Bleeding brake system on an ABS equipped NC 750X

[auldian 1]

I’ve just changed the Rear brake flexi lines on my bike so have introduced a lot of air into the system. Is there a special technique required to bleed the brakes on an ABS bike? Or is just the standard pump the lever, hold lever down, open nipple, check for air being dispelled, close nipple. Release lever, the keep repeaing till no air seen. I understand some bikes like Triumphs require a visit to a dealer for sone software work to get ABS bled. Is this also necessary with the same NC750X? 

[Andy m 23,585]

It will bleed with a jam jar but won't be the easiest. Lots of nooks and crannies in the modulator.

 

A vacuum bleeder makes life much easier. Turning the key once in a while withbtge nipple closed to stir the modulator might also help (that's all Triumph and HD are doing with their diagnostic software having either stuffed up the installation and/or decided it's a good license to print money).

 

Andy

[Steve Case 955]

I'm not sure how relevant thi is to motorcycles but the last car i had needed air purged from the abs unit. I was having no joy bleeding it so i took it to a brake specialist who pressure fed the master cylinder while using diagnostic software to continuously run the abs so all the solenoids were operating.

This has the affect of slowly purging air from the cavities in the abs but it takes a lot of brake fluid to achieve.

I'm not sure if this is of use but i hope it helps.

[outrunner 4,457]

When I stripped my 2016 NC 750X to get stuff repainted and do a bit of tidying up I just reconnected the braking system,filled the reservoirs and bled as normal without any problems from the ABS system, perhaps I was just lucky?

 

Andy.

[MatBin 5,097]

When I replaced my brake fluid I just filled the reservoir and pumped until new fluid came through on the NC. On my K75 BMW years ago it had to go back to the dealer as I had no joy getting the fluid through, it too had abs (sort of).

[Andy m 23,585]

13 minutes ago, MatBin said:

 it too had abs (sort of).

The systems on bikes are stone-age so barely changed in 40 years.

 

What varies is the installation. Cram the modulator in a tight spot with a load of elbow connectors and you'll trap air. Same kit with the right pipe run and it'll bleed with a jam jar.

 

Andy

[Xactly 5,436]

25 minutes ago, MatBin said:

When I replaced my brake fluid I just filled the reservoir and pumped until new fluid came through on the NC. On my K75 BMW years ago it had to go back to the dealer as I had no joy getting the fluid through, it too had abs (sort of).

Those had two bleed nipples on the abs module under the tank, one for the front brake and one for the rear brake. I had no trouble bleeding them.

[Steve Case 955]

Sorry andy but the abs on the bmw was literally a piston per brake and the piston was probably 20 to 30mm.

The current systems use multiple 5 to 15mm pistons similar to the car which had approx 30 pistons per wheel pair.

I doubt bikes have as many but the old bosch 2 piston modules are long gone.

[MatBin 5,097]

9 hours ago, Xactly said:

Those had two bleed nipples on the abs module under the tank, one for the front brake and one for the rear brake. I had no trouble bleeding them.

Wish I had known that! 😁

[Steve Case 955]

Thats gotta be the bosch, 5kg of cast steel with pistons like dustbins.

[Xactly 5,436]

14 minutes ago, Steve Case said:

Thats gotta be the bosch, 5kg of cast steel with pistons like dustbins.

And a computer bigger than an iPad in the tail…

[Steve Case 955]

I thought mine had it screwed on the side of the abs block next to the engine computer which was about 2 ipads thick...

[Steve Case 955]

Basically one huge chunk of silicon for the injection and timing and one for the brakes, pretty sure they didn't share data apart from 'I'm on".

[Xactly 5,436]

Both my K100RS and K75S had the ABS 1 computer in the tailpiece. 

[Andy m 23,585]

4 hours ago, Steve Case said:

pretty sure they didn't share data apart from 'I'm on".

Permanant feed, Ignition feed and a brake light feed that actually didn't do anything. I never actually worked out if the brake light feed was a leftover from some sort of back-up power/anti-backfire thing or was a bit of future planning that was overtaken by K-line then SAE J1939. All analogue on the brake side of course.

 

Andy

[Steve Case 955]

They were pretty basic, and i believe were replaced in 2002 by the 'whizzy' servo brake system.

I had an R1100GS which had an enourmous tank with a large cavity underneath where they stashed the battery, complete ABS module, engine CPU and throttle cable box.

ABS was optional.

[Xactly 5,436]

The K series (ie original “bricks”) had ABS 1, the original system. There was a massive cylinder each side of the bike that controlled the hydraulics, the digital control side being controlled by a computer in the tail cavity, behind the dual seat. You knew without doubt when the system had actuated because of the distinct pulsing of the lever or pedal. A average to good rider could definitely beat that system (proven in tests) but it was the first on any bike and was reliable, if rather heavy and definitively clunky.

Then came ABS 2, in the earlier oilhead period ie 1100RS, 1100GS etc having the Moronic (Motronic) control unit. The actuator module was under the tank and had a bleed nipple for front and rear. It was lighter than ABS 1, lacking the massive actuators. It still had the double “clunk” as front and rear systems primed when setting off. A common problem was that the system didn’t prime, almost invariably because of low battery voltage (the starter motor had just heaved over compression a couple of 550cc pistons to start the engine). There was a wiring mod that improved the reliability of the ABS priming or you could just do as I did. Ride off. Stop after a while and try again with a warm engine. Always worked for me. The system was otherwise reliable until the modulator packed up. It could be repaired though, or just decommission the whole setup.

Then we had the stupendous update to the infamous servo version, around the latter period of 1150 oilheads. This didn’t work unless the engine was running and there were, possibly apocryphal, tales of dealers crashing the bikes through plate glass windows as they shunted the bikes round the showroom expecting them to stop when the brakes were applied. If the system failed (and it often did) there was supposed to be residual braking. I once went to see Steve Scriminger, the go to bloke for BMW repairs to drop off the gearbox from my 1100RS for repair (another common thing). I asked about the 1150RT outside. Apparently the owner had had brake failure just before the roundabout on the main road nearby and he had barely managed to scrape round on residual braking. He decided there and then to have a servoectomy done on the bike, a common practice , not least because of the ludicrous cost of replacement (some £1200-1400) back then IIRC and BMW wouldn’t even guarantee it a year against repeat failure. Wonderful. Modern BMWs? No thanks.

[Steve Case 955]

Bloody hell i'd forgotten about the starting problem, yeah used to do the same start up ride off then first set of traffic lights switch bike off and on and get the abs working. There was a mod to delay the abs priming till the engine started but never got round to it.

I rebuilt my own gearbox which was pretty simple but getting it out....

If i bought another beemer it'd probably be an airhead but i've done the bmw thing so prob not bother.

[Steve Case 955]

Oh it was motronic, i never knew. When it operated the vibration was enough to make teeth fall out, but it saved my arse and thats good enough for me.

Mind you the system on the transalp also saved my butt, but it took me a while to even realise it"d kicked in.

[MatBin 5,097]

I was told the discs on the k75 I had were so small it would be almost impossible to get the abs to kick in, I don't think I ever managed it apart from one time. I went for an overtake of 2 cars on the road between Harpenden and St Alban's as I got level with the nearest car they decided to overtake the leading car without signal or mirror, I anchored up and there was a definite rumble etc but that may have been the cat's eyes I was running across, all I was concerned with was not rear ending the car or hitting the oncoming traffic. Disc warping was also a feature on the K75. As I had the big pots on the side I am guessing it was a MK1 abs system.

[Xactly 5,436]

AFAIK all bricks had ABS 1. My K75S was N reg, so one of the later ones with Japanese forks, Showa IIRC. That had the two dustbins. Come to think of it I don’t think the ABS ever activated on mine either. It operated twice on my K100RS though, saving my bacon. My K75S was great at doing massive backfires at will. The FI system ran continuously ie unused fuel was returned to the tank, the injectors on the rail firing at the appropriate time. After a fastish run if you shut off the throttle then opened it very slightly you’d get a massive backfire caused by some fuel passing through the engine unburnt then firing in the exhaust. It once did it unexpectedly in a French village - I thought someone was shooting at me….Those bikes were the most reliable I ever owned, bar none. 

[Steve Case 955]

Bar one, don't forget which site your on.

[Steve Case 955]

The somestar disks on hondas seem to be quite good at warping.

I've had 2 so far, on 2 different bikes. Mind you that may be my habit of riding the back brake on tight turns.

[Xactly 5,436]

14 minutes ago, Steve Case said:

Bar one, don't forget which site your on.

Didn’t keep mine long enough to find out. 

[MatBin 5,097]

8 hours ago, Xactly said:

Didn’t keep mine long enough to find out. 

I wasn't as fortunate as you. When it ran well I loved it, mine had Showa forks too. It was a pretty bike. Build quality on certain parts was definitely a Friday afternoon job. But it did tour well and was reasonably quick if a bit thirsty at high speed, as I found out chasing a Porsche through Belgium along the coast, didn't realise Belgium was so small 😉