1973 620 Truck Disc Front Brakes

[dats-injin]

Hello you all, I looked in the search are but could not find any information on my problem. Anyways, my question is I changed my from brakes over to disk, the master is the original from the drums but I am having an issue, when I apply my brakes it doesn't seem to want to release. A friend told me that there is a valve that I need to remove or something. Any of you guys know what I need to do? I was thinking of getting a master from a 280z, but if there's a valve in line I would still need to find it. I followed the hard lines from the master and it runs on the firewall to a copper T-block that splits to right and left brakes. Is there a valve inside the T-block or do I just need the 280z master or better option?

[dats-injin]

Sorry, here are pics of truck, I am new so not sure if the pics will show. I have a photobucket account with the pictures in there.

 

 

 

 

 

[sycloned916]

Sorry, here are pics of truck, I am new so not sure if the pics will show. I have a photobucket account with the pictures in there.

 

 

 

 

 

Nice truck those rims look bad ass on it. On the brakes i think most people swap to the 280 master i think and some use the power booster if i remember.

[motavated]

I was not sure of keeping my truck Mustard. But after seeing your truck. I want to keep it the same! ITS ALLLLLLL RIGHT!

 

For the awesome pics. I present you a thread were a guy had a similar problem. Good luck! :D

http://community.ratsun.net/topic/11707-gustavs-1975-low-620/page__p__156042entry156042

[motavated]

http://community.ratsun.net/topic/3908-broken-brakes/page__view__findpost__p__51477

[kaoss]

God I wish they still made those wheels!

[SHADY280]

the problem is that the drum brakes use residual valves to hold pressure against the drum to help reaction time. you can fix that by installing a 78/79 620 master. this will retain the rear drum residual and have no residual on the front. you may need to replace the factory rear bias valve with a manual one to set the balance. this is found under the passanger seat. if you use a 280 master, you wont have the rear residual valve built in, this causes the rear brakes to work a bit slow, also causing increased panic stop distance.

[SHADY280]

the problem is that the drum brakes use residual valves to hold pressure against the drum to help reaction time. you can fix that by installing a 78/79 620 master. this will retain the rear drum residual and have no residual on the front. you may need to replace the factory rear bias valve with a manual one to set the balance. this is found under the passanger seat. if you use a 280 master, you wont have the rear residual valve built in, this causes the rear brakes to work a bit slow, also causing increased panic stop distance.

[dats-injin]

Thanks guys for your fast response to my post. I read the post you all hit me up on and totally agree with adjusting the push rod. I had forgotten all about that when I did the disc conversion because it worked great for a week until today when it really started getting noticeable tighter. Come to think about it, I installed some new pedal plates and had to drill through the old plates to mount the new ones and do remember having to really push down to drill. I am sure that helped in creating the added pressure that I am experiencing.

 

Yeah, the mustard color isn't the most likeable color out there but in my case it makes the truck pretty unique and original paint is always better, hehe.

 

Thanks, I will get back with results tomorrow after I adjust push rod. I am 100% sure that is the problem because I remember that happened before on friends honda afte new booster/master install.

[herculesinwyoming]

great looking truck, the door dings must piss you off, i have them in all 4 of my vehicles. people just dont care

[dats-injin]

Tell me about it, I am not liking them holes. They were from the previous owner using them triable bar with those huge rear merrors. I want to fix them but then that would mean repainting the whole truck and I want to keep the original paint. O well, it just adds to the originality of the truck, hehehe....

 

 

[slowdown]

heck ya keep it original!!! what color was the truck that always had to take a crap...

 

 

 

musturd

[Jersey]

nice looking truck...love the color and the wheels!

[nis720]

God I wish they still made those wheels!

 

I always wanted Timeless 6 wheels too.

[motavated]

I always wanted Timeless 6 wheels too.

They were on cragslist for a while. Maybe a week? They came of a white 620 I believe with a crazy paint job. I think that truck is in ratsun as well....

[nis720]

They were on cragslist for a while. Maybe a week? They came of a white 620 I believe with a crazy paint job. I think that truck is in ratsun as well....

 

This truck was at the SWDP BBQ last year.

[kaoss]

I'd love to have them if you ever want to sale them. What size are they?

[budsaipan]

Where did you get the front valance?

[dats-injin]

Sorry, the wheels aren't going to be for sale. I've had the wheels on the truck for a long time now, if ever, they will go with the truck, hehe.

 

The rims are 8x18, I have 215/35/r18 on them, I wanted the stretch look and was also concern about rubbing the fenders.

 

These rims aren't from that truck unless he sold them to me about a yr ago. I have been slowly working on my truck for a while now, been reading here but never register as a member until I ran into this brake problem and couldn't find the anwser. Most of the other stuff was just cosmetic which I can handle.

 

The valence I made from a peice of sheet metal I had laying around. It didn't cost me much but time, skin, elbow grease, and sum blood.

 

I did split the master from the booster and turn the push rod all the way in on the threads, essentially making it shorter. I hope that's the right direction but I haven't had a chance to drive it enough to see if its made a difference. I drove it around the block and the only noticeable difference is I have to step deeper before I could feel the brakes working. I played around with the clip that bolts behind the pedal to the rod that goes through the booster but only difference I could see there is that it just moves my pedal down or up, so I just left it alone. I will drive it to work tomorrow and hope it doesn't lock up on me. I really didn't notice any changes.

 

 

[mklotz70]

I could be wrong, but my understanding is that the residual valve is built into the bottom of the m/c, right where the line connects. That really big nut is holding it in. If you use a m/c of a disc/drum 620 or 280z, it should work fine, but I'd put an adjustable proportioning valve in the rear circuit. The biggest difference between the 620/280 m/c's are the bore....280 has a 15/16" bore...your pedal will be firmer and not travel as far.

[dats-injin]

Thanks for that bit of info, I was looking for someone to tell me where that valve was located. What I did probably isn't going to change my condition. Looks like I am going to have to get me a 280z master and proportioning valve.

 

Will the booster from the 280 bolt up? What booster should I get?

[dats-injin]

Well, just wanted to close this post. I went with a new 79 booster and master. I had to grind the spacer between the booster and master in order to make it work. Did some adjustments of the push rod and everything is looking good. I got good brakes, yeeeehaaa!!!!

[SHADY280]

yes the valve is in the master where the big nuts are. thats why you cant use a 280zx master for rear drums. you may still need the bias valve. go find a gravel parking lot, take a friend. the rear should lock just before the front, like 1/4 second before. if not adjust the bias with said valve.

[Grey_Matter]

how did you swap the 73 to front discs? i cant find a write up anywhere. i did read the 620's with discs front suspension parts arent interchangeable

[Grey_Matter]

N/M i found my answer

http://community.ratsun.net/topic/10169-73-620-disc-brake-swap/page__hl__disc+brake+conversion__st__20