Installing Sargent EM-5 Backrest on OEM Seat (w/ pictures)

2508 Views 14 Replies 6 Participants Last post by Chucho, 3 mo ago

jmcwhirter

Discussion Starter · Jan 17, 2022

This is spawned out of an earlier thread in this forum, asking about backrest options for the RT -
Backrest Options for an RT

In that thread, I and others were intrigued with the Sargent backrest, but Sargent claims that the EM-5 is only compatible with their seat pan, not the OEM pan. roadriderg posted with pictures of his Sargent seat with the backrest, and the OEM seat. It seemed pretty clear that the seat pans are identical except for holes needed to attach the backrest.

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OEM seat at left, Sargent at right. Note the six holes in the Sargent seat - only four are needed for backrest installation.

Encourged by this photo I contacted Sargent by email, and asked if there were any differences between their seat pan and the OEM pan (other than the holes), explaining that I was interested to modify my OEM seat pan to work with the EM-5. In particular I wondered if there was anything structural inside the Sargent pan related to supporting the back rest bracket. Sargent's reply was

HI Jim!

While I can see trying this on an OEM pan, other than the material difference between the OEM and Sargent seat pan, our seat isn't different in this area, I must inform you we cannot be held responsible for any alterations or damages you do to your OEM seat in trying this. We have not created instructions for this process to be mounted to the OEM pan. Please do keep in mind that the locking nut plates circled in the photo below must be used. These are the re-enforcement to help distribute the weigh across a broader area of the pan.

Hope this helps.

The "locking nut plates" he refers to will be clear in photos to follow. It seemed a pretty simple modification, and based on the above response I felt it was a risk I was willing to take, so i pulled the trigger and ordered the EM-5.

In that previous thread, I posted that I was going to move forward with this and would post later on the installation experience - here we are.

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jmcwhirter

Discussion Starter · #2 · Jan 17, 2022

Here is what came out of the box when I received the EM-5

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The plastic bag contains the previously mentioned "locking nut plates" and four M8-1.25 screws

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The installation is very straightforward - if you have the holes that the Sargent seat has. You put the bracket on the front of the seat pan, push the screws through that and the holes in the seat pan and screw them into the nuts that are spot welded (!) into the plates. I added the "!" because I question the robustness of this design - I'll get to that later.

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jmcwhirter

Discussion Starter · #3 · Jan 17, 2022

Note that there are four bolts, four nuts - and five holes in the bracket and in the Sargent seat. I have no idea what the "middle" hole is for - there is zero reference to it in the documentation. So all you need is four holes, as illustrated in this image from roadriderg (my annotations)

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jmcwhirter

Discussion Starter · #4 · Jan 17, 2022

Sargent could clearly make a "kit" for modifying the OEM seat, with a template for locating the holes. But in the absence of that, I used the backrest bracket as the template. I positioned the bracket and then clamped it in place, and used a 5/16 drill bit (close enough to 8mm) to drill through the pan.

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jmcwhirter

Discussion Starter · #5 · Jan 17, 2022

And this is where I made my mistake, and pretty much the rest of this will be me recovering from the mistake (which I did). What I failed to do was to listen to roadriderg's advice (in previously mentioned thread), where he said (in regard to modifying the OEM seat pan for this) "When drilling the hole slightly ease each side of the hole." I didn't really understand what he meant by that - but I do now. Note the holes in the Sargent seat pan, below. Note that they are not perfect, round circles, but rather shaped more like an ellipse:

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There is a reason for this, and I now realize this is what roadriderg was refering two when he said to "ease each side of the hole". But I am an experimental physicist (retired) who likes making things and making them precise, so not listening to what roadriderg tried to tell me, I drilled the four holes almost exactly 8mm in diameter to just fit the M8 bolts, with no room for adjustment. And then I tried to attach the "locking nut plates" and ran into the problem. Which I solved - but honestly not the easiet and best way. Read on.

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jmcwhirter

Discussion Starter · #6 · Jan 17, 2022 (Edited)

Boldly moving forward, thinking I was nearly done, I put the bolts through the mounting plate from the front - so far so good!

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In the above image, note how close the bracket comes to hitting the seat pan protrusions, where the two yellow circles are drawn. This is where, in my opinion, Sargent screwed up the design. And this has nothing to do with OEM vs Sargent seat pan. The bracket really inteferes with that bit of plastic, and if (as I did) position it so that the bracket it is ~1-2 mm shy of riding up onto that protrusion, then you have the following problem when you turn the seat over and try to attache the support brackets on the back side:

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Note that the rectangular plates holding the nuts are no longer rectangular. I had to grind them down on my bench grinder to get them to fit without interfering in the highlighted area (below);

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jmcwhirter

Discussion Starter · #7 · Jan 17, 2022

It is a matter of what you define as the starting point. I started with locating the bracket as low as I thought it would go without interfering with the plastic "tabs" on the seat. But note this picture (again) form roadriderg, showing his Sargent seat pan with that bracket removed. You can see that the bracket is actually interfering with the plastic tab (yellow circles), to the point that it has sort of notched away some of the plastic.

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So - what you should do (what I wish I had done) is to

1) When you drill the four holes, be sure to "..ease each side of the hole", i.e., make the hole oblong, top to bottom, to give up/down play for when you push the bolts through. It is plastic - not hard to use the drill bit to enlarge the hole. Then,

2) take as your starting point the position of the back mounting plates - place them as high as you can up towards the ridge that runs along the seat pan (area I had to grind off), and then

3) attach the bracket to the front of the seat, push bolts through and tighten up - making sure back plates are as high as possible and not caring to much if the main bracket digs into the plastic tabs (as shown in yellow circles above).

If I had followed this procedure it would have been a simpler, cleaner installation. But in any case it worked, and three months in I am happy with the backrest. I had a Best Rest backrest on my previous RT (2008) and I liked it, but I am liking this Sargent design even more. It is more substantial - offers greater support.

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jmcwhirter

Discussion Starter · #8 · Jan 17, 2022

Here are my complaints with the design (and again - I am overall happy with the backrest; I'd do it again but with above changes). And these comments are general and in my opinion not specific to my installation on a non-Sargent seat pan.

1. The bracket and the backing plates clearly are poorly designed in terms of fitment. So frustrating - a few mm of material removed here or there would make a huge difference. It is clear form roadrdierg's photos that this same issue exists w/ the Sargent seat pan.

2. The backing plate design - I question it. I think I said earlier that the nuts were spot welded to the brackets; actually I'm not sure that is correct - more like they are stamped into the plates. And several of them came out while I was installing! The intent of the backing plage is to distribute the forces across a larger area, to minimize local stress in the plastic seat pan. For that to work, the force needs to be transmitted from the bolt to the nut and then from nut to the backing plate and then distributed across the seat pan over that contact area. But if the nuts are just stamped in, they are not well-engaged with the plate and the force transmission from nut to plate is not guarunteed. Bad design. Whey they did not use a simple plate with through holes and a couple nuts with washers - I have no idea. The bolts would have to extend a bit more through the back side for this, but there is is room - I checked. I will inspect my installation periodically and if there is any sign of stress failures due to forces being centralized around the nut-seat contact area, I will get some longer bolts and make my own backing plates using bar stock, adding through holes and connecting with washers and nuts.

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Shma1

· #9 · Jan 17, 2022

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Here is a picture of mine installed on the OEM passenger seat. Overall, it was an easy 30 minute install.

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jmcwhirter

Discussion Starter · #10 · Jan 17, 2022

Shma1 said:
Here is a picture of mine installed on the OEM passenger seat. Overall, it was an easy 30 minute install.

Curious about your experience drilling the holes: Did you have any issues with fit tolerance of bracket and supports like I ran into? I think it must have been a tight fit if all seat pans are the same?

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LIRider

· #11 · Jan 17, 2022

jmcwhirter said:
Here are my complaints with the design (and again - I am overall happy with the backrest; I'd do it again but with above changes). And these comments are general and in my opinion not specific to my installation on a non-Sargent seat pan.

1. The bracket and the backing plates clearly are poorly designed in terms of fitment. So frustrating - a few mm of material removed here or there would make a huge difference. It is clear form roadrdierg's photos that this same issue exists w/ the Sargent seat pan.

2. The backing plate design - I question it. I think I said earlier that the nuts were spot welded to the brackets; actually I'm not sure that is correct - more like they are stamped into the plates. And several of them came out while I was installing! The intent of the backing plage is to distribute the forces across a larger area, to minimize local stress in the plastic seat pan. For that to work, the force needs to be transmitted from the bolt to the nut and then from nut to the backing plate and then distributed across the seat pan over that contact area. But if the nuts are just stamped in, they are not well-engaged with the plate and the force transmission from nut to plate is not guarunteed. Bad design. Whey they did not use a simple plate with through holes and a couple nuts with washers - I have no idea. The bolts would have to extend a bit more through the back side for this, but there is is room - I checked. I will inspect my installation periodically and if there is any sign of stress failures due to forces being centralized around the nut-seat contact area, I will get some longer bolts and make my own backing plates using bar stock, adding through holes and connecting with washers and nuts.

I felt the same way on item #2 when I installed the Sargent seat & backrest that I purchased from a forum member about a year and a half ago. Never felt all that comfortable putting a great deal of stress on the backrest because of it. That said, I've noticed no issues with the seat pan that I could attribute to improper bracket support either. I know it's a short time to pass judgement though. I may make some of my own modifications at some point after we settle into our new home in NC ... moving is hard

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Shma1

· #12 · Jan 17, 2022

jmcwhirter said:
Curious about your experience drilling the holes: Did you have any issues with fit tolerance of bracket and supports like I ran into? I think it must have been a tight fit if all seat pans are the same?

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I didn't have any fit issues with the bracket. I just lined up the bracket, marked the holes and used a 5/16" bit. It bolted right up. I tightened it up snug to where there was no movement. My RT is a 2021 maybe the oem passenger seat is different from yours or maybe they changed the bracket.

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roadriderg

· #13 · Jan 18, 2022

jmcwhirter said:
Curious about your experience drilling the holes: Did you have any issues with fit tolerance of bracket and supports like I ran into? I think it must have been a tight fit if all seat pans are the same?

Sent from my iPad using Tapatalk

Nice install pictures👍

Happy riding😊.

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anandkrish1

· #14 · Apr 23, 2022

Thank you so much for the detailed pictures and guidance. I have a 2015 RT and have been looking for a good backrest to go with the OEM seats and this was the perfect. Followed your guide and made the 4 holes slightly oval vertically and was able to install it without any grinding or collision on the rear seat. Love the LT forum for this exact reason!!!!

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Chucho

· #15 · 3 mo ago

Thanks for the detailed instructions. I just finshed the install on my 2019 RT with zero issues. Drilled "elongated" 5/16" holes, installed the back mounting plates with no need to grind, tightened the bolts, and that's it - about 20 minutes total, including a cup of coffee.

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