Hey guys,

Just got done installing my 9" that i bought used. Has 4.30 gears (to big for my a4 but they will be getting changed over the winter), 35 spline axles and Detroit locker with aluminum pinion support. Install wasnt to bad, just time consuming but what else is new. have some questions though about some things ive noticed I was hoping some people could chime in on...

Using a stock driveshaft with the stock U joint. Replaced the U joint last year and had found a few people using the stock driveshaft with u joint but also a lot of people had changed over to a napa 447 u joint (as it states on brute speeds website). Is there a problem using my original u joint? the caps went back on nice and tight and I cant see or feel any play in the universal????

My other concern is that im getting a loud clunk/bang sound when it goes into gear. It is sometimes happening in drive but much more common in reverse. almost sounds like something is smacking the floorboard but ive been under the car and put it back on the lift several times but am not seeing any marks on the floor and tranny mount looks good. Im wondering if the issue is the rear clanging into gear and the new umi torque arm and relocation bracket absorbng the vibration which is now resonating into the car since there bolted to the floorboard? cant find many people with a locker to see if this is common or not? pinion angle is set to 0 degres if that makes a difference. I also have a slightly high idle (1000-1100 rpm at idle) which im not sure what is going on with that since it was idleing at 700-800 before the rear and havent touched anythig under the hood at all but assuming it could be a vacumn leak coming from somewhere? assuming this high idle could also be contributing to the sound? any opinions on any of this stuff feel free to chime in....

 

Yes the clunk you hear is the Detroit locker, it free spins for a split second then locks and that's what you hear..

Give it a little gas while in D to take the slack up, once that happens you can take off like a mad man..

I would use the right u joint, there's a reason there are different series of them.. You wouldn't want the driveshaft to break off under the car at high speeds

 

the clunk going into reverse and drive is the locker? im familiar with them making sound in gears once they are looking and un locking which im fine with but was not aware they would make that sound just being put into gear with the foot on the brake and the wheels not turning.at this point shouldnt the trans just be in gear, no movement in the rear? I assummed it stayed unlocked until gas was given so didnt understand why it would clunk without the car being in motion...I can feel it lock after I take off for a few feet then it takes off real nice.

Id would rather use the "recommended" u joint as well but im not understand what the difference is between it and the originals that would have been used with the stock 10 bolt. I cant see or feel any play in the one curently in there so if I put one with bigger u joints in there isnt it not going to fit? is it possible to have the napa 447 on a stock 10 bolt? maybe thats whats already in my driveshaft.

 

"...the clunk going into reverse and drive is the locker?"
yep, mine (9" Detroit locker-4.11) does same.
however the Detroit locker in my 7 1/2 " was very quite,
you may try lower idle as much as possible which will help.

"...the "recommended" u joint " -" 447 on a stock 10 bolt?"
has 2 cup which are larger to fit the yoke on the 9"

also a stock driveshaft is about 1" short ( some ppl use them, may cause vibs,) if you have adj LCA you may adj rear forward to take care of some of slack

just my 0.02, Johnny

 

deff getting some vibrations after putting some more miles on it but not 100% these new vibrations are not part of the exhaust system vibrating either as we altered it some to clear the new torque arm mount. Im going to pick up one of the 447 u joints and check it out/install just for piece of mind.

If i still get vibrations i am going to look into the driveshaft though. Mine is steel but it seems like most have aluminum. would I be better off getting it extended, getting the longer pinion (think there like 50-$75), getting a aftermarket performance driveshaft, or buying adj LCA's and pulling the rear forward some?

 

I would not extend your stock DS, I would leave the pinion alone as well.

adj lca's are not for pulling your rear forward, they are for adjusting your rear end to make sure your wheels are straight and not ****-eyed.

I would measure for proper DS length first, unhook your DS from the rear end and lower it to the ground but leave the DS yoke still in the transmission.

push the tranny yoke in until it bottoms out, then pull it out 3/4'' and measure from the center of the trans u-joint to the center of the rear pinion yoke.. that's the length you need... now measure your stock DS center of trans yoke to center of the rear DS u-joint... if its not the same length as your first measurement then you need to order a new shaft..

if they are 1/16''-1/8'' off then I wouldn't worry too much but anymore and you could have serious problems once you start pushing your car at high rpm/speed..

 

Ill put it on the lift tomorrow and see if I can get some numbers by the weekend

 

You'll notice if you're under the car that with a locker you can grab the driveshaft and rotate it about half a turn. This is why you here the clunking when you put it into gear.

To measure for the driveshaft length, you need to have the rear in the loaded position, such as with jackstands place under the rear end. The "x" dimension in the chart in this link is what we use for ordering driveshafts. http://shop.brutespeed.com/PST-DRA35...-PST-DRA35.htm Bob