Genuine Porsche Suspension Auxiliary Spring Coil 99633310503

Genuine Porsche Rear Shock Absorber Auxiliary Spring 99633310503 - 996 Bump Stop

The Genuine Porsche Rear Shock Absorber Auxiliary Spring 99633310503 is the small rubber bump stop that protects your 911's rear suspension from damaging bottom-out impacts. Mounted on the rear shock absorber, this auxiliary spring acts as a progressive cushion: under normal driving it barely engages, but when the suspension compresses hard over a bump, pothole, or under heavy braking, it absorbs the final travel so the damper never slams into its end stops. It is a genuine Porsche part, engineered for the exact compression behaviour the 996 chassis expects.

This part is fitted to the rear shock absorbers of the Porsche 911 (996) range — Carrera, Carrera 4, Carrera 4S, Targa, GT3, Turbo and Turbo S — and is specifically specified for cars with the M030 sport suspension as well as the C4S and Turbo variants. Porsche calls it an auxiliary spring because it supplements the main coil spring in the last part of the suspension travel, smoothing harsh impacts and keeping the chassis composed over rough roads.

A worn or missing auxiliary spring announces itself in several ways. You may hear a harsh metallic clunk when the rear wheels hit a sharp bump, because the damper is reaching its end stop unprotected. Ride quality deteriorates over speed bumps and broken tarmac, and the unprotected impacts can damage the shock absorber internals, the strut mountings, and the dust cover over time. Because the rubber hardens and cracks with age and heat exposure, it is one of the first suspension parts to degrade on a 996 — many owners find the original is crumbling when they finally inspect it.

This genuine Porsche part uses the factory-specification rubber compound and geometry for the 996 rear damper. Unlike universal bump stops, it matches the original length, profile, and progressive compression rate, so the suspension behaves exactly as Porsche tuned it. It slides directly onto the shock piston rod with no modification and works together with the genuine strut bellows and dust protection to keep the damper assembly sealed and operating smoothly.

Fitting is straightforward for a qualified technician during shock absorber service: the old auxiliary spring is removed and the new genuine unit is seated on the damper rod before reassembly. It is common practice to replace both rear units together, and to inspect the accompanying bump-stop hardware while the suspension is apart. Order from European Auto Spares for genuine OEM Porsche suspension components with worldwide delivery.

Specifications

Genuine vs Aftermarket Comparison

Verification note: Compared against genuine Porsche parts catalogue data for 99633310503, cross-checked with fitment listings from design911 and heritagepartscentre (accessed 2026-10-13). Aftermarket behaviour described from commonly reported fitment and durability issues.

Why Choose European Auto Spares

OE Rubber Spec for the 996 Chassis

This genuine auxiliary spring uses the factory rubber compound and progressive compression rate, so the rear suspension cushions exactly the way Porsche tuned it — no harshness, no vague wallow.

Protects Shocks and Strut Mountings

Bottom-out impacts that go unprotected travel straight into the damper internals and mountings. The genuine bump stop absorbs them, extending the life of far more expensive suspension components.

Restores Composure Over Bumps

A crumbling original bump stop is a common cause of rear clunks and harshness on the 996. Replacing it returns the quiet, controlled ride these cars had when new.

Direct Replacement, No Modification

The genuine part slides straight onto the shock piston rod with no trimming or adaptation. Your technician fits it during normal damper service in minutes.

Global Express Delivery

We ship genuine OEM Porsche suspension hardware worldwide with careful packaging, so small precision parts arrive ready to fit.

Complete the Job

When replacing rear bump stops, it is worth inspecting the rest of the damper assembly. See the Genuine Porsche Additional Spring For Shock Absorber 97034330103, the Genuine Porsche Suspension Spacer Plate 99633351102 for the 996, and the Genuine Porsche Shock Absorber Bearing 98133305901 if your strut work extends to the top mounts. For the full range of dampers, bushes, and mounts, browse the Suspension & Steering Parts collection.

Need Help Finding the Right Porsche Part?

Auxiliary springs vary across 996 model years and suspension codes such as M030, and a wrong-spec bump stop changes how the car rides. Send us your complete VIN before ordering and our parts team will confirm the exact 99633310503 application for your 911. We verify compatibility before dispatch so you get the right bump stop the first time.

Keep Your 996's Rear Suspension Protected

Every hard bump is an impact your dampers should never take unprotected. Replace worn rear auxiliary springs with the Genuine Porsche Rear Shock Absorber Auxiliary Spring 99633310503 and restore the quiet, composed ride your 911 was built with. Order today from European Auto Spares and protect your rear suspension the factory way.