750 FD swap - Torque and no turn

[DGXSER]

I got a 750 FD to install on Thunderstruck. It is from a 79 model. I went to install it today and found that as soon as I put even 40 ft pds of torque on the nut that holds the new washer on, the drive is VERY hard to turn on the wheel and impossible by hand. It was not like this before the washer swap. When I swapped the washer and filled the holes, I did not remove the pinion at all, I just pulled the nut and washer, added some black RTV and put the 1/2" flat washer on and the nut and tightend by hand. Let the RTV set and now when I torque things down it will not turn.

Do I have a bad FD? Did the RTV possibly get into the pinion and screw thigns up? any suggestions are welcome.

[DiverRay]

No the drive is good. You just need to loosen the nut until you can turn the FD easily by hand. I had the same problem the first one I did. The second one, I just tighten down the nut until I just start to feel the resistance. The first drive was set up the same way, and has about 35K on it. I guess it's correct!

[Bigfoot]

Hmmm, wonder if torqued mine down too tight. I made it pretty tight. Guess I will check it next time I replace the rear tire.

[Mr. Schweer]

I don't any first hand experience with this swap, but I noticed that when I rebuilt the front end of my sf that torquing the wheel to stock specs, the wheel was completely locked. Same with the rear wheel. I did the same as Ray, which is essentially the same as setting up a dumb.....er, drum brake front spindle on an older car.
Tighten till it drags, back off 1/8 turn and you're done. Now I'm sure someone's going to chime in and tell me that my wheels will fall off and I'm going to die....but that's what worked for me for what it's worth....

[DGXSER]

OK, Thanks Ray...will do. Thanks for all the input!! Laving for a week trip tomorrow so I wanted to wrap this thing up today.

[DGXSER]

Uggghhh...Ok..I know there is somethign easy I am missing here. Trying to pull the drive shaft out. I can not get a vice grip to grab it, do not own a slide hammer, but do not see how you get ahold of it with one. Any one got a pictorial for the idiots like me on how to pull that thing out. Even Clymers just says "disengage it and pull it out the rear."

Thanks for any help for the uninformed and challenged.

[dbeardslee]

Don - I got mine out by prying with a couple of large screwdrivers. Once the circlip pops off it'll slide right out.

[Schming]

I pulled mine out with the help of tie wire, used for tying rebar,doubled wrapped around the end of the shaft. I left the wire long enough to slide a five to ten pound weight with a hole in to run the wire through over the wire and then wrapped the end of the wire around a wood 2x2. Then using the weight as a slide hammer it popped right out. HTH

[DGXSER]

Got it

After spending hours packing a trailer of food, got home and read the great ideas here. Pulled apiece of 12 ga wire out and locked on with vice grips. few rubber mallot blows and out she popped. Now I just have to find my rubber o-rings back.

The 750FD is still just a bit notchy when I first try to rotate it. After it moves it spins fairly easy, a little noisy but I have almost no gear oil in it. So I am hoping once I get a few miles on it it will even out and run nice. Otherwise, I get to do all this again to put my original FD on. WOOHOO.

[Schming]

Glad You Got The Shaft (out)

To Quote DiverRay if I may; " You just need to loosen the nut until you can turn the FD easily by hand." You just might need to loosen it enough that the notchiness just goes away. I used red locktite on mine when I put the nut back on as an extra measure of security. YMMV

[XJOK2PLAY]

DGXSER...

I've been told by a reliable source how important it is to get that torque just right... too tight and it will work for a while... but eventually spells catastrophe. (That was their experience talking.) They got theirs too tight, and it worked for a few thousand miles... then locked up going down the road.

Not sure I'd rely on the oil to take away the "notchiness" you're describing...

I'd hate to hear that same thing had happened to you.

But many others now have done this swap and know far more than I do about it.

I do know both John & Trbig have done the swap, and love it. Perhaps they can chime in.

Good luck, Don.
Bob

[John]

Chime Chime Chime

I have found it difficult to actually torque the pinion nut back on, because it is difficult to hold the unit still enough to get a decent torque on the nut. I have an impact here at home, so I just zapped it until I felt it was tight enough, and went from there. I don't think that torque value is as critical as having the pinion gear shimmed correctly as to maintain the proper gear lash. If the pinion isn't removed from the housing, and the shims disturbed, then I don't think the torque on the nut is all that critical. After all it has been a few years now, and trbig and Wildkat, just made the I 35 corrider run to Bob Falters house in Iowa, with no problems at all, and I was involved in setting both of those FDs up.

[Paul Kelley]

750 FD swap

Hi DGXSER, I've had my 750 FD in for 3k now and still good. Had same problem with the torque on the pinion, so I went back to turning resistance of the pinion. type 1(750) is 10 to 15 inch lbs. to turn the pinion, unless you put in A new expantion sleeve you won't be able to get the proper torque. At least that is what I've found out.
Keep haven fun Paul

[trbig]

After all it has been a few years now, and trbig and Wildkat, just made the I 35 corrider run to Bob Falters house in Iowa, with no problems at all, and I was involved in setting both of those FDs up.

We (You) put that 750 final drive on when I had a different motor in the bike. I've got somewhere @ 30k miles on this motor since the rebuild with many hard miles and wheelies.. and not a single problem from the final drive done the way John explained.


Tod

[Ivan]

Paul nailed it. There is a crush sleeve between the two timken bearings on the pinion.

The torque value for the nut is assuming the use of a new crush sleeve. Once the sleeve has been crushed, you can not torque it to that value, it will give the bearings too much preload.

As Paul said, the only RELIABLE way to check the pinion preload is to use a bar type torque wrence and measure the inch pound rolling value. After setting enough of them up, I have a "calibrated elbow" that clicks when it is right.

In my experience (lots of car diffs, one XS FD )it seems that the nut is left a tad loose, so make sure the self locking feature is working well on the nut.