General Question about Driveshafts

[cleanone]

Hello,

 

Could someone please help as I am new to the RWD layout.  I just purchased a '72 510 with a Mazda 12A rotary and transmission already installed.  You can see my project datto thread here

 

http://community.ratsun.net/topic/52955-florida-dime/

 

 

When I am driving the car all seems fine while accelerating but as soon as I let off the gas there is all kinds of noise coming from below.  I swear it sounds like the drive shaft is going to fall out.  I stabilized the rear sub frame by flipping the stock bushing washers and that helped a little.  While under the car I noticed some off axis play at the front end of the drive shaft where it slides into the transmission.  When I disconnected the drive shaft from the rear end, I was able to slide it up into the transmission over 1-3/4"!  My question is;

 

What is the appropriate amount of plunge for a drive shaft?

 

I.E. when I disconnect it from the rear end should I be able to slide it up into the transmission 1/4"?  1/2"? how much?

 

I am pretty sure 1-3/4" is too much as there is not enough engagement to prevent the yoke from moving around off axis.

 

 

Any help would be appreciated since this is new to me.  

 

 

Thanks.

 

Russell

[datzenmike]

Are you sure the front U joint isn't the cause of the wobble?

[cleanone]

Mike,

 

There is some play in the bearings on the front U-joint. But with the drive shaft attached to the rear end, I can move the whole front U-joint, both parts, up and down about 3/16".  When I disconnected the drive shaft from the rear end and slide it all the way into the transmission, that up and down play goes away.

 

I suppose it may help to pull the drive shaft and see how long the transmission end of the yoke is.

 

Am I correct in assuming that when I pull the drive shaft from the transmission the gear oil will leak out?

[datzenmike]

It will leak if the tail center line is below the fill bung. I've tucked a rag in the end before.

[ssnapz]

Sounds like its too short of a drive shaft. Take it to a driveline shop so they can measure it and make one the right length.

[cleanone]

I am just going to slide the engine back some to make up for it.  There is plenty of room to move the engine the required amount.  Plus the angle of the engine to the drive shaft could be improved upon too.  It does not cost me anything but time to redo the engine and transmission mounts.

 

I was planning on allowing about 5/8" of plunge for the drive shaft.  Does that sound about right?

[datzenmike]

Maybe 3/4" is better. Is the spline worn and just how much spline is making contact where it sits right now?

Can you find a front spline that is longer?