expandable driveshaft

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Im wanting to build a drive shaft for a project that will have atleast 18 inches of travel.  what would you guys think would be the best parts to do it with, i built one with some tractor parts at TSC but tractors dont turn 6800 rpm's either and im worried its going to fail.
Reply:I hate to say it, but a driveshaft shop is the best place to go to answer your questions.  They use several formulas to determine critical speeds, etc on driveshafts based on your application.  6800 rpms is up there for a driveshaft - tell us more about it.
Reply:Get the drive shaft ends... the yokes and such.Buy either round or square tubing , at least 2 inch diaOne of the steel pieces should fit in the other , that way it will expand. I don't think you can get any cheaper and that , i have seen it done before.
Reply:I built one out of tight fitting square tubing for my derby cars,  it slips a total of 3 foot so on most cars it will slip in 18" or out 18" which is way more than i need for any application.  I dont know how many rpm's it has turned but i would venture to say somewhere around 5000?  I'm not sure what you plan on doing with this but I would highly recommend a driveshaft shop for any kind of street application for safety reasons and i even question the safety of it in my derby cars but i am fairly comfortable with my work as i have alot of time invested in making sure things are straight and fit together tightly.   If i had to do it over again i think i would use a splined pto shaft for the slip to decrease the weight,  Hope this helps you and if you need any other advice i would be glad to help you in any way i can,  good luck.Matt
Reply:Originally Posted by BikespotGet the drive shaft ends... the yokes and such.Buy either round or square tubing , at least 2 inch diaOne of the steel pieces should fit in the other , that way it will expand.
Reply:You can buy splined shaft pairs to do this. Any GOOD driveshaft shop can handle this.Depending on torque, you could do one end in round stock and on the end of it, weld the female spline piece to the tube. The male splined shaft will go through the piece you welded on and into the round tube and slide to the correct length. When short, the male splined shaft will slide into the tube.One end of each will get your U jount yoke or whatever is driving the shaft and being driven.I'd definitely use a pillow block on the slip end of the stationary shaft, if possible.
Reply:Originally Posted by turboblownYou can buy splined shaft pairs to do this. Any GOOD driveshaft shop can handle this.Depending on torque, you could do one end in round stock and on the end of it, weld the female spline piece to the tube. The male splined shaft will go through the piece you welded on and into the round tube and slide to the correct length. When short, the male splined shaft will slide into the tube.One end of each will get your U jount yoke or whatever is driving the shaft and being driven.I'd definitely use a pillow block on the slip end of the stationary shaft, if possible.
Reply:Originally Posted by zapsterI know what your trying to say..ButSquare yes..Round no....zap!
Reply:Originally Posted by BikespotThe one i saw was square , i said round because drive shafts are round.Why not round?
Reply:its going into my demolition derby car, i run the same motors/trannys and rear ends but different makes/models of cars so a drive shaft that would not only move from car to car but be able to move as the cars bend is my goal.  trying to keep the budjet around 500 bucks.  it doesnt need to be balanced to a T  but i think this is something i can/want to make
Reply:well mine cost me nothing to build since i have lotsa scrap to work with and more time than money and as stated in my above^ post it is made of tight fitting square tube and seems to work well,  but it WILL take you quite some time to find two pieces of tubing to fit together nicely.  Take your time and search around and you will find just the right stuff,  if i recall mine is 1.5" 1/8" wall for the "inside" tube and and 1.75" 1/8" seamless slider tubing for the outer.  I used two rear halves with gm cv joints for the rest of the shaft.  I had to step down the inside of the original driveshaft tubes with heavy wall round tubing to make them accept the square tube since it is much smaller.     I will snap some pics tomorrow if i get time but the city is getting on my case about the junk derby cars in my yard so moving them may very well occupy most of my day tomorrow  The moral of the story is that once you run a slider shaft you will never go back cause no matter how bent the front or back is my cars are still moving especially with having cv joints on both ends you can put some serious angle on the shaft and it doesnt bind at all.  I have had my shaft on Imperials, Impallas, Buicks, Cadillacs, Pontiacs, late 90s Crown Vics and others.  So far there isnt anything it hasnt fit.... Mopar Gm and Ford alike.  I have had to make my own yokes for ford 9" and mopar 8.75" rear ends and TH 350 and TH 400 Gm transmissions to accept the GM cv joints.  You will need a lathe and some decent machining skills fot this.sorry 4 the long postMatt
Reply:Are you really seeing even close to 6800 driveshaft rpm's on a demolition car?  I know practically nothing about them other than seeing a little bit on cable tv every now and then.  But, of all the ones I have seen they aren't going very fast, and I can't imagine the driveshaft speeds being that high.  But, now that I know what it's in I will take back my statement about needing to go to a driveline shop!  Surely you could design and build one that will work well for that application - and you can easily add a loop or two to make sure it doesn't come through the car at you if it does fail!
Reply:I say go small square inside a big square, all the travel you want. Trucks(PTO), and AG equipment has been using them for years.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:I run a square driveshaft on my offroad truck, its outlived 2 pinions and 3 u-joints and plenty of rocks so its plenty sturdy. Just get 2.5x.25 receiver tube (2" ID with no weld seam) and 2x.25 square tube.  Cut the yokes off the old shaft, center them and weld away.  Keep it greased, I cut grooves (lengthwise) in mine with the grinder to retain some grease.Have we all gone mad?
Reply:Originally Posted by sn0border88 Keep it greased, I cut grooves (lengthwise) in mine with the grinder to retain some grease.
Reply:Originally Posted by MoparGuy313its going into my demolition derby car, i run the same motors/trannys and rear ends but different makes/models of cars
Reply:Originally Posted by zapsterWithout splines you are going nowhere..Square inside each other works naturally.....zap!
Reply:Ah, but no form of racing is ever cheap.I agree on the 6800 RPM thing. I can't see a DD car doing that RPM at the driveshaft unless you do a REAAALY deep rear axle ratio.Install the rearend upside down. Now you'll have 1 forward and 3 reverse gears. Reverse makes a great hammer.
Reply:Originally Posted by denrepnow.... How do you keep the slip yoke from walking out of the transmission?Interesting that the drive shaft is allowed.Sounds like the parts swapping rules have become more liberal since then!?!In which case; How about an air-cooled diesel, driving a hydrostatic pump, to propel hydraulic wheel motors!
Reply:Originally Posted by TubularFabAre you really seeing even close to 6800 driveshaft rpm's on a demolition car?  I know practically nothing about them other than seeing a little bit on cable tv every now and then.  But, of all the ones I have seen they aren't going very fast, and I can't imagine the driveshaft speeds being that high.  But, now that I know what it's in I will take back my statement about needing to go to a driveline shop!  Surely you could design and build one that will work well for that application - and you can easily add a loop or two to make sure it doesn't come through the car at you if it does fail!
Reply:Originally Posted by MoparGuy313on the drive shaft isssue coming out of the transmission, you drill and tap the splined shaft on the transmission.If i could find someone who had the parts, and knowledge for cheap or a sponsorship i would LOVE to try it, ive thought it would work awesome.Where was this derby at that you watched?
Reply:Originally Posted by MoparGuy313Ive got a built big block mopar 383 with a rear end with 5.33 gears and a 2200 stal con.  in the mud and slop trying to get away from people or hitting people i know ive hit over 7 before
Reply:Here are some pics of the shaft that i mentioned in earlier posts Attached Images
Reply:One more Attached Images
Reply:Iweld that's a nice driveshaft build. Thanks for the pics.I noticed the special high-clearance "export" yokes! "I don't know, that's how I bought it." There are no rules. Are those the new rules?There were some '76 Caprices built with Perkins diesels. If we have the documentation can we run one??Last edited by denrep; 03-02-2008 at 01:34 AM.Originally Posted by denrepIweld that's a nice driveshaft build. Thanks for the pics.I noticed the special high-clearance "export" yokes! "I don't know, that's how I bought it." There are no rules. Are those the new rules?There were some '76 Caprices built with Perkins diesels. If we have the documentation can we run one??
Reply:Thanks for the compliment Denrep   were there really 76 caprices with diesels in them?  Thats really interesting if true.  76 caprices and impallas have got to be my favorite cars to wreck!  Other than 67-73 imperials that is
Reply:Originally Posted by Iweld...were there really 76 caprices with diesels in them?  ...76 caprices and impallas have got to be my favorite cars to wreck!  Other than 67-73 imperials that is
Reply:Originally Posted by denrepThe Chevrolet diesels came up when I was looking for Perkins re-power parts, and  stumbled across a reference to  the original application. This is from memory and I didn't see the cars myself, so take your salt. As I recall, they were '74 to '76 full size Chevrolets. The original engines were replaced with  Perkins 4.236 diesels to be evaluated in taxi fleet service. I believe there were about 150 cars re-powered, and they went to Dallas and New York.  Again - I can't be positive, but I'm pretty sure that's a fairly accurate story of the Perkins/Chevrolet project.The Imperials - ‘66 was the last of the really tough ones;  still had a frame. The Imperials could destroy one car after another, and not suffer any real damage! Some guys used to win several derbies with the same Imperial! The ‘60 -'64 Fords were a distant  second, nothing else really had a chance against those two.  Before the engine swapping was legal, if the Ford could just stay alive long enough, eventually the big 413 would burn itself up, or run out of fuel. Meanwhile the little Fords could still run all night, even  after having the radiator and water pump torn off!What's the toughest thing out there now, maybe ‘99 up Crown-vic?I enjoyed building and running a few cars, rules and inspection used to be strict; welding was a big no-no (unless covered with mud)!  With all the custom parts and reinforcements allowed now, it sounds like a whole new game. Enjoy!
Reply:here is a picture of what i was wanting to make.  A guy sells them for 580 its all tractor stuff im sure.My question to you guys is do you think its going to be too heavy?  ive felt the stuff at TSC before and its gotta be about 40-50 lbs and thats not even with the weight of the yoke or anything
Reply:I'm not worried about weight, and perhaps I'm not really grasping the full scope of the project, but I'd be worried thats too small.
Reply:Originally Posted by EnderI'm not worried about weight, and perhaps I'm not really grasping the full scope of the project, but I'd be worried thats too small.