Allowable backlash

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512Stroker

512Stroker

We are all here because we are not all there.
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Late sixties 8 3/4, 489 case, 3:23 gear
What is the backlash to be set to?
I really dislike that loud "clunk" when you put it in gear.
Thanks in advance
 
.006-.010 A lot of the time it's not the backlash you hear. It can be spider gear wear or axle splines tend to roll as they wear out or splines in the axle gears.
 
You might look for any motion of the pinion fore and aft on a 489 if it still has a crush sleeve if it's not the u-joints.
 
SGBARRACUDA said:
.006-.010 A lot of the time it's not the backlash you hear. It can be spider gear wear or axle splines tend to roll as they wear out or splines in the axle gears.
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THIS RIGHT HERE. It all adds up, especially going from reverse to forward. The splines on one side twist, all the spider gears "add up", the pinion moves, and then the splines on the other side finally move.
 
Backlash usually does not show up as a clunk. That's normally slop in the pinion "somehow" OR bad U-joints.
 
RustyRatRod said:
Backlash usually does not show up as a clunk. That's normally slop in the pinion "somehow" OR bad U-joints.
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Rusty and others
I installed a new driveshaft, tranny yoke and replaced both u joints last year, it made no difference in the "clunk" The old shaft was bent and the slip yoke was junk from 50 years of use.
At this point I am leaning toward the spider gears and shafts.
I will learn more and report back next week when we tear into it.
 
512Stroker said:
Rusty and others
I installed a new driveshaft, tranny yoke and replaced both u joints last year, it made no difference in the "clunk" The old shaft was bent and the slip yoke was junk from 50 years of use.
At this point I am leaning toward the spider gears and shafts.
I will learn more and report back next week when we tear into it.
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If the spider and side gears (and case) are worn badly enough, that could certainly cause it.
 
You know what else happens with power, is that the cross-pin saddles egg out. If you don't catch it early and the cross-pin retainer lets go, then the crosspin can take off and try to exit thru the rear cover. It doesn't usually make it but when it jams up in there, nothing turns anymore. Yahoo! You're in for a ride
 
AJ/FormS said:
You know what else happens with power, is that the cross-pin saddles egg out. If you don't catch it early and the cross-pin retainer lets go, then the crosspin can take off and try to exit thru the rear cover. It doesn't usually make it but when it jams up in there, nothing turns anymore. Yahoo! You're in for a ride
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Well AJ you and Rusty called it.
Tore it down today and found that the shafts had worn into the case halfs, its junk.
Amazingly the ring and pinion look OK.
Question: Has anyone tried one of Doctor Diff's Sure Grip units?
For $395 it may be a deal, I also wonder about his $185 ring and pinion set?
 
Put new pinion seal in and weld the pin to the carrier. Done.
When the pins in the caravan transmissions were sawing the cases in 1/2 the rebuilders were scrounging all the good cases they could find. Part of the update was to weld the pin to the carrier.
i know, more horsepower and it wont work. Bet it will if its welded right.
 
512Stroker said:
Tore it down today and found that the shafts had worn into the case halfs, its junk.
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I have had those repaired for me at the machine shop, I took 4 or 5 of them in one time. I didn't watched them do it, as it was several weeks before they were ready for pick-up. But it looks to me that they brazed it up with some hard yellow material, and then machined the saddles to fit the Good pins I supplied. I got a repaired one behind my 367HO that runs a manual and 295/50-15s. It's been in there for about forever? I think. That 3.55 has been following me around since the late 70s or early 80s. But I think I transferred in a repaired case in around 1999.The gears have survived at least 4 cars that I can think of. I transferred in the repaired case to see if it would survive, before I started selling the rest. Ima thinking I put about 100,000 on the repaired case now. I put another one in my 3.23s and another in my 4.30s both of which were long ago sold. I still got a couple kicking around. Hey that's 5 for sure already,lol.
So when you say junk; I think; only if it costs more to repair than what you would pay for new.
I don't recall what I paid, but it mustabin cheap, cuz that's the kind of guy I am,lol. If I had to guess; I don't think I would have authorized more than 40/50 bucks Canadian, apiece.
 
AJ/FormS said:
I have had those repaired for me at the machine shop, I took 4 or 5 of them in one time. I didn't watched them do it, as it was several weeks before they were ready for pick-up. But it looks to me that they brazed it up with some hard yellow material, and then machined the saddles to fit the Good pins I supplied. I got a repaired one behind my 367HO that runs a manual and 295/50-15s. It's been in there for about forever? I think. That 3.55 has been following me around since the late 70s or early 80s. But I think I transferred in a repaired case in around 1999.The gears have survived at least 4 cars that I can think of. I transferred in the repaired case to see if it would survive, before I started selling the rest. Ima thinking I put about 100,000 on the repaired case now. I put another one in my 3.23s and another in my 4.30s both of which were long ago sold. I still got a couple kicking around. Hey that's 5 for sure already,lol.
So when you say junk; I think; only if it costs more to repair than what you would pay for new.
I don't recall what I paid, but it mustabin cheap, cuz that's the kind of guy I am,lol. If I had to guess; I don't think I would have authorized more than 40/50 bucks Canadian, apiece.
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I will research it but I do not believe that there are any machine shops here in the Ozarks that I would trust to do the repair.
Keep post'n we'll keep reading.
 
I would think that if one of them has a lathe,an operator, and the right sized drill and reamer,you'd be over 3/4s of the way home-free; but like I said, I didn't watch,so what do I know,lol.
It don't have to be pretty .It can be prettied up after it gets home, if a guy felt the need. I didn't. As long as the new material clears the pinion,and doesn't interfere with the pinion washers, yur good to go.
For me the modest cost to repair the 5 of them was less than the cost of just one new SG; maybe closer to half the cost..

But, I guess.......... if the saddles were that bad, it might be prudent to also check the splines on the axles,the side-gears, and the cone-clutches.
 
Check this out.

Rear diff 2.jpg


Rear diff1.jpg
 
AJ/FormS said:
Wow! That's about the worst I have ever seen; I can't believe the crosspin stayed in there.
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I believe that I dodged a bullet.
One more holeshot would have put me on the wrecker.
Strange that it was not making more noise other than the "clunk" when I put it in gear.
 
spider gears welded themselves to the cross pin due to lack of lubrication and unless the case blows itself in half the cross pin will stay in place and eat up the case-- have a scrap bin with several sure grips in that same condition
 
john-9 said:
spider gears welded themselves to the cross pin due to lack of lubrication and unless the case blows itself in half the cross pin will stay in place and eat up the case-- have a scrap bin with several sure grips in that same condition
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Rear end was full of grease since I have owned the car - 3 Years
Cant speak for the prior history and other owners, only god knows what they did.
 
Anecdote;
You know what grease is?
It's oil and soap homogenized together. Ergo; soap and oil/oil and soap;lol.
If you let a dyno wheel-bearing grease sit in a warm enough place, for a long enough time, the oil will separate out and float to the top.
IDK about synthetics.
Well that's how it used to be when I was younger. I can't say if that is still true today. But some of the greases in my shop are older than am I ..........
 
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