How to shorten your driveshaft

[Jacfourteen]

Lately I've been working on converting my truck to 1/2 ton and shortening my frame down to a SWB. One of the things that I had to deal with was the driveline. I did some research online and found a site where a guy outlined the steps that he had followed to shorten many drivelines with no trouble, so I figured I'd give it a shot. Here is the link http://www.fordmuscleforums.com/tran...riveshaft.html If it ended up out of balance I figured I'd go get another from the local junk yard for $25, and if it went well I'd save about $150 for paying someone else to do it. So first I wire wheeled all of the rust and undercoating off of the driveline, I don't know how this thing wasn't out of balance to begin with because all the undercoating was on one side. Next I decided to take the 12 inches out at the splined end because there was no balance weights to mess with. Here it is after cleanup:



So I used a thin cut off wheel on my grinder to cut a shallow groove near the weld on the yoke, it only had to be about 1/16" deep to get through the shaft. Here's a pic:



After that the yoke popped right off with a few taps from a hammer:



Then I measured to see exactly how much needed to be removed, I determined that I needed to cut out 11 and 7/8". Then I clamped it into my chop saw and made sure it was square:



Then I made the cut, and cleaned it up using a file on the inside of the tube and a grinder on the outside and end. Then I had to press the yoke back in, I made a contraption out of 2 chunks of 2x4 and 2 clamps then I had to heat the tube with a propane torch and whack the block with a hammer and keep tensioning the clamps till it was seated:



Next I bolted the driveline into place a spun it and adjusted the runout of the splined section until I got just right. I didn't have a dial gauge to check runout so I rigged up a piece of wire to see how much it was wobbling:



Once satisfied I tack welded a few spots and removed the shaft. Then I welded it up good and used a grinder to knock down any high spots in the weld to help keep things balanced. Then I shot it with some flat black and threw it on.







Since I did this I have had my truck up about 75 and haven't had any vibrations from it, so I think it has been a success. If I missed anything or you have any questions let me know.

[bobs409]

Cool! I was wondering if this is something a DIY'er could do. Guess it is!

[Jeffs70]

great job.

[jondancer]

how did you know how much to cut out ?

[Jacfourteen]

Originally Posted by jondancer

how did you know how much to cut out ?

I measured from the center of the u joint on the tranny to the mounting pad for the carrier bearing.
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[prostreetC-10]

That is slick but I'm curious why you wouldn't want to go with a one piece and eliminate the carrier bearing??

[68gmsee]

Good job! I did one similar to that on a beach buggy I built way back in 1970 and it came out good. Only difference in mine is I ground down the welded portion and then cut the shaft with a hack saw going around it until I cut all the way.

****Word of caution****

This is not for the amateur welder to do. The drive shaft is under a lot of stress and has to be welded by a professional. You don't want it to come undone due to stress fractures. Minor vibrations combined with stess can quickly cause a hairline fracture to completely destroy the weld.

The repair bills on a broken drive shaft can far exceed the cost of a new one. I had mine welded by a professional welder.

[brad_man_72]

that spline needs to be within .002" of straight. How much did the stub move from the heat when welding? About 1 in 500 shafts won't require weight on one end, did you get the stub back in exatly where the factory had it, don't forget to compensate for the mass of tubing removed, and the stub wasn't 100% straight from the factory.
you should have removed the section of tue from the weld yoke end as they are far less sensitive than a carrier stub.
I build drivelines every day, and this isn't a project I'd do at home!

some people don't notice their driveshaft vibrating when it's about to fall out of the truck. It's an old truck, it shakes and shimmies, that's what it's supposed to do, right?!
when most people work on their own driveshaft they make it to where even I cant fix it, costing them even more money.

please at least take your "finished" driveline to a rea driveline shop, not a mechanic, not a machine shop because these guys are about the worst at working on drivelines. But a real driveline shop and have them check and ballance the shaft.

why does it feel like I give this advice every week here?...

[brad_man_72]

broken shafts can ruin your (things I've actually seen) transmission most common, rear end, gas tanks, fuel lins, air lines, body damage, frame damage, wiring. But hey ya saved $60 right

[LockDoc]

-
I have cut my own drive shafts for every car I ever built that needed one cut, (at least 6) with a hack saw and welder. I have only had to re-do one that I welded too much on one side instead of alternating sides and it pulled it. I have never had one crack or come apart. The guy that showed me how to do it shortened all of the ones for his drag cars. Don't get me wrong, I don't advocate that "everyone" shorten their own shaft but it can be done successfully by a DIY'er.

Just my 2¢ worth.

LockDoc

[Jacfourteen]

Thanks for the input guys. I agree that having it checked out by a pro is a good idea, but the people I've talked to gave had good results. If I was pouting down huge power or going to the track of def spring for a custom shaft. I plan on going one peice when I swap to a t56.
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[LONGHAIR]

I'm with brad_man_72 on this one. It is not a job for a DIYer to tackle, especially w/o a dial indicator.

Just because you may not "feel" a vibration, does not mean that it isn't there....and tearing up something.
I partly blame those week-end TV shows that continually do this kind of thing. Sure they run a disclaimer saying that the info provided is not "complete".....but who reads that?

[prostreetC-10]

Oh great.......so you are going to tell me I sholdn't have welded my crank back together when it broke?

Yeah those shows always show the host hands and the tech hands but you don't know which is which.

[Richard H.]

Originally Posted by Jacfourteen

Thanks for the input guys. I agree that having it checked out by a pro is a good idea, but the people I've talked to gave had good results. If I was pouting down huge power or going to the track of def spring for a custom shaft. I plan on going one peice when I swap to a t56.
Posted via Mobile Device

Nice write up , If you do it again , the sleeve on the other end is longer I believe to get better alignment when you force it back in. If you have the tube square and the yoke as square as possible for a good beveled mating surface it ain't gonna move. Keep up the good work!

[brad_man_72]

the pilots are generally the same size on a weld yoke and a slip stub, but the alignment of a slip stub is far more critical than the weld yoke. I've seen both weld yokes and slips stubs move .020 from welding heat. To make the shaft straight again requires heating and cooling. Just because it's straight doesn't mean it's ballanced. Variations in tube thickness (even dom) and parts being partially machined contribute to off ballance condition.

why the pilot looks so short in this thread is because the original weld wasn't removed. I cut all of the parts I will reuse out with a lathe.

not really a prob with our gen trucks but some trucks w 3r style weld yokes dont have a straight pilot and can be a real pita to reuse because they are wedge shaped.

[Fastfun]

Originally Posted by brad_man_72

that spline needs to be within .002" of straight. How much did the stub move from the heat when welding? About 1 in 500 shafts won't require weight on one end, did you get the stub back in exatly where the factory had it, don't forget to compensate for the mass of tubing removed, and the stub wasn't 100% straight from the factory.
you should have removed the section of tue from the weld yoke end as they are far less sensitive than a carrier stub.
I build drivelines every day, and this isn't a project I'd do at home!

some people don't notice their driveshaft vibrating when it's about to fall out of the truck. It's an old truck, it shakes and shimmies, that's what it's supposed to do, right?!
when most people work on their own driveshaft they make it to where even I cant fix it, costing them even more money.

please at least take your "finished" driveline to a rea driveline shop, not a mechanic, not a machine shop because these guys are about the worst at working on drivelines. But a real driveline shop and have them check and ballance the shaft.

why does it feel like I give this advice every week here?...

BEST LEFT TO THE PROFESSIONALS. I would not want to risk it.

[72freak]

I have done my share of them also....but for $40 with new U joints and ballanced its not a hard decision or worth the trouble or time anymore. I now take them to Driveline Services.

[Jacfourteen]

Originally Posted by 72freak

I have done my share of them also....but for $40 with new U joints and ballanced its not a hard decision or worth the trouble or time anymore. I now take them to Driveline Services.

Thats cheap I would have let them do it too. The closest shop to me was 45 minutes away and wanted about $150 to do it.
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[brad_man_72]

$40 for 3 ujoints is too cheap much less labor to install them a Cut and weld and a ballance!

[72freak]

Originally Posted by brad_man_72

$40 for 3 ujoints is too cheap much less labor to install them a Cut and weld and a ballance!

Short bed 1 piece....1 cut, 1 weld, 2 u-joints and balance. I had the yoke.

We took one the other day and had the u-joints and I think it was $32.

[BIGKEV]

Originally Posted by 72freak

Short bed 1 piece....1 cut, 1 weld, 2 u-joints and balance. I had the yoke.

We took one the other day and had the u-joints and I think it was $32.

That's ridiculously cheap! I'd be skeptical at that low of a price. Dad always says, cheap things are of no value, and valuable things are not cheap.

[1971 GMC SHORTY]

When I was About 24 years old when i did a small block to big block with a 400 tranny,
didnt relize i need a shorter Driveshaft so My Buddy Said We Can Shorten The Drive Shaft Being Young Thought It Would Save me Some Money.
We Cut It Down But Keep Makeing Sure It Was Good Drove it For 3 -4 Years Street Raced It Still Being Driven Buy My Old Buddy Still Driveing that Short Bed with Same DriveShaft..

[72freak]

Originally Posted by BIGKEV

That's ridiculously cheap! I'd be skeptical at that low of a price. Dad always says, cheap things are of no value, and valuable things are not cheap.

+

That is the main drive shaft pace in our area. They have been here 20+ years and have a great reputation. EVERYONE uses them.

[Altec]

You know, I've shortened drive shafts, and even my Dad's '84 Monte survived YEARS of 900+HP and 130MPH runs with a home shortened shaft with no vibrations, and no issues. Frankly though, I still recommend having a pro do it. At the end of the day, it is good insurance, and if the shop warranties their stuff, then even better.

When we do them we would level the tube, and tie it down so the uncut yokes side is facing up. Then put a level on the uncut yoke, and level that. Then adjust the cut yoke to match. Using three machinist levels at the same time to make sure nothing moves... Then taking a forth level check the uncut yoke for vertical level, and make the cut side match. Tack weld it, and welding from their. Then check it all again...

I think the key is not disturbing the original weights. I still don't recommend doing it. Simply posting for knowledge sake...

[Hottrucks]

thumbs up for another DIY...yep did mine and have abused 2 sets of wrinkle wall pro streets....but yea I would not do it for anyone else but myself and I do plan on a 1 piece DS when the U joints fail