Topic: 1978 CB750F Brake Problems

[TwoTired]

Were there no pads?

[aperry]

Wait a minute, are my eyes deceiving me, or does the top of the piston (the round cylinder "cup") look like it has been ground down?  Seems to me like it was running without a pad.  If that's the case then you'll need a new piston.

Aaron

[madmtnmotors]

We are going to need a picture of the rotor too. My first impression is you are going to need a piston, piston seal, AND a rotor. A used rotor shouldn't be too hard to find and aftermarket pistons are available for a pretty reasonable price (OEM is pricey). Throw in a new seal for good measure and you're back in business. By the way, be sure to use pads this time...

The body of the caliper should be okay, small consolation...

The grinding on that piston looks bad...

[LiquidYogi]

Here's the best pictures of the rotor. I don't know about any pads, remember I just got this bike off of craigslist so anything that's wrong with it is the first owners fault. The rotor doesn't look bad to me, however what do I know...if a new rotor is cheap that's good the only problem I have is with removing the rear wheel, seems like a really tough job to get right.

[TwoTired]

If you didn't remove the friction pads, there was some major dufus work done to that bike.
I recommend you check out a parts list for the rear brake caliper, and use the correct parts for reassembly.

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
http://www.servicehonda.com/parts.html

[madmtnmotors]

A NEW rotor would not be cheap, IF they were available. A used rotor should be able to be had reasonably though. Have someone check the old rotor for you before looking for a replacement, it's hard to tell the condition of the current rotor from the pictures.

[LiquidYogi]

If you didn't remove the friction pads, there was some major dufus work done to that bike.
I recommend you check out a parts list for the rear brake caliper, and use the correct parts for reassembly.

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
http://www.servicehonda.com/parts.html

Yeah I've got the list and the parts that I'm gonna buy all looked up. I just having spent the money yet cause I'm looking on Ebay if I can just avoid this and buy a whole caliper. I figure it's worth a shot.

[LiquidYogi]

A NEW rotor would not be cheap, IF they were available. A used rotor should be able to be had reasonably though. Have someone check the old rotor for you before looking for a replacement, it's hard to tell the condition of the current rotor from the pictures.

I was also thinking of just redoing the whole thing with an entirely new braking system. I think it'll be hard to retrofit one though, I don't have a tool shop or anything so not my best plan.

[madmtnmotors]

A NEW rotor would not be cheap, IF they were available. A used rotor should be able to be had reasonably though. Have someone check the old rotor for you before looking for a replacement, it's hard to tell the condition of the current rotor from the pictures.

I was also thinking of just redoing the whole thing with an entirely new braking system. I think it'll be hard to retrofit one though, I don't have a tool shop or anything so not my best plan.

You may also be able to have the old rotor resurfaced. I believe a member here does resurfacing, and cross-drilling too! Pretty reasonable from what I recall.

[LesterPiglet]

Scrape your fingernail over the rotor, if you can feel ridges it's knackered. Some light ridges are usually fine but not deep grooves.

[LiquidYogi]

Ok so the parts finally arrived. I couldn't put the new piston in with the old seal so I removed the seal as in the picture. I have the new seal but I don't know what to use to make sure it stays in there. Any sort of glue or anything? Also what should I use to clean the seal ring, is there any sort of spray that'll help with my elbow grease?

[TwoTired]

Get yourself a can of spray Brake Parts cleaner.
All the white stuff (corrosion) must be removed from the caliper and, in particular, the seal groove.

 Use a small inspection mirror to see the blind side of the seal.  Scrape off ALL the stuff that doesn't look like aluminum.  I use a right angle scribe and a bent flat tip screwdriver to scrape the groove completely clean.  Wad up some aluminum foil over the end of an allen wrench to polish the groove clean.

I use Brake parts assembly lube when installing the seal back in the groove to retard further corrosion.  However, it has been suggested that a very thin coat of High Vacuum Grease can also be used.

Did you get the rubber boot and spring retainer (13 & 5), too?
http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
What about 14, 10, and 12?

[LiquidYogi]

Get yourself a can of spray Brake Parts cleaner.
All the white stuff (corrosion) must be removed from the caliper and, in particular, the seal groove.

 Use a small inspection mirror to see the blind side of the seal.  Scrape off ALL the stuff that doesn't look like aluminum.  I use a right angle scribe and a bent flat tip screwdriver to scrape the groove completely clean.  Wad up some aluminum foil over the end of an allen wrench to polish the groove clean.

I use Brake parts assembly lube when installing the seal back in the groove to retard further corrosion.  However, it has been suggested that a very thin coat of High Vacuum Grease can also be used.

Did you get the rubber boot and spring retainer (13 & 5), too?
http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
What about 14, 10, and 12?

Awesome thanks so much for the tips. I got numbers 4, 5, 11, 13, 14, and a couple of 10s.

[TwoTired]

The pads are going to rattle without part 12.

[LiquidYogi]

The pads are going to rattle without part 12.

I have the old 12 still, seems to be in working order.

[TwoTired]

Ah, as long as you have a 12, you should be ok.

[LiquidYogi]

Ah, as long as you have a 12, you should be ok.

Again thanks for all the help, I'm off to buy the various cleaning implements to get this job done and hopefully the brake will be on and bleeding tomorrow.

[LiquidYogi]

Ok trying to put it together but I don't really get how it goes together all that well. The rubber parts attaching to the piston and what not, I guess I didn't pay enough attention in how I took it apart. Anyone have directions or can give me a hint or something?

Ok I actually found the page I was looking for in my thousands of manual pages...I've put it together a bit like this, I'm not really sure how the clip goes in without hitting the rubber of the seal. It doesn't look like it will depress down so I need some help.

[TwoTired]

The big rubber stretches of the the end of the piston and fits into the groove.  I like to put HVG in the groove  to rubber interface.  After the piston is is inserted into the caliper (no more than to get it started), then the rubber mates with the caliper and the metal ring expands over the rubber to hold it in place on the caliper.

In the pictures, it look like the rubber isn't in the piston groove.

[LiquidYogi]

The big rubber stretches of the the end of the piston and fits into the groove.  I like to put HVG in the groove  to rubber interface.  After the piston is is inserted into the caliper (no more than to get it started), then the rubber mates with the caliper and the metal ring expands over the rubber to hold it in place on the caliper.

In the pictures, it look like the rubber isn't in the piston groove.

I updated the photos above. How's it looking? Can you tell me about the big metal clippy thing that guides the pads and how it fits without hitting the rubber?

I got the clip in like this...but it's obviously in the way of the rubber thingie when the brake is operated. I'm wondering if that's proper or I'm doing something wrong.

[madmtnmotors]

Hard to tell from the picture, but it looks like the edge furthest from the piston is not fully seated. Apply EASY pressure on the clip directly in front of the piston and apply some easy pressure towards the piston and the opposite side of this clip (furthest from the piston) should slip into a recess in that part of the caliper (beneath the horseshoe cutout). When the caliper is installed over the pads this clip is compressed slightly against the top of the pads to help prevent squeal.

[TwoTired]

It looks like you have it in correctly.

The metal clip is a spring.  It will deflect inward as you install the caliper over the pads.  There is a metal protrusion on the pads that will push the spring clip inwards.

[MRieck]

If you didn't remove the friction pads, there was some major dufus work done to that bike.
I recommend you check out a parts list for the rear brake caliper, and use the correct parts for reassembly.

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
http://www.servicehonda.com/parts.html

That's funny. Unfortunately I saw brake pads put in backwards or simply forgotten when I owned my shop. After working with special needs kids I felt it was a lateral career move working on some peoples bikes.

[LiquidYogi]

If you didn't remove the friction pads, there was some major dufus work done to that bike.
I recommend you check out a parts list for the rear brake caliper, and use the correct parts for reassembly.

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
http://www.servicehonda.com/parts.html

That's funny. Unfortunately I saw brake pads put in backwards or simply forgotten when I owned my shop. After working with special needs kids I felt it was a lateral career move working on some peoples bikes.

One day I will put in this forum how horrifyingly terrible the guy who owned this bike before me was. Everything...absolutely EVERYTHING this human being touched made this bike worse. I thought it was a means of transportation and an educational experience. Now, it's a rescue effort.

[TwoTired]

If you didn't remove the friction pads, there was some major dufus work done to that bike.
I recommend you check out a parts list for the rear brake caliper, and use the correct parts for reassembly.

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=2037017&category=Motorcycles&make=HONDA&year=1978&fveh=123330
http://www.servicehonda.com/parts.html

That's funny. Unfortunately I saw brake pads put in backwards or simply forgotten when I owned my shop. After working with special needs kids I felt it was a lateral career move working on some peoples bikes.

I'm seeing a lot of dufus work done to my newly acquired GL1100I, that I am now correcting.
They replaced the front wheel bearings...with a hammer, of course they feel "crunchy" now, damaged upon installation.  And after prying out the dust seal and damaging it, they just put it back in corrupted and ineffective.
Goldwing has roller neck bearings that should last forever, unless you use the torque of god while tensioning the bearings.  Yup, little ruts in the races, parts on order.
It was also impossible for them to put back all the specialty shoulder washers, collars, and correct length bolts for the baggage and fairings while adding 20 extra lights and chrome bits.  The assortment of hardware removed during dissassembly is mind bogglingly NOT of Honda manufacture.  The bars were held in place with only one tree clamp.  One of the four bolts was too long to put pressure on the clamp.  However, I feel fortunate that the top tree threads weren't stripped out like the one for mounting the fuel pump to the cylinder head casting was.  Heli-coil fix should help keep the oil inside the engine now instead of misting the entire right side of the bike for the last 25000 miles.

Did you know that duct tape is the preferred method of keeping the rubber gaskets on the hard saddle bags?  This is to be used after the gobs of Gorilla glue failed to grab the grimy rubber effectively.  If the bike wasn't free, I'd be pissed off, rather than just disgusted and appalled.
I am danged fortunate the engine has no owner repair history.

...I hope.