GS750 front brake caliper piston help.

[fatnfast]

Firstly, I would just like to say hi. I have been lurking for a while now, and this seems to be an excellent forum.

Now for my problem, I have a '77 gs750b with the wire wheels and single front disc (I am in the UK, but the bike came from Ohio). The bleed nipple has been sheared of, and I have been unsuccessful in removing it. I obtained a replacement caliper, which I have stripped to replace the piston and seals.
However, my original caliper has a piston that is approx 43mm, but the replacement caliper has a piston of approx 38mm. The caliper holder and pad bolts are also slightly different in design, but parts appear to be interchangable (pads are the same). The main caliper body is identicle apart from the diameter of piston that fits.
Has anybody come across this before, and if so what 750 model caliper has the 38mm pistons?
I am about to order a piston and seal kit, but there seem to be a varity of pistons to choose from.
Thanks in advance,
Phil

[hampshirehog]

Hi Phil, welcome to the best GS site in the world and the one filled with the most nutters. Fortunately most of the nutters live in the US / New Zealand / Oz / SA......

Yes, there are a few different types of calipers and you have to make sure you know what you've got. If you've just busted off the bleed nipple the easiest thing to do is replace the banjo bolt with 1 fitted with a bleed nipple. Like this chap on Ebay:

http://cgi.ebay.co.uk/GOODRIDGE-BANJO-BOLT-W-BLEED-NIPPLE-m10x1-PLATED-STEEL-/310222346073?cmd=ViewItem&pt=UK_Motorcycle_Parts&hash=item483ab15759

If you're local I think I've got a new one you can have for a fiver. I've also got a box of calipers you're welcome to dive in to. Let me know.

Cheers - Wally

[fatnfast]

Thanks Wally,
Yes, this looks like a great site with lots of good info. I am down in Kent, so a bit far with only a back brake .

I have seen the banjo bolts you describe, but the caliper is beyond that after my hamfisted drilling! I had a caliper of ebay, which arrived with the nipple sheared off, then I got another which was pretty good bar a bit of pitting to the piston. Both of these have the same size piston, but both are pitted. As its brakes, I think its better to fit a new seal and piston, but its trying to ident what year caliper I have. All I know is the original single caliper had a big 43mm piston, and the two I have now are 38mm, which is what I am after.

[hampshirehog]

Phil, are the calipers for the round pads, the square pads with straight (little) ears or the similar ears but with a right angle? Plus what length / depth are the pistons? I may be able to measure the known ones I've got.

[fatnfast]

Cheers Wally, they all use the round pads. All the pads look identicle. The piston from my 750B measures 42.82 (so approx 43mm) with a depth of 41mm (this is the original knackered caliper).

The replacement caliper piston is 38mm diameter with a depth of 41mm.

I posed the question to 'wemoto', a UK parts supplier and they were very helpful:

The early (single) caliper models have a larger piston.
The DB model is 38mm x 40mm
The C/DC/EC IS 38mm X 22mm
The N/D/EN is 38mm x 41mm

So I have ordered the 38 x 41.

Hopefully I should be sorted, although I cant see that it matters if you fit the 40mm or 41mm depth pistons, unless the seal arrangement differs.

Thanks for the offer of help, if I get the wrong piston, I will give you a shout if thats ok?

Phil

[49er]

Hi Phil, welcome to the best GS site in the world and the one filled with the most nutters. Fortunately most of the nutters live in the US / New Zealand / Oz / SA......

Yes, there are a few different types of calipers and you have to make sure you know what you've got. If you've just busted off the bleed nipple the easiest thing to do is replace the banjo bolt with 1 fitted with a bleed nipple. Like this chap on Ebay:

http://cgi.ebay.co.uk/GOODRIDGE-BANJO-BOLT-W-BLEED-NIPPLE-m10x1-PLATED-STEEL-/310222346073?cmd=ViewItem&pt=UK_Motorcycle_Parts&hash=item483ab15759

If you're local I think I've got a new one you can have for a fiver. I've also got a box of calipers you're welcome to dive in to. Let me know.

Cheers - Wally

Who mentioned nutters? Giday Phil.

What's the condition of your shocks? If they need servicing, you could kill 2 birds with one stone and fit some later model ones off '80 or later GS 750/850's. You would then end up with twin discs with square shaped pads which are superior to the round ones. I changed my '79 850 over to the square ones and what an improvement. Ali wheels too?

Cheers Ian

[fatnfast]

The brake is all sorted now and works as well as a single disc could . Thanks for the info Ian, but I'm going to keep the bike pretty stock so I can scare myself without going to fast. Nothing like bouncy shocks and a single stainless disc in the rain! Mind you, the previous owner did fit braided lines to give some hope of stopping .

[Adrian1]

Old thread alert! I got caught with this. I ordered part no 69107-38B00 which is the caliper seal. BUT it’s too big for my calipers (twin disc). I need the 38 mm size, anyone know the correct part number?