Lowering springs - Change pinion angle? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

newbe351 · 07-31-2012, 10:53 AM

I have drop spindles on the front of the '66 GMC and installed drop leaf springs from Early Classic over the weekend. The truck vibrated so bad, I took them off after a trip around the block. The original leafs have a wedge attached to the bottom of the spring that points the differential down. The new springs raised the diff angle up quite a bit and even looked bad just eyeballing it. If I get a wedge of the same angle as I have now on the new springs, will everything be OK? The springs just drop the body right? There should be no change in the geometry of the running gear? It's a longbed with the dual drive lines.

Thanks

**lolife99** · 08-01-2012, 07:55 AM

The drop leaf springs move the rearend up in the chassis.
Since you have the 2-piece driveshaft,... you might have issues there as well.
Some people shim the carrier bearing to help with the driveshaft.
You driveshaft will actually be trying to push itself into the back of the transmission, since it will be "straighter" with the drop springs.

Do you have any pics you can post?

newbe351 · 08-01-2012, 04:08 PM

Thanks for the response. The front driveshaft looks like it is already "pushed" into the transmission, but it looks like its pretty stationary with the carrier bearing holding it in place. The back driveshaft has 2" or so of spline remaining. This looks like where all the action is (length adjustments during driving).

I took it to a spring shop (really neat old school folks http://sacramentospring.com/). They aren't even sure I can make up the pinion angle difference with spacers. The perches may have to be relocated, which kinda ticks me off as I just had the rear end rebuilt from lug nut to lug nut, including perches (ring and pinion, axels, bearings, tube alignment, etc.). They will re-install the lowering springs for me (as I can’t drive it there if I put them on at home) and check it all out to see what needs to be done to make everything work. $$$

**lolife99** · 08-01-2012, 06:14 PM

I would look somewhere else for the vibration.
I have installed at least 3 sets of drop leaf springs and never ran into this issue,... but I had a single 1-piece driveshaft.

07-31-2012, 10:53 AM	#1
newbe351 Registered User Join Date: Dec 2004 Location: West Sacramento, CA Posts: 368	Lowering springs - Change pinion angle? I have drop spindles on the front of the '66 GMC and installed drop leaf springs from Early Classic over the weekend. The truck vibrated so bad, I took them off after a trip around the block. The original leafs have a wedge attached to the bottom of the spring that points the differential down. The new springs raised the diff angle up quite a bit and even looked bad just eyeballing it. If I get a wedge of the same angle as I have now on the new springs, will everything be OK? The springs just drop the body right? There should be no change in the geometry of the running gear? It's a longbed with the dual drive lines. Thanks Last edited by newbe351; 07-31-2012 at 11:10 AM.

08-01-2012, 07:55 AM	#2
lolife99 67-72 parts collector,… Join Date: Nov 2002 Location: Mid-MO Posts: 22,700	Re: Lowering springs - Change pinion angle? The drop leaf springs move the rearend up in the chassis. Since you have the 2-piece driveshaft,... you might have issues there as well. Some people shim the carrier bearing to help with the driveshaft. You driveshaft will actually be trying to push itself into the back of the transmission, since it will be "straighter" with the drop springs. Do you have any pics you can post? __________________ Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823

08-01-2012, 04:08 PM	#3
newbe351 Registered User Join Date: Dec 2004 Location: West Sacramento, CA Posts: 368	Re: Lowering springs - Change pinion angle? Thanks for the response. The front driveshaft looks like it is already "pushed" into the transmission, but it looks like its pretty stationary with the carrier bearing holding it in place. The back driveshaft has 2" or so of spline remaining. This looks like where all the action is (length adjustments during driving). I took it to a spring shop (really neat old school folks http://sacramentospring.com/). They aren't even sure I can make up the pinion angle difference with spacers. The perches may have to be relocated, which kinda ticks me off as I just had the rear end rebuilt from lug nut to lug nut, including perches (ring and pinion, axels, bearings, tube alignment, etc.). They will re-install the lowering springs for me (as I can’t drive it there if I put them on at home) and check it all out to see what needs to be done to make everything work. $$$

08-01-2012, 06:14 PM	#4
lolife99 67-72 parts collector,… Join Date: Nov 2002 Location: Mid-MO Posts: 22,700	Re: Lowering springs - Change pinion angle? I would look somewhere else for the vibration. I have installed at least 3 sets of drop leaf springs and never ran into this issue,... but I had a single 1-piece driveshaft. __________________ Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823



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