View Full Version : RotoFlex coupling question

09-15-2004, 12:46 AM
These are the strangest things I've ever seen....obviously I don't have very much experience with British cars.
Can anyone tell me exactly what they are for...why not just a solid shaft?
Second question is how hard are they to replace? Mine are very very cracked and old. The only way I can see would be to separate the outer drive shaft from the wheel hub (excuse me if I'm using the incorrect terms here).
Thanks /ubbthreads/images/graemlins/confused.gif

09-15-2004, 05:33 AM
Hello Mikey,
because of the geometry of the suspension, a solid shaft just will not work. The Rotoflex coupling allows both a hinge movement and axial thrust, i.e. with any deflection of the drive shaft the outer shaft moves away or towards the driven stub shaft.
They can be changed without dismantling the whole suspension, but ensure that you do not remove the steel band that is fitted around a new coupling until it is fitted in place, or it will be almost impossible to fit the bolts through the coupling.
By the way that type of coupling is also used in industry, we have a sanding machine at the factory I work that have Rotoflex's about five times the size of the car version.


09-15-2004, 09:19 AM
Mikey - Pimans right but to put it more simply the solid shaft such as found on the Spitfire and the early GT6's was prone to a nasty little characteristic known as "Jacking" or "wheel hop" - go around a corner a bit too enthusiastically and the outside rear wheel would jump up and down with enough unnerving force to cause your peerless parts to retreat up into your pelvis -

The steel band tip IS very important - If you take the band off it rapidly expands, in fact the Piman's sanding machine may just be outfitted with couplings which were turned loose prematurely.

Seriously tho, When I did my couplings I removed the entire shaft assemblies from the car so I could replace the inboard U-joints along with the Rotoflex - If your couplings are as bad as you say the U-joints are probably worn also. - You must dissassemble the hub to replace the coupling and sometimes this can be a job for a machine shop with a good size arbor press. Taking the shafts OUT is relatively easy, reassembly poses one sticky propostition ( See below)

The only REALLY tough part of reassembly is prying the transverse leaf spring up far enough to engage the spring eye and the vertical link and line up the holes to pass the bolt thru - This can be a bear - If you have access to a Bentley shop manual there is a diagram for build a lever-like device for bullying the spring back in position.

Good luck!

Bob M.

Webb Sledge
09-15-2004, 06:54 PM
One of my first jobs when I started work at the shop was to swap out the Rotoflexes on a GT6, so I know a bit about them. Like Bob said, the hardest part is getting the suspension up, but we created a reletively easy and pain free way to do it. What you need is a piece of 1 inch square tubing (about 2 or 2.5 feet long will do) and 2 large D-shaped brackets. I'm not sure exactly what these are called, but it's a U shaped piece of ~1/4inch round metal, with threaded ends, and another flat piece of metal goes across the open end and is held on with bolts. The whole thing is probably 3 or 4 inches from the top to the bottom of the U. If you hook these D-brackets together and put them on the square tubing, and then put one (the one that's not directly touching the tubing) onto the axle, or leaf spring (I don't recall exactly what part) and then place the tubing on top of the piece that needs to be lifted up, and have someone pull up hard on the tubing, the suspension will compress. Once someone has pulled it up a sufficient amount, get a 2x4 and place it vertically under the tubing to hold it up.

I know that's a horrible explanation of the way we did it, but that was 3 months ago, so I don't remember all the details. I imagine if you look and experiment a bit you'll figure it out. It was done with the car up on jack stands. BE CAREFUL WITH THE TUBING AND 2X4!!!! THERE IS A LOT OF PRESSURE ON IT AND IT WILL SNAP OUT QUICKLY IF YOU HIT THE BOARD OUT FROM UNDERNEATH IT!

09-15-2004, 11:12 PM
Webbs absolutely correct - I tried to sidestep making the correct tool and instead employed a weightlifter buddy of mine to pry on the leafspring with a long prybar - He almost flipped the car off the jackstands and still couldn't get the spring high enough to tilt the vertical link up and line up the bolt!

But being as I'm home now I broke out the jolly old Bentley manual and made a scan of the special tool schematic and the procedure for dismantling and replacing the rotoflex coupling - If you need the full procedure for removing and dismantling the halfshaft assembly and hub email me off forum - email address is available in my profile - and I'll scanit, pan it and send it over. ( Mind you - that's my work email so it may be a few hours before I respond - Manual's at home) ps this is a large file dimensionally if you print it out you'll need 11x17 paper - I'd just zoom in and pan around and take notes!

Good Luck Lad!

Bob M.

09-15-2004, 11:14 PM
Mikey - The scan I sent is what Webb describes in his email -it attaches to the leasf spring and can be held in place by a jack stand - The reason it works is where it attaches to the spring - way out near the end - thusly employing the spring;s attachment to the hypoid unit as an effective fulcrum - trying to use a prybar there's no place to get the corect purchase on the **** spring - So save yourself some skin and aggrevation - BUILD THIS TOOL! - won't cost more than a couple bucks in scrap steel and a little welding.

I looked at the jpeg I attached - may or maynot be good enough quality - If not send me an email off forum and I'll attach some high quality jpeg's to the email and return it to you.

Bob M.

09-18-2004, 11:13 PM
Thanks! you guys are great!!!
I'm going to have to read and re-read these to make sure I understand what you are talking about...my inexperience is showing through.
Man am I glad I found this forum!!