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GMC - clunking noise shifting 2nd to 3rd
- Thread starter bczoom
- Start date
My 93 1500 Silverado has the clunk. It didn't' have it until the last 30k miles. I just turned over 190k on it. Never have changed tranny fluid in it. The tranny guy advised not to. So, I reluctantly went along with the pro's suggestion.
I hope it will get up to 270k+ like CB's.
I hope it will get up to 270k+ like CB's.
Cityboy
Banned
Hey doc - I do change my tranny fluid & filter every 25K miles. When it was new the first year, I did the first three changes every 10K, and didn't see much metal accumulation around the pan magnet after the third change and went to 25K service after that. It just seems to me if there is a filter installed, it occaisionally needs to be changed. Worked for me so far.
BC: Check the u-joints (even the front drive shaft if 4WD), and maybe check the ring and pinion in the rear for potential slop. These will cause clunking.
U-joints could need replacing and if the rear is sloppy you could either turn up the radio or have it repaired depending on the severity.
U-joints could need replacing and if the rear is sloppy you could either turn up the radio or have it repaired depending on the severity.
Well, I'm trying to see if there's consensus with the dealers reply of it being normal.
I got the truck with 130k on it. I didn't have the tranny checked until 160k, and by then the mechanic advised not to. It's wored so far (knock on wood). With the towing I do with it I hate to hear the "CLUNK".
thcri
Gone But Not Forgotten
One of our fleet trucks chevy half ton is that way. It started about 60K and continually has gotten worse. We took it in and was told it was normal. Problem now it has gotten so bad that when it shifts it about knocks your head into the back window. It goes in early next week to have it checked out. But I am afraid we will told to replace the tranny.
murph
murph
Snowcat Operations
Active member
Its a GMC. Whats the problem? They all do that. BUT check your u joints. but most likely your tranny is getting ready to grenade!
Dargo
Like a bad penny...
Doc, on hundreds of thousands of transmission failures the number one COF (cause of failure) can be attributed to fluid breakdown leading to hundreds of other symptoms. I work with some of the top techs in the business as well as the top techs from the manufacturers on Lemon Law cases and, except in cases of abuse, a surprisingly large percentage of transmission failures can be prevented by changing the fluid and filter a minimum of every 50k miles. If your fluid is that old, it likely is not providing much lubrication at all; only hydraulic functions.
15K miles on truck. It started at around 10-12K. Fluids haven't been changed.
I'd say it does it every time. Probably more noticeable under harder acceleration. It happens during both load & no-load conditions.
Dargo
Like a bad penny...
Short of putting a gauge in line and giving me line pressures at shift points, my guess from what you are telling me is that your line pressures from your valve body are just a tad bit high. Your torque converter does not lock up until after you are in 4th; generally at 47.5 mph at a "no load" situation.
The clunk really isn't bad, but can be hard on U joints and annoying. Line pressures can be lowered to give a smoother shift, but that will greatly reduce the life expectancy of your transmission clutches because it will slip them more between shifts. Your fluid does not need to be changed.
Believe it or not, many people report good results by adding Lucas transmission addative to their transmissions that is formulated for exactly the symptoms you describe. If you have an AutoZone or similar store, look in the transmission addative section for Lucas bottles. Once you see the bottles, read what they say and you'll see one that says it corrects exactly what you describe; hard shifts. I'm normally not big on addatives, but GM, and Dodge both have their own addative for limited slip rear differentials that are basically the same thing that this Lucas stuff is. I've seen some GM and Dodge pickups chatter the rear wheels really bad going around corners and the dealerships just add a bottle of the factory addative and drive them for about 50 miles and the wicked chatter goes away. People have reported to me that the Lucas has done the same with hard clunking shifts in transmissions.
Good luck.
The clunk really isn't bad, but can be hard on U joints and annoying. Line pressures can be lowered to give a smoother shift, but that will greatly reduce the life expectancy of your transmission clutches because it will slip them more between shifts. Your fluid does not need to be changed.
Believe it or not, many people report good results by adding Lucas transmission addative to their transmissions that is formulated for exactly the symptoms you describe. If you have an AutoZone or similar store, look in the transmission addative section for Lucas bottles. Once you see the bottles, read what they say and you'll see one that says it corrects exactly what you describe; hard shifts. I'm normally not big on addatives, but GM, and Dodge both have their own addative for limited slip rear differentials that are basically the same thing that this Lucas stuff is. I've seen some GM and Dodge pickups chatter the rear wheels really bad going around corners and the dealerships just add a bottle of the factory addative and drive them for about 50 miles and the wicked chatter goes away. People have reported to me that the Lucas has done the same with hard clunking shifts in transmissions.
Good luck.
sleeper
Member
bczoom,
The pinion nuts on the differentials in these trucks are known to loosen up. They didn't all do it but many of them did. They weren't properly torqued at the factory and the crush collars weren't collapsed enough to retain the nut. When they do loosen up the first thing you will notice is the clunk......then pinion seal leakage.....then total failure of the differential if it's not corrected. I have seen some go without first leaking so you might want to check this out for piece of mind.
There are so many possibilities as to the cause of the "clunk" and without actually hearing it, it can be near impossible to diagnose. Some other things to consider.....driveshaft hanger bearing if it has one, U-joints as was previously mentioned. If everything checks out OK than it's probably in the transfer case and possibly nothing to worry about. I have seen these t-cases self destruct (not often) but almost all of them clunk after 15,000- 20,000 miles. I have a 1991 full size 4 x 4 Blazer with 212,000 miles on it that has had a T-case clunk since 15,000 miles. I'm on my second transmission and second differential. I was a victim of the loose pinion nut and my diff. exploded with no warning.
Dargo's idea of trying the additive is sound advice. I will be interested to see how you make out.
Good Luck!
The pinion nuts on the differentials in these trucks are known to loosen up. They didn't all do it but many of them did. They weren't properly torqued at the factory and the crush collars weren't collapsed enough to retain the nut. When they do loosen up the first thing you will notice is the clunk......then pinion seal leakage.....then total failure of the differential if it's not corrected. I have seen some go without first leaking so you might want to check this out for piece of mind.
There are so many possibilities as to the cause of the "clunk" and without actually hearing it, it can be near impossible to diagnose. Some other things to consider.....driveshaft hanger bearing if it has one, U-joints as was previously mentioned. If everything checks out OK than it's probably in the transfer case and possibly nothing to worry about. I have seen these t-cases self destruct (not often) but almost all of them clunk after 15,000- 20,000 miles. I have a 1991 full size 4 x 4 Blazer with 212,000 miles on it that has had a T-case clunk since 15,000 miles. I'm on my second transmission and second differential. I was a victim of the loose pinion nut and my diff. exploded with no warning.
Dargo's idea of trying the additive is sound advice. I will be interested to see how you make out.
Good Luck!
sleeper
Thanks for the info. I picked up the stuff Dargo mentioned and will be adding it later today (as it says to do it after warmed up). It says the results are almost immediate so my plan is to add it at my first errand stop tonight and see what happens by the time I get home.
Now I'm looking into the clunk in the front left axle area. It sounds like I probably have the dreaded intermediate steering shaft issue...
Thanks for the info. I picked up the stuff Dargo mentioned and will be adding it later today (as it says to do it after warmed up). It says the results are almost immediate so my plan is to add it at my first errand stop tonight and see what happens by the time I get home.
Now I'm looking into the clunk in the front left axle area. It sounds like I probably have the dreaded intermediate steering shaft issue...
Thanks for the info Brent. I missed your post when you originally posted it.
The tech advised me not to because of shavings that will be stirred up when changing fluid, since it was running okay, and I didn't know when it was last changed. Thinking back on it I guess it was a lazy mans advice ....and I took it.
I kind of like the truck though, and I'm towing more with it than I did in previous years. Figure I'll change it and see how it goes.
Thanks for brining this thread back up Sleeper.
I'm also interested to see how Brian (BC) made out.
Cityboy
Banned
Doc,
The key when servicing your tranny is to not allow any contaminants to get back into the pan, like RTV or other gasket sealer, etc., and to clean the pan thoroughly, making sure all the old gasket material is scraped off before reinstalling the pan. Just plain old good workmanship.
I think there are a lot of old wives tales out there about not servicing old trannys.
If the manufacturer equiped the tranny with a filter, they meant for the filter to be changed, and the fluid along with it.
The key when servicing your tranny is to not allow any contaminants to get back into the pan, like RTV or other gasket sealer, etc., and to clean the pan thoroughly, making sure all the old gasket material is scraped off before reinstalling the pan. Just plain old good workmanship.
I think there are a lot of old wives tales out there about not servicing old trannys.
If the manufacturer equiped the tranny with a filter, they meant for the filter to be changed, and the fluid along with it.As noted, I took the truck to the farthest point in my travels and went to add the Lucas stuff Dargo recommended.
Well, I wasn't aware that it comes out like molasses. I clipped the top and started squeezing some out of the bottle. Apparently, it couldn't take the little I pumped in and it started coming back out and dropping on the exhaust manifold.
The smoke that came out reminded me of previous encounters (don't ask for details) with stuff dripping on the exhaust manifold. Expecting the ensuing fire I dropped the bottle, got the kids out of the truck and took off my Carhartt as it was the only thing I had to try to suppress the potential fire.
Anyway, I only got a few ounces in (so far), but the clunk is still there. The truck doesn't get driven much so it'll be a bit before I have a warm tranny, the bottle of Lucas, a funnel and fire extinguisher all together at the same time.
