4 wheel disc brake conversion

[b29fred]

I just bought a 70 pick up with modified 4 wheel disc brakes.

 

It has a dead Master Cylinder but no part number to replace it?

 

My mechanic can't get a matching replacement without proper part.

 

I need to do the leg work to find the Year and Model of Master Cylinder that is on the truck now.

 

Has anyone modified their brake system on these older pick ups?

[datzenmike]

http://community.ratsun.net/topic/54932-photobucket-ratsun/

 

Post a picture of it. Very unlikely it's the original if running disc brakes.

[HOGIE]

For your '70 datsun pickup' the correct, stock, brake master cylinder is a single reservoir and this part can be sourced through rockauto.com. But having gone to all 4 wheel disc brakes you should probably upgrade to a dual-reservoir master cylinder. Datsun 510's from the same year came with dual-reservoir brake master cylinders and these can also be sourced, not sure through rockauto, but you will have to run a proportioning valve, but I'm sure you mechanic has already installed on of those for your brake set up

[wayno]

First I would ask if it has front and rear circuits(dual reservoir master) like in the photo below.

 

Then I would just find a Z car year that had 4 wheel disc brakes and buy that, hopefully it will be the same bore size, but whatever master you buy, it needs to be from a car/truck with 4 wheel disc brakes.

[Stoffregen Motorsports]

Datuns are bastards. Tons of parts parts of the same era will transfer over with a little work.

 

Your mechanic may not be willing to add a dual circuit master because it's outside his comfort zone, but if you did all the legwork and brought him parts known by others to work, then he would probably go for it.

[flatcat19]

There should be a cylinder size listed on the MC.

 

 

I would lean towards getting a MC from a 1978 or 79 280zx as it is 7/8" bore and from a car that came stock with 4 wheel discs.

 

 

Pics would help. Wondering if you have a prop valve installed or not.

[wayno]

As far as any of us know he could have the stock 521 brake master with a defective or removed residual valve, or he could have a dual circuit system already.

We are guessing right now as we don't have the info we need to make a informed suggestion.

[flatcat19]

Very true.

[datzenmike]

VERY unlikely it's the single stock master with disc brakes.

[hosestop@msn.com]

I am running 4wheel disc on a single master seems ok must have an e brake incase of failure ( maybe a 311 one)and if was not going to work , Wilwood make some bigger bore ones that will .

[datzenmike]

The trouble with larger masters is you need more effort to push them. Think hydraulic jack. This is why most Datsuns after the 60s have brake boosters. Larger cars and trucks need larger brakes, need larger masters to work them.

[wayno]

I used the stock 521 brake master for 15 years with front disc brakes in the work truck, I actually went thru a couple of them, all I did was remove the residual valve.

I recently(last week) changed/converted over to a dual circuit system using a early 620(74) booster and a late 620(79) brake master, it definitely stops better now, but since the trailer had electric brakes I did really have an issue with stopping before, I just had to push harder, I will admit the rear brakes didn't really work though, not sure they are working now either, I need to raise the rear off the ground and see if they work to know for sure.

This is what I have now, I posted it earlier in this thread asking if he had a dual circuit system but have received no reply to that question.