How to replace the flex coupling on the rear driveshaft of a Land Rover Discovery 1.
A routine inspection of the under carriage of my D1, the flex coupling that interfaces the rear drive shaft to the rear differential was ready to give up. Just hanging there out of habit.
As you can see large cracks, just as bad on the back side.
Ordered a "Flex Coupling Kit" from "Atlantic British"
3 bolts, 6 washers, 3 lock nuts, the flex coupling, and the dreaded centering bushing. (12 in. rule for scale)
Oh, the nerd'er folks!
You will need a total of 6 bolts and locking nuts, and 12 washers, 3 for the drive shaft spider flange, and 3 for the diff spider flange. Before I did anything else, I cleaned the flanges, rear drive shaft, and the u-joint on the front of the drive shaft. After cleaning I marked timing lines across all joints and interfaces along the drive line. I removed all bolts from the flex coupling, plenty of room for a 14mm box end wrench and a 14mm ratchet with a 1.5 inch extension.
Next, I moved foward to the u-joint and removed the 4, 3/8-24" self locking nuts from the parking brake/u-joint interface. Note of caution here: you will not be able to remove all 4 nuts without rotating the drive shaft (parking brake off, truck in netrual) recommend that you get the truck up on four jack stands. If that is not an option make real sure the truck is secure, if using two stands in the back, place it in 4-low, and chauk the front wheels. Like when you are wheel'in, have a spotter!
Ok, everything is loose and hanging on the 4, 3/8-24 studs sticking out of the parking brake drum. You will need to compress the u-joint into the drive shaft untill it clears the studs. Care needs to be taken here, you will swing the u-joint down until it is clear of the brake drum and no farther. Here is why, the u-joint and drive shaft make a really long lever and there is a really small "centering stud" sticking out of the diff. Very easy to knock off center by yanking on the far end of the drive shaft. Instead once you are just clear of the brake drum remove the u-joint from the drive shaft, then you can slide the drive shaft off of the centering stud. Ta Da, the whole mess is in your lap!
Drive assembly. Note the white timing marks.
Centering bushing, you see it just sticking out of the end of the drive shaft. Looks harmless enough!
Here is where you have to get creative, believe it or not there is 0.0015" clearence between the bushing and the bore in the end of the shaft, better known as a "slip fit", so it should just come right out, NOT! If there is any out of roundness between the bushing and the bore they lock up and do not want to seperate. My solution was to dig out the rubber liner, the bushing itself is made of a mild steel, fairly soft. I went and purchased a 3/16" carbide burr, a cutting tool reseller, or hobby shop should have this. Chucked it into my cordless drill motor and carefully cut a groove into the inside of the bushing lengthwise. You do not have to cut through, about half to two thirds of the way through the wall of the bushing will do. Rotate 180 degrees and cut another groove. Set the shaft up onto a block of wood supporting it on the spider flange. With a drive punch and a ball peen hammer strike the part of the bushing that is extended out of the drive shaft, near the groove that you have cut, driving the bushing wall inward. The bushing will start to collapse and tear along the groove that you cut, repeat on the other groove, keep at it, it will give up and come out!
Now's the time to clean everythig up, deburr any dings or nicks. Since you have the u-joint out take a real good look at it, check for slop, does it rotate through it's range of motion smoothly? Check the splines for wear. Check the bore on the diff end of the drive shaft, is it smooth and clean? Check the centering stud on the diff, clean away rust and dirt on all the mating surfaces.
Assembly time, I took a small amout of "never seize" and coated the inside of the bore, and coated the outside of the new centering bushing, set the bushing in place over the bore and lightly tapped the bushing with a soft faced hammer to start the bushing into the bore, always checking for alignment. (I would prefer an arbor press for this, don't have one.) Continue the light tapping until the bushing is half engaged, place a block of wood on top of the bushing and encourage the bushing to go the rest of the way in. It will seat onto a counter bore near the bottom of the main bore, with approx. 3/16" of bushing will protrude from the drive shaft.
I have read some vague articles about the flex coupling haveing a right way and a wrong way of installation. Some say yes, and some say no just bolt it on! I am in the yes there is a right way camp. Here is why. This next photo will show the coupling installed and attached to the rear diff. note on the the outer wall of the coupling aligned with the shiny new nut and bolt is a little arrow pointing foward in the same direction as the bolt that I installed.
If you stop and look at this photo for a moment you will noitce that the coupling is actually made up of three lobes with a thinner web joining the lobes. Each flange leg shares a lobe. There is also a slight off-set to the faces of the lobes, if bolted up incorecctly it would or could intoduce a pre-load into the coupling and warp it. Instant drive shaft vibration or pre-mature failure. So, with that being said this is how I installed the coupling. At test drive time it was very smooth side streets and highway.
U-joint end install.
I just got the whole drive shaft up there and hanging on it's bolts, nothing tight. I then wiggled it around until it looked netrual making sure that all the timing lines were lined up and started to tighten the flex coupling first, for it has the centering bushing and stud. I staggered how I tightened everything on the back end and then repeated the process on the u-joint end. Done, with no extra pieces! Oh, don't forget to fill the splines and gator with grease at the zerc fitting! I hope this is helpful.