GSX-R Torque arm mounting

[aviationfred]

I know there has been discussions in the past about the forward mountain of the GSX-R torque arm. I have had 3 FJ's with the GSX-R rear wheels. I am currently working on my 1990 model and re-doing some of the work from previous owners. The forward end of the torque arm has a bearing installed. It also has to rubber washers/dampners that are used on each side of the bearing. I use a 1/4" standoff between the right side of the bearing and the main frame. The lower foot peg bolt hole is threaded completely through the frame. I use a bolt that extends through the bearing and spacer about 1/4 of an inch. I coat the threads with blue loctite and tighten until snug.This has worked very well on my 1989 and 1995. It should work perfectly on the 1990.

Number 21 in the photo is the rubber washers and they are still available from Suzuki
Fred

[MACHV]

So you've done 3 of these conversions and mounted that torque arm like that in all of them and had no issues whatsoever with breaking bolts?

[ZOA NOM]

I've done it twice without issue.

[aviationfred]

So you've done 3 of these conversions and mounted that torque arm like that in all of them and had no issues whatsoever with breaking bolts?

I use brand new Stainless Steel bolts and with an estimated 50,000 mile between the 3 bikes not a single one has broke.


Fred

[FJmonkey]

FYI, not all SST bolts are the same strength. Did you use a particular brand or SST type? Looking at McMaster Carr they have 18-8 at 70,000 psi, a 316 at 110,000 psi and  A286 at 160,000 psi. If it was from the hardware store then I would assume the 18-8 or softer.

[MACHV]

So you've done 3 of these conversions and mounted that torque arm like that in all of them and had no issues whatsoever with breaking bolts?

I use brand new Stainless Steel bolts and with an estimated 50,000 mile between the 3 bikes not a single one has broke.

I figured.
I got sent into a minor conniption when I found out those peg hole bolts were breaking for some guys, because I had JUST finished the the wheel mod and complete rear end tear down. Ended up building a steel bracket to put the bolt into a double-sheer to be safe.


Fred

[fj-f3a]

Fred

As you have mentioned, this topic has been discussed in detail.

http://www.fjowners.com/index.php?topic=18973.msg192131#msg192131and

Please take note of the comments in this post by woodcreekpeet and myself.
I also understand that allot of FJ riders have done this mod, but, to me, that does not make it correct.
Under heavy breaking on a bumpy road, the amount of force transmitted to this bolt is enormous.

I suggested later in the above Post that one consider making an Offset Torque Arm and personally, I still think this is the best and safest option.

IMHO

Gavin

[aviationfred]

The following is my opinion on the function and operation of the torque arm when mounted to the FJ using the foot peg bolt hole.

With the forward end mounted to the frame and the aft end mounted to the caliper, there is the requirement of rotational movement at the forward end. If you run a bolt through the bearing and use nothing between the torque arm and the frame, the torque is now held tight against the frame and there will be an extreme stress load on the bolt while the swing arm is moving over road irregularities. By using a cap head bolt and no washers with the stand off. The bearing that is installed is allowed to rotate freely and also allows for any slight left to right movements without hindrance.

For the strength of the bolt, I will differ to Mark, he knows more about metallurgy than I ever will.

Fred

[fj-f3a]

Fred

What you are saying is true, but only while the brake is not applied.
If you were to apply the brakes hard enough to lock the wheel and subsequently hit a bump, the rear suspension will of cause move up.
In order for this to occur, the caliper MUST rotate counter clockwise on the axle shaft, view from the right, or, the torque arm must stretch, or, the bolt, well!

It's not Rocket Science, it's Geometry.

Think of a parallelogram.

Gavin

[aviationfred]

Fred

What you are saying is true, but only while the brake is not applied.
If you were to apply the brakes hard enough to lock the wheel and subsequently hit a bump, the rear suspension will of cause move up.
In order for this to occur, the caliper MUST rotate counter clockwise on the axle shaft, view from the right, or, the torque arm must stretch, or, the bolt, well!

It's not Rocket Science, it's Geometry.

Think of a parallelogram.

Gavin

Gavin,
I agree with you 100%. What you said is exactly why a stand off is need at the frame mount. As for locking up the rear brake. The GSX-R rotor is much smaller in diameter than the FJ rotor. On all 3 of my FJ's that have had the Suzuki wheel mod, I have never been able to lock up the rear wheel. Before anyone mentions the quality of the brake bleeding. I use a pneumatic vacuum brake bleeder. This thing will suck a goofball through a garden hose..


Fred

[giantkiller]

Locked mine up, although momentarily. On the last, well almost last deer confrontation. Were I was as hard on both brakes.as I could be with out locking them. Back brake locking and resultant squeal. Is what broke the deer out of his, in the lights freeze. He scrambled out of the way just in time. If I hadn't been on the brakes so hard I could have reached out and slapped him on the ass as I passed by.

I prefer no torque arm.

[X-Ray]

I have used the underslung GSXR brake for a few years now, but I was never 100% comfortable with the footpeg bolt having to actually hold the torque arm in place while braking, but also deal with the swingarm rotational force at the same time. My FJ is still in pieces but I have just revised the braking setup for the GSXR wheel and have gone back to a top mount/swingarm mount.

I have used a Suzuki GSX600F brake caliper fully rebuilt, and the original FJ torque arm. However to clear the 180 tyre, the torque arm had to be bolted to the outside of the swingarm forward mount. I used hi tensile bolts and even though its not ideal mounting wise, the bolt no longer has to deal with the swingarm rotation. Hopefully I have a back brake now that actually slows me down a little.

Just a different take on the rear brake setup. I will be giving it a good test during our rally in March          

[giantkiller]

I have used the underslung GSXR brake for a few years now, but I was never 100% comfortable with the footpeg bolt having to actually hold the torque arm in place while braking, but also deal with the swingarm rotational force at the same time. My FJ is still in pieces but I have just revised the braking setup for the GSXR wheel and have gone back to a top mount/swingarm mount.

I have used a Suzuki GSX600F brake caliper fully rebuilt, and the original FJ torque arm. However to clear the 180 tyre, the torque arm had to be bolted to the outside of the swingarm forward mount. I used hi tensile bolts and even though its not ideal mounting wise, the bolt no longer has to deal with the swingarm rotation. Hopefully I have a back brake now that actually slows me down a little.

Just a different take on the rear brake setup. I will be giving it a good test during our rally in March          

That's what I had originally. On mine. Except I used  torque arm from an 87 Fr1000. And I took the tab off the top and had it welded on the bottom of the swingarm.  Bolted it all up to the swingarm. Wheel and all. Bolted the tab to the fzr1000 torque arm. That way tab didn't have to be offset. Just the arm at the caliper Took swingarm wheel and all to the welder. And he just welded the tab on where it fell...  Before going with gsxr 600 brackets. With no torque arm.

[ribbert]

Depending how your conversion was done, some calipers will pinch up when the axle is tightened and some with remain free to rotate. Some torque arms are fixed to the swing arm and some are fixed to the foot peg sub-frame. You can probably figure out which combination is dangerous. This could also explain why some have broken multiple bolts and some have broken none.

What I've never understood every time this comes up is why not just weld a lug on the swing arm and be done with it. These are your brakes for goodness sake, not something to frig around with amateur experimentation and backyard engineering and claiming the fact it hasn't broken yet as vindication that you got it right.

I'm sure some of these brake mods survive only on the basis that the brakes and suspension never see extreme use.

OK, having a lug welded on may not be convenient but these are your brakes! Losing the rear brake is not the problem, an uncontrolled lock up or jack knifing from a fallen torque arm is what should scare you.

"Well, it hasn't failed yet" is hardly gold standard when it comes to home grown brake mods! If you don't understand leverage and the forces at play, take a lead from folks that do. If you want to stick to your guns, experiment, go your own way, take the easy route, whatever, do so on something that won't kill you if you get it wrong.

The absence of an adverse outcome is not in itself proof of the best procedure.

Noel

[Millietant]

This has been a really enlightening discussion Noel and the first time I "got" the issue was Gavin's reference to the parallelogram effect and how hitting a severe bump with the back brake on could put unexpected forces through the "semi-supported" bolt protruding through the footrest mount.

I suppose the simplest solution would be for someone to work out the force/torque such a bump could impart to the failure point of the bolt (where it protrudes from the frame) at say freeway speeds and then determine what strength bolt would be necessary - that would take the "guesswork" out of it - and it may either vindicate Fred's (and others) findings/approach, or indicate a bit of "luck".

It's a bit of a moot point for me as the GSXR wheel swap, although attractive and good looking, seems to involve too much "faffing about" with the brakes  (hence I took the easy T/Cat approach).