able to use

1973 STEP A SIDE

iTrader: (4)

Can someone tell me the measurement from center of bolt hole to the backing plate of the 4 gen F body motor mount ?

Project GatTagO

iTrader: (7)

You can approximate the angle of the driveshaft by stretching a string from the center of the output shaft to the center of the pinion gear. It takes a little effort, but it should give you a really close idea.

Also, it looks like you have poly inserts that you installed in the 4th gen shells. I am wondering if those inserts are not quite right or if they are installed upside down. The engine looks high to me. If it drops some in the front and the back of the trans get lifted higher, that will level out the engine and give you a little more room between the back of the crossmember and the oil pan.

Andrew

Project GatTagO

iTrader: (7)

If you turn the steering wheel to the extremes, does it look like this?





Andrew

CMQuickcoupe

I"ll have to jack it up and turn it full lock tommorow,if I remember right i think the polly inserts would only go in 1 way inside the gm shells and your pan seems to have about the same clearance to the cross member as mine does. I can try the string method and see if i can get it to work.

Toddoky

Do you know enough of the history of the car to be able to confirm it still has its original frame? Is the stock transmission crossmember you have the bent tubular type commonly found in the Chevelles?

Unlike the Chevelles, the other BOP A-bodies used a stamped sheet metal transmission crossmember and I've never been able to figure out exactly why the Chevelles used the proprietary tubular crossmember.

Project GatTagO

iTrader: (7)

As far as I understand it, Chevrolet was the lowest in the GM line-up, so many parts were built as cheap as possible. The Pontiacs, Olds, and Buicks all got the rubber isolated crossmembers because they were more upscale. My GTO has the rubber isolated crossmember.

Andrew

Toddoky

Yes, I have seen those also here in the lab Andrew.

CMQuickcoupe

not sure of the history of the car,I bought it about 4 years ago and it had been in storage since 97 and most everything on it looks pretty original including about 80% of the interior.frame looks original because car was red when it was found in storage and the guy i bought it from painted it black and the frame shows these colors and most all the suspension i changed out last year was worn out original stuff. yes it has the bent tube cross member. The only inconsistent thing i found in the old drivetrain was the 10 bolt rear was dated for a 70 chevelle and i could tell someone in the past had messed with the rear brake line

1973 STEP A SIDE

iTrader: (4)

Can someone tell me the measurement from center of bolt hole to the backing plate of the 4 gen F body motor mount ? I found these and they are 1 5/32" from the backing plate to center . I am told by the manufacturer they are the same as stock . Just trying to make sure before I bolt them in and then find out they are different .