How much clearance should I shoot for between tunnel and driveshaft to prevent rubbing? Currently trying to set the crossmember and at 1/2" clearance. If I increase clearance then obviously driveline angles will suffer a bit. Probably need more clearance than 1/2".

 

Your driving style and suspension set-up will have a lot to do with how much clearance you can get away with. The neck-down in the middle of the tunnel of the A-bodies certainly makes things a tight squeeze and lowering the rear suspension worsens the issue if you go much beyond an inch of drop when using a GM 10 or 12 bolt rear end. Be sure to check the condition of your body mounts as they can reduce clearances quite a bit if they are old and collapsed. What is the diameter of your driveshaft?

 

Thanks for the reply.

My car is lowered about 2" all around. Body bushings are probably original and will replace them at a later time.

Driveshaft diameter is 2.75" and increases to 3.25" after the first 6" or so.

FYI, the 1/2" clearance was with car level and trans 4.5° down. If I go to ~5.0-5.5 I get 1" of clearance.

Maybe shoot for the 5-5.5 down and can add a spacer to the mount to always have the option to go up?

 

The absolute engine/transmission inclination angle degree is only important in as much as it affects your U-joint working angles. You are far enough into your install now that you need to install a driveshaft (actual or a mock-up made from pipe/tube) so that you can measure its inclination angle, along with the eng/trans and pinion angles to be able to calculate your U-joint working angles...you can't get there by measuring the eng/trans and pinion angles alone. U-joints by design are only intended to operate at a maximum angle of three degrees and that is RPM dependent (the faster they're spun, the less they will tolerate).

2in. suspension drop all around is going to be problematic to compensate for in terms of optimizing your U-joint working angles without resorting to additional efforts such as notching/rebuilding he floor for the needed clearance, using a CV driveshaft, or switch out the rear end for a Ford 9" to take advantage of their lower pinion height. So, you have options and just need to develop a plan that works best for your situation. Spending the time to minimize your U-joint working angles is also going to ensure your engine inclination angle will also be as small as possible, which for a T56 install is critical in my opinion to keep the bottom of the rear case half as high off the ground as possible.

 

Matt,

Todd speaks the truth on all accounts. Your best bet is to raise the back of the trans as high as possible. Other limitations will be in the front of the engine as various accessories may start hitting things, but this will depend on the accessory drive that you plan to use.

Andrew

 

Sounds good. I was using a string yesterday to start calculating driveline angles, however I think a PVC pipe will work better. I'll keep you posted.

BTW, just built a 12 bolt last winter, so I would hate to go 9" LOL.

I also planned to run a turbo crossover under the trans for this build, but now I'm seeing this as a bad idea.

 

Thanks. Truck acc which need to be thrown on for mock up. I'll keep you guys posted.

 

If you are going to use the truck accessories you will need to swap out the pulley on the PS pump as it is going to experience interference with the PS box. The pulley to use is one off of an early 90's Camaro V6, or S10 truck engine. I can get you the part number of the pulley if you need it from my development notes.

 

I bought the dorman 300-202 to try out. It measures 5.142" OD. Sure, post the PN in case this one doesn't work out, much appreciated!

 

Here you go, an image of the pulley installed with the part number visible on it. If the Dorman pulley is plastic, I would be hesitant to use it even if it fits. There are documented cases of the plastic pulleys disintegrating at high RPM operation.

 

Thanks! The 300-202 is metal.

 

For comparison sake, in case you need it, the GM pulley is 6.625" O.D. and the diameter measured at the peaks of the belt ribs is 6.125".