The Stovebolt Site Forums The Shop Area Engine Shop rear end perches

I have a 12 bolt gm rearend that i am going to place in my 1951 chevy truck. If i have to replace the perches on it,what degree of angle should the rearend be set at,yoke,driveshaft to transmission?

The same angle as what the transmission tailshaft sits at, plus or minus a few degrees, usually plus to acount for spring deflection,
Scott

I'm not sure but I think its 3 degrees positive. I am about to "lower" my pinion back down as it is defintely to high but I didn't know better back when I did it. My nephew says they use a guage of some sorts at Freightliner Chassis Co. and he may be able to help me get it right. He mentions something about checking it at the starter and tranny but it would depend on what set up you are running. I think the tranny as mentioned above would do it. I'm sure someone else will be along that can be more positive help.

Check out WWW.NOVAK-ADAPT.COM Go to their knowledge base, click on dirvesaft angularity. it also has a lot of transmission info as they make adapter kits for jeeps for a wide range of transmissions.

Go to classictruckshop.com/driveline.asp

Speaking of perches....I noted that one of the popular vendors sells a perch/u-bolt/shock mount kit for $139. I checked out the local trailer repair shop and scored the u-bolts, bottom plate, and 1-3/4 wide perches (new) for $20 retail. This does not include the shock mounts but from what I've heard you have to adjust to match your new diff. Mine with outboard discs would have required I modify anyways. Just a thought.....my $.02.

Dave

I believe it's 3 degrees offset but read about it from the driveline guys and ask questions, B-4 you do the job.
I used a kit from a 4x4 supply shop but added to it by adding the offset 'back' more to 2.5'' The wheels set looks MUCH cleaner, filling the tire well better than the kits offset of 1.5''. That was w/ two pieces of 1.5'' x .25''x 6'' strap welded to the 3'' diameter precut spring perch hanger. The U bolts supplied w/ these popular kits were TOO SHORT. So I had to visit my OTHER local 4x4 supply house and they made me 4 new ones @ about $26.00. Cut/strip/grind off all old hanger components before you place the new rear end under the truck. Set the engine/trans in situ and plan your angles first. Planning these component angles is critical. Set the components up so their center lines are parallel and so that the angle made THROUGH the U-joints is 3-degrees or less. While it is possible to run at zero degrees through the U-joints, something more than actual zero and less than three degrees seems to run smoothest.
It will be worth the effort to set the engine and transmission in the frame and the axle under it to experiment. Fairly reliable angles can be measured from the starter motor case and of the pinion yoke. A piece of 2x2 or 2x4 (wood) can be cut to length to simulate the drive shaft for measuring its angle and to check for interference (or contact) with other chassis and body components. When you are satisfied that you have the proper angles in place you can mount the components. You will be married to the engine and transmission placement but must plan for adjustability at the rear axle


see Inland Empire Driveline Service:
http://www.iedls.com/ptsetup.html

see my web photos


http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=DSC00369.jpg

http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=DSC00366.jpg

http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=Scan1_0001-1.jpg

http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=Scan3_0003.jpg


fresh out of the paint shop shows rear axle


http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=587685-R1-040-18A-1.jpg

http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=587685-R1-048-22A.jpg

http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=587685-R1-042-19A.jpg

Thanks,i have been reading some articles on the subject. I just want to make sure i do this correct the first time.I will take a look at the link you provided.

You say the 2.5" offset looks better than the 1.5" ?

yes.
once you get it mocked up per the kit (if you use that)and many do cause it's easier, just move it back one more inch and snug up the U bolts.
take a view and you can decide.
you know measure three times cut/tack weld once.
sit on looking at it overnight w/ a fresh unobsturcted side view in the morning.
you have to have a new driveline made anyway
http://local.sacramento.com/sacramento/Auto-Parts-~26-Supplies---New/drivelineserviceofsacramento_3713332--drive-line-service-of-sacramento.zp.html
http://www.iedls.com/measure.html
http://www.drive-lines.com/


so what the hay.

good luck

You can turn your springs around and you will have correct offset.

?????????

I have heard many say this, but have never seen it done. On torque tube rear springs supposedly if you flip the springs (and obviously switch the bushing and shackle piece) the axle pin will center in the wheel well so as to avoid having to offset the spring perch hole. Do remember however, that the stock look is to have the rear wheels sit somewhat forward from center of the wheel well.
Steve O

I tried the old "turn the leaf springs around" trick and it didn't work for me - the rear axle ended up being about 1" too far BACK in the wheel well opening. Here's a pic of it before I got the bed on and realized that it was too far back:

http://i48.photobucket.com/albums/f214/tkeahi/novarear015.jpg

I ended up taking the rear end back off and drilling new holes in the spring perches where I wanted them. Some good advice (that I wish I followed) is to drill holes about 1" apart in your axle perches/bottom plates before you put them on so that you can tweak the location once you've got everything back together.

why KEEP that old crap
buy a modern rear end and you will be better off for it. Better brakes better drive ratios.