Redline Monocog Ovalized Sliding Dropout Fix

Sliding dropouts on a Redline Monocog Flight.

These are sliding dropouts on a 2009 Redline Monocog Flight 29er mountain bike. The problem is this isn't a picture of my Monocog because my dropouts didn't look like this. Mine were bent. I noticed this because my rear wheel had a tendency to not stay aligned. It would move around some and the tire would rub on the chainstays or seatstays. So heres how I fixed this problem. 

The Problem:

Shown in the video is the bent sliding dropout. This extra movement allowed the rear axle and wheel to slide about while riding. I could explain the problem in writing but my 7 second video sums it up perfectly.

The Welding, Forming, Heat Treating Solution:

I came to the conclusion that the slot was ovalized and all I had to do was form it back into its original shape. I spent a few hours messing around with clamps and my bench vise, but I failed. The frame didn't have any parallel sides to clamp on so always slid out. So I did exactly what the title suggests. The solution was:
  1. Weld some small bolts to the outside of the slot close to where it was ovalized the most.
  2. Use the small bolts as a firm place to form the slot back to its original condition.
  3. Remove the bolts.
  4. Heat the dropout to a mild orange color with a propane torch.
  5. Dunk the hot dropout into a bucket of oil for the heat treatment.
  6. Paint the area of the frame that lost its paint. Black!

Note: I don't have many pics from this repair because I did it long before I had even thought of this blog. 

Bolts welded on and ready for forming. Unfortunately
I don't have a picture of it in the vise.

Test fit of the newly fixed slot.
(Not heat treated yet.)

Finished test fit. Also not heat treated yet and again
unfortunately I don't have pics of the heat treatment.

Painted and getting a clear coat.

Finished paint and clear coat.


This repair was a bit extreme but worked well and only took a few hours to complete. I took it out for several rides after this repair and it was a lot better. The sliding dropouts still moved a little on really steep climbs or during hard breaking but it wasn't noticeable and it wasn't enough movement to make the tire rub.

The down side to this repair was risk. Welding and forming part of the frame could have caused a crack or some other unrepairable damage to the frame. It also takes some equipment not everyone has like a welder.

A not so extreme repair would have been to use a Surly Tuggnut chain tensioner. (Link: A Tuggnut costs about $30 and wouldn't have risked unrepairable damage to the frame. Its a great solution and while I did have one in my junk box at the time I never thought to use it until much later.

Finish assembled bike.

Surly Tuggnut chain tensioner.


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