strange noise after rear drop - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SnS C10 · 06-01-2009, 09:52 PM

ok everyone so today i lowered the rear of my 73 lwb c10. it has a 454 with two piece drive shaft. i pull the 2 leaf springs form each side so now it has a total of 3 on each side. i took the two shortest ones out. now, the bump stops are only half inch from the frame rails. when i take off somewhat hard, just enough to open the secondaries, there is a horrible vibration feeling/noise coming from the rear end. my guess is the driveshaft angle is off what do you guys think? can i fix this by dropping the front a little more or do i need to add one leaf in back? thanks for looking

**Captkaos** · 06-01-2009, 09:58 PM

Generally on LWB's you have to shim the rear.
pulling leafs down to 3 will also enhance wheelhop.

Driveway Dreams · 06-01-2009, 10:46 PM

Shim the rear for a better pinion angle.

SnS C10 · 06-01-2009, 11:21 PM

i did a search, exactly what is involved in shimming the rear end? let me get this straight, if i drop the front which will slightly raise the rear end, this will not fix anything?

Driveway Dreams · 06-01-2009, 11:24 PM

No, you need to shim to correct the angle of the driveshaft to the rear end. It needs to almost be a straight line down the shaft, into the rear end. I think I explained this right. correct me if that isn't 100% right.

SnS C10 · 06-01-2009, 11:33 PM

how and where exactly do you shim to get the correct angle

Driveway Dreams · 06-01-2009, 11:39 PM

Spring perches to springs.

SnS C10 · 06-02-2009, 12:13 AM

so put some sort of shim between the leaf spring and the axle? wouldnt that raise the truck back up? sorry i havnt done this portion of suspension before

Jonboy · 06-02-2009, 10:05 AM

the shims are tapered, and pretty thin. It will not raise the truck noticibly, but will rotate the pinion to correct the angle.

Keith Seymore · 06-02-2009, 02:48 PM

In addition to the static pinion angle concern: Taking those extra leafs out may be allowing even more rear axle windup during acceleration than you had before, making the pinion angle worse than what you see statically.

You might check, too, to see if you are bottoming the drive shaft out in the end of the trans.

K

Driveway Dreams · 06-02-2009, 03:45 PM

Quote:

Originally Posted by Jonboy

the shims are tapered, and pretty thin. It will not raise the truck noticibly, but will rotate the pinion to correct the angle.

They are shaped like a very thin wedge. If it is your driveshaft bottoming out you will have a couple options to correct it. Either move the axle back a smidge, or get the shaft shortened.

Wild83C10 · 06-02-2009, 07:34 PM

When you accelerate hard the front of your rear rotates up and could be pushing your driveshaft forward or throwing your driveline angles way off. You want your angles to add up to 0 (-3 at the trans and 3 at the rear pinion) under normal driving conditions or if its a track truck under hard acceleration.
You may want to consider caltrac bars, especailly if you are going to keep only 3 leaves.

06-01-2009, 09:52 PM	#1
SnS C10 Registered User Join Date: Jul 2004 Location: Lomita, Ca Posts: 1,225	strange noise after rear drop ok everyone so today i lowered the rear of my 73 lwb c10. it has a 454 with two piece drive shaft. i pull the 2 leaf springs form each side so now it has a total of 3 on each side. i took the two shortest ones out. now, the bump stops are only half inch from the frame rails. when i take off somewhat hard, just enough to open the secondaries, there is a horrible vibration feeling/noise coming from the rear end. my guess is the driveshaft angle is off what do you guys think? can i fix this by dropping the front a little more or do i need to add one leaf in back? thanks for looking

06-01-2009, 09:58 PM	#2
Captkaos www.73-87chevytrucks.com Join Date: Dec 1999 Location: Birmingham, AL Posts: 6,935	Re: strange noise after rear drop Generally on LWB's you have to shim the rear. pulling leafs down to 3 will also enhance wheelhop. __________________ Chris Lucas 1973 Chevy C-10 1978 GMC Jimmy (2WD) - SOLD 1987 R10 twin turbo LS 1991 R3500 SRW CrewCab 1985 K5 diesel swapped project 1989 K5 2WD conversion w/ Vette susp Project Captkaos Customs 73-87chevytrucks.com

06-01-2009, 10:46 PM	#3
Driveway Dreams I have car A.D.D. Join Date: Feb 2009 Location: Greeley, Northern Colorado Posts: 4,147	Re: strange noise after rear drop Shim the rear for a better pinion angle. __________________ -Gerald Building vehicles in memory of the first "car guy" I ever knew, my Grandpa. Bob Dunham 1935-2009. Rest in peace. 61 GMC Suburban SOLD The 86 build thread SOLD Are you a Colorado member?Click here.

06-01-2009, 11:21 PM	#4
SnS C10 Registered User Join Date: Jul 2004 Location: Lomita, Ca Posts: 1,225	Re: strange noise after rear drop i did a search, exactly what is involved in shimming the rear end? let me get this straight, if i drop the front which will slightly raise the rear end, this will not fix anything?

06-01-2009, 11:24 PM	#5
Driveway Dreams I have car A.D.D. Join Date: Feb 2009 Location: Greeley, Northern Colorado Posts: 4,147	Re: strange noise after rear drop No, you need to shim to correct the angle of the driveshaft to the rear end. It needs to almost be a straight line down the shaft, into the rear end. I think I explained this right. correct me if that isn't 100% right. __________________ -Gerald Building vehicles in memory of the first "car guy" I ever knew, my Grandpa. Bob Dunham 1935-2009. Rest in peace. 61 GMC Suburban SOLD The 86 build thread SOLD Are you a Colorado member?Click here.

06-01-2009, 11:33 PM	#6
SnS C10 Registered User Join Date: Jul 2004 Location: Lomita, Ca Posts: 1,225	Re: strange noise after rear drop how and where exactly do you shim to get the correct angle

06-01-2009, 11:39 PM	#7
Driveway Dreams I have car A.D.D. Join Date: Feb 2009 Location: Greeley, Northern Colorado Posts: 4,147	Re: strange noise after rear drop Spring perches to springs. __________________ -Gerald Building vehicles in memory of the first "car guy" I ever knew, my Grandpa. Bob Dunham 1935-2009. Rest in peace. 61 GMC Suburban SOLD The 86 build thread SOLD Are you a Colorado member?Click here.

06-02-2009, 12:13 AM	#8
SnS C10 Registered User Join Date: Jul 2004 Location: Lomita, Ca Posts: 1,225	Re: strange noise after rear drop so put some sort of shim between the leaf spring and the axle? wouldnt that raise the truck back up? sorry i havnt done this portion of suspension before

06-02-2009, 10:05 AM	#9
Jonboy Slots go on anything! Join Date: May 2003 Location: Richardson, TX Posts: 5,957	Re: strange noise after rear drop the shims are tapered, and pretty thin. It will not raise the truck noticibly, but will rotate the pinion to correct the angle.

06-02-2009, 02:48 PM	#10
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,178	Re: strange noise after rear drop In addition to the static pinion angle concern: Taking those extra leafs out may be allowing even more rear axle windup during acceleration than you had before, making the pinion angle worse than what you see statically. You might check, too, to see if you are bottoming the drive shaft out in the end of the trans. K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 06-02-2009 at 02:48 PM.

06-02-2009, 07:34 PM	#12
Wild83C10 Registered User Join Date: May 2002 Location: NJ Posts: 910	Re: strange noise after rear drop When you accelerate hard the front of your rear rotates up and could be pushing your driveshaft forward or throwing your driveline angles way off. You want your angles to add up to 0 (-3 at the trans and 3 at the rear pinion) under normal driving conditions or if its a track truck under hard acceleration. You may want to consider caltrac bars, especailly if you are going to keep only 3 leaves. __________________ 83 C10 Stepside (SOLD, it was a blast!) 383 MASS-FLO EFI/TKO II 600/3.90 Posi 10 bolt S475 and C4 DM running, fine tuning turbo= Douchebag Racing: Runs Fine all the Time



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