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Endplay is the axial free movement of a shaft and the geartrain hanging off it, measured between the thrust surfaces that limit it. Grab the input shaft on an assembled automatic and pull it in and out along its own centerline — the total travel you get is endplay. It is set with a selective thrust washer, a selective snap ring, or a shim, and it is checked at least twice during a proper rebuild: once before teardown, and once after assembly before the pump gets its final torque.
Skipping it is the most common corner cut on a home rebuild, and it is why some rebuilt units come back with a converter hub that has eaten the pump bushing at 8,000 miles.
Browse endplay and selective washer kits
Why Endplay Matters
Everything inside an automatic is stacked between thrust surfaces, and every one of those surfaces has to run on a hydrodynamic oil film. Endplay controls whether that film can form.
- Sealing ring position. Drums carry sealing rings riding in machined bores. If the geartrain walks axially more than spec, the rings shift relative to their bores and the apply circuit bleeds — a soft or slipping shift on a unit with brand new clutches.
- Converter hub and pump bushing. Excess endplay lets the hub hammer in and out of the pump. The bushing wears oval, the front seal leaks, and you get a fresh rebuild with a puddle under it.
- Thrust washer survival. Too little clearance leaves no room for oil between the washer and its mating face. The washer wipes, turns blue, and welds itself to whatever it was touching.
One detail worth understanding: an aluminum case grows more with heat than the steel stacked inside it, so endplay opens up slightly as the unit comes to temperature. That is why specs are given cold and why the goal is the middle of the range, not the tight edge.
Typical Spec Ranges
Always use the spec for your exact family and revision from the service manual or a current rebuild guide. These are the ballparks so you know when a measurement is obviously wrong.
| Measurement | Typical range | Set with |
|---|---|---|
| Automatic input shaft / geartrain endplay | Roughly 0.005 to 0.035 in on most domestic 3- and 4-speeds | Selective thrust washer between pump and drum |
| TorqueFlite-family input shaft endplay | Wider than GM, commonly in the 0.030 to 0.090 in region | Selective thrust washer, stepped in roughly 0.012-0.014 in increments |
| Output shaft / rear unit endplay | Often 0.005 to 0.025 in | Selective washer or snap ring at the rear stack |
| Clutch pack clearance (related, not endplay) | Roughly 0.010 in per friction plate as a rule of thumb | Selective pressure plate or selective snap ring |
| Manual box / transfer case bearing preload | Preload, not clearance — measured as rolling torque | Shim stack behind the bearing race |
If you measure something wildly outside the family range — 0.150 in on a unit specced at 0.008-0.030 — stop measuring and go looking. That is a missing washer, a wrong-length shaft, a collapsed bearing, or a stack that is not fully seated.
Measuring Endplay With a Dial Indicator
You need a dial indicator reading in 0.001 in increments, a magnetic base, and a way to move the shaft. Ten dollars of technique matters more than a hundred dollars of indicator.
- Set the unit level with the bellhousing face up. Front pump installed and torqued to spec, converter out. Endplay measured with the pump loose is meaningless.
- Clamp the magnetic base to a machined surface on the case, not on paint or a casting web. Any flex in the base goes straight into your reading.
- Put the plunger square on the end of the input shaft. Off-axis contact reads short by the cosine of the angle. Preload the indicator about 0.050 in so it stays in range in both directions.
- Push the shaft fully down, zero the dial. Then pull it fully up. The needle sweep is your endplay.
- Do it three times. Take the average. If the three readings spread more than about 0.003 in, your setup is moving and the number is not trustworthy.
- Wiggle nothing sideways. Radial movement contaminates the reading. Pull and push straight along the shaft centerline.
Take the same measurement before teardown on the core. Knowing that the unit came in at 0.045 in when the spec is 0.008-0.030 tells you what wore, and it gives you a sanity check on your final number.
Full walkthrough: checking endplay with a dial indicator →Dial indicator and magnetic base sets
Selective Washer vs Shim Stack
These get talked about interchangeably and they are not the same part doing the same job.
Selective thrust washer
A single washer, available in several graded thicknesses, that sits in a thrust position and sets running clearance. You pick one thickness and it lives in the load path, riding on an oil film. Kits typically ship four to seven steps, and the step size is what determines how precisely you can hit the middle of spec — a kit with 0.012 in steps cannot put you closer than about 0.006 in to your target.
Shim stack
Thin shims, often 0.002, 0.005, and 0.010 in, stacked behind a bearing race or a bearing cup to set preload or depth. Shim stacks belong in manual transmissions, transfer cases, and differentials where you are setting rolling torque rather than free clearance.
Do not substitute one for the other. Stacking two thrust washers to fake a thickness is a classic mistake: the two faces fret against each other, one of them starts spinning, and you get metal in the pan. If your kit does not have the thickness you need, buy the right washer instead of improvising.
Measure every washer with a micrometer before it goes in. Selective washers are stamped or color-coded, and both stampings and colors get misread, mixed in bins, and occasionally shipped wrong. A 0-1 inch micrometer settles it in five seconds.
Overhaul Kits and Hard Parts
Gearbox Insider stocks the bushings, thrust washers, bearings, sealing rings, and full overhaul kits for the units on your bench. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →Calculating the Washer You Need
The math is simple and people still get it backwards, so here it is in one line:
New washer thickness = current washer thickness + (measured endplay − target endplay)
A thicker washer takes clearance away. A thinner washer gives clearance back. Work an example.
- Spec is 0.008 to 0.030 in. Target the middle: 0.019 in.
- You assembled with the washer that came out. Micrometer says it is 0.062 in.
- Dial indicator gives an average of 0.041 in of endplay.
- 0.062 + (0.041 − 0.019) = 0.062 + 0.022 = 0.084 in.
- Your kit offers 0.074 and 0.087. Take the 0.087, which lands you near 0.016 in — comfortably inside spec. The 0.074 would leave you at about 0.029, right on the loose edge.
When you have to choose between two steps and neither is centered, favor the one that puts you toward the looser half of the range. A unit slightly loose within spec runs. A unit tight enough to lose its oil film does not, and aluminum thrust surfaces gall long before anything gives you a warning.
Recheck after the swap. Do not calculate a washer, install it, and bolt the converter on without measuring again — a stack that was not fully seated on the first measurement will hand you a different number the second time, and that second number is the real one.
Too Tight vs Too Loose
| Too tight | Too loose | |
|---|---|---|
| What happens | No oil film between thrust faces; the stack is preloaded instead of clearanced | Geartrain hammers axially against its thrust surfaces on every engagement |
| Early evidence | Thrust washer turns blue, wipes, or seizes to its mating face; case bore galls | Front seal weeping, converter hub with a polished band, pump bushing worn oval |
| Driving symptom | Drags when cold, may bind or squeal; overheats under light load | Delayed engagement, soft or slipping shift as sealing rings walk out of position |
| Where it ends | Aluminum transfer, metal in the pan, pump damage | Front pump and bushing failure, then a second teardown |
Both ends fail the same job, and both cost you the same labor twice. Ten minutes with a dial indicator prevents it.
FAQ
Do I measure endplay with the torque converter installed?
No. Measure with the converter out and the pump torqued to spec. Converter installed depth is a separate check and it is done differently.
Can I use feeler gauges instead of a dial indicator?
For clutch pack clearance, yes. For shaft endplay, no — there is no accessible gap to feel. Endplay is a dial indicator measurement.
What if my kit does not have a thick enough washer?
That usually means something else is wrong: the wrong thrust bearing, a missing spacer, or a stack that is not seated. Recheck the assembly before you hunt for a thicker washer.
Does endplay change once the unit is hot?
Slightly, and generally in the loosening direction because the aluminum case grows more than the steel stack inside it. That is exactly why specs are published cold and why the middle of the range is the target.