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Endplay is the axial free movement of a shaft — how far the input or output shaft slides forward and back before something stops it. On an automatic it is set by selective washers and thrust bearings, and it is the single best check that the gear train and thrust stack went together in the right order. Too tight and you cook a thrust washer in the first hundred miles. Too loose and you get a clunk and premature wear. The factory window is usually narrow, often something like 0.008 to 0.040 inch depending on the unit and the shaft.
You cannot measure that with feel. You need a dial indicator on a solid base, and most of the bad readings people get come from a cheap magnetic base that flexes, not from the indicator itself. This guide covers what actually matters when buying for endplay work.
What Actually Matters — Four Specs
1. Resolution: 0.001 is the minimum, 0.0005 is better
A standard dial indicator reads in 0.001-inch increments. That is fine for endplay because the spec windows are measured in thousandths. A 0.0005 (half-thou) indicator is nicer for splitting a reading near a limit, but do not pay a premium chasing 0.0001 resolution — you cannot hold a transmission case that still on a bench anyway.
2. Travel: get a full 1 inch
Cheap indicators have 0.25 or 0.5 inch of plunger travel. That is enough for endplay itself, but a 1-inch travel indicator is far more useful: you can preload the plunger to mid-range, you have room to find a clean contact point, and the same tool checks runout, flexplate wobble, and ring gear lash. Buy the 1-inch.
3. The magnetic base is half the purchase
This is where readings go wrong. A weak or flexy base lets the indicator drift as you pry the shaft, and you read base flex as endplay. You want a base with an on/off switch (so you can place it dead and then lock it), a holding force around 130 to 180 lb, and a stiff articulating arm with a single fine-adjust knob. A floppy three-joint arm that needs both hands to lock is worse than no base.
4. Contact point and a way to pry
You need a flat or ball contact tip that sits square on the shaft end, and you need to be able to pry the shaft in and out repeatably — usually two screwdrivers or pry bars under the gear set or against a fixed point. The indicator measures; your prying technique determines whether the number repeats.
How to Actually Take the Reading
- Mount the base to something rigid — the case itself or a bench fixture, not a part that can move with the shaft.
- Set the plunger square against the end of the shaft you are measuring, preloaded about halfway into its travel so it can read in both directions.
- Push the shaft fully one direction, zero the dial.
- Pry the shaft fully the other direction and read the total swing. That number is endplay.
- Do it three times. If the three readings do not agree within a thou or two, your base is flexing or the plunger is not square. Fix the setup, not the number.
Compare the result to the spec window for your transmission and shaft. If it is out, the fix is a selective thrust washer or shim of a different thickness — that is exactly what the measurement is telling you to change.
Typical Endplay Windows
These are representative ranges to show the order of magnitude you are measuring. Always use the service-manual figure for your exact unit and shaft, but this is why 0.001-inch resolution is required, not optional.
| Check | Typical Window | What Out-of-Spec Means |
|---|---|---|
| Input shaft / front unit endplay | ~0.008–0.040 in | Wrong selective washer; recheck thrust stack order |
| Output shaft endplay | ~0.005–0.030 in | Wrong rear selective washer or worn thrust surface |
| Flexplate / converter runout | under ~0.030 in | Bent flexplate or converter not seated |
The Picks
Mitutoyo 2416S Dial Indicator (1-inch, 0.001) — Buy Once
If you rebuild more than occasionally, buy the Mitutoyo. The 2416S is a 1-inch travel, 0.001 resolution indicator with the smooth, consistent plunger action that makes a half-thou reading actually mean something. It is the indicator that does not introduce its own error. Pricier than the import sets, and worth it if measuring is part of your routine.
Check Mitutoyo 2416S
Indicator + Magnetic Base Combo Set — Best Value for One Rebuild
For a single rebuild, a combo of a 1-inch, 0.001 indicator with a switchable magnetic base gets you a real reading for a fraction of the Mitutoyo. The trick is judging the base: look for an on/off magnet (not a permanent magnet you fight to remove), a stated holding force north of 130 lb, and a stiff single-knob articulating arm. The indicator in these sets is good enough; the base is the part that varies.
Browse indicator + base combo sets
Standalone On/Off Magnetic Base — If Your Indicator Is Fine but the Base Flexes
If you already own a decent indicator and the problem is a wobbly base, buy a better base on its own. A 176 lb on/off base with a fine-adjustment arm transforms a struggling setup into one that repeats every time. This is the single cheapest upgrade that fixes inconsistent endplay readings.
Check magnetic indicator bases
Mistakes That Give You a Fake Number
- Base mounted to a moving part. If the magnet sits on something that travels with the shaft, you read zero motion that is really there. Mount to the fixed case.
- Plunger not square. An angled contact tip reads a cosine of the real travel — always low. Set it perpendicular to the shaft end.
- Reading at the end of plunger travel. Indicators are least accurate at the extremes. Preload to mid-range.
- Prying inconsistently. If you do not push the shaft fully to each stop the same way every time, your readings scatter. Three matching readings is the proof you did it right.
- Dirty or burred shaft end. A nick under the contact point adds phantom thousandths. Wipe and inspect first.
Selective Washers and Thrust Parts? Ships Same-Day
When endplay reads out of spec, the fix is a different selective washer, shim, or thrust bearing. Our companion shop gearboxinsider.com stocks thrust washers, bearings, and full rebuild kits to dial it back into the window. Same-day ship on orders before 2pm Eastern, free shipping on every order.
Shop Gearbox Insider →FAQ
Can I check endplay with feeler gauges instead?
Only in the specific spots where the manual gives a feeler-gauge method (some clutch packs, some thrust clearances). True shaft endplay is an axial-travel measurement and needs a dial indicator. Feeler gauges measure a static gap, not movement.
Do I need a 0.0005 indicator or is 0.001 enough?
0.001 is enough for endplay. Spec windows are several thousandths wide; you are not splitting tenths. Spend the saved money on a better magnetic base, which matters more.
Why do my three readings not match?
Almost always the base is flexing or the plunger is not square, not the indicator. Re-seat the base on the rigid case, set the contact tip perpendicular, and pry to a hard stop each direction.
What else can this tool do?
A 1-inch indicator and base also check flexplate runout, converter seating, ring gear backlash, and shaft runout. It earns its keep beyond endplay.