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| Drivetrain random clunk https://slantsix.org/forum/viewtopic.php?t=67296 |
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| Author: | wjajr [ Wed Jun 14, 2023 11:12 am ] |
| Post subject: | Drivetrain random clunk |
67 Dart, 904, Suregrip 8 3/4 489 case with Auburn limited-slip 3.55:1 ratio. New U joints installed around 5000 miles ago. Rear end not noisy when underway. When I got the car in 2008, I had a machinist go through the pumpkin, and shim some slop out of it, as at that time I had a reverse shift manual valve body, and it would clunk into every gear almost every time. He told me the cone was getting worn, and where it was a slant six and not a torque monster 440, it probably would be good to go for a while. Fast forward from 2008 and 30,000 miles ago, today's loud clunk is not a constant event. Sometimes it will clunk on 1-2 or 2-3 light throttle up shifts, other times it may do it changing from D to R , and other times it will clunk just letting off the throttle while under way. At times it almost sounds like it may be coming from the transmission which was rebuilt 5000 miles ago, and other times from the back of the car. The clunk has a hollow tone to it. When I installed disk brakes front and back 5000 miles ago, and switched to large bolt pattern wheels, I purchased new rear axles and green bearings. All that equipment is working just fine, I discovered one day not long ago while horsing around power breaking, the Auburn unit is not doing its job, and only one wheel was spinning. The clunking started long before the burn-out. I have read that these Auburn units can be clunky at times. So is the worn Auburn S-L most likely the source of the clunk? I see they don't give those thing$ away. I haven't been under the car to check tightness of transmission mounts, which probably I'll do in a day or so. Transmission mount is new with less than 5000 miles on it. |
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| Author: | Dart270 [ Wed Jun 14, 2023 11:31 am ] |
| Post subject: | Re: Drivetrain random clunk |
Hmmm. Usually I think of clunking as being slop in the ring and pinion on old or badly shimmed/backlashed gearsets. However, I did blow one of the side gears (ALL teeth gone) on my old 3.55 clutch SG about 2 yrs ago. It started with loud clunking on cornering and sometimes the car would lurch, which must have been chipped/missing tooth or teeth that were jumping and/or binding with the spider gears. I drove it for maybe 100 miles before it shaved the gear smooth and I had zero drive power. Driving it up and down one of my favorite roads (>50 turns and 2000 ft elev gain in 6.5 miles) "hillclimb style" finished it off. Not sure if this helps, but it is a recent piece of learning I received... I ordered all the internal "hard parts" and clutch plates from Doctordiff and am just about to get it back together. Note that you can buy a brand new clutch SG with bearings and ring gear bolts from Doctordiff for about $500 shipped. I bought one of those too that I am putting into another 3.23 chunk. Personally, I would not mess with rebuilding/shimming a cone SG, but some people do... Lou |
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| Author: | wjajr [ Fri Jun 16, 2023 9:48 am ] |
| Post subject: | Re: Drivetrain random clunk |
Today I got a chance to trouble shoot the clunk. With the car jacked up with both rear wheels off the ground, transmission in neutral, and turning one wheel back and forth an inch or so beyond the range of run-out of the rear end, and the clunk is coming from the transmission tail shaft. Both U joints are like new. When rotating the 24" dia. rear tire gently feeling for run out it, feels to be about an 1/8" of slack. In the 1/8th inch of travel I could feel the gears meshing with a bit of roughness, perhaps roughness is not the correct description, but it did not feel like the movement was dead air. In other words there is about an 1/8th inch of slack between forward rotation and rearward rotation of the tire before the drive shaft begins to rotate. What could be sloppy in the transmission causing that metal on metal clunk. I did not check how much drive shaft run-out there was at the tail shaft, but is a lot more than the rear end has. Maybe 1/4 inch. not sure. I had the transmission rebuilt about 5000 miles ago, and they did not report any deficiencies of the hard parts. I do plan on rebuilding the third member this winter with parts from Dr Diff where the Auburn unit is on it's last legs. I have been viewing various YouTube 8 3/4" rebuild videos, some very informative and others total redneck BS. |
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| Author: | Dart270 [ Fri Jun 16, 2023 11:05 am ] |
| Post subject: | Re: Drivetrain random clunk |
Could be a worn trans output shaft bushing that goes around the slip yoke? Slip yoke could be worn too, I suppose. There are also bearings on the trans output shaft, but I've never heard of those going bad. Charlie might be a good source for trans issues... Lou |
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| Author: | wjajr [ Sat Jun 17, 2023 10:03 am ] |
| Post subject: | Re: Drivetrain random clunk |
The bushing at the driveshaft end of the transmission was sloppy before it was rebuilt. It must have been replaced as there is no slop in it now. The noise seems to be a bit deeper than where said bushing resides. |
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