Team Camaro Tech banner

1 - 9 of 9 Posts
S

·
Guest
Joined
·
0 Posts
Discussion Starter #1
I just replaced the powerglide in my '69 with a rebuilt th350, and now when I shift from reverse to drive or drive to reverse I hear an audible "thunk" (not terribly loud but noticable) as the tranny engages. If I shift from drvie to neutral to drive it doesn't do it, and it doesn't do it on shifts from 1-2 or 2-3, the shifts are firm but not noisey. My rear end is original, i.e. well used. Also, the torque converter seems to have a stock/low stall not sure what the exact rpm is.

My question: does this sound like a tranny or rear end issue, or is it not an issue at all, just the behavior of the tranny?

Thanks in advance,
Marc
 

·
Registered
Joined
·
671 Posts
its probaly your pinion gear has loosened up over the years. the tighness of your pinion(which pre loads the bearing) gives you how much backlash you have in the rear end. when you set a rear up you have to have between .008 and .0012 thousanths back lash, you achieve this by one a shims or shims behind the pinion bearing. you then torque the pinion nut until you have .015-.025 inch pound torque to turn the flange.now, the back lash is how much the pinion moves before it contacts the ring gear, so as you can see 8- 12 thousanths isn't much, more than likely over 30 years your rear as loosend up and never been checked, remove the driveshaft from the rearend and then spin the flange on the rearend(the part the driveshaft u-joint bolts to and you will probaly find your problem. then when you feel like it makes 1/4 turn before it starts to spin the wheels,it is loose, it should spin very little before engaging the wheels.this is where you clunk in coming from,there is so much play that after going forward ,when you shift to reverse the flanges turns so much that it is able to make that clunk. the reasonit doesn't do it going into neautral is because the driveshaft does not turn or when doing so, you get the clunk after you get to drive or reverse and the clunk is the intial contact of the pinionn and ring gear hitting each other, thats why you get this only when going from forward to reverse, because you are changing dircetion, well hope i didn't confuse you, goodluck
Jake oh y a email me if you need some more help
if i forgot, the remedy is to tighten the pinion bolt up slowy until you get it so there in a little slop when you turn it back and forth. for the weekend warrior the easiest way to do this is to use an air gun, but the proffesional way is they make a tool that holds the flange while you tighten the pinion bolt, then you can check the inch pounds it takes to turn it.if you are not putting in a new ring and pinion i would use the air gun and tighten it up intill it feels good,if you go to tight it will turn hard, you want to get it so there is only a little play inbetween going one way and the other, goodluck
Jake
[email protected]
 
S

·
Guest
Joined
·
0 Posts
Discussion Starter #5
thanks for the help, the U-Joints look ok

BBCamaro, you've given me hope, at first I was affraid I got a bad rebuild, but after reading your post, I believe this is more likely the cause, I did notice that the rear was loose, but I wasn't sure how loose is too loose. Your post is pretty clear, I'll take a look at fixing it this weekend.

Thanks a bunch!
 

·
Premium Member
Joined
·
1,010 Posts
Tightening the pinion nut will not decrease the backlash!! All that will do is add preload to an old and worn set of pinion bearings.

Leave the rear end alone if it is working correctly. It's very likely that your TH350 just drops into gear a lot more crisply than the old tired PG did. If the drivetrain is all original, there is bound to be a lot of backlash in everything that gets "taken up" when you drop the trans into gear.

There is at least some lash in the ring and pinion, the differential gearset, and the drive axle to differential splines. This is normal for an old car.

If the driveshaft is tight, and the rear end isn't making any bad noises, I would leave well enough alone.
 

·
Registered
Joined
·
671 Posts
no s... the shims inbetween the pinion bearing and the pinion increase or decrease backlash, sorry i wrote it like that, if my rearend was loose and made a thunk and i did not want to rebuild it it would be STUPID!!! not to tighten the pinion nut up a bit to get rid of some slop until the time came when i rebuilt the rear, i would not want to be at a cruise in and shift into reverse and have everyone hear a THUNK!!Would you???, also i did not say this was a problem, i said to check it out and explained it alittle, but anyway sorry for trying to help, i'm sure he took my advice and at least checked it out. thanks anyways
jake
 

·
Registered
Joined
·
76 Posts
The shims between the pinion and bearing have NOTHING to do with backlash!!! The pinion shims set pinion depth which relates to the contact pattern on the gears. Backlash is set and adjusted by the carrier shims!! The carrier is moved closer to the pinion to reduce backlash or farther away to increase it.

Tightening the pinion in the manner suggested will only ruin the pinion bearings over time.

I work on rears every day and I see my share of things that were "fixed" by car owners or backyard mechanics who think they know what they're doing. Then the owner brings it to me and pays dearly for me to fix it right(after other parts were ruined due to the previous "fix").

If you just changed your trans and the rearend showed none of these signs before the change, why would you suspect the rear? What is different? Did you put a new trans mount in? Did you change anything else? Is there a growling noise or just the clunk?

My suggestion would be to bring the vehicle to a good driveline shop and see if they can give you some expert advice on what might be wrong.

Good luck

------------------
70 & 1/2 RS
SB406 & M20 4spd
9" rear

70 Malibu 350/TH400

Gold member #103
Driveline Technician

http://www.geocities.com/carguy63/
 

·
Registered
Joined
·
127 Posts
I think you might want to check your spring bushings.. When the bushings wear out you'll hear a clunk every time you do what you mentioned. My 68 did that the minute I got the motor back up and running. One of the things that got overlooked when buying a car that didn't have a running motor. My clunk is on the front passenger leaf spring bushing.
 
1 - 9 of 9 Posts
Top