rear end vibration
 

I have a vibration in the rear end,that starts around 75 mph,do I need to change the pinion angle,with some washers.

I would start by doing the mod Jason talks about here https://www.v8miata.net/build-thread...ion-162/page5/. It is post #44.

Bolting the transmission crossmember to the floor pan helps to take out vibrations inherent to the drivetrain.

That and check the relative angles of the diff pinion and trans and make sure they are within 3 degrees of each other. Remember this does not mean that the driveline has no angles, it just means that if you were to make an imaginary line through the center of the diff and the center of the crank they should be within 3 degrees of parallel to each other in all dimensions (the known ones at least 8-B ).

-Jason

Sorry if that last post fell a little in the:

https://www.v8miata.net/attachment.p...ine=1368642972


-Jason

thanks for the help

LOL! Nice of you to go all techy just before I weld mine up! I've doing a Martian 8.8 and will probably weld it up in about a week. How do I tell what my angles are and is there a desired amount of difference?

A digital angle gauge like carpenters use to set up table saws works perfect. They are about $40. If your smart phone has a fairly square outer shell you can use it and a free app instead. Your looking for no more than 3 degrees of difference.

-Jason

You may just have a tire vibration. If you have a driveline vibration at 75mph, you should also feel it around 40-45mph. Be sure to drive the vehicle at least 20 miles before any work is performed in order to eliminate flat-spotting on tires.

Cool I have one to do front end alignments. The diff looks easy but how do you take your reading from the trans?

Place the level on the trans yoke where the cup for the u-joint is. Make sure the cups are at 12:00 & 6:00 position.

Basically, you want the engine/trans shaft and the rear end pinion shaft to be parallel. The easiest way to measure that is to put your angle finder on the pinion flange, note the reading, then go to the front crank pulley and measure that. They should be the same. If not, its usually easier to adjust the rear.

The attached drawing should show the idea. It shows the engine/trans and the rear to be "level", that's not important, they just need to be parallel. IE if the rear of the trans is slightly down, the front of the diff should be slightly up.

It's considered good practice to have a small angle in the system to keep the ujoints working slightly, otherwise the rollers don't roll and can wear in one position.

Mike

Great idea to measure off the crank pulley! I was thinking it would be tricky to get a good reading from the trans yoke but will try both. I find it interesting that there is not one word about this subject in any of the build manuals I have read yet it seems to be a critical issue. (Monster, Flyin Miata and Boss Frog) Thank you!

A friend sent me this which I think is also helpful.

There is usually a flat area on the back of the bell that can be used as well.

Hey now there is an idea! I could get about a piece of threaded rod or a bolt about a foot long and stick it in any number of bolts on the trans or bell housing. Cool beans!