Does anyone know the front caliper brake piston size 1979 gs850g ?

[Guest]

It looks like I need to rebuild a front caliper and replace the piston on my 1979 gs850g to fix a slow leak from the left side front brake. (Once I get a couple things paid off.)

I have the older style single piston brakes on the front, with a plain flat rotor.

Does anyone know the size of the pistons?

Thanks

Sean

[hannibal]

I believe your bike uses similar calipers to mine. I spent a lot time understanding the different calipers.

My conclusion remains that single disc bikes used a larger piston than the dual disc bikes. This thread has some pics to help you distinguish between the two. If your caliper looks like the 78 caliper, I'll bet it uses a 38mm piston.

http://www.thegsresources.com/_forum/showthread.php?235337-GS750-master-cylinder-and-caliper-rebuild-kits

[Datsa Noydb]

His 850 should have dual disks, but a single piston in each one.

[seanarthurmachado]

It does have dual front disks (one left, one right), as well as a single rear disk.

The calipers were changed in 1980 onwards to a dual brake piston model with slotted rotors instead of the plain flat rotors on mine.

sean

[Who Dat?]

The calipers were changed in 1980 onwards to a dual brake piston model with slotted rotors instead of the plain flat rotors on mine.

No, the newer ones still have just a single piston, but it's a much improved design.

The rear caliper has a single piston on each side of the disk, for a total of two, but the fronts are just one piston per caliper.

[seanarthurmachado]

So, does anyone knows the size in mm of the brake piston or are there other years and models that will work for a brake piston replacement ? Trying to cross check part numbers did not work.

I can find plenty of rubber gasket kits for rebuild but the pistons seem few and far between.

Sean

[hannibal]

If you order the OEM rebuild kit, it comes with a new piston.

[seanarthurmachado]

The 1979 kit is out of production and not available.

Sean

[steveb922]

http://www.wemoto.com/bikes/suzuki/gs_850_gn/79/picture/stainless_steel_piston_and_seals_front_caliper/

Might help. If I recall correctly, the pistons are good, the seals not so good.

[seanarthurmachado]

It seems the size of the front brake caliper piston is 38mm by 38mm OD size.
(In case any else needs this information for the future.)

[tkent02]

Why not just get a pair of the newer style calipers? They really do work a lot better.

[seanarthurmachado]

Why not just get a pair of the newer style calipers? They really do work a lot better.

I thought about switching over, but I was thinking I would need to replace not only the calipers, but the brake pads (just put on) , and the rotors too. pretty fast downhill slope to spending more money than necessary. I finally had to order the piston kit from the UK to the tune of $56.00 but thats still cheaper than replacing everything else.