1968 with T56 and Ford 9" Vibration - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Trsmotrhed · 02-23-2020, 05:26 PM

My 68 I picked up the other day has a vibration at 65 mph and above. I knew that on the test drive and discussed with owner.

The PO told me he installed a T56 and a Ford 9" all at once and ended up with the vibration.

He left the low tranny hump and angled the tranny down to clear it. Looking at pics online, this needs the high hump and some lovin to make the T56 fit.

I'm thinking he got the driveline angles all messed up. He has the back of tranny down 6 degrees. The 9" rear end is up 5 degrees. I'm thinking he has way to much down angle on tranny and tried to fix it angling the rear end up causing the vibration.

I broke my hip a couple weeks ago so I can't really crawl around under the truck very good right now. I'm thinking this is a great place to look when I can.

I've been reading driveline angles until my eyes hurt. Lol. I've done several engine, tranny and rear ends on trucks and never had any issues following the tranny down 2 to 3 degrees and match the rear to that.
Think I'm headed in the right direction? Thoughts?

Driving me crazy not being able to work on it. Thanks.

Heavymetl · 02-23-2020, 05:57 PM

What rear gear? The. 50 overdrive is awesome but with a deep rear gear (4.56 for example) the driveshaft speed it high. Usually need a good aluminum 3.5" driveshaft to run smooth.

If its too nose high in the rear, it will typically vibrate worse under load as the pinion angle increases slightly. Opposite if pinion is nose down. At least in my experience.

**HO455** · 02-24-2020, 04:17 PM

1 or 2 piece drive line? Long or short bed? How are you measuring the angles? Just trying to get on the same page.

LS short box · 02-24-2020, 05:42 PM

I have a T56 in 68 short box. High hump is a must. Also motor mounts that place the engine as low as possible to reduce engine angle. Also as said above a one piece 3.5" drive shaft will be very close to the trailing arm cross member pass thru hole. I had to trim the top of the hole for more clearance on my 4/6" drop. Also double check the drive shaft balance. My engine angle is about 3.75 degrees. I did not change the stock rear axle angle. I have zero vibrations.

02-23-2020, 05:26 PM	#1
Trsmotrhed Registered User Join Date: Mar 2012 Location: Pueblo West, Colorado Posts: 430	1968 with T56 and Ford 9" Vibration My 68 I picked up the other day has a vibration at 65 mph and above. I knew that on the test drive and discussed with owner. The PO told me he installed a T56 and a Ford 9" all at once and ended up with the vibration. He left the low tranny hump and angled the tranny down to clear it. Looking at pics online, this needs the high hump and some lovin to make the T56 fit. I'm thinking he got the driveline angles all messed up. He has the back of tranny down 6 degrees. The 9" rear end is up 5 degrees. I'm thinking he has way to much down angle on tranny and tried to fix it angling the rear end up causing the vibration. I broke my hip a couple weeks ago so I can't really crawl around under the truck very good right now. I'm thinking this is a great place to look when I can. I've been reading driveline angles until my eyes hurt. Lol. I've done several engine, tranny and rear ends on trucks and never had any issues following the tranny down 2 to 3 degrees and match the rear to that. Think I'm headed in the right direction? Thoughts? Driving me crazy not being able to work on it. Thanks. __________________ Sold the 63 and have a 68 now. 63 SWB C10 LT1/4L60E, PS, PB, Disk Brakes, CPP 4" drop coil rear, 2.5" drop spindle w/ 1" drop coil. slotted rotors, front and rear sway bars. 18"x8" Cragar SS w/ 245/45R18 http://67-72chevytrucks.com/vboard/s...d.php?t=544174

02-23-2020, 05:57 PM	#2
Heavymetl Registered User Join Date: Feb 2012 Location: Southern Ohio Posts: 292	Re: 1968 with T56 and Ford 9" Vibration What rear gear? The. 50 overdrive is awesome but with a deep rear gear (4.56 for example) the driveshaft speed it high. Usually need a good aluminum 3.5" driveshaft to run smooth. If its too nose high in the rear, it will typically vibrate worse under load as the pinion angle increases slightly. Opposite if pinion is nose down. At least in my experience. __________________ 1970 C10 Turbo LM7 5.3/LS6 cam PT7675/4L80E/Holley Dominator EFI/E85 Moser 9" 3.25/4 wheel discs 11.16@121.07

02-24-2020, 04:17 PM	#3
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,351	Re: 1968 with T56 and Ford 9" Vibration 1 or 2 piece drive line? Long or short bed? How are you measuring the angles? Just trying to get on the same page. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

02-24-2020, 05:42 PM	#4
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 2,132	Re: 1968 with T56 and Ford 9" Vibration I have a T56 in 68 short box. High hump is a must. Also motor mounts that place the engine as low as possible to reduce engine angle. Also as said above a one piece 3.5" drive shaft will be very close to the trailing arm cross member pass thru hole. I had to trim the top of the hole for more clearance on my 4/6" drop. Also double check the drive shaft balance. My engine angle is about 3.75 degrees. I did not change the stock rear axle angle. I have zero vibrations.



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