Posi Traction "clunking" on my 1967

[Gerald C.]

Hi,

I just took my car out after having the engine and tranny rebuilt. After about 45 minutes of reasonable driving, everything was working great.

Then while pulling in the driveway and backing up, I heard a clunking in the rear end and some slight movement.

This also happened in my 63 and the posi clutches were replaced. The Corvette Center in CT, said those clutches were too frozen to be freed and had to be replaced. I drove the car once after I bought it and there was no issue in the rear end.

Is there something I can try to put in my 67 rear end to release those clutches? The car had been sitting for several years when I bought the car. This is the first time I really had the car on the road this long.

Thanks

Jerry

[Edward J.]

Re: Posi Traction "clunking" on my 1967

Jerry, Was the noise while moving straight ahead? Or while turning? generally posi clutches only grab while turning. If so have you tryed the a botle or two of additive to the rear end?

[Gerald C.]

Re: Posi Traction "clunking" on my 1967

Ed,

When you say a bottle or two...could this mean the rear end is dry? It made the noise while turning.

Thanks

Jerry

[Edward J.]

Re: Posi Traction "clunking" on my 1967

Jerry, sound like a typical posi clutch chatter, I would add a few bottles of limited slip, or posi-traction additive.can be had a GM dealer or your local parts store.

[Michael G.]

Re: Posi Traction "clunking" on my 1967

Ed,

When you say a bottle or two...could this mean the rear end is dry? It made the noise while turning.

Thanks

Jerry

Not uncommon if the car has sit or has old(er) grease in diff. Your rear end is most likely not dry but your clutches are sticking together most noticeable when turning a corner....even more so when diff is hot (road time). This is similar to a situation I encountered with my '66 after being off the road for a while. I replaced the rear diff grease with new/clean fluid and added 2 tubes of Trans X Posi Lube to the diff. Then....your love this.....went out and did many, many figure 8's in several parking lots. This exercised the posi clutches getting the new grease and posi lube inbetween the plates. The issue gradually went away. Now I hear and feel nothing from the posi unit. Got the Trans X at Advance Auto Parts.

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_trans-x&174;-posi-trac&174;-limited-slip-gear-oil-additive-k-&-w-chemical_7070977-p

[John H.]

Re: Posi Traction "clunking" on my 1967

Ed,

When you say a bottle or two...could this mean the rear end is dry? It made the noise while turning.

Thanks

Jerry

Jerry -

The GM Posi Additive bottle is only 4 ounces. If one bottle does the job after turning some low-speed figure 8's, you're in business; it might take two. If two doesn't do it, it's time to have the Posi unit rebuilt.

[Jim T.]

Re: Posi Traction "clunking" on my 1967

My 1968 gave me indications 15 years ago similar to what you experienced. I removed the lubricant from the rear end and installed GM's rear end lubricant and GM's posi-additive. Did the circle 8's and the problem went away, yesterday it still functions great with 96K miles on the odometer.

[Kenneth B.]

Re: Posi Traction "clunking" on my 1967

Jerry -

The GM Posi Additive bottle is only 4 ounces. If one bottle does the job after turning some low-speed figure 8's, you're in business; it might take two. If two doesn't do it, it's time to have the Posi unit rebuilt.

JOHN is right It works like magic. We called it GM whale oil. Remember to do the figure 8"S. I try to remember to do it when I got my cars out in the spring to wet the clutches.

[Duke W.]

Re: Posi Traction "clunking" on my 1967

Rather than adding the expensive additive to the existing axle oil, which is likely of indeterminate age, I suggest you completely replace the fluid and add one bottle of additive to begin with.

There is no drain plug on the axle, so the oil will have to be suctioned or siphoned out. You don't need to buy the oil from GM. The spec is SAE 80W-90 GL-5 gear oil, which is readily available at auto parts store.

Most buy the Positraction additive from GM, but I know Ford and Mercedes offer the same produce. I suspect it's also available at NAPA, but I don't have a number.

Short fill the axle at first to leave room for a second bottle of additive is it's needed. If not, top off the axle as specified in the service manual.

Duke

[Tony L.]

Re: Posi Traction "clunking" on my 1967

Agree, had the same problem with my C3. Put in the GM additive and drove figure 8's. However, just recently the rear end was actually banging very hard when letting off on gas or hard take offs. Seems the linkage hoding the rear had bushing disintegrate and had metal on metal. New bushing solved it.

[Gary R.]

Re: Posi Traction "clunking" on my 1967

Sounds like the typical posi hammering which is usually from the sticking clutches. I would do as the others mention, suck out all the old gear oil and install 1 bottle of the GM additive, the new stuff works fine. I use Lucas 85-140 gear oil but you can use 90wt if you like. Do the figure 8's and see how it goes. The way the posi is setup will go a long way in how much the posi hammers. Production built posi's are all over the place some with tight lash-001-002 others with loose lash. The 4 springs and 2 plates will keep constant pressure on the clutches and if too tight will hammer or chatter in corners, especially when hot. Think about a 4x4 rock climber, it is setup with tight posi and will climb up a wall but take a corner on the street and you will chatter your teeth out of your head.

The concern with the 65-68 Eaton posi's are they are very prone to cracking. So if you can't resolve it and you drop the diff be sure to check the posi case. I am not saying that is your problem, most likely it is not. If the car was pushed hard during it's life then when the spider lash open, due to cracks, it will make clicking noise but then it won't last much longer. Again this is just FYI, I hope you resolve it with the oil change.

[Gerald C.]

Re: Posi Traction "clunking" on my 1967

Thanks everyone! I'll drain the rear end and put the additive in and try to get the car out before the snow flies!