Why can't I change the pinion angle?

[GreenMystChevy]

I bought some 3/4 ton axles for a '75 that are going on my '72 GMC. The rear spring hangers for the Corp-14FF are different widths than the stock ones for '72.

Why can't I rotate the pinion up to compensate for the 8" lift springs when I re-weld the perches on there? I have heard that this would knock pinion angle off, but so will the lift...


Also, what is the easiest way to relocate them? Gring off the weld and re-weld the old ones, can I buy new ones, etc?

[JIMs70GMC]

Does the lift come with the shims already? If they do then you'd have to remove them. Your probably only talking a few degrees on a long wheelbase truck. I don't think you'd have a problem. I think some off-road shops sell the perches. I believe the 14 bolt has 3.5" tubes.

[Beast388]

I just finished swapping in a set of '77 3/4 ton axles under my '71 Burb.

For the 14BFF, I had to make my own perches and weld them on at the correct 40" center to center spacing. The worst part was grinding off the old perches, spent about 6 hours doing that. You can find new perches at www.echobit.com .

I welded my perches on at the factory pinion angle, but you can weld yours on at whatever angle you want. I would suggest mocking up the axle under the truck and matching the t-case/driveshaft angle with pinion/driveshaft angle. Then you could tack the perches in place and pull the axle back out to fully weld them on.

I did a rear disk swap on the 14BFF as well.

[stan79chevy]

"Why can't I rotate the pinion up to compensate for the 8" lift springs when I re-weld the perches on there? I have heard that this would knock pinion angle off, but so will the lift... "


my brother in law cut off his spring perches and put them back on at a better angle and he hasnt had any problems with u joints since. i think it is safer than the angled shims because you wont have to worry about one slipping out or anything

[srhart71]

STAN has the right idea about shims. After working in a 4WD shop, I would also follow Beast's suggestion and mock up the axle to make sure of your angles. Just as an added bit of info, if you replace your hangers with later model ones, they will match the width of the perches on your axle. That is what I did and also performed a shackle reversal at the same time. Good Luck, Have Fun, and post some pick of before and after.
Shawn

[Scrub]

I did mine just as you are thinking about. I would recomend you take it to a welding shop and have the perches removed with an"Air Arc". It is a carbon stick that melts the weld out while at the same time a strong blast of air blows the molten metal away. A good artist can remove just the weld and do a very clean job.

30 bucks seem to be the going rate to have this done. It is cooler and much safer than a torch, which can easily blow a hole right through your axle tube.

Check your shock mounts, I think you will have to move them also, so get them burned off too.

Good luck

[soleeagle]

Can a person somehow just rotate the diff on the tubes instead of cutting and moving all the other things? If so how can this be done, do you just cut out the welds on the sides of the diff, rotate and reweld?

[Mike C]

The rosette welds can't just be "cut" as they are basically a filled hole. You might be able to drill them out, but without a SERIOUSLY large press, you can't get the tubes out. It is not very difficult to torch the old perches off and weld new ones on. You can buy them for about $20 a pair, but they are not as strong as the tubing built ones like Beasts would be.

My first cut and grind took a LONG time. I can remove the perches and grind all the welds down in about 15 minutes now.

[Beast388]

Here are a few pics.....the first is of one of my homemade perches tacked into position.

[Beast388]

Here is a view of the 14BFF installed...still had to hook up shocks, driveshaft etc......

[Beast388]

And another......

[soleeagle]

Originally posted by soleeagle
Can a person somehow just rotate the diff on the tubes instead of cutting and moving all the other things? If so how can this be done, do you just cut out the welds on the sides of the diff, rotate and reweld?

On my question i asked the other day I was talking about the front. Would there be a better way to do this without disturbing the steering.

[misfits]

If i'm not mistaken the axle tubes are pressed in, but yes you COULD do it but I would highly reccomend having a professional do it. Just my 2 cents.

I did the same thing "beast388" did with the rear spring perches. Only I did it out of necessity because i broke the rear output yoke on the transfercase and wrapped the rear axle which flattened my spring perches.
I used 2 1/2" x 1/4" square tube and capped the open ends of the tubes. I used a plasma at work to cut the tubes to fit over the axle. I wish I had done it sooner, I haven't had any u-joint problems yet.
I can put up some pictures if anyone is interested...

[nu2-72]

Cut mine off with a plasma and finished with a grinder. Took only a few minutes. I then machined a set of 15 degree blocks and welded the original pads back on. Did the shock mounts also.

[GreenMystChevy]

Thanks for all of the help guys. I will attempt to rotate the angle up a bit being that I am welding on new mounts anyways.

Beast388. Very nice setup you have there! I would love to go with rear discs but the money just isn't there. It all looks real good. Where did you buy the u-bolts?


Thanks again guys

[Beast388]

Thanks for the compliments Jeremy.

I had my local spring shop make the u-bolts for me. They were around $8.50 each. You can also get them from the popular lift companies like Rough Country.

It really wasn't that expensive to go to disks. By the time I added up what it would cost to rebuild the drum brakes, it wasn't too far out of line. The rotors and calipers are just pieces from the front of a '77 K20. The rotors and calipers are stock items. The only custom items were the caliper brackets which I purchased from www.echobit.com. I also bought a flexible hose kit from www.azkickin.com.

Here is the break down (no pun intended ):

2 Rotors = $50
2 Calipers = $28
Brackets = $70
Hose kit = $62
Pads = $15

[GreenMystChevy]

Beast388: I am very interested in this disc swap that you did. You wouldn't happen to have any step by step instructions or pictures do you?

What year rear did you use for the 14Bolt? Was it a '77 or how did you know to use the front rotors and calipers for it?

Was this as easy as you are making it seem? You have really peaked my interest and it looks like I can have rear disc brakes for only $225.

Thanks for the time.

[Beast388]

It really is as easy as it seems.

As far as calipers and rotors go, any from 1973-80 should work. Most of the bracket kits out there are made to use parts from those years.

I did take a few pics of the disk install, but here are a couple of websites that have plenty of info.

Site 1

Site 2

I would also recommend going to www.ck5.com and search in the message forums on "14BFF disk brakes". You will find TONS of info on the subject.

I still need to bleed the rear brakes and see how well they work. It should stop my heavy Suburban better than the little 12 bolt drums.

[GreenMystChevy]

Beast388- Thanks a lot for all of your help on this. It is really something that I want to tackle until I got to thinking a bit more. Hmm, I drive a manual and it sure would be nice to have an e-brake. So, until I can find a way to get an e-brake on there, I gotta just put it out of my mind.

Thanks again.

[Beast388]

Incorporating an e-brake is a easy. All you need are rear calipers off of a 76-78 Cadillac Eldorado. Those calipers have a lever that operates the e-brake. They are dimensionally the same as the 73-80 K20 front calipers.

The only thing you would have to do is rig up your e-brake cable. www.azkicken.com is working on a kit to do just that.

The only downside is that the Caddy calipers are pretty pricey compared to the truck calipers. But it can be done.

Like I said before, do some searching over at www.ck5.com, there is more info than you will be able to read over there about all of this.

[GreenMystChevy]

Well aren't you just a wealth of information

I gotta go do some reading on this now. Or I could just skip the reading and ask you, lol.

You'll probably have a few more questions form me yet. Thanks again.