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The strut bump stop on a Porsche is the progressive cushion fitted on the damper rod inside the coil-over strut: it compresses during the last part of suspension travel and stops the damper, the top mount, and the chassis from meeting metal to metal. This page covers the Strut Bump Stop with OE reference 996 343 301 02 (99634330102) and Bonpora No. 4110202, a polyurethane front axle bump stop produced in China for Porsche applications such as the 911 type 996 (non-GT3), the Boxster 986 and 987, and the Cayman 987C. The sections below explain how the part works, list the dimensions and material, show how to source by OEM number, describe wholesale supply from a Chinese auto parts factory, outline custom and OEM programmes, and add fitting notes for workshops, European specialists, importers, and distributors buying Porsche suspension bump stops in volume.
The type 996 Carrera, the 986 and 987 Boxster, and the 987C Cayman all use a MacPherson strut at the front axle. In normal driving the coil spring carries the vehicle weight, while the damper controls how quickly the body moves over the road. When the front wheel drops into a deep pothole, clips a kerb, or hits a sharp seam in the tarmac at speed, the available travel is used up in an instant. At that point the bump stop is compressed between the damper rod and the top of the strut. Polyurethane compresses along a progressive curve, so the part behaves as a secondary spring: soft on first contact, then progressively firmer. That staged ramp takes the final phase of the impact and shields the damper rod, the top mount, and the surrounding body structure from a hard bottom out.
Porsche parts catalogues list this item as a shock absorber additional spring or auxiliary spring, alongside the more common description of bump stop. Because the 996 platform carries a flat six close to the front axle and the Boxster and Cayman run a mid engine layout, the front dampers work through a short stroke and rely on that cushion to stay within their travel. On a sports car that is driven briskly on mountain roads or entered in track day sessions, the front stops are compressed far more often than on a family saloon. Once the buffer cracks, crumbles, or takes a permanent set, the damper reaches the end of its stroke unaided. Drivers report a sharp knock over expansion joints, a sudden harshness at the front end, and body movement that no longer settles after a bump. Many worn stops are only discovered when the strut is removed for a damper or top mount job.
Catalogue listings for 996 343 301 02 cover the Porsche 911 type 996 in Carrera 2, Carrera 4, and Carrera 4S forms from 1998 to 2005 (GT3 models use a different specification), the Boxster 986 from 1997 to 2004, the Boxster 987 including the 987 MKII from 2005 to 2012, and the Cayman 987C and 987C MKII from 2005 to 2012. The part is fitted to the front strut, one piece per side, so a complete front axle refresh takes two units. Some Porsche parts diagrams also show this reference in a rear axle position on certain derivatives, which is why application should always be confirmed by chassis type, model year, engine, and axle position rather than by model name alone. Sending the VIN or the chassis number to the supplier removes nearly all ambiguity before a quotation is prepared.
| Parameter | Value |
|---|---|
| Product Name | Strut Bump Stop |
| Country of Origin | China |
| Bonpora Nos | 4110202 |
| OE | 99634330102 |
| Fitment | Porsche |
| Size | Φ21xΦ57x81 |
| Material | Polyurethane |
| Warranty | 1 Year |
| Delivery Time | 15-30 Days |
| Packaging | Neutral Export Packaging |
| Custom Service | OEM & Custom Design Support |
The size listing Φ21 x Φ57 x 81 mm describes a long, slim front stop: a 21 mm bore that slides over the damper rod or the dust cover core, an outer diameter of about 57 mm, and a free length of 81 mm. On this platform the free length matters as much as the bore. A stop that is too long preloads the suspension, reduces available travel, and can lift the front ride height, which changes corner weighting and steering feel. One that is too short lets the damper bottom out early and pushes the impact straight into the top mount and the body. Because Porsche revised damper and top mount details across the production life of the 996, 986, and 987 families, measuring the removed original part, or comparing bore, free length, and outer profile against the catalogue entry, remains the safest way to confirm a match.
Polyurethane is chosen ahead of ordinary foam or rubber because it resists oil, ozone, road salt, and constant compression cycling far better. It holds its shape under sustained load, which matters on a sports car where the front dampers are worked hard under braking and through fast direction changes, and it stays consistent in hot and humid climates where foam buffers tend to crumble early. For a distributor selling into the Porsche aftermarket, where customers expect a suspension overhaul to last, the longer service life of polyurethane also means fewer warranty claims and more stable repeat demand on the same part number.
Sourcing by OEM number is the most reliable route when the original marking is still legible. Porsche prints the number in the 996 343 301 02 format, and the same reference also appears in catalogues as 99634330102 and 996.343.301.02. All three identify one Bonpora No. 4110202, which means distributors and repeat buyers can reorder a single known specification without checking drawings for every order. For mixed orders that span several systems, the auto parts catalogue groups references by system and by vehicle model, which shortens the quotation workflow considerably.
If the OE number has worn away, identify the part from vehicle data instead: chassis type (996, 986, 987, or 987C), model year, engine size, axle position, and damper type. A photograph of the removed part beside a steel rule, together with the VIN, lets the supplier confirm the match before shipment. Workshops and specialists that service several Porsche generations can consolidate their bump stop stock under Bonpora numbers, keeping one part code per application and simplifying reordering across a mixed customer base.
This bump stop is manufactured in China for wholesale distribution. It runs as a catalogue item, which means tooling already exists, dimensions stay stable between production batches, and pricing is structured for carton, pallet, and container quantities rather than single piece retail. Typical buyers include Porsche specialists and independent workshops, European and North American importers of suspension and rubber components, distributors serving the classic and modern Porsche aftermarket, and online sellers who need a dependable source for a fast moving German application. The suspension and rubber parts range from the same production site covers the companion items usually renewed at the same time, such as strut mounts, dust boots, and spring seats, so a container can be built around complete front axle refresh kits instead of single references.
Orders ship in neutral export packaging by default, so goods arrive ready for relabelling under the own brand of the distributor. Delivery time is 15 to 30 days depending on order volume and production scheduling, and the warranty period is 1 year. For first time customers, sample quantities can be arranged before a bulk commitment, so fitment can be verified on a real vehicle before the container is booked.
Each production batch is checked for free length, bore, outer profile, and material hardness. Visual inspection covers flash, voids, and surface defects that could lead to early cracking in service. Dimensional records are kept per batch, so repeat orders match the approved sample rather than drifting over time. That batch level traceability is one of the reasons the part can be offered with a 1 year warranty for export markets, and it lets a distributor answer technical questions from workshops with confidence.
Beyond the catalogue part, the same production line supports OEM and custom design work. Available options include tailored polyurethane hardness, adjusted free length, bore, or outer profile, coloured material for brand recognition, branded packaging, and private label marking. Specialists who prepare track oriented cars sometimes request a firmer compound or a shorter free length to suit a specific damper and spring combination, while distributors building a complete suspension kit usually combine several references in one shipment to reduce freight cost per unit. For a custom project, send a 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.
Replace front bump stops in pairs, one per side of the axle, and inspect the dust boot, the top mount, and the spring seat at the same time. A collapsed or crumbling stop usually indicates that the damper has been bottoming out, so check the strut assembly for fluid loss before refitting, and replace the dust boot if it is split. On the 996, 986, and 987 families the stop sits directly in the load path of the front suspension, so torque the top mount fasteners to the figure given by Porsche for the specific chassis type and confirm that the stop is fully seated on the rod before the wheel goes back on. A wheel alignment after reassembly is standard practice on these cars.
A polyurethane stop should seat flat on the rod shoulder or the dust cover core. If it does not sit flat, it will wear unevenly and may generate noise within a short mileage. Because the buffer works behind the dust boot, a light coating of the grease specified for the application makes future removal easier and reduces the chance of squeaking. When the car is used on track, the stops should be inspected at every damper service, since repeated hard compression accelerates wear.
Catalogue listings for 996 343 301 02 cover the Porsche 911 type 996 in Carrera 2, Carrera 4, and Carrera 4S forms from 1998 to 2005, the Boxster 986 from 1997 to 2004, the Boxster 987 including the 987 MKII from 2005 to 2012, and the Cayman 987C and 987C MKII from 2005 to 2012, at the front axle, one piece per side. GT3 derivatives use a different specification. Confirm the application by chassis type, model year, engine, and axle position, or send the VIN for a precise match before ordering.
Typical signs are a sharp knock over expansion joints and potholes, a sudden harshness at the front end, and visible cracking, crumbling, or permanent compression of the old stop. Because the stop sits on the damper rod behind the dust boot, it should be inspected whenever a front strut is removed. If the damper has been bottoming out, check for fluid seepage at the same time, since a failed buffer often shortens damper and top mount life.
Both names describe the same component. Porsche parts diagrams often list it as a shock absorber additional spring or auxiliary spring, while the aftermarket and workshop trade generally call it a bump stop, jounce bumper, or strut bumper. All of these terms point to the progressive cushion fitted on the damper rod inside the strut assembly.
Yes. OEM and custom design support is available, including adjusted polyurethane hardness, modified bore, free length, or outer profile, coloured material, and private label packaging. Send a drawing or a sample together with the target annual volume to receive a quotation and a sampling schedule.
Delivery time is typically 15 to 30 days depending on quantity. Packaging is neutral export packaging by default, with branded options available on request, and the warranty period is 1 year. Sample quantities and mixed container loading with other Porsche suspension parts can be arranged for new customers.
Send the OEM number 99634330102, the Bonpora number 4110202, the quantity, and the destination port, and the sales team will confirm specification, packing, and delivery schedule. Buyers comparing several sources can review the full auto parts line, which covers suspension, steering, and rubber components from the same factory under one catalogue.
