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620 brake master ?'s


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I noticed a problem recently on my 74 620. When i step on the brakes i notice the idle goes way down almost to the point that the truck dies. When i let off the brakes it goes back up. Could this be caused by a bad brake master? Bleach told me it could be a bad vaccum assist. can this part be replaced or should i just buy a new brake master??

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Not a bad master- a bad booster will do that. The master cyl doesn't have any connections to the engine.

 

I had one car with a decent-sized short in the taillight wiring that loaded the alternator and dropped the idle though. The voltage drop was pretty obvious- lights dimmed and the voltmeter went from 13.5 to 11 when I hit the brakes.

 

But I'd be more inclined to think it's the vacuum booster. They eventually do give out.

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I noticed a problem recently on my 74 620. When i step on the brakes i notice the idle goes way down almost to the point that the truck dies. When i let off the brakes it goes back up. Could this be caused by a bad brake master? Bleach told me it could be a bad vaccum assist. can this part be replaced or should i just buy a new brake master??

You can Mark, but they're so damned expensive that you might as well replace the whole thing. That is if they have one, you might have to j/y hopping. If you're gonna replace it, you might just get a newer generation one so you're already set up for when you put discs on her.

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Ok Kragen [shucks] carries the booster

http://www.partsamerica.com/ProductList.aspx?parttype=250&ptset=A&searchfor=Power+Brake+Unit

I was thinking of replacing the master cylinder too just to be sure.

http://www.partsamerica.com/ProductDetail.aspx?mfrcode=BAR&mfrpartnumber=0722678&parttype=230&ptset=A

I know they are expensive but i dont wann ago cheap on the brakes..! Jason..if I do want to "upgrade" what year Datsun vehicle booster should i buy?

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  • 4 weeks later...
I've got one from a '87 sentra, it's a 7/8 bore I believe? I'm thinking of using it because it has the single res. like on the hb's.

Take my advice and go Dual circuit!

I lost a line and it could have been disastrous as i was on the freeway the day before bringing home a motor...

thank goodness I had fixed my e-brake..

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I had a '71 521 and seem to remember it was a dual system. My previous '68 dime was a single. I did get a dual and separate the front from the back. The lines were a different shaped flair and wouldn't seal against the M/C properly. I used a file to re-shape the taper and all was good.(geez... I can't believe I did that and lived to tell it). Anyway, the brakes worked at least as good and I knew if there was a sudden leak, I still would have some brakes.

Dual systems were an innovation of the late '60s. Prior to that you would often hear of accidents involving brake failure, when do you hear that now? Kids today will say they remember when cars didn't have Anti Loc brakes!

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