First HC post: How to measure length of driveline after front spring flip

[slickrock]

First time HC poster, long time lurker.

I flipped my front springs (4" SUA + .5" shackle sits level with my rear SOA stock flat springs) and need to lengthen my driveline. This is for a 73 FJ40 See sig below for info.

From what I can gather and searching, I only need about 1" of spline compression in my front driveline. In that case, to get the proper length to extend the D/L, I take the ride height and subtract 1" and that should be how long my new shaft should be from the surfaces of the T-case and axle. I am not using a minitruck yoke, I am retubing my stock shaft and will make another for a trail spare.

1" seems like very little compression, but this appears to be what peois suggested. I wanted confirmation. Should I leave more than 1" compression?

Thanks.

[Mace]

You do a Shackle reversal?

[slickrock]

No I didn't do a reversal. Didn't want to do it with this rig.

[Dusty]

Dan its probably easier to just go ahead and link that thing rather than mess with the driveline. And do an engine swap. And get a new stereo. AND THIS POST IS USELESS WITHOUT PICS!!!

[bustanutley]

Since you are SUA and not SR there is no thought that needs to take place. Measure flang to fange and take that number and your shaft to your driveline guy. done. Visualize the path your axle travels thru its articulation, the drivshaft will not change length much thru its motion with your setup:(up the axle moves forward, down the axle moves backward.

[slickrock]

I am building the shaft myself since it only spins in 4 low when I need the front locker to engage and goig less than 10 MPH. Most of the time, 2 low with the rear locker works fine. I figure I will measure flange to flange and subtract an inch so I will have an inch of up travel. Sound right?

[slickrock]

I know this has gone over many times, but to actually test to see if I have enough slip on my extended drive line, I need to find something good to flex my rig on. Easy enough, but most likely I will be doing it by myself and since I can’t see under my rig to see if I run out of slip and would therefore ram my DL into my Tcase, I will not know to stop compressing the shaft.

I could therefore destroy my TCase testing to see if my DL is long enough without access to a spotter. SO I need your help. I read and reread threads about lengthening DLs and it was a varied response. I went with an inch and a quarter on an SOA rig. It is a stock driveline that I extended so it still has the original Yoke length.

Will this be enough or should I pull it and give it two inches?

I can’t afford to test it and have it destroy my T-case.

How much compression does a DL actually need? I know it needs a lot more extension, but the up travel is less.

[Mace]

shackle reversal or not?

pull the driveshaft. Measure static, Go drive on a rock and measure. Drive the other tire on a rock and measure.

that should give you a good comparison..

[slickrock]

No SR. I am afraid to flex it without someone looking at my shaft while doing it. Wish I could train my dog to be a spotter, but no luck.

[bustanutley]

use a fork lift or hoist..

[slickrock]

true that, now to track one down. I have an engine hoist, but it doesn't go high enough to cycle my suspension.

[Isotel]

there has got to be a Loading dock, or Mound of dirt, or something around your neighborhood that you can flex on, Ive got a nice one across the street from my house