Shop All Transmission Parts →
Endplay is not optional. Set the endplay wrong on a rebuild and you either wear the thrust washers to copper in a few thousand miles because there was too much, or you burn a bushing and cook the fluid because there was none. The service manual gives you a number in thousandths of an inch, and the only way to hit it is a dial indicator on a base that does not move. A tape measure and a feel for it does not get you there.
Two questions decide what to buy: what resolution does your tightest spec need, and where do you have to mount the indicator. Resolution picks the indicator. Mounting picks the base. Most rebuilders get the indicator right and then cheap out on the base, which is exactly backwards.
The Measurements You Are Taking
Endplay (Input Shaft / Assembly)
How far the input shaft or the geartrain moves fore and aft. You mount the indicator to read the end of the shaft, pry or push the assembly one way, zero the dial, push it the other way, and read the total travel. The spec is usually a few thousandths to a few tens of thousandths, and you correct it by changing selective washers or shims.
Shaft Runout
How much a shaft wobbles as it rotates. You put the indicator tip on the shaft, spin it, and watch the needle sweep. Excess runout means a bent shaft or a bad bearing. Runout is a total-indicator-reading measurement, so you care about the full swing, not one direction.
Converter Hub / Pilot Runout
How true the converter hub or pilot runs. A hub that runs out will chew the pump bushing and seal. You clock the indicator on the hub, rotate the converter, and read the sweep before you ever install it.
All three want the same two things: a base that stays put and an indicator with enough resolution to see the spec. The measurement you take least often, converter hub runout, is the one most people skip and then wonder why the pump seal leaked.
Resolution and Travel — The Numbers That Matter
Buy an indicator whose graduations are at least ten times finer than the tolerance you are checking. If the spec is 0.005 in to 0.025 in, a 0.001 in indicator reads it fine. For finer runout work, a 0.0005 in indicator earns its keep. Travel (range) matters too: too little travel and the plunger bottoms out before you finish the measurement.
| Task | Typical Spec Range | Indicator Resolution | Travel Needed |
|---|---|---|---|
| Input / assembly endplay | ~0.005-0.040 in | 0.001 in | 0.5-1.0 in |
| Shaft runout | ~0.001-0.010 in TIR | 0.0005-0.001 in | 0.25-0.5 in |
| Converter hub runout | ~0.003-0.010 in TIR | 0.001 in | 0.25-0.5 in |
| Pump / bushing checks | Varies by unit | 0.001 in | 0.5 in |
A 0-1 inch, 0.001 in resolution dial indicator covers the vast majority of transmission work. Step to 0.0005 in only if you do a lot of runout work where the last half-thou matters.
The Options Worth Comparing
0.001 in Dial Indicator, 0-1 in Travel — The Workhorse
A standard AGD-style dial indicator with 0.001 in graduations and one inch of travel is the tool that reads endplay on almost every unit. Get one with a lug back and a revolution counter so you do not lose track of full turns. Under $30 buys a perfectly usable one for hobby and independent-shop work; the plunger action is what separates good from junk, so look for smooth, drag-free travel.
Check 0.001 in dial indicators
Magnetic Base with Fine Adjust — Do Not Cheap Out Here
The base is where measurements go wrong. A weak or floppy magnetic base drifts while you pry on the assembly and you chase a number that is really the base moving. Buy a base with a strong on/off switchable magnet (look for a high pull rating), a rigid articulating arm, and a fine-adjustment knob so you can dial in preload without wrestling the whole arm. This matters more than the indicator itself.
Check magnetic bases
Dial Indicator and Magnetic Base Combo Kit — Easiest Start
A combo kit pairs a 0.001 in indicator with a magnetic base and the contact points in one box, and for most people setting up to rebuild it is the fastest, cheapest way to get everything that fits together. Just confirm the base is a real switchable magnet with a fine adjust, not a token weak magnet thrown in to pad the kit.
Browse indicator and base kits
Digital Dial Indicator — Fast Zero, Easy Read
A digital electronic indicator zeros with a button, switches between inch and metric, and is easy to read under a work light with tired eyes. It is a genuine convenience for endplay work where you zero, push, and read. The trade-offs are batteries and that the cheapest digitals can be less repeatable than a good mechanical dial, so buy a reputable one if you go digital.
Check digital indicators
How To Actually Measure Endplay
The tool only helps if you set it up rigid and read it consistently. The steps people get wrong:
- Mount to something that does not flex. Clamp the magnetic base to the case or the bench, never to a part that moves with the assembly you are measuring.
- Set the tip square. The contact point should sit as close to parallel with the direction of travel as possible. A cocked tip reads short.
- Preload the plunger. Bring the indicator into the shaft so the needle moves a quarter turn before you zero. If the plunger is at the end of its travel it cannot read one direction.
- Push firmly and consistently. Pry or push the assembly fully one way, zero, then fully the other way. Uneven force gives you a different number every time.
- Read the whole sweep for runout. Endplay is total travel; runout is total indicator reading over a full rotation. Do not confuse a one-direction reading for the total.
What Goes Wrong — Five Failure Modes
- Weak base drifts. The magnet is not strong enough or the arm flexes, and you are measuring the base moving instead of the shaft. The most common bad reading.
- Plunger bottomed out. No preload, so the indicator only reads one direction and you undercount the endplay.
- Cocked contact point. The tip is not aligned with the travel direction, so every reading is short by a cosine error.
- Lost a revolution. Without watching the small revolution counter you read 0.015 when it was really 0.115. Use an indicator with a clear rev counter.
- Grit under the base. A chip or a smear of ATF under the magnet lets it rock. Wipe the mounting surface clean before you clamp.
Need Parts? Ships Same-Day
Once you have the endplay number, you need the selective washers, thrust washers, and shims to hit spec. Gearbox Insider stocks the thrust washer sets, bushings, and rebuild kits that dial it in. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →FAQ
Do I need a 0.0005 in indicator or is 0.001 in enough?
For endplay on almost every transmission, 0.001 in is enough — the specs are in thousandths. Step up to 0.0005 in only if you do a lot of shaft or hub runout work where the last half-thousandth changes your decision.
Why does everyone say the base matters more than the indicator?
Because a perfect indicator on a floppy base reads garbage. If the base drifts a couple thousandths while you pry, your endplay number is wrong no matter how fine the dial is. Spend on a rigid, strong-magnet base.
Can I use one indicator for endplay and runout?
Yes. A 0-1 inch, 0.001 in indicator on a good base handles endplay, shaft runout, and converter hub runout. You just read total travel for endplay and total sweep over a rotation for runout.