nks06

I have a weird clunking sound coming from the back of my car whenever it shifts from 2nd to 1st. It doesn't happen any other time. Me and my dad checked the U-joints and both are fine. Any ideas?

SpitotRs305

well you have something that needs to be replaced... it wont do it from 1 to reverse?

Corky

You'll have to crawl under and take a look. Check rear trans mount (may look OK, but put a pry bar under and check for movement), check all mounts - sway bars, shocks, muffler & tail pipes. Look for rub marks on all external parts before looking at internal parts.
Corky

F-Body Demon

iTrader: (1)

Oh hell yeah i can answer this for you. Its your tranny mount im almost positive. Heres how you can tell. Lift the car up on to some jack stands and take your jack under the car with you, jack up the rear part of the tranny on the tail shaft and see if the mount just comes apart or is all beat up. If so (which im betting it will be), go to autozone and get one of their Energy Suspension Polyurethane tranny mounts. Then go back under your car jack up the tranny SLIGHTLY, undo the crossmember bolts then remove the old mount and replace with the nice and shiney new one. Bolt the crossmember back up, torque to spec and whala problem solved.

I had that problem in my 85 and I was lucky enough to have the mount already for the build. It sounds like a *thump thump thump* huh? Its the tranny hopping up and down against the crossmember not good por favor. Another way to determine if it isnt or is the tranny mount is the noise will be reduced if not eliminated under hard acceleration.

Glad to help and in advance

nks06

hey, thanks yall

to answer spits question, it shifts pretty rough from drive to reverse, is that what you mean?

thanks f-body for the in-depth description, i'll check it out today =]

i got it taken to a trans shop about 2 months ago and its under warantee. would they forget to check for something like that??

SpitotRs305

no if they had to do any work to the tranny out of the car they would have probably noticed... when was the last time you took you diff cover off? did you check the driveshaft bolts or did you just look at the universal joints...

KrisW

iTrader: (5)

I have had 3 of these cars (only standard shift ones, though) that made a rear end clunking sound when deccelerating and the pinion nut had come loose and actually allowed the pinion to fall in too far and rubbed against the differential cover!

I changed the front seal, torqued down the pinion nut, and then tacked the nut with a mig welder. They all held but I can't guarantee that yours will...

take off the rear cover and look inside. Look for oil leaking from the front seal on the rear end...

nks06

my dad went under the car yesterday and looked underneath while i shifted from reverse to neutral

he described that the drive shaft and the diff+rear axle rolled/rotated up and then dropped. kind if like going from --- to /-\ back to ---

to add to the mix, when there is added weight to the car, nothing happens. for example. when its me, the clunking sound happens. with my dad in the passenger, it happens sometimes. with my dad in the back passenger, and my gpa in the front passenger, it doesnt happen at all. (our weight range is from 210-250. takes about 440lbs to have it stop) I have REALLY stiff springs (came that way from previous owner). Could those also be a factor?

to answer spits question: we just checked for wiggle from the u-joint and it didnt on both ends

to answer kris': i saw a single bead of green liquid on the front part of the diff that connects to the u-joint (the front seal? im still learning)

89RsPower!

I think by front seal hes talking about the pinion seal.. I'm still trying to imagine how the pinion gear could get in front of the diff carrier and ring gear to make contact with the cover.. pretty much imposible without destroying everything in the diff... maybe hes talking about it hitting the housing or ring gear...

SpitotRs305

there is damage in your rear diff get a new gasket for it open er up and have a look clean out any metal... and go buy replacement parts.... might need a shop to do this if you havent done a couple before

sully91rs

Well, if the ujoints are good, I would think the thing moving is the trans. Get a new trans mount. Its the simplest first thing to do.

transam85dudeman

You need to get a "Prothane" Poly-urathane TRANSMISSION BUSHING/MOUNT, an "Energy Suspension's" polyurathane TORQUE ARM BUSHING.

Get a car book at autozone (HAYNES), and a torque wrench.

Use the torque specs from the book to tighting all suspension components when done. Torque them on a level surface with out jacks or jack stands, (gotta crawl underneith) (its very important you dont over torque or under torque the suspension components, because you could send your car off the road or a cliff. and overtorquing the torque arm bolt at pinion differential will result it damage to the car.........Double check your tires in the back, if they're directional make sure the arrow on the sidewall points forward.

I also recommend but not really important.:

-Haynes for 3rd gen BOOK-15 bucks

-Drive shaft loop-30 bucks

-New fresh u-joints-25 bucks

-New KYB gas shocks-40 bucks

-Various Rear suspension bushings, Panhard bar, control arms, sway bar (if equiped.-$50ish

-Mike s.

rv1890

iTrader: (3)

Mine does the same thing. I just swapped with a fresh 350, and new 700r4. When I slowing down there is a clunk from 2nd into 1st. Im gonna check it as soon as I get off work. I have a new energy tranny mount, and there is a small amount of lateral movement in the driveshaft. I think Ill be replacing teh ujoints first,a nd then going from there. keep us posted.

nks06

my dad and I are going to be working on it today

things we're doing:
*checking tranny mount
*replacing u-joints
*bleeding the brakes (replaced wheel cylinders last week, dbl checking)
*possibly other misc stuff

i'll let you know how it goes tonight

nks06

well, we replaced the rear u-joint, and it didnt fix the problem. it got rid of the rising of the drive shaft+axle, but theres still a clunking. heres a video..
View My Video

we also ruled out the trans mount...looks pretty good:


PARTS:
*new u-joint
we used a u-joint made by brute force. its about $12 at discount advance auto.

so heres how it went down. we spray-painted both ends of the drive shaft and the surrounding area so we knew how it would mount back up. we then took off the retaining clamps that held the back of the u-joint in place. we then pushed the drive shaft forward, pulled down, and then took the drive shaft out of the transmission. when we did this only a few drops of tranny fluid came out. my car has a mod'd exhaust, so we had to push it so we could have enough clearance to get it out (there was the exhaust pipe and some plate thing that i imagine is to protect the driveshaft from any debris on teh ground.

heres how the old u-joints looked:




the u-joints had never been replaced, so the nylon goo was still in the yoke keeping them in place. if you don't know how to check, if there are little beads of white stuff on both sides of the yoke where the ujoint connects to it, then it has never been replaced. we took an acetylene torch to them to melt them out. after so long, they snaked themselves out. it smelled kinda bad so be careful. we then took a hammer and a 17mm socket and pounded on one end to get the other end out. we took a vice grip when the bearing cap (the silverish thing) had cleared the yoke ear and pulled it out. we did the same thing for the other side.
heres how it looked:


now, the semi tricky part is getting the new u-joint in. what we did was we took off one of the bearing caps and pushed a little bit of it in the yoke ear. you then take off opposite bearing cap and place it to the side with the hole facing up, so that the needle bearings down fall out (just in case). put one of the ends into the bearing cap that is in the ujoint in. after it is firmly in, place the other bearing cap into the yoke ear. make sure that it is aligned with the ujoint! we didnt and ended up destroying one of the bearing caps because we broke a lot of the needle bearings (ill explain in a second). we used a bench vice to squeeze the bearing caps into the yoke ears. do this slowly, making sure that it is aligned! we put the "holding pins" on the ends that are in the yoke. they came in a little plastic bag with the new u-joint. here is a picture of how it looks after:

(we took off the other bearing caps so they wouldnt fall off)

after we got it secure, we went back to the car, slipped the end that goes into the transmission into it, aligned with the spray paint marks. we then aligned the other end with the other. we put the retaining clamps on next. we then put the "holding pins" on the parts of the u-joint that didn't have them. we torqued down the nuts to 16lbs, as the chilton said.
heres another pic:


and thats it!

but yeah, now I need to figure out whats up with my differential/axle =\