Driveline angle help! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Low Elco · 11-04-2012, 01:25 PM

I've built a 70 swb with a 72 burb rear and sb/700r4 combo. We have a severe vibe between 58-63 mph and a little in other speeds. Seeing as it was built with all stock stuff and only lowered in the rear with a 3" spring, I assumed the driveline angles were fine. Judging from research and leveling the frame this weekend and measuring, that ain't so. Measured off the rear trans face, with /\ being the directions of tilt, I am / 5 deg. The driveshaft is / 5 deg, and the yoke face is / 5-6 deg. This is telling me I am running in a straight line, which I'm gathering ain't good. I am willing to fix this, but I wanna be sure I'm right. Im going to shim the trans up so I'm / 1 deg, and shim the rear so it is / 1 deg, which should put me in the guidelines of 1-3 deg down at the trans face and parallel to that at the rear. Shaft is rebuilt and balanced, ujoints are new. Am I nuts? Is the correct track? Any help is appreciated.

**lolife99** · 11-09-2012, 01:05 PM

There are many articles on the internet about this.
This is just one.
http://www.roadkillcustoms.com/hot-r...nion-angle.asp

Your /\ lines aren't real clear to me.
Saying 5 degrees down and the trans and 5 degrees up at the rearend is more clear to my little brain.

Can anyone else add some input?

**LEEVON** · 11-09-2012, 04:01 PM

In really simple terms, assuming your trans is 5 degrees negative and you have a one piece driveshaft then your rear end should be opposite or 5 degrees positive. Forget about the angle of the driveshaft, it's relative. Keep in mind you may have around 1-3 degrees rise under load so 2-4 degrees positive on the rear end should be close. Honestly though, you can read every article there is and plan to the milimeter but every one is different and some lowered trucks are just going to vibrate. I've had a fully adjustable flip kit and gone in increments of 1/2 degree for a full 10 degree sweep and it still vibrated. It doesn't have to be severe though. As for shims, assuming you're working with trailing arms the best bet is to get two or three different ones and try them out. Don't spend a fortune:

http://www.stockcarproducts.com/trkarm1.htm

Low Elco · 11-09-2012, 04:33 PM

Have shims coming from them, thanks! I am 5 down at the trans and 5 up at the yoke. Problem is, I'm 5 down at the shaft, so straight line, which is bad. I may have some time to make some BS Spacers just to mock it all up at the 1deg up down number I'm aiming for. Well see. Thanks for the input!
Posted via Mobile Device

11-04-2012, 01:25 PM	#1
Low Elco Registered User Join Date: Apr 2003 Location: Indep, MO Posts: 5,893	Driveline angle help! I've built a 70 swb with a 72 burb rear and sb/700r4 combo. We have a severe vibe between 58-63 mph and a little in other speeds. Seeing as it was built with all stock stuff and only lowered in the rear with a 3" spring, I assumed the driveline angles were fine. Judging from research and leveling the frame this weekend and measuring, that ain't so. Measured off the rear trans face, with /\ being the directions of tilt, I am / 5 deg. The driveshaft is / 5 deg, and the yoke face is / 5-6 deg. This is telling me I am running in a straight line, which I'm gathering ain't good. I am willing to fix this, but I wanna be sure I'm right. Im going to shim the trans up so I'm / 1 deg, and shim the rear so it is / 1 deg, which should put me in the guidelines of 1-3 deg down at the trans face and parallel to that at the rear. Shaft is rebuilt and balanced, ujoints are new. Am I nuts? Is the correct track? Any help is appreciated. __________________ Boppa's Old Yeller Truck Build, Old Yeller's New Heart! Project Buzz Bomb Flyin' Low!

11-09-2012, 01:05 PM	#2
lolife99 67-72 parts collector,… Join Date: Nov 2002 Location: Mid-MO Posts: 22,700	Re: Driveline angle help! There are many articles on the internet about this. This is just one. http://www.roadkillcustoms.com/hot-r...nion-angle.asp Your /\ lines aren't real clear to me. Saying 5 degrees down and the trans and 5 degrees up at the rearend is more clear to my little brain. Can anyone else add some input? __________________ Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823

11-09-2012, 04:01 PM	#3
LEEVON Moderator Join Date: Jul 2006 Location: Ozark, MO Posts: 4,888	Re: Driveline angle help! In really simple terms, assuming your trans is 5 degrees negative and you have a one piece driveshaft then your rear end should be opposite or 5 degrees positive. Forget about the angle of the driveshaft, it's relative. Keep in mind you may have around 1-3 degrees rise under load so 2-4 degrees positive on the rear end should be close. Honestly though, you can read every article there is and plan to the milimeter but every one is different and some lowered trucks are just going to vibrate. I've had a fully adjustable flip kit and gone in increments of 1/2 degree for a full 10 degree sweep and it still vibrated. It doesn't have to be severe though. As for shims, assuming you're working with trailing arms the best bet is to get two or three different ones and try them out. Don't spend a fortune: http://www.stockcarproducts.com/trkarm1.htm __________________ '20 Silverado Trail Boss ~ '17 Tahoe ~ '79 K15 Sierra Grande ~ '76 Blazer 2wd ~ '71 Cheyenne swb ~ '55 Pontiac Safari ~'50 3100 bagged ~ '80 Wife ~ Late model kids

11-09-2012, 04:33 PM	#4
Low Elco Registered User Join Date: Apr 2003 Location: Indep, MO Posts: 5,893	Re: Driveline angle help! Have shims coming from them, thanks! I am 5 down at the trans and 5 up at the yoke. Problem is, I'm 5 down at the shaft, so straight line, which is bad. I may have some time to make some BS Spacers just to mock it all up at the 1deg up down number I'm aiming for. Well see. Thanks for the input! Posted via Mobile Device __________________ Boppa's Old Yeller Truck Build, Old Yeller's New Heart! Project Buzz Bomb Flyin' Low!



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.