Brompton Rear Hinge Replacement

In this week, a 2013 Brompton with excessive play in the rear hinge requiring a rear hinge replacement. Please read on for more information on replacing the rear hinge on most Brompton bicycles. Play can be checked yourself by releasing the catch and rocking the rear triangle from side to side. You will feel movement and may even hear a clicking noise if worn. Acceptable play is a judgement call but generally if you get any more than one millimetre side to side movement at the suspension block, it probably needs attention.

This job calls for a new spindle and bushes to be fitted. Rear hinges are available from outlets such as SJS in standard steel or exotic lightweight titanium for those wishing to shave every gram from their ride.

Starting – The prep-work

As with all jobs, it’s all about the preparation. With the bike clamped into the work-stand, it’s very important to support the rear triangle. Once the first screw is removed, the entire weight of the rear end will be transferred to the other and frame damage can occur. I do this by supporting it from above. If done this way, there is no need to remove the rear wheel or disconnect any cables.

Brompton rear hinge worn
Figure 1

Removing the screws

With prep-work complete, the next job is to remove the two high tensile ¼ inch allen machine screws. This is the hardest part of the job as they are loctited in place. Normally when thread-locker is used on a screw or bolt, heat is applied to soften the compound. However, if you value your paintwork you might want to avoid this. From experience I find one bolt will crack loose but the remaining one will either not budge or just spin with the pin. Your options then are normally left to carefully drilling the old screw out. I have however created a tool that avoids this and speeds the whole job up.

Remove and inspect pin and bushes

Now that the rear triangle is separated from the main frame and securely supported, the hinge pin can be tapped out with a drift. Figure 1 is a good example of a worn one. Notice the wear and pitting to the shaft as well as the dry bearing surface. It is possible to reused the pin if in good condition however generally speaking, it’s replaced as a matter of cause.

Removing the old bushes

Next steps with the Brompton rear hinge replacement is to remove the bearings, or more accurately “bushes” from the frame. The best way to do this is with a 7/16 inch UNC or UNF hand tap (Figure 2). This bites into the old bushes allowing them to be driven out using a drift from the the opposite side. The bore is then cleaned and prepared to accept the new bushes.

Press in the new bushes

The hinge bushes are made of a copped/brass material lined with perforated nylon. Brompton decided nylon was a good choice for this application due to its low friction and reduced need for periodic lubrication. To reduce the risk of damage, they are pressed into the frame using a little grease. The grease helps to seal the shaft and stops water and other dirt from getting in.

Extracting the bushes
Figure 2
New hinge bushes fitted to the Brompton
Figure 3
Reaming the bushes to size
Figure 4
Reaming the bushes to size
Figure 5

Reaming the bushes to size

Now both new bushes have been pressed into place, you’d think it’s just a case of reassembly. Not just yet. Brompton make their bushes ever so slightly undersized so a good tight fit can be achieved. A special hand tool called a reamer used to “shave” just enough of the bushing so the pin passes through without being loose. This stage is critical; remove too much and you will have to throw the bushes away and start again.

Here in figures 4 and 5 you can see reaming of the bushes (this time on a different Brompton). After a few passes, checking the fit of the pin each time until a good fit has been achieved, the pin is installed using a good quality waterproof grease. The rear triangle is manoeuvred back into position and new bolts and washers are always used. Bolts are loctited and tightened to a torque of 10Nm.

Finally a test ride takes place and the bike folded to make sure all is as it should be.

Is your Bromoton suffering the same and needs its rear hinge replaced? Please checkout my Brompton page here for more information on services I offer or get in touch for prices.

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