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Bonpora supplies the strut bump stop 1J0412303, a front suspension cushion designed for Volkswagen applications in the 1J0 part number family. Produced in China from micro-cellular polyurethane, the part is aimed at distributors, suspension rebuilders and workshop chains that need a dependable aftermarket source with OEM & custom design support. This guide summarises the specifications, fitment notes and sourcing workflow, and answers the questions buyers raise most often before placing a first order.
A strut bump stop - also called a jounce bumper or suspension bump stop - is the progressive cushion fitted around the piston rod of a front strut. It rarely appears on a service checklist, yet it influences how the suspension behaves every time compression travel approaches its limit. The 1J0412303 reference follows the original Volkswagen geometry: an 18.5 mm inner diameter seats over the strut rod, while the 57.3 mm outer diameter and 53.6 mm free height determine when and how firmly the cushion engages.
In a MacPherson-type front suspension the bump stop sits on the damper rod, normally between the top mount and the dust boot. Under normal driving it stays clear of the strut housing. When the wheel hits a deep pothole, or a heavy load compresses the spring close to coil bind, the bump stop compresses first and absorbs the final part of the travel. This progressive engagement helps protect the damper internals from metal-to-metal impact, reduces the harshness transmitted into the chassis and lowers the risk of damage to the spring seat and top mount. Many suppliers mould the bump stop together with the dust cover as one assembly, which is why suspension kits frequently list the two parts together.
Polyurethane and rubber bump stops degrade gradually rather than suddenly. Typical indicators include knocking from the front axle over sharp bumps, harsher than usual impacts at full compression, and visible cracking, powdering or permanent compression on the stop itself. Because the part is hidden inside the strut assembly, many workshops inspect it whenever a strut, dust boot or top mount is replaced. Fitting a new stop is a low-cost step compared with replacing a damper that has been damaged by repeated bottoming-out.
The table below lists the published parameters for Bonpora reference 4110061.
| Parameter | Value |
|---|---|
| Product Name | Strut Bump Stop |
| OE Number | 1J0412303 |
| Bonpora Nos | 4110061 |
| Fitment | Volkswagen |
| Size | Φ18.5 × Φ57.3 × 53.6 mm |
| Material | Polyurethane (micro-cellular) |
| Country of Origin | China |
| Warranty | 1 year |
| Delivery Time | 15-30 days |
| Packaging | Neutral export packaging |
| Custom Service | OEM & custom design support |
The 1J0 prefix places this bump stop in the Volkswagen parts family used across the Golf IV and Bora platform generation (marketed as Jetta in several markets). Volkswagen revised damper hardware over the production life of this platform, so Bonpora recommends confirming fitment with the full OE number from the original part or from a parts catalogue before ordering. If the number on your sample carries a letter suffix, such as 1J0412303A, send it to our team together with your measurements; we will check whether the dimensions above match that variant or whether a production equivalent is required.
Professional buyers normally source suspension elastomer parts by OE number rather than by vehicle description. OE numbers are specific; vehicle lists are not. The following three-step workflow keeps inquiries efficient and reduces the chance of ordering the wrong variant.
Send the OE number, a photo of the existing part and three measurements: inner diameter, outer diameter and free height. For this reference the expected values are approximately Φ18.5 mm, Φ57.3 mm and 53.6 mm. Matching all three confirms that the stop will seat correctly on the rod and engage at the right point in the travel. The polyurethane bump stop range on this site groups references by application, which is a useful starting point for cross-checking.
Micro-cellular polyurethane is the standard material for modern bump stops because it combines progressive compression with low permanent set. Buyers replacing an original rubber stop should expect a somewhat different stiffness curve; sharing the Shore hardness and free height of a reference sample allows the factory to match the ride characteristic more closely.
For a first order, dimensional inspection and material verification on samples are the practical way to control risk. Bonpora supports sample-level approval before batch production and applies IATF 16949-based process control to volume supply, so inspection records can be requested alongside shipment documents.
Both materials remain common in the aftermarket, and each has a sensible place. Rubber stops are economical for standard replacement work, while micro-cellular polyurethane shows lower compression set, better resistance to aging under ozone and temperature cycling, and a more progressive rate as compression increases. Polyurethane also accepts colour and branding options more readily, which matters for importers building their own brand ranges.
| Property | Conventional Rubber | Micro-cellular PU |
|---|---|---|
| Compression set | Higher | Lower |
| Aging and ozone resistance | Moderate | Higher |
| Progressive rate behaviour | Good | Good |
| Colour and branding options | Limited | Flexible |
Apart from catalogue references, Bonpora develops bump stops and other shock absorber parts from customer drawings or physical samples. The custom workflow covers dimension confirmation, material formulation, hardness matching and pilot production, with neutral or customer-branded packaging. This service suits importers establishing their own suspension programme as well as projects that require batch documentation for each delivery.
Standard supply uses neutral export packaging marked with the Bonpora number 4110061 for traceability; branding can be arranged through the custom parts service. Delivery takes 15-30 days depending on order size and production schedule. A 1-year warranty applies to manufacturing defects, and batch traceability information is provided so deliveries can be matched to production records if an issue arises.
To receive pricing for the 1J0412303 strut bump stop, send the OE number, target quantity and destination port via the contact form on this site. A typical quotation includes unit pricing by volume break, packaging specification and the earliest available production slot, so total landed cost can be compared rather than unit price alone.
The reference belongs to the 1J0 number family used on the Volkswagen Golf IV and Bora (Jetta) platform generation. Because damper hardware changed across model years, verify the fitment against the OE number on the original part before ordering.
Measure inner diameter, outer diameter and free height. For this reference they are approximately Φ18.5 mm, Φ57.3 mm and 53.6 mm. If your measurements differ significantly, the sample is likely a different variant and the OE number should be re-checked.
The standard delivery time is 15-30 days after order confirmation, depending on quantity and the current production schedule. Custom projects may need additional time for material and sample approval.
Yes. OEM and custom design support is available, including branding options on packaging. Standard shipments use neutral export packaging, which keeps goods unbranded for distributors.
