How exactly do you check your U-joints on a RWD vehicle? I watched Scotty's video on inspecting them and had a little bit of a hard time telling what movement is normal and what isn't.
I went under my truck today to see if the downshifting thud I feel from 2-1 could be from worn U-joints, and I had a hard time telling if they're worn. I crawled under, grabbed the driveshaft and tried to twist it. I could twist it back and forth a bit. The parking brake was on and I couldn't tell if the parking pawl was in its slot or not, as I always put my brake on before going to Park. In my mind, the driveshaft shouldn't rotate at all if the parking brake is on, regardless of the pawl position. I released the brake and gradually let it roll back onto the pawl and tried to twist it again, and it would not twist. Every once in a while taking off, I feel a little bit of a shimmy under the seat that goes away after getting up past 5 mph or so. .
You should not feel any play in the U-joints. Look closely at the joints as you move the driveshaft and see if the there is actually any play in them. (With rotating the driveshaft you could be feeling a bit of gear backlash.) You could also use a screwdriver or pry bar between the cross shaft and yoke, there should be no play. If they need replacement, joints with grease fittings are preferable if available.
I'll take another look when I get home. My thought was that weird, very subtle shimmy might be related to the thud and not actually be the rebuilt transmission doing it. The only problem is I've never noticed the thud when the tranny isn't warmed up. I would also think you'd feel that every time it shifts.
Just be thankful you have an open driveline where it's easy to check and replace those joints as needed! I had to deal with a worn U-joint in my Marlin years ago and what a PITA that was! (The "big" Ramblers through 1966 had torque-tube drive with a single joint behind the trans. To get to it the rear axle has to be removed.)
That sounds like a nightmare and overly complicated! I always thought the open driveline was the most simple and common sense solution to getting power to the rear wheels from the front. Haha. I checked the joints again. They don't seem to have any play when I press them up and down or sideways.
It is a royal PITA, have to pull the rear axle out to get at the U-joint or if you have manual trans to get at the clutch. Also car cannot be moved when trans is out because there's nothing to hold the rear axle in place. The only advantage I can see is that, being enclosed, the U-joint is shielded from the elements.
Try prying those joints with a big screwdriver to be sure. If only slightly worn pressing on them by hand might not show the problem.
Corvettes have torque tubes don't they? I guess the amount of torque they make would result in too much torque steer or axle wrap.
Not sure, but there have been variations on the torque-tube idea over the years. The Model T used torque tube drive with a transverse leaf spring. Nash adopted the setup for its coil-spring rear suspension in 1949 and continued to use it on the larger AMC vehicles through 1966. You can see it in this cutaway diagram of the 1965 Marlin:
wow that's quite the engine for a coupe
That's what mine has, 327 V8 (Nash, not Chevy) rated at 270 gross horsepower. Those engines are known more for smoothness than power though, very heavily built with forged internals but has small valves that restrict breathing. Also note that unusual for its time the 1965 Marlin came standard with power front disc brakes (4-piston Bendix fixed calipers).
how does the "twin grip" differential work?
It's just a fancy name for a limited slip differential. As far as transmissions ahead of the torque tube, the hot setup was "twin-stick" manual transmission. This was a conventional 3-speed trans plus an overdrive shifter that works in 2nd and 3rd, yielding 5 usable cogs if you wanted to work at it. Typically though the overdrive would just be used as a 4th gear. (My Marlin has automatic trans though, can't have everything.) One last note about the U-joint to keep this at least related to the topic at hand, V8 models used a constant-velocity joint inside the torque tube to minimize vibration and noise. Basically a double U-joint with a spring-loaded centering mechanism, just try to get replacement parts today!
https://www.streetmusclemag.com/news/twin-stick-transmission-coolest-tranny-ever/
I'll check for that kind of motion, thanks!
I don't try to rotate the shaft, I push straight up and pull straight down to check for any significant play. I only use grease fitting u joints and maintain them regularly, since I have a 4x4 with two drive shafts.
My Ranger's also a 4×4, I thought about just replacing the U-Joints anyways, they look like they're the originals and have over 270,000 miles on them. Mine don't have zerk fittings that I've noticed.
replacing them is an easy job. used to do it all the time on army jeeps. remove the circlips and use a c clamp and socket to pop them put. fill the new ones with grease before you install them and give them a squirt of grease every 1000 miles or so.
I can almost guarantee that with that mileage, your original u joints are toast.