vanzen@rockerboxer.com wrote:
IMO, and given that the rest of the system is adjusted properly and in good condition,
the choice of an MC swap may be the best single improvement to the antiquated disk brakes – perhaps even more effective than twinning
which has the disadvantage of adding unsprung mass.
Certainly a single with the "correct" MC ratio would be superior to the stock dual setup. A correctly setup dual would be even better, but, yes, you do pay a weight penalty.
Modern discs are SO much lighter than the 70's designs, in spite of being much larger in diameter. You give up the ability to turn them and reuse a scored rotor, but the lighter weight is totally worth it IMO.
All this information is bringing up all sorts of issues. I agree with the unsprung issues and the benefits of a single rotor. I will do mostly mountan riding on windy roads between Tahoe and Reno so I do want great handling and good brakes. I have not had a chance to bring the bike into the shop yet, but from what I have seen it appears that the stock caliper doesn't allow any other type of caliper to be installed, so does that mean if I want a bigger choice I have to go to a front end from a R65 or K100, both which I have seen on e-bay for good prices. Both appear to have stouter triple clamps and I like that bit and both appear to have lugs that would accomidate a hanger for a bigger or different caliper than the stock IDE unit. The R100Rs unit was twice the price of the others but it had a pair of IDE calipers from a 77-78 model year bike.
i guess when I said I was planning on restore this bike I used the wrong term, I want a stock looking bike with good handling and better brakes. I have made frame kits before to add rigidity on Z-1 Kawasakis, added 3 pieces to trianglulate the area behing the steering head, Cross pieces below the head and above the swing arms pivots. I was thinking of looking at that option too as I have read about flexing in the stock set up.
My concern about changing over to the R65 or K100 front ends is how will the sorter distance between the front axle and steering head affect the handling and steering response. Will it make it just quicker or squirrely and will it affect stability at high speed????
1974 R90/6 built 9/73
1987 BMW K75S
1994 BMW R1100RS
1964 T100SR Triumph
1986 Honda XL600R
Just be aware that the R65 forks will be a different offset and the fork legs are spaced wider apart. The axle goes through the centre of the fork and not the front of the fork like it does on the R80/100.
Assuming you are talking about a fork set from a twin shock model.
A good choice, but you need to be aware of all the issues
Yes that ofset with the different axle position is what has me hesitating a bit. Found a nice set of complete forks from a 85 K100Rt along with a set of Brembo calipers for the same year model. I did check MACBMW for the changes in the hubs and the hubs were the same between the 14mm and 17mm models, just 17mm internal bits. These items can be had fore a about $300, plus shipping.
Then a set of R90S lowers appeared on ebay.
Some times I think it may be just easier to install stainless brake lines, good EBC splinter pads and just try the bike out, Add that heavier modifed upper triple clamp and perhaps a fork brace and see how it goes.
I have gone off on tangents before and ordered items that I eneded up I couldn't use, like the 6 piston calipers I have still boxed for a Kawasaki.
1974 R90/6 built 9/73
1987 BMW K75S
1994 BMW R1100RS
1964 T100SR Triumph
1986 Honda XL600R
I swapped the entire front end on my R90/6 over from a K100RS, 1986 I think. The wheel (if you want spokes) required an R100R front hub and custom wheel from woody's. The stock /6 MC works fine; just come up with a splitter to get the dual lines. As for handling, everything off the K100 was bigger and better, so it was a big improvement (to me). That included properly weighted aftermarket springs of course. Maybe not the easiest route, but do-able and defintely netted an overall improvement while keeping stock-ish appearance.
From what I have been reading and trying to understand is that the K yokes (triple trees) put the forks more forward from the steering stem than the earlier 'R' affair so increasing the 'offset' - this decreases the 'trail' and would therefore quicken the steering.
The sliding part of the forks on the K's and the Mono's are the same castings(?) but the Mono has a leading axle -decreases the trail - quicker steering, the K's sliders are turned around and therefore has a trailing axle and so has an increased trail giving slower steering.
What the combined efforts make I don't know - should you use a leading or trailing axle - who's done the maths?
Well I finally made a decision and went for the 90/S lowers and calipers off a 74 S model. The clincher to the deal was that they were early models and fitted my existing axle on the bike. I did discover that during it's lifetime the front caliper was replaced with a 40mm unit. I haven't pulled the tank yet to see what master cylinder is under there. The next search is for a larger pistoned MC unit as I believe the stocker is 14mm.
Ran a compression test on the bike, It was 110 on the left, 120 on the right, don't know how good or bad that is, tried to start it, but no luck. The battery has been on the charger for a couple days, never quite reaches full charge, but cranks it over pretty good.
I will probably check things out a bit more completely to see if I can get it to run and ride it a bit to see what is wrong with it other than the cosmetics.
1974 R90/6 built 9/73
1987 BMW K75S
1994 BMW R1100RS
1964 T100SR Triumph
1986 Honda XL600R
jagarra wrote:Well I finally made a decision and went for the 90/S lowers and calipers off a 74 S model. The clincher to the deal was that they were early models and fitted my existing axle on the bike. I did discover that during it's lifetime the front caliper was replaced with a 40mm unit. I haven't pulled the tank yet to see what master cylinder is under there. The next search is for a larger pistoned MC unit as I believe the stocker is 14mm.
Ran a compression test on the bike, It was 110 on the left, 120 on the right, don't know how good or bad that is, tried to start it, but no luck. The battery has been on the charger for a couple days, never quite reaches full charge, but cranks it over pretty good.
I will probably check things out a bit more completely to see if I can get it to run and ride it a bit to see what is wrong with it other than the cosmetics.
Don't rush into getting a large MC. Early Airheads had MC - Caliper piston ratios that were far from optimum, and smaller MC pistons make the braking much better. Check here for specific numbers:
jagarra wrote:Well I finally made a decision and went for the 90/S lowers and calipers off a 74 S model. The clincher to the deal was that they were early models and fitted my existing axle on the bike. I did discover that during it's lifetime the front caliper was replaced with a 40mm unit. I haven't pulled the tank yet to see what master cylinder is under there. The next search is for a larger pistoned MC unit as I believe the stocker is 14mm.
Ran a compression test on the bike, It was 110 on the left, 120 on the right, don't know how good or bad that is, tried to start it, but no luck. The battery has been on the charger for a couple days, never quite reaches full charge, but cranks it over pretty good.
I will probably check things out a bit more completely to see if I can get it to run and ride it a bit to see what is wrong with it other than the cosmetics.
How do you know that it never reaches full charge? A lot has been written about the stock charging system, so start reading and you will find the answer.
Ask the Indians what happens when you don't control immigration.
