Dirrential pinion float

[Nigel Allen]

During recent maintenance on my roadster, I have identified a potential issue with the differential. There is a noticeable float in the pinion. I have not tried to measure it yet, but the pinion will clunk when moved up and down by hand. A little background:
- It is an IRS from the 2011 mk4, so I think that makes the early version, from T-bird?
- The differential is from Ford Racing and is all aluminum housing.
- It was shipped from FFR with the kit, as we don't have cars with this differential running around Oz.
- My understanding is it was new when shipped, and it certainly looked that way. I don't recall noticeable float when originally installed.
- Total 9,000 miles. Driven with enthusiasm, but not thrashed.

Along with the float in the pinion, oil is weeping from the pinion seal. Still drives fine, with no noises other than the occasional clunk when applying power after a gear change (although TKO is known for this issue also).

As mentioned earlier, these are not a common differential (that I know of) in Australia. Can anyone shed some insight on how to correct the fault, or share where I might find service information? Would definitely appreciate any help.

Many thanks,

Nige

[edwardb]

I can't help you with your specific issue. I have no knowledge or experience. But I can confirm that is not the newer Mustang "Super 8.8" diff now used in the IRS option for these builds. Those first came out in 2015. Definitely has to be the previous T-Bird version. I've seen posts where Mike Forte has sold and perhaps can help support that version. Maybe worth a try. Good luck.

[MB750]

Just based on my knowledge of differentials, the pinion is only supposed to rotate. There should be NO play in any direction. After the pinion crush washer is set, there's 100% contact between the bearings and races, which means the pinion is locked into rotation only.

I would dive in and see what's doing on. No noises doesn't necessarily mean everything's good to go.

[rich grsc]

If you can actually move the pinion side to side then it need to be fixed soon. Sounds like the nut has loosened, very rare, and unusual. It will require the removal of the drive shaft, and then the nut and yoke to replace the oil seal and a new crush sleeve. Find a shop that works on rear ends & transmissions

[Railroad]

You can try to tighten the pinion yoke nut and see what you get. It needs to be tightened until there is no lateral movement.
With the diff assembled, it will be difficult to feel, but the turn resistance with out engaging the ring gear is 25 inch pounds. This is rotating the pinion gear, yoke and all.
If you take all the slack up in the yoke, you should have a little resistance. You should have no in and out slack of the pinion shaft.
Be sure to top off the lubricant.
Watch for leaks, seal may be damaged. Check the yoke after some trips, verifying it is still tight.
good luck,

[CraigS]

I agree w/ Railroad. Remove the driveshaft and tighten the pinion nut. As he says the spec for how tight to make the nut isn't the usual use a torque wrench to X lbs. The technique is usually remove the center diff w/ ring gear so when you turn the pinion that is all you are turning. You tighten the nut some beyond snug and then measure how much effort it takes to rotate the pinion. You are actually tightening the bearings beyond contact so they develope some friction. But that is a bunch of work. As a test, I'd tighten it until it is snug, then maybe 1/6th to 1/4 turn further. See if that gets rid of the slop. If it does, drive it some. If it drives OK for 25 miles, you know what you need to do. It is a fair amount of work, but as rare as that diff is in Oz, I'd buy a pinion seal and do the full procedure. Oh, and download a manual or find youtubes to verify the exact procedure and the exact spec.

[Railroad]

Put sealer on the splines of the yoke and under the flange of the washer nut.
Lube will migrate out otherwise.
If you are not removing the yoke, just under the nut.
good luck,

[Nigel Allen]

Hey everyone, thanks for your input on my dodgy diff. Winter is only around the corner, but this project might get started a little earlier. I recently purchased a 2 post hoist. Testing out the new hoist is how I ended up finding the problem I didn't know I had... :rolleyes: At least it will make the repair easier. Also have a suitable torque wrench for measuring the preload on the pinion assembly.

Cheers,

Nige

[MB750]

Hey everyone, thanks for your input on my dodgy diff. Winter is only around the corner, but this project might get started a little earlier. I recently purchased a 2 post hoist. Testing out the new hoist is how I ended up finding the problem I didn't know I had... :rolleyes: At least it will make the repair easier. Also have a suitable torque wrench for measuring the preload on the pinion assembly.

Cheers,

Nige

Good luck. I actually had fun doing my gears. Getting the preload was the hardest tho. Crushing the crush sleeve had me using a lot of leverage on the pinion nut. I'm talking a breaker bar with a 4' piece of 1.5" exhaust tubing. It also sucks that the first couple full turns of the nut have no impact on the preload because you're just starting to crush the sleeve.

After bearing contact I'd only turn it a tiny bit, then take the wrenches off to test preload with a beam style inch-pound torque wrench. Make sure you spin the whole pinion a few times before checking preload too, just to make sure nothing is hung up.

I'm tellin' ya, it's REEEEEEALLY easy to go past the spec on the bearing preload. If I ever do that again I'm gonna buy that Crush Sleeve Eliminator kit from Yukon Gear.

https://www.yukongear.com/shop/sk-csf8-8

[phileas_fogg]

Hey Nige,

This begs the question of why the nut loosened in the first place. I had a leak in my '88 Thunderbird differential pinion seal, and it turned out that a clogged vent was root cause. With no room for the heat-expanded fluid to go, it pushed the seal out causing a leak. I'm fortunate to have a really good mechanic relatively local, and Forte shipped me a new seal for free ('cuz he's awesome like that) so the repair cost me the price of a tow plus some labor. All of which is a long way of saying, be sure the differential vent is clear!


John

[Jacob McCrea]

All good advice above but I would use a new OEM nut, which I didn't see mentioned.

[ggunter]

If your pinion nut was not loose, it would indicate that your pinion bearings are failing. Here is a very poorly drawn cross section of a pinion with bearings and crush sleeve. As MB750 said its very easy to go passed the recommended preload on the bearings the crush sleeve allows. It's much better to sneak up on it, because once its too tight you need to start over. The crush sleeve only acts as a spacer between the bearings to allow a certain amount of preload. A much better way of obtaining preload is with a bearing spacer and shims. The crush sleeve is only an OEM manufacturing way of doing it cheaply. 212065

[Steve1979]

There is a website by the name of Bad Shoe Productions that might interest you. The owner is Ken Collins and he has put together some videos on rebuilding certain Ford transmissions and rear ends.
On this site, if you click on the 8.8 DVD, you will see near the bottom of the page a short video on setting the preload on an 8.8. He is doing this on a straight axle, but it is the same as an IRS.
While it’s been a number of years since I contacted him with some questions on the 8.8 IRS, he was really good at replying to emails and answering questions if you have any.

Best,

[edwardb]

There is a website by the name of Bad Shoe Productions that might interest you. The owner is Ken Collins and he has put together some videos on rebuilding certain Ford transmissions and rear ends.
On this site, if you click on the 8.8 DVD, you will see near the bottom of the page a short video on setting the preload on an 8.8. He is doing this on a straight axle, but it is the same as an IRS.
While it’s been a number of years since I contacted him with some questions on the 8.8 IRS, he was really good at replying to emails and answering questions if you have any.

Best,

I changed the ratio in an 8.8 solid axle on my #7750 build 10+ years ago. From 3.73 to 3.27. Used the videos from Bad Shoe which were very helpful. I don't remember who suggested it, but I used a Ratech Smart Sleeve Crush 11001 instead of the OE one. It's supposed to be easier to set and better in the long run. I don't know because I don't have anything to compare it to. But it wasn't difficult. I'm not sure how you would set that relatively light inch-lbs torque with the diff assembled though, e.g. ring gear in place.

[tnt_motorsports]

The rolling torque value is for the pinion shaft only and not the complete ring and pinion.

[Railroad]

IMO preload is not that critical. It is sorta like tapered front wheel bearing. Snug it down, get the slack out and have a little drag.
You can put the crush sleeve in a vice and start the crush. It makes it easier to tighten. Make sure you do not distort the inside diameter of the sleeve. It makes it more difficult to put on the pinion shaft.
good luck,

[edwardb]

The rolling torque value is for the pinion shaft only and not the complete ring and pinion.

That’s what I was trying to describe.

[Presdough]

Agreed. When I replace pinion seals I don't replace the crush sleeve. I use a new nut and take it down to zero lash. Haven't had a failure in all my years...

[Nigel Allen]

Many thanks to everyone. I have been on the forum for many years now, and this is the first time I have requested help where I have been uncomfortably out of my depth. The responses have been excellent, and I know as a two finger typist, that they take time to put together, so please accept my gratitude. I understand differential basics, but certainly have never taken tools to one, but am learning fast.

I am wondering if the pinion was potentially incorrectly assembled from the get-go. It is an all aluminum pumpkin (new) from Ford Racing. I cannot recall if I checked for float when assembling the car as it was too long ago. Interestingly, I have had a slight weep from the pinion seal from new. As John (Phileas Fogg) suggested, I did check the breather way back when I first noticed the weep, the flow through the breather was unrestricted. It now makes me wonder if the preload was never correctly set. I was carefull to run the differential in as it was new. As mentioned earlier, it has 9,000 miles total, driven with enthusiasm, but not thrashed.

I think I am more concerned about removing the pumpkin (it was such a b***ard to get in despite being the first item I fitted to the chassis) than I am of fixing the pinion float issue. Would I be right to guess that the pumpkin (T-bird IRS) will need to come out of the car to remove the crown wheel assembly in order correct the issue of preload?

Cheers,

Nige

[Nigel Allen]

If your pinion nut was not loose, it would indicate that your pinion bearings are failing. Here is a very poorly drawn cross section of a pinion with bearings and crush sleeve. As MB750 said its very easy to go passed the recommended preload on the bearings the crush sleeve allows. It's much better to sneak up on it, because once its too tight you need to start over. The crush sleeve only acts as a spacer between the bearings to allow a certain amount of preload. A much better way of obtaining preload is with a bearing spacer and shims. The crush sleeve is only an OEM manufacturing way of doing it cheaply. 212065

Thanks GG for the drawing, I now understand how the crush tube works. I do wonder about the bearing condition. This differential is quiet, loaded / unloaded, hot / cold, and the oil is good. It is almost brand new at 9,000 miles. I am leaning toward incorrect factory assembly.

If I am correct in believing that I will need to remove the pumpkin to remove the crown wheel to set the preload; What is the opinion on tightening the nut in very small increments and measuring the pinion float with a dial indicator as a stop gap measure?

Option 2: If I tighten the nut, can I measure the preload effectively in the small pinion rotation in between the backlash of the gears in the pinion / crown wheel, where there is no load on the pinion? Or am I just a dreamer?

Cheers,

Nige

[MB750]

Many thanks to everyone. I have been on the forum for many years now, and this is the first time I have requested help where I have been uncomfortably out of my depth. The responses have been excellent, and I know as a two finger typist, that they take time to put together, so please accept my gratitude. I understand differential basics, but certainly have never taken tools to one, but am learning fast.

I am wondering if the pinion was potentially incorrectly assembled from the get-go. It is an all aluminum pumpkin (new) from Ford Racing. I cannot recall if I checked for float when assembling the car as it was too long ago. Interestingly, I have had a slight weep from the pinion seal from new. As John (Phileas Fogg) suggested, I did check the breather way back when I first noticed the weep, the flow through the breather was unrestricted. It now makes me wonder if the preload was never correctly set. I was carefull to run the differential in as it was new. As mentioned earlier, it has 9,000 miles total, driven with enthusiasm, but not thrashed.

I think I am more concerned about removing the pumpkin (it was such a b***ard to get in despite being the first item I fitted to the chassis) than I am of fixing the pinion float issue. Would I be right to guess that the pumpkin (T-bird IRS) will need to come out of the car to remove the crown wheel assembly in order correct the issue of preload?

Cheers,

Nige

That's good thinking regarding pulling the pumpkin to do this, but if you used a fixed shim kit (Yukon Gear), or one of those easy crush sleeves (Ratech Smart Sleeve) that work can be done with it installed. If you don't mind doing the labor on your back if you don't have a hoist.

Otherwise, if you go with the OEM style crush sleeve, that's where you'll need Hulk to get er' done and having the whole works out of the car is much easier.

Oh, one other thing to remember... If you go with new bearings and races around the pinion the preload is actually different than with used bearings. Since you've got play, I'll assume you're going with new ones, which means there's slightly more bearing preload per spec. Also with new bearings, it would be wise to check the mesh pattern again as well. And, since you've got the diff out, maybe check the limited slip shims as well if you've been dealing with one-wheel burnouts lately. :cool:

Here's a link to the Ford Performance procedure for doing gears in the 8.8:

https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4209-8.PDF

[Nigel Allen]

That's good thinking regarding pulling the pumpkin to do this, but if you used a fixed shim kit (Yukon Gear), or one of those easy crush sleeves (Ratech Smart Sleeve) that work can be done with it installed. If you don't mind doing the labor on your back if you don't have a hoist.

Otherwise, if you go with the OEM style crush sleeve, that's where you'll need Hulk to get er' done and having the whole works out of the car is much easier.

Oh, one other thing to remember... If you go with new bearings and races around the pinion the preload is actually different than with used bearings. Since you've got play, I'll assume you're going with new ones, which means there's slightly more bearing preload per spec. Also with new bearings, it would be wise to check the mesh pattern again as well. And, since you've got the diff out, maybe check the limited slip shims as well if you've been dealing with one-wheel burnouts lately. :cool:

Here's a link to the Ford Performance procedure for doing gears in the 8.8:

https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4209-8.PDF

Thanks heaps, Matt.

[CraigS]

I'd try your option #2 in a heartbeat. No I don't think you can get an accurate measurement in the backlash play. But I think you can sneak up on it by feeling your amount of float gradually decrease. It is certainly worth a try to see if you are comfortable w/ your results. Maybe comfortable enough to get through this driving season?? Looking at the pics I was able to find I guess you can't get the diff rear cover off w/ the diff in the car. So to do it right, the diff will have to come out. Maybe over next winter?

[MB750]

I'd try your option #2 in a heartbeat. No I don't think you can get an accurate measurement in the backlash play. But I think you can sneak up on it by feeling your amount of float gradually decrease. It is certainly worth a try to see if you are comfortable w/ your results. Maybe comfortable enough to get through this driving season?? Looking at the pics I was able to find I guess you can't get the diff rear cover off w/ the diff in the car. So to do it right, the diff will have to come out. Maybe over next winter?

The way I snuck up on my preload was by cranking down on the nut until the crush washer just started to crush. Then I physically lifted the pinion flange up and down to feel play (the pinion was pointing up, my axle was removed). Using a dial caliper, I could measure how much play there was. I also knew the thread pitch on the pinion was 20 (it's 3/4" x 20), which means 20 threads per inch, or one turn equals 1/20 of an inch (which is 50 thou, 0.050"). I'd do some math to see how many turns would at least close up the play, then I marked the pinion nut and went to town with my impact gun on WFO. Make sure you do NOT go past the number of turns in the nut to eliminate the play. Be advised, it's probably around one full turn so depending on your impact gun, go easy. Short quick bursts, like in Vietnam.

Then when the play is gone take baby steps to get the preload perfect with an inch-pound torque wrench and an extended breaker bar. Also, to keep the pinion flange locked I drilled two holes in a 4' piece of 1.5" angle iron. I had so much leverage on the pinion nut that based on my own power, I'd estimate I was putting down around 400 ft-lbs to get that crush sleeve to compress.

[CraigS]

Matt I did the same 4ft bar on my solid axle diff. It was a little easier since it was in the car so I could let the floor hold the other end of my custom pinion holding tool.

[ggunter]

All tapered roller bearings require preload. Having seen training films for my work at Mack Trucks that showed the reason for this, is, that under load the case that supports the bearings distorts and will let the bearings become loose in the cones they ride in. Any shaft that has a tapered roller bearing on each end is trying to push itself apart by design of the bearing. When you think about it, the ring gear sets in the carrier with a tapered roller bearing on each side. When torque is applied to the pinion, the pinion transmits that torque as a side load on the ring gear. It is trying to push the ring gear out the side of the case. It does this with such force the case will distort and allow the carrier to have excessive play in the bearings, that is why there is a tool to spread the case so shims can be added to gain the proper amount of preload on a rear that has an internal ring and pinion. Of course, a jack pot rear has adjusting rings for setting preload. Preload accounts for this case distortion so the carrier stays slack free and rotates forward without trying to move sideways. Same thing for the pinion. It tries to move forward under load and can distort the case as well but from a different angle. Preload is your friend, but too much preload generates heat and will prematurely wear out your bearings. Preload is measured with an inch pound torque wrench or a fish scale with a string wrapped around the component to be tested to see how many pounds of force is needed to rotate it. Hope this helps.

[CraigS]

For us old folks standard front wheel bearings were a good example of this. They were always tightened to 'take out the slop' and then further tightened something like '1/4 to 1/2 turn beyond that' spec.

[Nigel Allen]

This forum is the best! Thank you to everyone who has reached out with a good post. The support has been excellent. I have been collating the information and it looks like the pumpkin will be coming out shortly for repair. Will give feedback on what is found.

Cheers,

Nige