RED LINE SKU: 57-6521

Red Line Transmission Oil w/Shockproof - W/ Shockproof 1 QT (12/Case Sold Ea) — Harley-Davidson (1984-2006)

$27.27
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NOT SURE ABOUT FITMENT?

Red Line Transmission Oil with Shockproof is a full-synthetic transmission fluid designed for Harley-Davidson and Indian V-twin engines. It reduces transmission noise, lowers operating temperature, and protects gear teeth with a thicker oil film than conventional fluids.

Features

  • Dampens transmission noise and shifting clunk
  • Reduces transmission operating temperature
  • Thicker oil film between gear teeth
  • Resists throw-off at high RPM
  • Compatible with aftermarket transmissions (Baker, JIMS, S&S)
  • Works with Evolution, Twin Cam, and 6-speed Cruise Drive engines

Specifications

  • Brand: Red Line
  • Manufacturer Part #: 42804
  • UPC: 083522428040
  • Quantity: 1 quart
  • Weight: 2.15 lbs
  • Dimensions: 4 in L × 4 in W × 8.8 in H

Fitment

Fits all Harley-Davidson and Indian Motorcycle V-twin transmissions, including Evolution, Twin Cam, and 6-speed Cruise Drive models. Also compatible with aftermarket transmissions such as Baker, JIMS, and S&S.

Frequently Asked Questions

Will this work in my aftermarket transmission?

Yes — Red Line Transmission Oil with Shockproof is formulated for all aftermarket V-twin transmissions including Baker, JIMS, and S&S.

Does this reduce shifting clunk?

Yes — the Shockproof formula dampens transmission noise and the characteristic hard shifts found in V-twin gearboxes.

How much does one quart of fluid cost compared to conventional transmission oil?

Red Line synthetic costs more per quart than conventional, but lasts longer and improves performance and cooling.

What's the difference between this and Red Line Heavy Shockproof Gear Oil?

This transmission oil is the same fluid as Red Line's Heavy Shockproof Gear Oil — formulated specifically for V-twin transmissions.

Can I use this in my primary or final drive?

This product is formulated for transmissions. Check Red Line's product line for primary and final-drive specific fluids.

BRANDRed Line
TYPEChemicals
SKU57-6521
WEIGHT2.15 lb
Please contact us to confirm fitment for your specific motorcycle, or check the product title for compatibility notes.
CUSTOMER REVIEWS
4.92
229 RATINGS
5★ 210
4★ 19
3★ 0
2★ 0
1★ 0
✓ VERIFIED
Apr 21, 2025

Better be good trans oil for the price

Seems to do the job, only put 10 miles on the bike before i got an email requesting a review. For $25/bottle, it better work!

— DUSTIN R
✓ VERIFIED
Jul 13, 2024

I bought 2 bottles Good stuff

— Lewis H
✓ VERIFIED
Aug 3, 2016

Good stuff

I did my first service on my new road glide and used all red line products. This definetely smooths out the shifting and has made neutral much easier to find.

— Rowdy M
✓ VERIFIED
Nov 20, 2016

The previous owner of my Softail used this product in the gearbox, so I continued, with very favorable results.

— David P
✓ VERIFIED
Feb 20, 2010

Great Stuff!

Great stuff. If you had this stuff in your tranny and it drained out accidentally, you would still get home. Really coats the gears and make shifts smooth. Pink color would let you see it was a transmission leak instead of an oil leak if you had a tranny gasket leak problem. It ain't cheap, but quality stuff isn't. You could probably go 10 K between fluid changes instead of the normal 5 with this stuff. Only downside is that switching from RedLine to another transmission fluid would be messy - it would take a couple of changes before you got all the pink stuff out.<br /><br />PROS: Really Sticky, Pink<br /><br />CONS: Difficult to switch from<br /><br />

— Big Bird B
✓ VERIFIED
Nov 3, 2015

Works Well

Smoothed out shifting noticeably and a really good price, great buy.

— BrooklynHarley B