transmission question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DMAN · 07-31-2002, 01:00 PM

My th350 goes into gear with a hard " clunk " whenever I shift into gear from a standstill. What's the most common reason for this problem? I'd kinda like to have an idea before I take it to a shop. It shifts fine between 1st, 2nd and 3rd. Any ideas? thanks.

*67Fleetsidedream* · 07-31-2002, 01:13 PM

My first thought is the u-joints are about to go on you. Check them out for slack.
Ben

68 with 350 TPI · 07-31-2002, 10:02 PM

I agree that it is probably the U joints.

Always replace both at the same time.

Scott70Chevy · 07-31-2002, 10:09 PM

I agree on the u-joints, but might want to check the carrier bearing while your under there (if you have a 2-piece driveshaft).

dion · 07-31-2002, 10:37 PM

U Joints and carrier bearing.

DMAN · 08-02-2002, 01:02 PM

thanks to all.

**COBALT** · 08-02-2002, 05:33 PM

Not always. Check the end play of your output shaft on your transmission. Disconnect the driveline from the differential, and twist the slip-yoke to see if it rotates at all. It shouldn't; either with the truck running or off. The play may be in the transmission.

Mine clunks like that because of the detriot locker in my differential carrier. It was actually worse AFTER I got new U-joints. The reason was because the U-joints weren't loose any more, so all of the "play" was in the differential. Sometimes it clunks a bit pulling away from stops, or decelerating. It really does it after I've turned a corner, because the inside wheel hasn't engaged yet. I got so worried about it I took it back to the shop (reliable) that did the work on the axle and they just laughed. They said they get that kind of scared look that I had on my face all the time. They told me to get used to the sensation of my diff. making that noise.

**COBALT** · 08-02-2002, 05:38 PM

Oh, one more thing. The "carrier bearing", or center support bearing won't make much of a "clunk" unless it's either pulled loose from the frame, worn through all of the rubber in the housing, or simply broke in two. If that were the case you'd hear rubbing 24/7 that would make you think your truck is breaking apart.

General rule of thumb is to replace the support bearing whenever you have the driveline out of the truck. If it's the in-line "I" beam type (vs. the larger "U" shaped one) don't put those dust shields back in after replacing it. Trust me they're not worth it.

I'm gonna go with a 1-piece some day. Yee-haw.

Good luck.

07-31-2002, 01:00 PM	#1
DMAN Registered User Join Date: May 2002 Location: Benicia,Ca. Posts: 128	transmission question My th350 goes into gear with a hard " clunk " whenever I shift into gear from a standstill. What's the most common reason for this problem? I'd kinda like to have an idea before I take it to a shop. It shifts fine between 1st, 2nd and 3rd. Any ideas? thanks. __________________ '71 Custom Deluxe K10, shortbed, fleetside.

07-31-2002, 10:02 PM	#3
68 with 350 TPI Registered User Join Date: May 2002 Location: Wingate NC Posts: 456	I agree that it is probably the U joints. Always replace both at the same time. __________________ Life is good with a 6-71 supercharged 355 in a 72 camaro

07-31-2002, 10:09 PM	#4
Scott70Chevy Registered User Join Date: Jan 2001 Location: Waxahachie, TX, USA Posts: 114	I agree on the u-joints, but might want to check the carrier bearing while your under there (if you have a 2-piece driveshaft). __________________ Scott70Chevy '70 CST: LWB, Fleetside, black ext., black/gray int., 350-4bbl, 3-speed, 12 bolt 3.07, deep dish rallye wheels, NO RUST!

07-31-2002, 10:37 PM	#5
dion 72 Cheyenne Join Date: Oct 2001 Location: San Diego Posts: 2,086	Mine does the same thing U Joints and carrier bearing. __________________ Burnout Idle 1972Cheyenne 1966/67Stouts

08-02-2002, 01:02 PM	#6
DMAN Registered User Join Date: May 2002 Location: Benicia,Ca. Posts: 128	thanks to all. __________________ '71 Custom Deluxe K10, shortbed, fleetside.

07-31-2002, 01:13 PM	#2
67Fleetsidedream Wiseass secured himself a BAN Join Date: Nov 2000 Location: MOON!!! Posts: 2,282	My first thought is the u-joints are about to go on you. Check them out for slack. Ben

08-02-2002, 05:33 PM	#7
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Not always. Check the end play of your output shaft on your transmission. Disconnect the driveline from the differential, and twist the slip-yoke to see if it rotates at all. It shouldn't; either with the truck running or off. The play may be in the transmission. Mine clunks like that because of the detriot locker in my differential carrier. It was actually worse AFTER I got new U-joints. The reason was because the U-joints weren't loose any more, so all of the "play" was in the differential. Sometimes it clunks a bit pulling away from stops, or decelerating. It really does it after I've turned a corner, because the inside wheel hasn't engaged yet. I got so worried about it I took it back to the shop (reliable) that did the work on the axle and they just laughed. They said they get that kind of scared look that I had on my face all the time. They told me to get used to the sensation of my diff. making that noise. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

08-02-2002, 05:38 PM	#8
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Oh, one more thing. The "carrier bearing", or center support bearing won't make much of a "clunk" unless it's either pulled loose from the frame, worn through all of the rubber in the housing, or simply broke in two. If that were the case you'd hear rubbing 24/7 that would make you think your truck is breaking apart. General rule of thumb is to replace the support bearing whenever you have the driveline out of the truck. If it's the in-line "I" beam type (vs. the larger "U" shaped one) don't put those dust shields back in after replacing it. Trust me they're not worth it. I'm gonna go with a 1-piece some day. Yee-haw. Good luck. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.



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