'80 750L Refurb

[oblique]

I've never been comfortable for long rides on any of my sportbikes. I've seen people doing North American tours on R6's and the like but no matter how much effort I put into posture and position, I end up with a sore back, butt and a killer pain in my right shoulder.

While I'll never leaving the crotch rocket scene, I've been wanting to tour Ontario and the rest of Canada for some time and this has culminated into my first cruiser purchase: a 1980 GS750L that's been sitting garaged for the better part of a decade.

Here it is:

I didn't want anything fancy and wasn't concerned too much about aesthetics so when this popped up in non-running condition after long-term storage, I couldn't resist the chance to get familiar with 35-year-old Japanese engineering.

The goal is to bring it back to sound mechanical operation with minimal attention to aesthetics. Bling will be attended to only when it is cheap, convenient and fast.

Here we go.

 

[oblique]

So first things first: the brakes. Ive read a lot of commentary on here about 80's brakes being sub-par in general and that anything you can do to aid the situation, such as upgrade to braided lines is essential. I'd like to rant a little, if I may.

First, these brakes are not inferior to any modern system as 35 years of technological advancement would suggest. They use a large, single piston caliper to apply braking force via a standard linear master cylinder and reinforced rubber brake lines. From what I've seen, current technology on similar models has not dramatically improved: the same piston design on the master cylinder is still used. Similarly, the caliper side of things have improved marginally at best. The reason for modern multi-piston calipers is to evenly distribute braking force on elongated brake pads due to smaller modern wheel diameters. Pads are longer and thinner to accommodate the tighter dimensions. If you compare the surface area of old squarish pads to newer rectangular pads youll find theyre very similar.

Now the brake lines: people always rave about how dramatic an increase in lever stiffness and braking power they've achieved with their new braided lines. It's absolutely true they expand less but is it a coincidence that installing new brake lines corrolates with replacing brake fluid? Nobody has done a comparison on the same bike with fresh fluid on both stock and braided lines, back to back. Secondly, if you maintain your braking system with fresh fluid and good flushing a bleeding techniques then you shouldn't be able to bottom out your lever no matter how hard you try and Im willing to bet that if you do press hard enough on stock lines, you will be able to lock up the front wheel.

Speaking of locking up the front wheel: this is where braided lines are a disadvantage. If you suddenly get on the brakes hard you are far more likely to lock up the front wheel with braided lines than you are with the stockers. This is because the rubber lines' expansion helps to apply braking force over a slightly longer period of time. Why this is important is because in order to achieve maximum braking force at the contact patch of the front wheel the braking force has to be applied gradually. This is called 'loading' and it involves the distribution of forces through the chassis and suspension to achieve optimum braking power.

Braided lines are for racers. Keep your brake fluid fresh, your system free of air bubble and contaminants, and you will be braking happily and well with your factory Suzuki brake lines.

On to the build...

 

[oblique]

Getting started...

Getting started...

After removing the front brakes I noticed oil on the left fork leg and sure enough, a few more good pumps produced more oil. This is nothing fresh seals cannot fix but as I looked closer I found this:

I've never dealt with pitting before - is there a fix? Maybe some filler and polish?


Next I removed the front end. Steering stops were intact and everything looked in order. I decided to go a step further and check the steering stem bearings and races. Heres a shot of the bottom, looking up:

The bearing felt absolutely smooth to the touch - what to the marks indicate? Is this a metal reaction from sitting so long?



While I was jacking the front end I noticed I had an issue with the exhaust:

I hope this doesn't affect the engine negatively in any way....



I haven't taken a look at the rear end yet but heres how I left her....in suspended animation:

More to come.....

 

[Griffyn]

Braided lines are for racers. Keep your brake fluid fresh, your system free of air bubble and contaminants, and you will be braking happily and well with your factory Suzuki brake lines.

Having prepped street cars for racing, I concur with all of your points concerning braided stainless lines, fresh fluid and a properly functioning brake system. When I swapped my race car over to braided lines, I found myself making more braking errors as the modulation point shrank from a nice range with plenty of feel to a very narrow window that gave a lot less warning before locking up.

My 750's front dual discs are plenty strong enough with OEM rubber lines, so (like you) I'll continue my annual fluid flush schedule and keep on riding until the dry rot sets in.

 

[Gold01ca]

Watching your refurb with great interest.
Excellent photos, keep it coming and good luck with your project!

 

[ShadowFocus603]

I swear there must be goblins or elves or some damn thing that steals the side panels off of old Suzuki Gs's, assuming you didn't take them off before pics. When I got my second 81 750l it too had no side panels.

 

[eil]

Hiya and welcome. Very interested to see how the refurb goes.

The stock calipers on your model work very well, it was the earlier years that had somewhat iffy brakes.

I think most members here are going to disagree with you on brake lines, though. Braided stainless steel lines allow more power to be transmitted to the calipers than rubber lines. With good tires, you generally have to try to lock up the front wheel when braking due to the weight of these beasts. (And avoiding lock-ups is a matter of skill and experience, not choice of brake system components...)

But the main argument for going stainless with the lines is longevity. Suzuki specifies replacement of the OEM rubber lines every two years. The lines have date codes printed on them, you might pop out to the garage and see how old yours are. Odds are quite good you have the originals, meaning there should have been 17 brake line replacements already.

SS lines generally last the life of the bike, making them much more cost-effective in the long run if you plan to keep the bike awhile.

 

[oblique]

Thanks for the welcome!

The problem with braided lines is that they use a Teflon core to mitigate the expansion seen in rubber lines. Teflon is great but the main problem with it is 'cold set' - the tendency of Teflon to lose flexibility and become rigid over time. Brake lines see a lot of movement during use as the suspension works and older lines can kink and leak. Ive personally witnessed this on multiple bikes.

With regards to Suzuki's maintenance schedule, the 2 year interval sounds more like the one for brake fluid, not the lines. Depending on how much sunlight factory rubber brake lines have been exposed to, the outer layer will visibly start to crack as fissures appear around stressed areas such as near clamps and the banjos. My 35 year old brake lines on this bike show no such signs, are perfectly flexible and the banjos are rust- and corrosion-free.

I will report on how they behave after I get the bike up and running.

 

[eil]

The problem with braided lines is that they use a Teflon core to mitigate the expansion seen in rubber lines. Teflon is great but the main problem with it is 'cold set' - the tendency of Teflon to lose flexibility and become rigid over time. Brake lines see a lot of movement during use as the suspension works and older lines can kink and leak. Ive personally witnessed this on multiple bikes.

I'd be interested to know what exactly is the average life span of teflon brake lines. Gotta be more than two years?

With regards to Suzuki's maintenance schedule, the 2 year interval sounds more like the one for brake fluid, not the lines

Quoting the factory service manual:

* Replace hose every 2 years
* Change fluid every 1 year

Depending on how much sunlight factory rubber brake lines have been exposed to, the outer layer will visibly start to crack as fissures appear around stressed areas such as near clamps and the banjos. My 35 year old brake lines on this bike show no such signs, are perfectly flexible and the banjos are rust- and corrosion-free.

I believe as brake fluid ages, it gets acquires moisture, gets acidic (or something), and attacks the rubber lines from the inside. There are lots of photos on this forum of people who go to rebuild their calipers and find a brown-black sludge inside. That's old brake line. (Plus some rust from the caliper pistons.) It's what you get when you don't change the fluid regularly. Since the bike has had 34 years without you, you can't really know the condition of the existing lines without slicing them open.

Anyway, I'm just providing information. I'm honestly not trying to badger you about your decision. It's your bike, so it's your call to make. Looking forward to seeing it running.

 

[oblique]

Im really struggling with the pitted fork tube. The pits actually go past the oil seal when the fork is depressed and this can only amount to leaks and contamination of fork oil.

Has anyone dealt wit this before?

Additionally, when I took off the dust seal I noticed visible scoring on the fork tube vertically above the fork seal. My bet is that the pits have introduced sediment into the oil seal and this has been scratching the fork tube for quite some time to produce the scoring. It doesnt seem to be deep, however, as it doesnt feel any different than the fork tube. Any suggestions would be appreciated.