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A strut bump stop is a small but decisive part of the suspension system. It sits on the piston rod of the strut, inside the dust boot, and takes the last stage of suspension travel so that the piston rod and the top mount never meet metal to metal. This page presents the Strut Bump Stop with OE references 4A0512131 and 4A0512129 and Bonpora No. 4110057, a polyurethane buffer produced in China for the Audi A6, Audi 100, and their Avant and Quattro variants. The sections below cover function, specification, cross-reference guidance, custom supply, and installation notes for importers, distributors, and workshops.
Under normal driving the coil spring carries most of the load and the damper controls the motion of the body. When the wheel meets a deep pothole or a sharp bump, the remaining travel is used up quickly. At that moment the bump stop is compressed between the spring seat area and the top mount region of the strut. Because polyurethane compresses progressively, the part behaves like a secondary spring: soft on first contact, then firm as compression increases. That controlled curve protects the damper rod, the top mount bearing, and the surrounding body structure from a hard bottom-out.
When the stop is missing, cracked, or permanently squashed, the strut bottoms out directly. Drivers usually report a heavy knock over speed bumps, a bouncy or unsettled ride, and extra noise from the top mount. The Audi 100 and early A6 models are mature vehicles today, and suspension buffers on cars of this age are frequently hardened or crumbling. For a workshop, the bump stop is one of the lowest-cost items to renew while the strut is already opened, and for a distributor it is a fast-moving wear part with steady demand.
On the front MacPherson struts of the Audi 100 and the C4-platform A6, the stop slides over the piston rod and sits under the dust boot, above the damper seal area. The OE prefix 4A0512 is listed across the 100, 100 Quattro, A6, and A6 Avant application families of the early to mid 1990s, covering the model years quoted in the parts catalogue. Exact fitment always depends on model year, trim, and axle, so confirm the position and strut design of the specific vehicle before ordering. When in doubt, match the bore, outer diameter, and free length of the removed original part.
| Parameter | Value |
|---|---|
| Product Name | Strut Bump Stop |
| Country of Origin | China |
| Bonpora Nos | 4110057 |
| OE | 4A0512131 4A0512129 |
| Fitment | AUDI A6, A6 Avant, 100, 100 Quattro |
| Size | Φ23 x Φ56 x 90.5 mm |
| Material | Polyurethane |
| Warranty | 1 Year |
| Delivery Time | 15-30 Days |
| Packaging | Neutral Export Packaging |
| Custom Service | OEM & Custom Design Support |
The size note Φ23 x Φ56 x 90.5 mm describes a stepped cylindrical body: a 23 mm inner bore that fits over the piston rod, a 56 mm maximum outer diameter, and a 90.5 mm free length at rest. All three figures matter. The bore must seat on the rod shoulder, the outer diameter must clear the dust boot, and the free length sets the point at which the stop begins to work. Buyers should compare the dimensions against the original part or the vehicle data before confirming an order.
Polyurethane is chosen ahead of ordinary rubber for its resistance to oil, ozone, and repeated compression. It keeps its shape longer under load, which is valuable on vehicles that often run fully loaded or on rough roads, and it is the standard material class for this OE reference family.
Sourcing by OEM number is the fastest route when the original part is still readable. The number 4A0512131 identifies this bump stop in Audi parts listings, and 4A0512129 is a related reference for the same application family; suffix changes of this kind are common when the maker updates a part or assigns a variant to a different production batch. Both numbers point to the same Bonpora No. 4110057, so distributors and repeat buyers can reorder one specification without re-checking drawings. The wider auto parts catalogue groups these references by system and by vehicle model.
If the OE number has worn away, identify the part by vehicle instead: model, model year, engine, and front or rear axle. Supplying the VIN removes ambiguity between trim levels that use different strut hardware.
Beyond standard production, this bump stop can be supplied as an OEM or custom design. Options include tailored polyurethane hardness, adjusted free length or bore, branded packaging, and private-label marking. Distributors serving a defined vehicle fleet often combine several suspension items in one shipment to lower the freight cost per unit. Our suspension parts range lists the components usually ordered together, such as dust boots, top mounts, and spring seats.
For a custom project, send the drawing or a physical sample together with the expected annual volume. Tooling and sampling lead times are quoted separately from mass production, and a first-article sample is normally supplied for fitment confirmation before the production run starts.
Each production batch is checked for bore diameter, outer diameter, free length, and hardness. Visual inspection covers flash, voids, and surface defects that could lead to early cracking. Dimensional records are kept so that repeat orders match the approved sample.
Replace bump stops in pairs on the same axle, and inspect the dust boot, top mount bearing, and spring seat at the same time. A collapsed stop usually means the strut has been bottoming out, so check the damper for oil loss before refitting. Torque the top mount nut to the figure given by the vehicle maker, with the suspension at normal ride height where the design calls for it.
A polyurethane stop should seat fully on the piston rod shoulder. If it does not sit flat it will wear unevenly and may generate noise within a short mileage. On vehicles of this age, corroded related hardware, such as strut mounting components, should be renewed rather than reused.
Typical signs are a hard knock over speed bumps, a bouncy or unsettled ride, and visible cracking, crumbling, or permanent compression of the old stop. If the strut has been bottoming out, inspect the damper for oil seepage at the same time.
This reference is listed for the Audi 100, 100 Quattro, A6, and A6 Avant families of the 1990s, including the model years quoted in the catalogue. Because suffixes and axle layouts vary by market, confirm the model year and axle, or send the VIN for a precise match.
Yes. OEM and custom design support is available, including adjusted polyurethane hardness, modified free length or bore, and private-label packaging. Send a drawing or sample with the target annual volume for a quotation.
Delivery time is typically 15-30 days depending on quantity and whether tooling is required. Packaging is neutral export packaging by default, with branded options available on request. The warranty period is 1 year.
Send us the OEM number 4A0512131 or 4A0512129, the Bonpora number 4110057, the quantity, and the destination port. We will confirm specification, packing, and delivery schedule. For buyers comparing several sources, our full auto parts line covers suspension, steering, and engine components from the same factory.
