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The strut bump stop 4B0512131B, written as 4B0 512 131 B in VAG parts catalogues, is the rear axle jounce bumper used across the B5 and C5 platforms of the Volkswagen Group. It sits on the piston rod of the rear shock absorber, above the dust cover, and engages only during the final stage of suspension travel. When the rear axle compresses deeply over potholes, speed bumps or a heavy load, this foam buffer absorbs the last part of the movement so that the damper and its internal end stop are not forced metal to metal.
Bonpora supplies this reference under part number 4110038, moulded in microcellular polyurethane with a bore of 12.6 mm, an outer diameter of 61.5 mm and a height of 114.4 mm. The part is produced for the European aftermarket trade, shipped in neutral export packaging and available for OEM and custom design projects. In this guide we summarise the vehicle applications, catalogue data, replacement symptoms and sourcing options for this bump stop, so that importers, wholesalers and workshop buyers can check compatibility before ordering.
A jounce bumper, sometimes called a suspension buffer or compression stop, is made of microcellular foam. In normal driving the wheel travel is handled by the coil spring and the damper. The bump stop engages only near full compression: the foam cells collapse progressively, so the rising resistance feels close to an additional spring rate instead of a hard hit. Because the part works at the end of the travel range, a cracked or collapsed bump stop is often noticed late, usually as knocking noises and accelerated damper wear rather than a sudden failure.
The 4B0 512 131 B reference belongs to the rear axle programme of the VAG B5 and C5 platforms. Catalogue listings from several European aftermarket suppliers place it on the following model series:
| Model | Platform / Chassis | Production Years | Fitting Position |
|---|---|---|---|
| Audi A6 C5 Saloon | 4B2, 4B4 | 1997-2005 | Rear axle, left and right |
| Audi A6 C5 Avant | 4B5, 4B6 | 1997-2005 | Rear axle, left and right |
| VW Passat B5 / B5 Variant | 3B2, 3B5 | 1997-2000 | Rear axle, left and right |
| VW Passat B5.5 / B5.5 Variant | 3B3, 3B6 | 2000-2005 | Rear axle, left and right |
| Skoda Superb I | 3U4 | 2002-2008 | Rear axle, left and right |
Fitment notes: most catalogues list the reference with two pieces per vehicle, one per rear wheel station. Several suppliers additionally allocate this version to vehicles with factory sports suspension, so buyers should confirm the reference printed on the removed part or check the chassis number before ordering in volume. A separate polyurethane bump stop programme covers the adjacent references for standard suspension variants.
For the Audi A6 C5 saloon and Avant, built from 1997 to 2005, the rear suspension uses this bump stop family on both wheel stations. Adjacent references in the same programme, such as 4B0 512 131 N and 4B0 512 131 P, cover later build states and other suspension variants, which is why the letter suffix matters when a customer quotes the number from an old invoice or a used part.
The Passat B5 and the facelifted B5.5, together with their Variant bodies, share the rear axle design with the A6 C5. Aftermarket catalogues therefore list 4B0512131B across the 1997 to 2005 production range of the model series, which makes the reference a recurring line for wholesalers who serve independent VAG workshops.
The first generation Skoda Superb is technically based on the stretched Passat B5.5 platform, and several catalogues list the same rear buffer for it. Some supplier databases also show Audi A4 B6 applications; because the B6 generation introduced a revised rear axle, we recommend that buyers verify the application against the original part number before committing to stock.
The table below summarises the production data of the Bonpora strut bump stop for this reference:
| Item | Specification |
|---|---|
| OE Number | 4B0512131B (4B0 512 131 B) |
| Bonpora Part Number | 4110038 |
| Product Type | Rear suspension bump stop / jounce bumper |
| Material | Microcellular polyurethane |
| Bore Diameter | 12.6 mm |
| Outer Diameter | 61.5 mm |
| Height | 114.4 mm |
| Fitting Position | Rear axle, left and right |
| Quantity per Vehicle | 2, replace in pairs |
| Warranty | 1 year |
| Delivery Time | 15-30 days |
| Packaging | Neutral export packaging |
| Custom Service | OEM and custom design support |
| Country of Origin | China |
A note on dimensions: aftermarket catalogues list replacement heights between roughly 103.5 mm and 113 mm for this OE reference, depending on the supplier. Such differences come from the measuring method, material tolerance and revision level rather than a different application. When in doubt, measure the removed part at rest and compare the values, or send the dimension sheet to our sales team for confirmation before production.
Early bump stops were made from conventional rubber, which hardens and cracks with age, ozone exposure and temperature cycling. Modern references such as 4B0512131B are produced in microcellular polyurethane, a foam material whose cell structure allows progressive compression. Compared with standard rubber buffers, polyurethane bump stops generally provide steadier behaviour across a wide temperature range, better resistance to ageing and a more predictable force stroke curve. For the trade this matters in two ways: fewer warranty claims on a wear part that stays invisible until it fails, and consistent part geometry in volume production, which helps distributors who reorder the same reference for years. Buyers who build a wider suspension range can also review our rebound bumper and suspension buffer programme for adjacent references.
A collapsed or broken buffer no longer cushions the final travel, so the rear axle produces a hard knocking sound over sharp bumps. In many cases the dust cover is damaged at the same time, because the piston rod can contact the cover once the bumper has lost its shape.
During a spring or damper replacement the workshop should always inspect the bump stop. Cracked surfaces, torn segments or foam powder collected on the dust cover indicate that the material has lost its elasticity and should be renewed together with the repair.
Without a working buffer, the damper repeatedly reaches its internal end stop. The result is oil leakage and reduced damping force, which in turn shortens the life of the newly installed shock absorber. Replacing the bump stop together with the damper, and in pairs on the axle, is the cost effective way to protect the repair. Matching shock absorber dust covers are available for the same platforms.
Several European catalogues describe 4B0 512 131 B as the buffer for vehicles with sports suspension on the platforms above. The sports version is taller than the standard buffer, which matches the shorter travel of lowered factory setups. Because the same axle can carry different references depending on the build state, the reliable method for wholesalers is to sort enquiries by the full OE number, not by model and year alone. Our sales team can support chassis number based checks for larger enquiries, and mixed orders containing several revisions of the 4B0512131 family can be produced against a confirmed dimension list.
The 4B0512131 programme contains several revision levels, and the same family appears in aftermarket catalogues under different brand references. The table below lists the numbers that buyers most frequently ask for in connection with this buffer:
| Brand | Reference |
|---|---|
| VAG (OE family) | 4B0 512 131 A / B / N / P, 4B0512137B, 4B9512131 |
| FEBEST | ADSHB-A4IIR-KIT (boot and jounce bumper kit) |
| JP Group | 1152602200 |
| Febi Bilstein | 18376 |
| MEYLE | 100 742 0002 |
| TOPRAN | 110 246 |
| VAICO | V10-6033 |
When a customer enquiry quotes one of the adjacent numbers, first compare the axle position, the suspension variant and the measured height before offering a substitute. If a different revision is required, Bonpora can supply the corresponding version from the same tooling family or quote a custom production run for the specific geometry.
Bonpora manufactures polyurethane bump stops and related suspension components in China and exports to distributors, importers and workshop chains in Europe, North America, the Middle East and Asia. For the 4B0512131B reference we offer:
Beyond catalogue parts, our engineering team develops custom bump stops and buffers from drawings, samples or dimension sheets. Typical projects include adjusted heights for lifting or lowering applications, different foam hardness for load carrying vehicles, and private label production for importer brands. Samples are confirmed against a drawing before mass production, which keeps the approval process short for both sides.
Standard orders are packed in neutral export cartons, ready for consolidation with other suspension references in the same container. Delivery time is 15 to 30 days depending on order quantity and production schedule. Export documents and inspection reports are provided on request, so the goods arrive without additional handling on your side.
To receive a quotation for the strut bump stop 4B0512131B (Bonpora 4110038), send the reference, the required quantity and the destination port to our sales team. Enquiries that include a dimension sheet or a sample receive a drawing confirmation before production starts. Whether you need one pallet or a recurring container programme, the same contact point handles pricing, samples and production follow up.
Request a quote today: send your enquiry for Bonpora 4110038 and our team will confirm price, packing and delivery schedule within one working day.
Both numbers belong to the rear axle buffer programme of the B5 and C5 platforms. The letter suffix marks the revision, and each revision differs in height and stiffness so that the buffer matches a specific suspension build state. Match the reference printed on the removed part; if it is unreadable, compare the measured height with the catalogue data or send the details to us for checking.
Replacing both sides is recommended. The two buffers age at a similar rate, and one collapsed buffer makes the rear axle behave unevenly, which is noticeable in handling and braking. Most catalogues list this reference with a replace in pairs note, and the required quantity per vehicle is two.
On these platforms the buffer and the dust boot work as one assembly, and several suppliers offer them as a combined kit. Bonpora can supply the bump stop and the dust cover as separate references or as a set, depending on your programme, so the workshop receives every part needed for the damper replacement in one shipment.
Standard catalogue references are available in mixed container quantities with a low minimum per reference, which suits distributors who consolidate many suspension parts. Custom designs are quoted after the drawing is confirmed, and the minimum quantity depends on the tooling and the material specification. Contact our sales team with your target quantity for a confirmation of the terms.
