I need more boost from my Brake booster Which year did GM go do dual diaphrams?

[Chevy Muscle]

I put disks on the front of my '69 K5 and I replaced my M/C, prop valve for the correct disk/drum versions.

However, my booster isn't boosting enough and I have a very hard pedal. I'm getting 16" of vacuum at slow idle and over 20" of vacuum at driving RPMs.... but still too hard.

I want to replace my booster. I've been offered used ones from a '74 3/4 ton and one from a '87 1/2 ton truck.

Main question: What year did GM improve the design of the boosters? (go to dual diaphrams?)

[Rod]

Every year of this vintage had a dual diaphram option..but you'll only see it on 3/4 and 1 tons. It became standard equipment in 1971 on 3/4 ton and 1 tons...earlier years were options. You can put it on your 1/2 ton or blazers....its a bolt on upgrade.

[Chevy Muscle]

Attached is two pictures of the booster that a PO put on. (I know the vac hose routing is goofy)

I don't think this blazer originally had power brakes so I'm not sure what this booster came from...... says 'Delco' on it.

Is it a dual diaphram?

[da-burb]

looks like the 71+ style dual diaphram booster to me.

[Deuce]

Originally Posted by da-burb

looks like the 71+ style dual diaphram booster to me.

How can you visually tell??

[Chevy Muscle]

Originally Posted by Rod

Every year of this vintage had a dual diaphram option..but you'll only see it on 3/4 and 1 tons. It became standard equipment in 1971 on 3/4 ton and 1 tons...earlier years were options. You can put it on your 1/2 ton or blazers....its a bolt on upgrade.

I did a parts lookup for a 69 1-ton, 72 1-ton, 74 3/4 ton and 76 1/2 ton.

The 69 and 72 1-tons called out two different numbers (I thought that interseting.... but no indications of single or dual diaphrams)

The 74 and 76 shared the same number. They had this one in-stock at my local parts store and it looked very similar to the one I pictured above. (they didn't have the other numbers in stock)

[Rod]

The reason there two numbers is because one type was Moraine and the other was Bendix. Both were dual diaphram. And your looks like dual already..there thicker.

Here's a pic of a 1970 1/2 ton booster , note its thinner. Not the best pic to show that but its what I found quick.

[avejoe]

I had the same problem you had with braking.

I just purchased a new booster (which required at new master cylinder), for $150. It made all the difference in the world. Call Power Brake Supplies in Sacramento, CA. I took my truck in and they knew exactly what I needed. I am sure they could ship to you.

[Rod]

There are shops that rebiuld them around here..maybe something like that is available for you also near you.

[flip66]

I would like to know what you find out I have the same problem. I have the same master cylinder but a different booster. I was going to try the master cylinder that has the same size reservoirs I think it is the bendix. It looks like most of the 71 and 72 with disc have that one I do not know it will make a diff.

[Rod]

There's a seller up Hello!n wHello!nnHello!peg sellHello!ng booster on ebay now..rebuHello!lt unHello!t.


http://cgHello!.ebay.com/ebaymotors/ws/eBayHello!SAPHello!.dll?VHello!ewHello!tem&Hello!tem=7955377345&fromMakeTrack=true


[Hello!mg]http://Hello!16.ebayHello!mg.com/01/Hello!/03/64/6b/74_12_sb.JPG[/Hello!mg]

[poff]

When I converted to discs on my '70 I found that most auto parts stores only stocked one of the master and booster combos so I got that one. The one you have may be for power drums, don't know what the difference is but it is different. It is possible that you have the brackets for power drums which are also different and could effect the effective stroke and angle of the master.