8.75 question

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plymouth67

plymouth67

It be a lot cooler if you did...
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So the 742 case in my Challenger has been a mystery for some time now. Originally it had 3.55 gears in it, they were pretty loud going highway speeds on the both drive and coast sides. I pulled it apart adjusted shims and, that made a difference on the coast side but not really on the drive side. I changed the ring and pinion and had a HELLof a time getting a good contact pattern and it just went together kind of funny. Fast forward to about 25 miles later and....got really loud so I climbed under it and could move the yoke all around. I pulled it out took it apart, threw the original 3.55 ring and pinion in the case because I believe the pinion on the other set of gears is machined incorrectly since there is .12" difference between them from the bottom of the large inner bearing to the surface the shim or the smaller outer bearing would ride. That was about the same .12" I could move the yoke in and out....not sure why it was ok 25 miles ago but, oh well. So...anyway....no matter what I did with the 3.55 I could not get the drive side pattern off the toe of the gear. Shims out...backlash back and forth...coast side is perfect...drive side...not so much, so of course when you drive it...its loud on the throttle and quiet on when coasting. The first size shims i tried was .040" and it's only has .010" in it now. This seems like a pretty big change to me and it did make a difference on the coast side... So my question is after I have wasted a half an hour of your time reading my ramblings is....Has anyone else ran into something like this? Could there be something in the case that is not right?
 
If you can grab the yoke and move it a bunch like you stated you have other issues.
That appears to be more a bearing problem or perhaps an assembly issue IMO.
 
512Stroker said:
If you can grab the yoke and move it a bunch like you stated you have other issues.
That appears to be more a bearing problem or perhaps an assembly issue IMO.
Click to expand...
I believe the pinion gear was machined incorrectly.
 
Are you sure the pinion gear was for a 742 case?
 
plymouth67 said:
Same bearings that are in it now with the 3.55's
Click to expand...

Get a pic of the pattern next time you are in there and post it.
And I'd bet either the large end bearing or it's cup/outer race wasn't quite all the way seated.
(I'd guess by about .12)
 
Are you using a Belleville washer underneath the pinion nut or are you using a lock nut and lock washer?
 
So this is what I'm trying to say...the distance from the bottom of the large bearing to the bottom ledge of the shaft is .12" different on this brand new pinion than what was in the car.

20200405_110013.jpg
 
Still might be the bearing. Check dimensions from the ledge to the back of the gear on both pinions. Who made the gears? What brand of bearings?
 
I did check the bearings and they are the same size. They are both Timken bearings.
 
In my experience
once a pattern gets crossed up, I throw it away.
I used to work in a rebuild center, almost 6 years. For two of those I built rear ends. Our company bought up cores all over Canada. They came in and we had a guy who took them apart and sent them thru latge parts washers that cooked them clean. Them me and two other guys had the jobs of rebuilding them; which was just new bearings and fresh set-ups.
We only used ,used gears, cuz we had truckloads of then coming in all the time. And we never saw the cores when they arrived so we had no way of side-lining suspect gears.
Every once in a while I would get a gear-set that would just not pattern properly, so I would call the foreman over. And he would make the call.
Sometimes I would bias the pattern to the drive side, and leave the coast side be what it would be; it depended on the application; I was doing everything from pass-cars to semi-tractors and grain-trucks in between.And we had an army contract as well.
But most of the time a crossed up set went into the scrap heap.
I was under a lot of pressure to put out product, as we were doubling in size about every two years. During the time I was there we were in the fourth expansion.
So,there was no time to fool with patterns, just slam them out AJ, keep it moving.
Like I said we had truckloads of cores.
I got to reading patterns before bolting them in, as to how they had already run in the field, and when I recognized a bad pattern. I would call the foreman over for verification. After a while, I was very well paid, because not only did I perform, I avoided come-backs, which the business owner recognized as money in his pocket. I was not alone in this, my co-workers were doing the same thing, and we were a well-oiled machine.
Bottom line is, I had zero luck bringing crossed patterns to market.
I tried a few times in my personal vehicles.

My best advice is to pull the pinion bearing races out, and inspect the bores.
And second best is to not use thin shims under .005. You can use them to set the turning torque, but after you get that dialed in, pull the shimpack out and convert it to as few shims as possible, all thicker than .005.
After the pattern comes in, take the pinion nut off and loc-tite it, then retorque it. Then recheck the pattern. Test the pattern in at least three spots. If it changes between the points, or if the backlash changes, throw the gears away.

BTW;
some cars are more sensitive to noisy gears than others.
I once had 3.55s in my 68 Barracuda, that a friend wanted. I knew they had a hint of noise in them, so the friend and I went for a tour. He couldn't even hear it; so a deal was struck, with a proviso, that he could sell them back to me if they proved to be too noisy, but that, the RnR was on him.
The price was agreeable to him, so I swapped the chunks over, putting 4.30s in mine,lol.
I don't think a week passed and I got the call.
So I went for a ride with him, and sure enough, they were noisy and not just a little either. So I pulled them out and put the 3.23 chunk back in. He was a a happy guy.
As for the 3.55 chunk, by winter that year, the 4.30s had worn out their welcome, and the 3.55s went back in. And they have been in there almost ever since.
His car was an E-body.
 
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AJ/FormS said:
In my experience
once a pattern gets crossed up, I throw it away.
I used to work in a rebuild center, almost 6 years. For two of those I built rear ends. Our company bought up cores all over Canada. They came in and we had a guy who took them apart and sent them thru latge parts washers that cooked them clean. Them me and two other guys had the jobs of rebuilding them; which was just new bearings and fresh set-ups.
We only used ,used gears, cuz we had truckloads of then coming in all the time. And we never saw the cores when they arrived so we had no way of side-lining suspect gears.
Every once in a while I would get a gear-set that would just not pattern properly, so I would call the foreman over. And he would make the call.
Sometimes I would bias the pattern to the drive side, and leave the coast side be what it would be; it depended on the application; I was doing everything from pass-cars to semi-tractors and grain-trucks in between.And we had an army contract as well.
But most of the time a crossed up set went into the scrap heap.
I was under a lot of pressure to put out product, as we were doubling in size about every two years. During the time I was there we were in the fourth expansion.
So,there was no time to fool with patterns, just slam them out AJ, keep it moving.
Like I said we had truckloads of cores.
I got to reading patterns before bolting them in, as to how they had already run in the field, and when I recognized a bad pattern. I would call the foreman over for verification. After a while, I was very well paid, because not only did I perform, I avoided come-backs, which the business owner recognized as money in his pocket. I was not alone in this, my co-workers were doing the same thing, and we were a well-oiled machine.
Bottom line is, I had zero luck bringing crossed patterns to market.
I tried a few times in my personal vehicles.

My best advice is to pull the pinion bearing races out, and inspect the bores
Click to expand...
I rarely use used gears and such...the one think is machined wrong is brand new along with bearings and races..but it wont tighten up in the case..so I threw the old gears back in which only have about 2500 miles on them and couldn't get the pattern correct no matter what I did...always in the toe side of the drive side...coast side is perfect...that's why I think maybe it's the case?? The old gears tighten up and it works...just noisey on the throttle cause the drive side pattern issue...
 
I've never seen a bad case.
And the fact that one side pattern comes in, points straight to bad gears.
The idea that the pinion bearing preload is changing, points to the bearings moving, the shims hammering out, or the pinion nut coming loose. In your design, if the pinion nut keeps it's torque, then it kindof points to debris under the races, or a broken,cracked bearing support works. Which thing I have also never seen.
 
gear cutting is all automated so the theory the gear was cut wrong is probably a very long shot. Also the gear and pinion will have a matching stamp or mark on it as well as a shim pack measurement. Its usually engraved with a pen and may look like its hand written. I had 2 sets US gear and some other make and they both had matching marks on hem as well as a .*** number. when the races are pressed in, the case must be absolutely clean in the race bosses. It would show as a drag on the pinion as its turned with no load. Can't argue with AJ on this, he probably has more experience in this than anyone besides his co-workers.
 
pishta said:
, he probably has more experience in this than anyone besides his co-workers.
Click to expand...
Yeah, I was the low man on the totem pole. Altho I started there in their first year of operation. And I was the youngest as well, being about 25 at the time.
I stated in stripping, then graduated to standard transmissions, then differentials, and when they found out I could read schematics, they put me on heavy equipment powershift transmissions, A thing which until that time, they had not touched. Yeah I was rolling in the cash after that.....
 
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