3/4T 4x4 spring lift and rearend change - The 1947 - Present Chevrolet & GMC Truck Message Board Network

richardwilken · 09-03-2005, 02:31 AM

Hi guys. Im planning to drop a 1977 14bFF under the rear of my 69 K20. At the same time, I am going to get 2 inch aprings made for all around the truck. What kind of geometry issues will I run into. Someone needs to write a rearend change FAQ. Thank you all

**Yukon Jack** · 09-03-2005, 09:02 AM

The spring perches will need to be moved and you will need a conversion u-joint for your driveshaft. I don't know if the driveshaft length will actually change. My info on the u-joint conversion is at the office but someone will probably chime in on what it is.

You could PM Beast388 he has the specific info.

454_72_4X4 · 09-04-2005, 11:26 PM

Quote:

Originally Posted by Yukon Jack

The spring perches will need to be moved and you will need a conversion u-joint for your driveshaft. I don't know if the driveshaft length will actually change. My info on the u-joint conversion is at the office but someone will probably chime in on what it is.

You could PM Beast388 he has the specific info.

Curious...Did the 69 K20 use a smaller U-joint than a 72 K20? I had to move the spring perches also, (they were 1 spring width to wide on the 14FF), but I used the factory U-joint I think. It's been a few years though.

richardwilken · 09-05-2005, 01:09 AM

what is the factory angle that the front and rear differentials are set at? If I use 2 inch lift springs, maybe someone better at geometry could figure out what the new angle would be.

full foot notch · 09-05-2005, 02:01 AM

the 3/4 ton ujoint is proly gonna be a 1350, and the 14bolt axle is prolly a 1ton/1410 series, in which a conversion ujoint(like neapco, PDQ, fed mogul) of 3-3130(or maybe 3-3150) which one set is 1350 caps and the other pair of caps is 1410 caps)

Beast388 · 09-06-2005, 09:00 PM

The 14BFF uses a 1350 u-joint. Your original K20 driveshaft "should" be the 1350 as well. I had to use the Napa #348 conversion joint since my burb was a 1/2 ton.

The 14BFF in my Burb is also of the '77 variety. You will need to move the spring perches from the 42.5" spacing to the 40" spacing your '69 K20 requires. You will also need to move the shock tabs to the "both forward" configuration at the correct spacing.

Let me know if you want to see some pics and I will post them.

09-03-2005, 02:31 AM	#1
richardwilken Registered User Join Date: Sep 2003 Location: clifton, IL Posts: 114	3/4T 4x4 spring lift and rearend change Hi guys. Im planning to drop a 1977 14bFF under the rear of my 69 K20. At the same time, I am going to get 2 inch aprings made for all around the truck. What kind of geometry issues will I run into. Someone needs to write a rearend change FAQ. Thank you all __________________ 69 chevy 1/2 ton 2wd 72 GMC 1/2 ton 2wd

09-03-2005, 09:02 AM	#2
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,686	The spring perches will need to be moved and you will need a conversion u-joint for your driveshaft. I don't know if the driveshaft length will actually change. My info on the u-joint conversion is at the office but someone will probably chime in on what it is. You could PM Beast388 he has the specific info. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

09-05-2005, 01:09 AM	#4
richardwilken Registered User Join Date: Sep 2003 Location: clifton, IL Posts: 114	what is the factory angle that the front and rear differentials are set at? If I use 2 inch lift springs, maybe someone better at geometry could figure out what the new angle would be. __________________ 69 chevy 1/2 ton 2wd 72 GMC 1/2 ton 2wd

09-06-2005, 09:00 PM	#6
Beast388 Suburbans RULE! Join Date: Jan 2000 Location: Clinton, IA 52732 Posts: 689	The 14BFF uses a 1350 u-joint. Your original K20 driveshaft "should" be the 1350 as well. I had to use the Napa #348 conversion joint since my burb was a 1/2 ton. The 14BFF in my Burb is also of the '77 variety. You will need to move the spring perches from the 42.5" spacing to the 40" spacing your '69 K20 requires. You will also need to move the shock tabs to the "both forward" configuration at the correct spacing. Let me know if you want to see some pics and I will post them. __________________ --Ben 71 GMC Suburban 4X4 The "Beast" 388 CID Stroker, TH350, NP205, 8-lug D44, 14BFF w/ Detroit, 4.10:1 gears, 4-Wheel Disks 4" Lift, 35" MT/R's.

09-05-2005, 02:01 AM	#5
full foot notch Registered User Join Date: Apr 2003 Location: Central florida Posts: 3,223	the 3/4 ton ujoint is proly gonna be a 1350, and the 14bolt axle is prolly a 1ton/1410 series, in which a conversion ujoint(like neapco, PDQ, fed mogul) of 3-3130(or maybe 3-3150) which one set is 1350 caps and the other pair of caps is 1410 caps)



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