Driveshaft question

[ask0329]

4-link imca mod. Ford 9" rear. Falcon tranny. Just changed from a 3-link to a 4 over the winter. took it out for practice on tuesday and broke a brand new u-joint. Have a few different suggestions so far but wanted to hear what else people have to say. I have a 31" driveshaft and 5" yoke. Does this sound right or is the yoke too short? When it was a 3 link i ran the same driveshaft with a 4" yoke and had no problems. any opinions welcome.

[Confused?]

There are variables that play into the length, such as distance of the rearend from the back of transmission, and the yoke on the rearend. Is it a long or short yoke. The common lengths are 29" to 30" with an 8" yoke. I like haveing about 2" of exposed yoke sticking out of the tailshaft at a minium.

Also check your pinion angle. Too much can break u-joints as well.

There is a lot more movement with a 4-link than on a 3-link.

[MM90]

My car has a 29.5" driveshaft with and 8" yoke, Brinn trans. The u-joint on the rear end side is also the wide style which I think helps with the higher driveline angles. Now if I put my car on jack stands and let the rear end hang on the chains my driveshaft bottoms out into the tranny. Haven't raced at all this year, tomorrow should be the first night out. Now I know why the guy before me had a block of wood between the LR underail and the rearend when he had it on jack stands. My driveshaft is supposed to be the same as what the guy before me was running so I hope I don't have any issues.

I'm running about 6.5 degrees of pinion angle, my chassis recommends 7-7.5 to start. This is static and just putting a degree wheel on the rearend.

[ask0329]

from what i've been told localy and the reading that i've done in general, if your rear end is at the max 72" back and you have a bert tranny you want a 8" yoke with 31.5" driveshaft. If you have a bert or falcon tranny you want a 8" yoke and 29.5" driveshaft and you will have no problems with it pulling out or bottoming out.

[dirttrackrocker]

My car has a 29.5" driveshaft with and 8" yoke, Brinn trans. The u-joint on the rear end side is also the wide style which I think helps with the higher driveline angles. Now if I put my car on jack stands and let the rear end hang on the chains my driveshaft bottoms out into the tranny. Haven't raced at all this year, tomorrow should be the first night out. Now I know why the guy before me had a block of wood between the LR underail and the rearend when he had it on jack stands. My driveshaft is supposed to be the same as what the guy before me was running so I hope I don't have any issues.

I'm running about 6.5 degrees of pinion angle, my chassis recommends 7-7.5 to start. This is static and just putting a degree wheel on the rearend.



You need a limiter chain on the rear to not let it bottom out. You also don't want your LR upper bar to go past 45*

[JCSullivan00]

We had an issue with a falcon, where the shaft was not splined far enough, and the yoke would bottom out on the shaft inside the transmission.

[dirttrackrocker]

We had an issue with a falcon, where the shaft was not splined far enough, and the yoke would bottom out on the shaft inside the transmission.

I think the newer ones are turned down ahead of the splines. I have an older Brinn and had the same problem. I took the tail shaft out and took it to a machine shop and had it turned down

[MattMitchell]

So with the falcon tranny, and a 8 inch yoke, (6 inch snout) how much should be in the trans?

[MM90]

You need a limiter chain on the rear to not let it bottom out. You also don't want your LR upper bar to go past 45*

Thanks, but I already know this and have them on both sides of the car already. It's an over/under slung rear clip. My only problem is when I have the car on jack stands. I checked it last night and with it on the ground I have about 2" of shaft sticking out of the trans.

[powerslide]

So with the falcon tranny, and a 8 inch yoke, (6 inch snout) how much should be in the trans?

you want atleast 2inches in the trans. so about 4inches out is ok.

MM90 if you set the pinion angle closer to what the chassis builder says it will pull it a little further out(not much but a little lol). Put a jack under the car infront of the driver and jack it up until chain is tight. Does it bottom? What type of pullbar do you have? Take pullbar travel into consideration.

See how far this thing moves?
http://www.youtube.com/watch?v=BqAoMRnNnoU&playnext=1&list=PLE2ABA35D0392CD3D&feature=results_main

[Dirtrunner35]

In my first year with a 4 link I had a stock length yoke

[LFMotorsports]

Worth double checking what torque link spring you are using. I broke u-joints last year (several before figuring it out) that I was getting more wrap in the housing than before. u-joints would bind in the gear yoke and break. Might unhook the torque link and verify how much travel happens before it binds.

Just a suggestion.

[ask0329]

Never thought of the torque link issue. I only have a 600lb spring in there now. Regardless, I picked up an 8" yoke, put it in the tranny 2" and then measured from hole center on yoke to hole center on rear end and came up with 29" each time. Going to have my driveshaft shortened.

[MM90]

Update: Ran the car for the first time Friday night. Ran the driveshaft into the back of the tranny, luckily it was only enough to take out the tailshaft seal. Talked to the previous owner and turns out he ran a 28.5" driveshaft. Taking ours in this week to have 1" taken out of it.

[ask0329]

Know of anyone that makes a 5" od by 4 or 5" height spring for torque link thats 800-900lbs or so? The one in mine is 5" od by 4" tall but only 600lbs. The way my torque link is designed I cant go any larger than 5.5" length.

[powerslide]

Know of anyone that makes a 5" od by 4 or 5" height spring for torque link thats 800-900lbs or so? The one in mine is 5" od by 4" tall but only 600lbs. The way my torque link is designed I cant go any larger than 5.5" length.

Call Afco or hypercoil i'm sure they can set you up with something. Is the spring you have purple?

[ask0329]

Call Afco or hypercoil i'm sure they can set you up with something. Is the spring you have purple?

Nah its a blue spring. I found a couple. Ordered and 1,000 black magic 4" from Southwest speed that may be here friday or saturday. But in case it didnt arrive I ordered an 800lb 4" from pitstopusa that will be here thursday. Atleast now i have two options.

[powerslide]

Nah its a blue spring. I found a couple. Ordered and 1,000 black magic 4" from Southwest speed that may be here friday or saturday. But in case it didnt arrive I ordered an 800lb 4" from pitstopusa that will be here thursday. Atleast now i have two options.

We have USRA rules around here and neither of those were enough for a 4-4 floated car. Not 100% sure on the IMCA hoosier tire but its likely you need 1200 or more. Also the closer to the centerline of the rearend you put that spring the softer the rate will seem.

[ask0329]

Found this amusing. Took the 600lb spring off the torque link and put in a new 800. I have a 1K being delivered today but put the 800 in jus tin case. Anyways, The 600lber, I could squeeze it with my hands and compress it probably 3/4 of an inch. Needless to say that sucker was completely shot.