Alllllrighty, folks. I have got a doozy for you all. Perhaps somebody might be able to shed some brilliance on my headache of a problem. Before I get started, I have done quite a bit of research and nothing matches my description. Well actually, many people describe similar noises but it was always fixed for them with a new throw out bearing or pilot bearing or what-have-you. But you see, that has all been done with no success. Vehicle in question: 1977 pickup, 20R, W50 transmission. First I will just briefly describe the work done: -Full trans rebuild (new synchro and bearing kit) -All new bearings from clutch back -Overhauled third member (new bearings, races, etc.) - also the ring and pinion are OK Now, on to the dilemma: I get this loud metallic grinding sound mainly in 3rd and 4th gear. The sound silences immediately with the clutch pedal pressed in. I can, however, play with the sound a bit with the throttle. It is not exclusive to the deceleration or acceleration. It happens in both (more audible while coasting in 4th from 40mph and down). The sound can only be described as metallic or two metal surfaces that don't like to rub next to each other. (Best way to describe the sound is to start by pronouncing the K sound but get some phlegm in there and ckkkkkkkkkkkkk away). It isn't a click or a thump, but a steady grind. The sound also does NOT change pitch with RPM. It only increases or decreases in volume depending on the load (I'm assuming it is load activated). I should add, the sound is faint when hard accelerating above 3000rpm in first and second as well, but it is very faint. I have been working with a very reputable shop and they have been super helpful, but I'm sure I'm annoying them with this. My questions is this: What the firkin' crap is going on? Could this be clutch related? The clutch was examined by the mechanics and they said it all looked great (clutch, plate, and flywheel).
Thanks. Yeah, I have already replaced all the bearings from the clutch back. I don't think it would be U-joints because the sound is oriented near the front of the trans. I hear it loudest in the cab toward the firewall on the floor. Right around where the main components for the trans would be.
Did you switch to synthetic oil when you put it back together? I just pulled my W58 to install a new clutch and short shifter and figured I'd do a stroke of business and go to redline mt90 rather than whatever conventional gl4 was in it. Now it sounds like the trans is going to fall apart when under light throttle, "floating throttle" neither on nor off the pedal fully and light deceleration. It has some major gear whine too in all but 5th. 4th being the loudest by far. The only thing that changed with the trans is the output seal. The pilot and throw out bearings are the same. I clearanced the shifter and base while it was on the bench so all of that is clear. I did some searching and apparently it's pretty common with the lighter synthetics. I'll be switching to 90/140 synthetic soon to see if the issue clears up.
If only the sound level but not the pitch varies with the throttle, perhaps something external is loose? And since it goes away instantly when the clutch pedal is depressed my guess would be something in the actuation path. The only parts that can get loose are the little pushrod between the slave cylinder and clutch release arm, the arm itself where it touches the throwout bearing holder (due to a loose pushrod), or maybe the little pivot for the release arm?
Does the noise in your trans change in pitch with the rpm? You mention gear whine, but on the other gears (4th being the loudest) does it change much other than volume? We tried a heavier weight like the 140 you thought about using and the sound was still there. I think there is a standard gl4 in it now.
That's what I have been wondering. The mechanics say that clutch components were all good. Is it possible to have a clutch or pressure plate rub but only at a certain rpm? It just seems like a very noticeable rotational metallic sound. I spent a few hours with the mechanics this morning and with three different road tests with three different mechs we all agree it isn't differential and pretty sure it isn't transmission internal based on the way we can produce the sounds. I'm about to ask something potentially idiotic, but is there a possibility it is starter motor related? since it is right in the area where the sound seems to be coming from.
Does it start up good? Only way I think I see the starter rubbing is that the starter shaft is stuck in the extended position hitting the flywheel, which would change the sound with the rpm changes. Seems unlikely but it's just two bolts so pull it out and check for wear on the starter and flywheel teeth.
what i took from ur first explanation - sound goes away when clutch is pressed. is it possible one or more of the clutch pressure plate teeth are loose and rattling on the TO bearing? it sounds like its a "rotational" noise that goes away when the clutch is pressed. if it was starter gear, i would suspect the noise would happen all the time, regardless if clutch was pressed or not. if it was internal bearings, u would hear the typical "whine" or bearing rumble. do not overlook the little tail shield thingy ( where the driveshaft yolk goes in to ) sometimes if that little shield is bent and rubbing on the driveshaft, it may make noise --just another idea. maybe one of the clutch springs ( on the friction plate ) is loose or starting to come apart? or just pull the trans back out and check EVERYTHING. turn by hand. look for any kind of wear/rubbing marks. oorrrrr, set the rear end on jacks and drive the vehicle, have someone underneath and listen for the noise.
No change in pitch but it does change from sounding like an old straight cut gear whine to a growl when transferring from on/off throttle to floating and back to on/off. Something to look into on your rig is if the slave is adjusted right. On that generation the pushrod between the slave and clutch release fork is adjustable and there should be a spring to hold the fork in tension to the slave. If the pushrod is too long the throw out bearing could be rubbing the diaphragm on the pressure plate. Also did you use a flat faced throw out or the later style bearing with the thin raised portion? For the most part all of the clutch related pieces are interchangeable from 75ish to 95 and there are certain combinations that cause issues. That stupid shield around the tail shaft caused me some issues a while back. I had a scraping sound if my wife was with me or I had parts in the bed that was constant but changed frequency when I'd hit bumps. If i hit a big bump the noise changed and sounded way worse as if my driveline was rubbing the frame. I tracked it the constant noise down the the yoke barely touching the shield with one ear. I cut the shield in half and that noise went away. When I pulled the trans to do the clutch etc I noticed the dust shield on the driveline was mushroomed and beat up. I looked inside the shield on the trans and noticed it was about cut all the way through. Turns out I need to build blocks that move the axle back about half an inch or so.
I wonder if it could be a clutch spring type noise.. I'm guessing new clutch? Also when you rebuilt the trany I'm guessing the 'crush' sleeve/washer was replaced for new? that could cause improper tension/preload in the trans assembly which could cause free play, improper gear wear and misalignment.
Everyone has come up with some pretty brilliant ideas. Thank you all for chiming in thus far. I really appreciate it. When the rebuild was done, I was told that all new components (minus the gears, forks, other non "kit" items themselves that is) were replaced. The clutch pedal is adjusted about 1/2" of play before engaging the arm. I believe the Haynes manual explains that this is normal. Now clutch pedal could be one adjustment and the actual pushrod on the clutch slave could be another adjustment entirely. I might try tomorrow to readjust everything. I would think the shop would have adjusted it properly when the trans rebuild was done. The shop keeps telling me the clutch was fine. And if they had any doubt after inspecting all components they would have had it replaced since they were down there. Mind you, this trans has been out twice and inspected twice. When my first set of synchros was put in, second gear was fussy as all hell and clicked like a motha. So they went back in and put the best original synchro I had on and inspected everything again. For all of you interested to know, they no longer make OEM synchros for the w50 and the aftermarket alloy or brass or whatever is just not as good as the original stuff. The sound I'm getting is definitely not gear noise (or so we all think). I have the usually trans gear sounds (frankly that won't go away since there is very little blocking the trans and me in the cab). I really feel like it has to be in the vicinity of the clutch and pressure plate. It's just gotta be!
quick update: I adjusted the clutch slave pushrod. It is now in spec. Before the adjustment it was pressed firmly against the clutch release arm which I thought might be putting too much tension on the release bearing. Well, the sound is STILL there and not changed at all. I might have to replace the clutch and pressure plate just to make sure it isn't that. Otherwise, I am at a total loss. For a sound to be so specific and so particular on what load/speed/rpm it likes to be audible at is quite mysterious especially when all bearings have been replaced.
Rather than toss money at it why not go burn some dead dinosaurs and turn up the stereo a bit? Odds are the noise will either go away or something will fail and you'll have your answer.
Check your exhaust system. Mainly, your down pipe, where it is supported off the bell housing/trans. Could possibly be your cat falling apart inside too(if you have one). I had a noise that sounded like gears grinding inside of the transmission at a high rate of speed, mainly while cruising and at certain rpms during acceleration....Then it went away when my cat started to rattle horribly loud, lol....Something finally broke off inside
I have had the exhaust system completely redone about a year ago with no change in the sound. And I wish in this instance it could be a falling apart cat, but my truck is non-catalyst. I might just have to deal with this noise. If it isn't harming anything but my soul then..... oh well.
Could it be possible that the exhaust is vibrating against your bellhousing? Or did you have the exhaust done after the noise?
Nah. I first noticed the noise many years ago and the whole exhaust was done within the last year so it hasn't effected the sound. I'm 99% sure it isn't exhaust related. I was driving around today and tested pushing the clutch pedal in different ways to alter the sound. When I get the sound going really well in 4th gear with light throttle at about 40mph I could slowly press in the clutch pedal and about half way down it would hush the sound. Slowly let off the clutch to re-engage the gear and match the speed and rpm and the sound reappears. Then I quickly press in the pedal and it instantly hushes the sound. I did different methods and it is very much a load/clutch oriented sound. It is the same exact sound in 3rd at a certain rpm as well and slightly quieter in second but also the same exact sound and pitch.