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Discussion Starter #1
Hi everybody,

I have a 1996 GL 1500. My left side front brake disc (the one which operates with the rear brake disc) is approaching its wear limit.

I found on the net, here in France, an original Honda front brake disc which seems to be in state close to new (no sign of wear) and at a good price.

The only problem is that it is a right side front brake disc.

Comparing my two front brake disc, I see absolutely no differences between them two.

So do you think there could any problem mounting a right side front brake disc on the opposite side ?

Moreover, it seems to me that aftermarket front brake discs (for the GL 1500 or other bikes) are sold with no consideration for their side.

Thanks a lot in advance for your advices.

Good day to you all.

Guillaume
 

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According to partzilla parts catalog, left and right disks have different part numbers such as
45251-MT8-000 DISK, R. FR. BRAKE
45351-MT8-000 DISK, L. FR. BRAKE.

And they are only interchangeable between 1990-2000 models. You may want to check the model year of the part.

Since they have different part numbers there may be some differences, I don't know.
 

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Discussion Starter #3
Thank you for you answer Erdeniz.

The seller says his disc is for GL 1500 from 1990 to 2000, so it should fit my 1996 GL.

I am going to think about and see if any other member of the forum has an advice on this issue.
 

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Thank you for you answer Erdeniz.

The seller says his disc is for GL 1500 from 1990 to 2000, so it should fit my 1996 GL.

I am going to think about and see if any other member of the forum has an advice on this issue.
I've got a pair of brand new OEM discs in my garage still in their original bags and box and the Honda part numbers are as stated by Erdinez above. I've just had a good look at them and can see no differences between them other than the left-hand one has an 'L' printed into it. I wondered whether there would be a directional arrow but there isn't. Both say the minimum thickness should be 5mm so it doesn't seem to be anything to do with that either.

Honda also list two different part numbers for front brake pads 06455-MT8-405 (for the left) and 06435-MT8-305 (for the right) with only one side having a shim. This makes me think there must be some design differences between the two sides but for the life of me I can't see it.
 

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To the best of my knowledge , the difference in the rotor is the sweep of the vent holes drilled in the rotor. Personally I do not believe it would make a difference , but I am no Honda Engineer :(
 

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My first thought was the direction of the sweep holes, but it would not seem to matter which way they angled as they are not continuous grooves or something that direct water/debris away with wheel rotation.
 

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The purpose of slots on the sides of brake rotors is: to provide an escape path for expanding pad gasses being generated by the braking torque.

In EXTREME situations the outgassing from HOT-HOT pads can physically push the pads off the rotor- despite having your foot or hand buried!

Not a situation encountered in sane street riding, mountain fun maybe, Maaaayyyyybe
On the track, yep

Getting Your Groove On: 2 schools of thought- forward or backwards in relation to direction of travel ~,
Or is that mostly for show- as its not about cooling or dissipating heat- its an escape path

Note: A rotor clearly marked LEFT shouldn't need a directional arrow as well
Just because you all drive on the wrong side of the road over there.........
 

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The purpose of slots on the sides of brake rotors is: to provide an escape path for expanding pad gasses being generated by the braking torque.

In EXTREME situations the outgassing from HOT-HOT pads can physically push the pads off the rotor- despite having your foot or hand buried!

Not a situation encountered in sane street riding, mountain fun maybe, Maaaayyyyybe
On the track, yep

Getting Your Groove On: 2 schools of thought- forward or backwards in relation to direction of travel ~,
Or is that mostly for show- as its not about cooling or dissipating heat- its an escape path

Note: A rotor clearly marked LEFT shouldn't need a directional arrow as well
Just because you all drive on the wrong side of the road over there.........
I've just had another look at my new rotors and laid one on top of the other in the same position they would be on the bike i.e. outside edges facing out. The vent holes exactly match each other, which presumably is intentional to get their direction right, and the holes don't look like they have been drilled through at any angle. There are no vent grooves cut into the rotors. The thickness of each rotor is identical and the mounting holes exactly line up. The service and runout specification is stated as being the same for each side so they do look identical.

Maybe Honda marked one as "left" and had a different part number just for assembly line packaging purposes or maybe just for research purposes on which side sold more replacements if they wore out faster (because of the linked brakes influence). It is though for each person to make their own decision on whether to use them on opposite sides.

And Aloha Tom...you are exactly right, we do need directional arrows here as we do get confused between left and right. You drive on the right which we think is wrong and we drive on the left which we think is right! :laugh::laugh:
 

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Just brain storming, can there be some microscopic differences on the surfaces of the disks due to machining process (clockwise /counterclockwise rotation etc.) during the manufacturing?
 

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John, if you were to lay the two atop each other as if you were putting them both on the same side you'd see the difference in the pattern of vent holes.

That said I doubt that you'd notice a difference in braking if you were to swap the rotors to the incorrect sides.
 

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John, if you were to lay the two atop each other as if you were putting them both on the same side you'd see the difference in the pattern of vent holes.

That said I doubt that you'd notice a difference in braking if you were to swap the rotors to the incorrect sides.
Very good point Ken, the holes do not line up when done that way. Your comments have changed my mind in that I now think the hole pattern (diagonal lines of 3 then 2 holes) is to get water etc directed to the outside of the rotor so, for me personally, I will use the correct one on each side. I accept though what you say in that you would probably not notice a difference when braking.
 

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I REALLY doubt a difference would be noticed because the water will easily disperse regardless of the hole-line direction. The pads only cover a small part of the rotor, most pads also have a channel cut in them, so there should be no ill effects.
But I can be a little OCD on some stuff and agree in in reference to correct direction preference.
 

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Ar you saying Euro spec 1500 front rotors do not have a grove set cut into the sides of them? They are flat faced?

On a 1500- the interlinked system may be the key to why the rotors are different
Honda doesn't use 2 different parts unless it absolutely has to

My decent Guess as to why the left front could be marginally thicker:
In Honda engineer dreams: Left rotor is getting more use than the right,
They meant for the rear pedal to be primary, while right front is supposedly used for additional stopping and final low speed to stop.
See also:
Why was the OE rear brake pad so thick-long wearing?!
Probably same theory- expecting rear weight and stopping needs based on inter-link system.
The EBC pads new... look like Min. on OE in comparison

Show of hands- if you use the front-right as your main/only stopping power?
 

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Another brainstorming, Honda engineers may have preferred using different part numbers although they are exactly the same rotors, thinking in case of any possible failure in the future, it would be easier to handle the issue.
 

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I noted the extra wear on our '97 while the wheel was off to mount a new tire, I measured both, found the left worn most but still within spec, and .... and so I swapped left to right and installed new pads. I used a dial indicator to check run out when reinstalled and they were as perfect as they could be. I did a few bedding in stops, they are fine.

One side wears more because it gets used more as always with rear brake. Only difference left to right is direction of hole pattern and the "L" and "R" stamp. No one sees either under the covers on the GL1500.

My '85 GL1200 likewise has a L & a R and again, it's the sweep of the holes pattern that differs.
 

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Hi everybody,

I have a 1996 GL 1500. My left side front brake disc (the one which operates with the rear brake disc) is approaching its wear limit.

I found on the net, here in France, an original Honda front brake disc which seems to be in state close to new (no sign of wear) and at a good price.

The only problem is that it is a right side front brake disc.

Comparing my two front brake disc, I see absolutely no differences between them two.

So do you think there could any problem mounting a right side front brake disc on the opposite side ?

Moreover, it seems to me that aftermarket front brake discs (for the GL 1500 or other bikes) are sold with no consideration for their side.

Thanks a lot in advance for your advices.

Good day to you all.

Guillaume
OK, to throw another thought or two in here I would say this. You mentioned that it was approaching the minimum. I'm sure for liability Honda is very conservative when they list the minimums to make it idiot proof. You know the guy who runs the bike another 1000 miles after the brakes are metal on metal. So, if it were me I would use the original again. Just be mindful of it and when you start to get toward the end of the pad life do a brake job again. The biggest worry is that the rotor would be so thin and some yokel wears the pads so low the caliper pistons pop out of the calipers and no brakes! It is not at the minimum so one more use at least will be no issue. At the minimum use it once more.
It's your decision but I will say this. If it were my bike I would put the original back on. At the end of the next pad change you might well see it still has not reached the minimum. Both of my rotors are just below the minimum and I just never let the pads wear past 3/4. For me it works out that I change brakes each time I change tires.
 

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Ar you saying Euro spec 1500 front rotors do not have a grove set cut into the sides of them? They are flat faced

Show of hands- if you use the front-right as your main/only stopping power?
Here's a picture of my new left-hand rotor. I'd always assumed they would be the same as the US spec ones. Have yours got grooves then?

Show of hands.... I tend to use only the right-hand lever when slow moving in town and both left and right brakes at speed. I'm probably too heavy on the right side in general though.
 

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I use them both on both the 1200 and the 1500 ...... but especially the 1500 as it's a heavier Trike with those generous 9" drums out back whoa-ing those two 215/70-15 tires on 17x7 wheels.
 
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