Cab shake while tracking comes down to four candidates: a failed excavator cab mount, the shock rubber between the track frame and the car body, wear in the undercarriage itself, or hydraulic pulsation. The noise will not separate them. What the shake follows will.
You track across the yard and the cab starts hammering against the frame. Stop, and it settles; track again and it comes straight back. No fault code, no leak, nothing visibly broken, and the machine still earns its keep.
So you keep going. That is the trap, because a loose cab is a safety item, not a comfort item, and the part that holds it down costs a fraction of what a moving cab damages around it.
Here is how the trade names the part, how to narrow four causes by when the shake shows up, how to inspect the mounts in one session, and what to send a supplier so the first order is right.
Key Takeaways
- What the shake follows is the strongest clue. Engine RPM and track speed are different faults.
- Owners say "cab mounts"; parts books say "Mount As.". Searching "cab shock" finds the wrong industry.
- Timing sorts the four causes: tracking only, idle only, or a working hydraulic function.
- Loose cab fasteners are a safety problem. Use your manual's torque figure, never a forum number.
- Before ordering, send the model, the serial range, and a photo of the mount with a measurement.
What the Part Is Actually Called (And Why the Search Word Matters)
Search a parts site for "cab shock" and you get car dampers. Search "cab mount" and the results make sense, because that is the word the trade uses.
Machine owners and mechanics write "cab mounts", or just "mounts" when the machine model is already in the sentence. That is the wording in a Forum4Farming thread titled "Mini digger cab vibrates when tracking", where the advice given was to check "the cab mounts in case one or all are loose or the rubber has let go."
Parts books and OEM catalogues take the other route. They list the complete part as an assembly, abbreviated "Mount As.", with a part number underneath. Same object, different label, and the catalogue side holds the number that lets a supplier confirm fit in a single reply.
Two trade-adjacent words are worth avoiding. "Cab shock" and "cab isolator" barely appear in workshop conversation; they belong to engineering write-ups and to other industries, and they send a search into the wrong category of part.
| Search term | Who uses it | What it actually returns |
|---|---|---|
| cab mount / cab mounts | machine owners, mechanics, forum posts | the right part on most aftermarket sites |
| mounts | the same people, shortened | the right part when a machine model is included |
| Mount As. | parts books, OEM catalogues | the assembly and the part number you need |
| cab shock | almost nobody in the trade | automotive dampers, wrong category |
| cab isolator | engineering text, other industries | little you can order |
The part number is the language both sides understand. Come with a number plus a machine model and the conversation takes one exchange.
When Does It Shake? Sorting Four Causes by Timing
A cab mount: the rubber isolates the cab from frame vibration.
Timing does most of the diagnosis, and measuring it costs nothing but attention. Before you touch a spanner, answer two questions: does the shake follow engine RPM or track speed, and does it appear while a hydraulic function is working?
Those answers separate the four candidates, because each one is driven by a different rotating or pulsing source. A thud that repeats once per track revolution comes from the undercarriage. A shake that stays with the machine while it stands still comes from the engine side or the cab mounting. A shake that appears only when a function moves oil is not about rubber at all.
| When it shakes | What it points to | First check |
|---|---|---|
| Tracking only, thud speeds up with the track | undercarriage: track tension, rollers, idler | track tension per the machine manual; lift one side and spin it |
| Tracking only, heavy bang on rough ground, felt through the whole machine | track frame shock rubber | the rubber cushions between track frame and car body |
| Idle, standing still, felt through the floor and seat, cab working against the frame | cab mounts | mount fasteners and rubber at every mounting point |
| Idle, engine visibly moving, cab shaking with it | engine mounts | rock and lift the engine to check it |
| Whenever a function works, follows engine RPM or load | hydraulic pulsation, pump coupling | listen at shutdown, then check the pump coupling |
| A rattle at a certain RPM with no real shake | resonance, hardened rubber, loose panel or glass | compare cold and warm, then look for chafe marks |
Loudness tells you little. A separated cab mount bangs harder than failing track frame rubber.
Shake Only While Tracking: Track, Rollers and Shock Rubber
Roller shock absorption rubber. A failed one feels like a cab fault from the seat.
When the shake appears only under travel, the cab is usually a victim rather than the cause. The cab bolts to the upper structure, which sits on the car body, which rides on the undercarriage. Fix the bottom of that chain and the shake at the top tends to leave with it.
Track tension comes first, using the figure and the procedure in your machine manual. Too tight loads the idler and the sprocket; too loose slaps the track frame and lets the track climb the sprocket teeth under load. Either way, the rhythm reaches the cab floor.
Rollers and the idler come next. A flat spot, a seized bearing, or a badly worn roller knocks once per revolution, and the knock speeds up as you track faster. Lifting one side and turning the track by hand is the cheapest test you have, if you stay clear of anything that can drop.
The third candidate is the shock rubber between track frame and car body, and it gets mistaken for a cab fault because the operator feels it in the seat. When that rubber separates from its steel plate, the two sides meet metal on metal.
One difference in feel separates the two. A failing cab mount shows up through the floor and the pedals, because the cab itself moves against the frame. Failing track frame rubber arrives through the whole machine at once, and it worsens on rough ground, not at a particular engine speed. The HeavyEquipmentForums thread "Cab shake while tracking", started by a CAT 305E2 owner, describes the cab version; the track frame and roller shock rubber range covers the other.
Shake at Idle With the Machine Standing Still
If the cab moves while the tracks are still, the undercarriage is out of the picture, and the question becomes whether the engine or the cab is moving. Watch from outside the cab while someone runs it up to the speed that shakes it, and look at the gap between cab and frame.
When the engine visibly rocks and the cab shakes as a passenger, the engine mounts are the suspect. Grabbing the engine and trying to rock it by hand is the classic field check, and the engine mount range covers that side of the problem.
When the engine sits still and the cab moves, you are looking at the cab mounts. The failure is rarely dramatic: a rubber block gone hard and shiny instead of dull, a crack running all the way through, or rubber lifting off the steel plate it was bonded to.
There is also a version that is not a rubber failure at all. A loose fastener, or a shim that has fallen out, lets the cab move with nothing cracked or perished. Check the hardware before assuming the rubber is finished, because a serviceable-looking mount with a missing nut behind it rattles just the same.
Hardened rubber explains the "cab rattles after 3000 hours" complaint on equipment forums. Nothing has split, so nothing looks wrong in a photograph. The rubber has stopped absorbing, so the vibration that used to disappear into the mount now travels into the cab, the door, and the glass.
Shake While Digging: Hydraulic Pulsation Is the One People Misdiagnose
A machine that shakes while the bucket is loaded and the tracks are standing still is not shaking because of the undercarriage, and often not because of rubber either. Something in the hydraulic circuit is pulsing, and the pulse travels through the frame into the cab.
Two tests narrow it. Does the shake arrive only when one function moves, so that using the boom produces it and swinging does not? Then look at that circuit, not at anything structural. A pulse that tracks engine RPM instead comes from the drive side of the pump, which brings the pump coupling into the picture, and a failed coupling announces itself with a knock when you shut the engine down.
Do not skip this test because you have decided the mounts are the problem. Replacing cab mounts to cure a hydraulic pulse leaves you with new mounts and the same shake.
How to Inspect Cab Mounts in One Session
Ten minutes of preparation saves a second order. Park on level ground, lower the attachment, shut the machine down, isolate the battery, and let it cool.
- Photograph the cab-to-frame joint at every mounting point before you touch anything; you will want those photographs for the supplier later.
- Clean the area, then read the rubber: cracks through the full thickness, rubber lifting off the bonded steel plate, a surface gone hard and glossy instead of dull.
- Check the fasteners. A missing nut, threads showing where a nut used to sit, or a rust streak from the joint all mean the joint has been moving.
- Test for movement at each point with a pry bar, gently, per the manual's procedure. If the cab moves where the rubber should hold it, that mount has stopped working.
- Compare corners side to side. A collapsed mount shows as a change in the gap at that corner.
- Torque the fasteners to the figure in your machine manual on refit, and replace anything stretched or badly corroded.
- Track the same route you started on. If nothing has changed, you have ruled out the mounts for the price of an afternoon.
A single failed mount is worth replacing by itself, on one condition: check the others while the machine is apart. A cab resting on three healthy mounts and one collapsed one loads the frame unevenly, which is how the second failure starts.
Why a Loose Cab Is a Safety Problem, Not a Comfort One
Operators live with cab shake because the machine still digs. That reasoning holds right up until you look at what moves when the cab moves.
Rubber mounts are the joint between cab and machine, and the fasteners through them carry the cab's weight. When those fasteners loosen or the rubber collapses, the cab shifts on the frame. The shift loads parts that were never designed to flex: control linkages, wiring harnesses, heater and air-conditioning lines, and door and glass alignment. Chafed wiring and a leaking line are the mild outcomes.
On machines where the cab structure is part of the operator protection system, the mounting is how that structure attaches to the machine. A joint that moves is a joint putting load somewhere else.
Torque values and inspection intervals belong to your machine's manual, not to a blog post, because they change with the model, the fastener size, and whether the thread is dry or lubricated. Look up the figure for your machine, and treat any number from a forum as a story about somebody else's machine.
One more thing worth naming: do not fix a loose cab with a solid spacer, a stack of washers, or a weld. Removing the rubber removes the isolation, and the vibration it absorbed moves into the cab structure. You trade a shake you can diagnose for cracks you cannot.
Matching the Right Excavator Cab Mount Without a Second Order
Cab mounts are listed by machine, not by the words buyers usually search.
Machine model alone is not enough, and the buyers who order correctly have worked that out. In a parts-identification thread on r/heavyequipment, a buyer listed what he sends to get a part confirmed: "machine model plus serial range / OEM number, part number, or casting/tag photo / old part photos and key measurements". That list takes ten minutes to assemble.
Serial range matters because manufacturers change mounting hardware mid-production without renaming the machine, so two excavators wearing the same badge can take different mounts. A part number, a tag photograph, or a casting mark survives every one of those changes, which is why a supplier asks for it first.
Photographs do a job that words cannot. Cab mounts come in several physical forms: a plain rubber block, a bonded rubber-and-steel sandwich, or a studded mount with a thread on each end. A photograph of your old part answers questions about form, stud thread, and height that a description gets wrong, so lay a ruler next to the part and count the mounting points on your own machine.
If you already have the number, the OEM cross-reference catalogue is the fastest place to check fitment, and model pages such as Komatsu PC200 parts show which rubber parts share a machine.
What to Expect From an Aftermarket Cab Mount
Aftermarket cab mounts are replacement parts for the original rubber, and they carry no affiliation with the machine manufacturer. The brand name on your machine tells you what the part fits, not who made the mount, so judge the part on its own.
Fit is verifiable before you buy. Ask the supplier to confirm the stud thread, the height, and the stud or hole spacing against your old part. A mount that is dimensionally right but built for a different load behaves differently in service, so ask what the rubber is and how it is bonded to the metal.
You may hear a supplier quote a durometer number. Plenty of buyers do not know what the word means, which is worth admitting. A durometer reading describes rubber hardness, and on its own it says little about how a mount behaves, because bonding and shape do as much work as hardness does. Ask how the figure was measured, and on which part of the mount.
Ask how the mount is sold, too. Some listings are a single mount, some are a kit for one cab position, and some include fasteners.
Frequently Asked Questions
What are excavator cab mounts called in a parts book?
Parts books list the complete part as an assembly, usually abbreviated "Mount As.", followed by a part number. Machine owners and mechanics say "cab mounts" or just "mounts". They are the same rubber part, so if a search for "cab mounts" comes up empty, search the model with the part number.
Why does my cab shake only when I am tracking?
Because the source is below the cab. Travel brings the undercarriage into play: track tension, rollers, the idler, and the shock rubber between track frame and car body. A shake that appears only in travel comes from the running gear.
How can I tell cab mounts from engine mounts?
Watch the machine at the speed that shakes it. If the engine visibly rocks and the cab moves with it, the engine mounts are the suspect. If the engine sits still and the cab moves against the frame, it is the cab mounts.
Can worn cab mounts cause a rattle at idle?
Yes, and hardened rubber is the usual reason. A mount that has gone hard no longer absorbs engine vibration, so it travels into the cab structure, the door, and the glass. Nothing looks broken in a photograph.
How do I find the right cab mount for my machine?
Send the machine model with the serial range, the OEM or part number if you have one, a photograph of the old mount next to a ruler, and the measurement across the mounting points.
Is a loose cab mount a safety issue or just uncomfortable?
It is a safety issue. The mounts and their fasteners hold the cab to the machine, so when they loosen or collapse the cab shifts on the frame and loads control linkages, wiring, and fluid lines that cross the joint.
Do aftermarket cab mounts fit as well as OEM?
Fit depends on the individual part, not the category. A correctly specified aftermarket mount that matches the stud thread, height, and spacing bolts up like the original. Verify those dimensions with the supplier first.
Can I just tighten the bolts and keep working?
Sometimes, if the rubber is still serviceable and only the fastener has loosened. Torque it to the figure in your machine manual and watch the joint. If the rubber has hardened, cracked, or separated from its plate, tightening will not restore the isolation.
Where to Go From Here
Work in this order: note what the shake follows, rule out hydraulic pulsation, check the undercarriage, and only then judge the mounts. That sequence costs one afternoon and stops you ordering parts for a fault you do not have.
If you take one thing from this, take the measurement habit. Write down the engine speed or travel condition that triggers the shake, photograph the old part against a ruler, and record the model and serial range before you call anyone. That is what gets the right part on the first delivery.
And one honest exception. If your machine is a small carrier with a one-piece cab and the shake appears only above a particular engine speed with no movement at the mounting points, you are chasing resonance, not a failed mount. New rubber will not fix that, and the money is better spent on the panel or glass that is rattling.
If you want the fitment confirmed before it ships, send the model, the serial range, and the photograph to the ShengFeng wholesale desk. The cab mount range shows what we hold, and if your number is not listed, the catalogue cross-reference usually finds it.
Rubber parts shown here are aftermarket replacement parts. They are not affiliated with, endorsed by, or produced by any machine manufacturer. Brand and model names are used only to describe fitment.
Reading Next
- Excavator Vibration at Idle: How to Tell If It's the Engine Mounts, how to separate mount shake from cab shake before you order a part.
- Why Your Excavator Clunks When You Shut It Down, the shutdown knock, a different failure with a different warning sign.
- OEM vs Aftermarket Excavator Rubber Parts: What Actually Differs, how to check a cab mount supplier before you buy.
- How to Measure Excavator Rubber Parts Without a Part Number, how to identify a part when the number is gone..
- Excavator Hydraulic Pump Coupling Sizes: How to Find Yours, how the size and family codes work, and how to read them off your old coupling..
- When to Replace Excavator Shock Absorption Rubber (And When Not To), how to tell a failed cushion from a shake that comes from somewhere else..