Pics of my Rotunda pinion depth tool in action

[Stranger in the Black Sedan]

Hi guys, although my previous DIY gear install thread got derailed by a bunch of people who told me I shouldn't set up my own gears, and take it to a "pro", I bought my own Rotunda pinion depth tool set on ebay for $255 and did the gear setup myself. The tool got the pinion depth right the first time (I started the install before I bought the tool. I tried a whole heck of a lot of different depths and pasted each time, then got frustrated, bought the tool, checked depth, installed once, and was done).I did this install in my apartment complex garage, which is not even wide enough to open both doors of the Marauder, using a $100 Harbor Freight shop press. You don't need a lift to do gears, I had the front wheels up on plastic Rhino ramps, and the body supported on the rear frame rails using 2 6 ton huge jack stands. I had a ton of room to work underneath.

Although the Rotunda tool isn't necessary if you know what to look for on a gear pattern, it would take the novice days to try enough pinion shim combinations to determine what the best pattern was. The pattern jumps around a lot with small changes in pinion depth, and then you have to reset backlash (using tons of crappy small shims from Ratech if you are unlucky like me -- buy somebody else's shims if you can, Ratech's were horrible quality) each time. Very very time consuming and frustrating.

The hardest part will be finding the Rotunda tool. It costs over $1200 new and is not available to the public. I only found it on ebay because I was looking specifically for it, and I knew the Ford part # for the kit. I lucked out and got it so cheap because the auction did not identify what the kit was, aside from the part #. You only need a few parts from the kit to do an 8.8, the rest are for the other Ford rears (this thing will come in handy so many times!). The parts are made by OTC/Rotunda for Ford. If you have an "in" with a dealer you can probably order the few parts you need separately. They will still be $$$$.

In case anyone was curious, here is the tool in action.





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda1.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda2.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda3.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda4.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda5.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda6.jpg








http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda7.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda8.jpg





http://homepage.villanova.edu/steven.hylinski/images/Marauder/rotunda9.jpg

The Rotunda tool is basically a dummy pinion gear and carrier gage block. The distance between them is the shim thickness you should need for an ideal gear set. It will only work with Ford OEM gears, and allegedly the FMS gears. The Rotunda takes into account the housing and bearing stackup deviations from what a published setup should measure. It will not correct for a pinion gear that is not machined to perfect specs, which does happen -- Ford ships pinion gears that deviate as much as +/-0.002 from ideal height, although most of the gears that come out of the factory should be very nearly nominal thickness and the Rotunda will be spot on. You can see clearly from the pics why the dummy pinion can not take into account any deviations the real pinion gear will have from nominal thickness, when installed in its place. The factory service manual indicates that the pattern needs to be checked after installing the pinion gear using the thickness shim(s) indicated by the Rotunda tool, and setting the backlash to spec (0.010"-0.012"), and adjusting the pinion shim thickness if the pattern does not look good. In my case, the pattern looked fine, so I put it together. The important part is that the pattern does not run off the tip of the gear, which would indicate too shallow a pinion shim -- there is a strip of clearance shown in the gear paste.

I am very glad I did not listen to the members who told me not to attempt the gear install.

I will definitely use the tool over and over again, since it will do most of the Ford rears. Plus, in my case buying the tool cost less than having someone else do the install for me.

[RCSignals]

Nice tool.

Did you still have the part number?

Of course you can set up a gear set yourself, if you know what you are doing. Having the right tools, particularly this one, is a benefit.

[Richy04]

So in essence,

The "pipe" fits in the carrier bearing channels and the metal block sweeps past it, the machined rings tell you the crush or mesh distance (clearance)that the pinion would be at from the ring?

[magindat]

I SAW and helped use this tool on my FMS gears. It DOES work on FMS gears.

Thanx for the pics.

[Stranger in the Black Sedan]

Richy, you got it. There is a published dimension from the pinion head bearing bore in the housing, to the carrier centerline. If my housing was perfect, and my pinion head bearing was perfect, the Rotunda would take an 0.030" shim in between the carrier pipe lookin thing and the pinion gage block. Mine took 0.024" because of housing and/or bearing differences from ideal.

[Drewstang]

I've changed 2 sets of gears and never once used any special measuring tools. 99% of the time, you don't need to change anything but the ring and pinion. I've never had any noise or issues with either install.

[BigCars4Ever]

I would buy that just to have in my tool collection! Very cool.

[Stranger in the Black Sedan]

Drewstang, that is fine if it worked for you, but my stock pinion shim was 0.028, and the pattern on the new gears looked awful with that shim. I wound up at 0.024 per the Rotunda tool, which gave a good pattern.

If you reuse your old pinion bearing (or your new bearing is exactly the same thickness as your old one), and the new and old gears were both close to nominal pinion head thickness (or both off by the same amount), then you will get away not changing the shim. This is a lot of "if's". Just my new pinion head bearing alone caused a several thousandths change in pinion depth, compared to the old one. They were both Koyo USA hi cap bearings, but they were not exactly the same thickness.

Ford wouldn't include so many pinion shims in a master install kit if you didn't need them.

[pantheroc]

I assume the area at the arrow tips are what your looking for as ideal?

http://www.mercurymarauder.net/showcase/files/2/5/4/4/gears.jpg

[Jon01]

I'm with Drewstang, tons of folks have swapped gears in 8.8's without having to change shims around, just have to use FMS gears. I just made a homemade depth tool to double check using some square tube steel.
Regardless, if I were doing it again and had that tool I'd sure use it.
Glad you got it done and the naysayers didn't beat you down, you can't beat the satisfaction of doing it yourself and knowing it's done right!

[offroadkarter]

I assume the area at the arrow tips are what your looking for as ideal?

http://www.mercurymarauder.net/showcase/files/2/5/4/4/gears.jpg


Yep if the center has the grease smeared off that means its lined up perfect.

[Stranger in the Black Sedan]

Jon I was replacing OEM genuine Ford gears with OEM genuine Ford gears. The stock shim would not have worked. Just the way it went for the housing and bearings I used.

[larryo340]

Jon I was replacing OEM genuine Ford gears with OEM genuine Ford gears. The stock shim would not have worked. Just the way it went for the housing and bearings I used.
I agree
Just swapping gear sets without proper tools I'm sure the car will drive, but the question is for how long without problems. If your building a disposable car for a PINK's episode fine. For the keeper I just wouldn't do it that way. Installing a ring and pinion is not a simple bolt on such as replacing clutches in the OEM carriers.