Author Topic: CB750K2 brake issues and question  (Read 162 times)

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Offline KuangGradeMark11

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CB750K2 brake issues and question
« on: February 05, 2019, 08:22:02 pm »
I posted the first question I had in the wrong part of the forum - http://forums.sohc4.net/index.php/topic,175954.0.html and rather than compound the error (sorry!) I have moved the follow up question here.

Now that I have established that here in sunny New Zealand our "K4"s are in fact K2- s (thanks /u/jaytee-nz)  it means I can look at the correct parts lists and diagrams and more importantly spend more money at David Silver buying bits - this time they should even fit....

I had a very difficult time getting the caliper arm to bits.  It involved a 4lb club hammer, a big drift, and lots of penetrating oil. The suggestion to apply heat was a good one.  I had a paint stripper gun (electric) and gave it a seeing-to with that. Eventually I got it to bits and I have cleaned up the pivot pin and the fixed and moving parts.  it all goes together well now.

My question is this:  The parts list I downloaded from this site shows that there are O rings and washers from stock.  I dont have them.  I will go buy some but I am just checking that they go at either side of the swinging part of the caliper with the assembly order between the fixed parts of the caliper being washer - O ring - swinging part of caliper - O ring - washer?  That seems logical and a way to trap grease in between the pivot pin and swinging part of the caliper but I would be grateful if someone would confirm.

I have only 1 -2 mm of vertical play between the swinging and fixed parts of the caliper but I can always file it to get the clearance I need.  I maybe closed it up a bit whaling on it with the hammer...... It was REALLY stuck though.  took a day of soaking to get to a point where I could shift it sideways with the hammer.  I hope that repairing this will assist with my brakes !

Offline bryanj

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Re: CB750K2 brake issues and question
« Reply #1 on: February 06, 2019, 12:50:10 am »
1-2 mm is maximum play there, i remember O rings but not washers
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Online pjlogue

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Re: CB750K2 brake issues and question
« Reply #2 on: February 06, 2019, 05:53:40 am »
As Bryanj said, there are two O rings and no washers.  When I rebuilt mine, getting the pin out was a bear.  Clean everything well and smooth the edges with 600 grit sandpaper where the O ring contacts the bracket so it is smooth.  Using marine grease on the pivot pin is good as it is subjected to spray during rain. 

-P.

Offline Johnie

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Re: CB750K2 brake issues and question
« Reply #3 on: February 06, 2019, 08:36:13 am »
Looking at my hardcopy parts book I see what you mean about the washer. The book shows a washer, but that is at the bottom of the pivot pin with the cotter pin last in the set up. No washers near the pin seals. I had a pivot pin stuck pretty bad. Used PB Blaster and it still was difficult to remove. Once out I had to polish the interior bushings again to get a smooth movement. Good luck with yours.
1969 CB750K0 - Candy Blue Green
1970 CB750K0 - Candy Ruby Red
1970 CB750K1 - Candy Gold
1973 CB750K3 - Candy Bacchus Olive
1974 CB750K4 - Flake Sunrise Orange
2000 1500 SE Wing
1971 CB750K1 (next project)
1969 CB750K0 (The Patina Bike - Blue / Green)

Oshkosh, WI  USA

Offline KuangGradeMark11

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Re: CB750K2 brake issues and question
« Reply #4 on: February 09, 2019, 08:29:39 pm »
Thanks everyone.  Its back together, moves freely, and I am about to go and put some fluid in it and see if the brake works.  Incidentally I had a real issue getting O -rings that fit. The manual calls for 10 x.7mm and all the ones I could get (2 x automotive parts stores and 1 x bigass general hardware store) had 9 x 2, 11 x2 in stock.  One had 10 x 2 so I bought the 9 and 10.  The issue was the thickness because the ring sits in a groove.  If the ring fits the outer part of the groove it is too small to let the pin pass through (9x 2).  If it allows the pin to pass it won't fit the groove and the caliper mount does not go together.
 I eventually bought a 239 piece made in China O-ring selection (if you need any, hit me up!) which had 10 x 1.5. That worked.  I wouldnt have thought the .5mm each side would be such an issue but I think it was just enough that it grabbed it and pulled it into the fitting.

Thanks for the responses and I will post about whether or not this has made any significant difference to my brake.

Cheers.

Offline Old Moe Toe

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Re: CB750K2 brake issues and question
« Reply #5 on: February 10, 2019, 12:17:27 am »
Wont make a hell of a lot of difference.
Brakes are ordinary at best.
That's what you get with a bike this age. Still fun to ride though.

Offline KuangGradeMark11

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Re: CB750K2 brake issues and question
« Reply #6 on: February 10, 2019, 02:08:45 am »
This isn't the first CB750 I've owned and all of them have had way better brakes than this one. When I pulled the (new, sintered) pads they had clearly been wearing  (in about 400km) unevenly.  I theorise that because the caliper mount was locked solid, most of the "bite" went out of the system.  I will definitely be looking forward to a test ride later this week.  In the meantime I have to drop the wheel off again because I forgot to put the mudguard back on before putting the wheel on...

 

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Honda