Need dimensions '81 GS750E front disc & pads

[Sidecar Bob]

I am trying to use a caliper from an '81 GS750E on my Honda sidecar outfit that I drive in the winter and I'm having a problem getting it onto the disc.
The FSM that I found online doesn't give the spec for new disc thickness but it says that the service limit is 5mm so I'd assume I should be able to fit a dist that's a hair under 7mm thick.
My caliper came with EBC FA51 brake pads that are 11.5mm thick (including the steel plate).
And yes, the piston is as far into the bore as it will go.

So my question is what is the thickness for a new disc and how thick should the pads be?

[salty_monk]

Pads sound right. There is no way a stock disk of that year is 7mm thick though….

[Sidecar Bob]

How thick do you think they'd be? They couldn't start much less than 7 if 5 is the wear limit.

Thinning the disc I have is not a simple proposition so at this point I'm contemplating milling 0.5mm or so from each of the pads....

[salty_monk]

I just measured one of the 1980+ rotors from my collection with a decent caliper. It has Min Tck 4.5mm stamped on the spider. It is showing very little wear. It measures 5.1mm. Hope that helps....

By the way... the rear brake rotors are thicker, I think min thickness 6mm. (the caliper is also opposed piston so stronger). Maybe a better match?

[Sidecar Bob]

I just measured one of the 1980+ rotors from my collection with a decent caliper. It has Min Tck 4.5mm stamped on the spider. It is showing very little wear. It measures 5.1mm. Hope that helps....

I was looking at the manual I downloaded yesterday and noticed that it is for the '83 model. So I went hunting again and found a GS750 manual that has an addendum for the '81 GS750EX. This one has a Service Information list that includes the standard thickness of 5.0mm and limit of 4.5mm, which matches what you found. Thanks.

By the way... the rear brake rotors are thicker, I think min thickness 6mm. (the caliper is also opposed piston so stronger). Maybe a better match?

At this point I've already rebuilt the front caliper. Besides, I don't want too much front brake on a sidecar outfit that is used on snowy/icy roads. If you lock the front brake the mass of the sidecar pushes you into the oncoming lane.

The main reason for changing to this caliper is that I'm fed up with having to un-stick the Honda/Nissin 2 piston caliper at least once every year. They don't have piston boots so the protruding parts of the pistons get coated with salt & dirt, not to mention that I have to replace them when the aluminum between the dust seal and the face of the caliper corrodes away. They simply weren't designed with winter in mind; The identical calipers on my summer machine hardly ever need any attention.
I have high hopes for the Suzuki/Tokico caliper (with new piston & rubber parts).

I filed the paint (& rust) from the back of the pads this afternoon and now the disc just fits between them. Knowing that the disc I want to use is 2mm thicker than stock and that the friction material on the pads is a mm thicker than on new Honda pads for the old caliper I think I'll see if I can mill half a mm off of the fronts of them too.

[salty_monk]

Good luck! Sounds like you have a plan!

[Sidecar Bob]

All I need now is to find somewhere I can get the aluminum I need. I used to get metal from a local fabricator but he retired and closed the shop last year

I'll post some pics when I've made more progress.

[Sidecar Bob]

Old (Honda/Nissin) caliper
05 - Old caliper.jpg

[Sidecar Bob]

Test fitting the "new" (Suzuki/Tokico) one. I didn't expect its bracket to bolt up directly but the upper bolt is pretty close (there is no clearance between bracket & disc but I can modify the disc I'll actually use for that).
07 - New caliper (test fit).jpg

[Sidecar Bob]

Here are the parts I made to attach the lower mounting points. 2 of them are links, the 3rd is a washer/spacer for the upper attachment made out of the same piece of aluminum as the thinner link. I left the tab to make it easier to get it into place during assembly.
Not shown is the 25mm long spacer for an M10 bolt I made on the lathe.
09 - Bracket parts.jpg

[Sidecar Bob]

When I put a bolt through the lug on the fork the bracket hit its head so I notched the bracket
10 - Caliper bracket modified.jpg

[Sidecar Bob]

Test fitting. I need to get a bolt the right length for lower fork lug and an acorn nut for it. With the bolts loose there is very little movement in the direction of rotation so this should work well
12 - Bracket close up.jpg

I've never been on a forum that only allows one image per post before.....

[Grimly]

I've never been on a forum that only allows one image per post before.....

You can upload ten images if you link to them on another image site like imgur, flickr, etc.

[Sidecar Bob]

Yeah, and when the hosting site decides to start charging for their service it plays havoc with the forums those pics were linked on. Remember Photobucket?

[Grimly]

Yeah, and when the hosting site decides to start charging for their service it plays havoc with the forums those pics were linked on. Remember Photobucket?

Host them yourself, then.