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Front disk brake conversion - additional info, notes and pictures


JesseR

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Hello all, I just completed a front disk brake conversion using Beebani's brackets and parts list. I wanted to share my experience. This conversion was on my 76 620 short bed regular cab. I had a leaky drum piston and the thing never stopped anyway so I treated myself. I was really surprised at how easy this conversion was but i wish i had some of the following info before starting.

 

I went with 15" US Wheel steelies in black to replace my 14s, they are 15x7, 3.75 backspace and the fit is perfect. tires are new Bridgestone Ecopias 205/65/R15. I went with 15s to have as much sidewall as possible to make up for the lack of suspension. The truck is lowered 2.5 inches in the front and 2 in the rear in case you are interested. I like the stance and it is still a usable daily driver and work/trash hauler.

 

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I began with the tear down, I was surprised how easily all the bolts and brake lines came free.

 

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Next I pressure washed the remaining parts with a little cleaner.

 

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Now Install Beebani's brackets, i primed them first. I was really happy with the fit.

 

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Beebani's kit did not include the bracket or caliper mounting bolts. I was able to reuse the drum mounting bolts but had to order the M12x1.25 pitch 30mm caliper bolts from Fastenal. They are grade 10.9. Fastenal also provided lock washers.

 

Next I used brake cleaner to clean all the bearings, hubs and spindle parts. Repacked all bearings and reinstalled the hubs.

 

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When i was installing the rotors I had one that would not fit over the hub. I used a grinder with a flap disk to sand the outer edge of the hub until the disk fit.

 

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I Ordered the calipers (loaded with pads), brake lines and rotors from RockAuto. One thing to mention is none of these parts came with the banjo bolts required to connect the brake line to the caliper. I had to get the metric (Japanese application) banjo bolts from Napa.

 

Now the calipers can be installed. I used 2 lug nuts to hold the rotor in place while assembling the calipers.

 

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The brake lines all got cinched down and bled with new fluid. I am, for now using the stock 3/4 master cylinder. Tires got reinstalled and road tested. The brake seems to have a little to much travel but i am guessing that is because the 3/4 mc is not moving enough fluid. I can order the larger one if anyone can confirm that that is my issue?

 

My biggest take away, easy conversion, order your banjo bolts and caliper mounting bolts well in advance of starting because it can take time. The banjo bolts and caliper mounting bolts could not be purchased from RockAuto.

 

Definitely a worthwhile upgrade. For less that a $1000 i got new rims, tires, and brand new disk brakes that stop!

 

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Could i just remove the residual valve from the 3/4 master cylinder I have? I have been reading posts about the differences between the 3/4 and the 13/16 and they both seem fine. Is there something I am missing other than the RV.

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I bought a Miyabi kit (made in Japan), off eBay, and it came with both.

There is a slight difference, and they included a diagram showing which was which.

I pretty sure I have the diagram, but it will take some digging to find it.

 

This Raybestos kit shows multiple residual valves:

http://www.ebay.com/itm/Brake-Master-Cylinder-Repair-Kit-Professional-Grade-fits-75-77-Nissan-620-/332028895068?fits=Model%3A620&hash=item4d4e76df5c:g:LNEAAOSwImRYJYd8&vxp=mtr

 

Here are some part numbers from the 1200 forum:

46050-M0800 VALVE-RESIDUAL,FOR DRUM (2)
46050-M0801 VALVE-RESIDUAL,FOR DISC
46050-M0800 VALVE-RESIDUAL,FOR DISC

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I am going to order the Raybestos MC39279, the MC for a 79 620. That way its setup for the disk/drum configuration and i get a larger reservoir for the front fluid. I have credit at Summit Racing i need to use anyway.

 

Took some getting use to the new brake feel today. It drives much better and its nice not having to guess which way the truck it going to go when you have to use the brakes.

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I always hated that, but I always knew which way it was going to go, counter clockwise spin, and I was never able to stop it from doing it, an emergency stop is an emergency stop, what can one do, let off???

It is why I fabricated disc brakes for my 521 back in the mid 2000s, now I control which way it goes although it would be better to have power brakes. 

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  A 205/65R15 is 1.5" taller than the stock tire and will affect your performance and your speedometer reading.  A 205/55R15 will be closer to stock height and still be 8" wide. 15" will have less sidewall that a 14" if sidewall flex is what you want.

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A 205/65R15 is 1.5" taller than the stock tire and will affect your performance and your speedometer reading.  A 205/55R15 will be closer to stock height and still be 8" wide. 15" will have less sidewall that a 14" if sidewall flex is what you want.

195/65R15 will give extra sidewall and the same dimensions of the 205/55.

 

I used the 195/65. I liked that there was just a light bit of stretching allowing it to tuck under my fender just right.

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Ah, the infamous counter clockwise spin. I had the truck go full 180 in that direction at 25 mph on a dry road braking to avoid an animal. Fortunately there was no one on the road around me. I think I ordered the disk brake parts the same week.

 

The speedometer does not work correctly. I got it that way. It is off by a random amount and does not register over 40mph. I gave up and just use DigiHud on an old phone that I have.

 

As for the tires. The truck had 205/75/14's when I got it, I just went equivalent size to that. I figured how the tire width would fit with the wider rim. I could not find any inexpensive 15x6 rims that would work for me. I got them at Summit for $53 a piece on sale. I am glad i went with the 15x7's. I went to the dump yesterday and the tires still were able to tuck under the fender with a load in the rear.

 

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Banjo bolts are pretty common at most supply houses.

 

https://www.mcmaster.com/#banjo-bolts/=15fre0b

 

https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=banjo%20bolt

 

https://www.pegasusautoracing.com/keywordsearch.asp?KeywordStart=banjo+bolt

 

Don't use aluminum banjo bolts on brake components though. Steel fittings throughout the brake system should be used. Safety reasons.

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Banjo bolts are pretty common at most supply houses.

 

https://www.mcmaster.com/#banjo-bolts/=15fre0b

 

https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=banjo%20bolt

 

https://www.pegasusautoracing.com/keywordsearch.asp?KeywordStart=banjo+bolt

 

Don't use aluminum banjo bolts on brake components though. Steel fittings throughout the brake system should be used. Safety reasons.

Aluminum vs steel corrosion...with brake fluid that is hygroscopic...recipe for failure.

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