XJ 650 Maxim Single caliper brake upgrade

Hi all
Looking to increase the stopping power on my single disc standard set up on my 1981 Maxim .
So far I have ;-

• Replaced the brake line with Stainless braided HEL line ( this made noticeable difference)
• Rebuilt the brake caliper and greased rotating pivot
• Renewed fluid and bled brakes
• Switched to sintered pads

Still have the standard solid disc on it and the standard Master Cylinder, untouched. The brake lever feel is firm but just needs great force to stop well.
Would changing the master cylinder to a different size help ?

If not, my next step may be a to add an additional caliper and disc and different m/c which would mean changing the fork leg also. Understand that I could also use the front end off something newer ie an R6 but I don't really want to go that far if possible .
Cheers

 

Changing the master cylinder to a different size will make it worse.
Are you downshifting and using compression braking as you slow?
Are you using the drum brake at the same time as the front, and has it been looked after?

Rebuilding the master cylinder may be advisable.

 

now that you have a SS brake line you won't need so much travel on the lever.
Try adjusting the lever closer to the bar, this might give you more leverage, or at least more comfortable to squeeze.
Everything you've done should give you all the brakes a 650 Maxim needs.

 

Is the MC original/correct size? I swapped my MC to one with a larger piston inadvertently and it greatly increased the amount of pressure I had to apply to the lever to stop. Larger piston moves more fluid with less travel which reduces the mechanical advantage.

The stock setup is completely adequate to stop the bike. To improve the brakes you have to go to bigger diameter rotor(s) or a double disc setup, both of which require extensive front end work.

 

Also keep in mind that you won't be doing stoppies on her. The brakes are perfectly fine for daily use in traffic, but aren't modern-sportbike (or even mid 90's sportbike) good.

 

Get a smaller diameter master cylinder - you will have longer travel at the lever, but greater pressure. Simple

 

This is 100% true but with a smaller diameter rotor it makes it easier to lock the front wheel if you panic. Depending on rider skill may not be an issue but in a panic stop you have to know how it reacts. Learning to recover from a locked front wheel takes practice.

No offense to the OP but I teach the BRS class and I’ve seen plenty of riders dump bikes by locking the front wheel with the stock setup.

 

It's also possible to run out of lever travel if the MC is undersize. There is math to be done. Critical math.

 

I think you need to learn to read - the op is finding he needs excessive pressure to make the front brake work. The answer is simple, a smaller master cylinder - not rotor.
There isn't much choice - what is the 650 maxim - 14mm or 1/2 inch? If it's 14mm a switch to half inch shouldn't be a problem, the maths is simple and the risk is running out of lever travel - locking up is surely the same risk as any big braked bike - given the xj tyre is narrow, but compounds have come a long way since 1980..,

 

I can read, that's why I initially asked if he was sure if the MC was the stock size. These bikes are old and have had many PO's so who knows what it on it. The math is simple but critical but I wouldn't advise someone to install a smaller MC without knowing what they currently have.

 

Yes sure, a seca mc on a maxim is just what you describe ( I've done that myself as a trial and it indeed was a hard pull).
The stuff about locking front wheels though - the seca has better brakes, but the same wheel, as have most other twin disced xj's. All designed for 1970s tyres...
Perhaps some info on master cylinder diameters would be useful..

 

1980's tires.

Please give more specific advice before you get somebody killed. I KNOW that you're more than capable of that.
Brakes are the MOST IMPORTANT system on any motor vehicle.
You never mentioned how much smaller of a master cylinder to use, or from which machine.

The machine has no ego. All it cares about is physics and chemistry.
Even when all of that is correct it'll be more than happy to kill a fella.

Math link, because I make mistakes too (it is for cars, but the math is the same): master-cylinder-math

 

I think brakes are generally a great upgrade item, but I've targeted those for the car that I take autocrossing and such. On the street, good quality pads & rotors with a clean system is normally plenty. No complaints on the S/S lines. Are you targeting something more than typical street use? I imagine the easiest (mechanically) would be to swap forks w/ a period/compatible twin caliper model (and all the associated hardware). Seca or maybe a different Maxim?

There are as many solutions as you are creative, but each has their own pros & cons, as stated above.

 

The main issue wth the 650 Maxim is the manner in which the Caliper is mounted. None of the other Xj series calipers were mounted with a vertical pivot. This limits what can be done wthout changing the forks.

 

I don't doubt that. But it really comes down to what the OP wants. If this is going to be a track bike, options (and headaches) abound. For the street, I stand by my last post.

I didn't note the bolded question about the MC in the original post. I would place that in the headache category.. @Robzzzr do you have aspirations beyond the street for your bike?

 

I was agreeing with you.

 

Hmmm, 650 maxim is a horrible tilted 14mm thing. An rd 350 (i will need to check), bought it for my maxim with flat bars, that has a 1/2 inch bore, but small volume reservoir. I fitted a 5/8 from a seca on the maxim, it is way too hard. I think I'll try the 1/2 inch to see how it behaves. I don't know of a yamah that uses a flat 14mm?

 

Note that the OP didn't mention changing the handlebars.
If he keeps the buckhorns then a dual disc setup won't even be an option unless he uses an '83 XJ750 master cylinder (at the minimum, though there are probalby other master cylinders for buckhorn bars that would work such as from a late model Virago maybe).
As it happens that might be the easiest and cheapest to do.
The front-end and MC from a '83 Maxim 750 will swap right over (there might not even be any need to change stem bearings, but I can't remember at the moment). I'll have to check on any geometry changes though.

 

Nope, same headpipe bearings.

Nope, same axle placement.


Headlight bracketry, gauges, etc..........all the same. Easiest/best swap ever.

 

The op's avatar shows what looks like a 750 maxim, with flat bars, so all this is probably moot anyway.
Still don't have a list of potential master cylinder sizes from Yamaha - is there a 14mm horizontal cylinder?
Looks like my 1/2 inch mc was from a 125 dragstar..

 

I thought I'd spend my lunchbreak constructively. So rather than cogitate about it, I decided to fit the 1/2 inch mc from the dragstar. It fits on my almost flat bars fine, the change in travel from the seca one previously fitted (5/8 seca) was significant. Note that this is on the 650 maxim single calliper.
Whereas the seca mc didn't allow any movement to speak of, the dragster one allowed me to squeeze the lever to within about an inch of the twistgrip. It feels good actually. That's not to say it won't cause issues with locking up and skidding under a lorry, and I certainly am not recommending it, but I will road test it when the weather improves and report back.
I have not, and will not be doing any calculations on ratios etc, my right hand will tell me all I need to know, I already know the travel is longer, but not too long, so it just needs one more test for me.

 

Exactly. With parts in hand you don't need to do the math.
Thanks for looking in to that combination.

 

X2, I was considering the same 1/2” swap but I didn't have one on hand to try. Looking forward to your results.

 

A quick spin tonight, in the house now warming up slowly.
Initial tests showed the lever to have the right amount of travel, but the brake performance was diabolical. But it got better and better, until after a while I was smiling broadly in my misted up helmet. - of course the brake was poor to start with, the disc was covered in dust from my workshop, and I'll have to check if I changed the pads last year a well.
So as a test, yes I'm happy with it. Good result.

 

Good to know. That opens up a lot of options for modification.

 

Update on this - my pads were the ones that came with the bike, and whilst fitting new ones I noticed some fluid. So a rebuild and new pads later, and the brakes are really good. I can't fault them.

 

This has made me wonder how good would a dual maxim disc, spaced out seca calliper set up work?
I don't think I've ever seen one done? Did the 750 seca have bigger discs than the 650?

 

I hated the front brake on my 650 Maxim. Plus, it's the ONLY negative point I ever read on ANY review of the 650. It really should have been designed with dual rotors for the front brakes.
My biggest adjustment to riding the CB900C I replaced it with was getting used to the efficient front brakes that would actually stop the bike more than adequately.

A previous post in this thread stated that the XJ650 maxim front brake is adequate for the bike...yeah...it's barely adequate as far as I'm concerned. It was the only complaint I EVER had about that bike.