3/4 ton brake booster - The 1947 - Present Chevrolet & GMC Truck Message Board Network

skid · 08-07-2004, 12:51 PM

Will a 3/4 ton brake booster bolt right up in place of a 1/2 ton booster? I have read that they will provide more stopping power, but am unsure whether they will bolt right up. I am going to buy one or the other today.

*FormerMember* · 08-07-2004, 01:22 PM

Yes, they will.

I used one on my 71 Blazer.

MC is the same part number.

You may have to move or extend your brake lines. The booster is longer.

skid · 08-07-2004, 01:34 PM

Thanks Grendal

I found this article on ColoradoK5 as well...

http://coloradok5.com/forums/showfla...o/fpart/1/vc/1

*FormerMember* · 08-07-2004, 03:33 PM

Quote:

Originally Posted by skid

Thanks Grendal

I found this article on ColoradoK5 as well...

http://coloradok5.com/forums/showfla...o/fpart/1/vc/1

Yep, Ryan's a good guy.

7gmc2 · 08-07-2004, 10:35 PM

i am noticeing that most of you responding to this post are blazer drivers.....is this a good idea for trucks too, or is this a really dumb question? great post though none the less....

Sweet72 · 08-07-2004, 10:55 PM

When I converted my half-ton '72 GMC I used a booster from a 3/4 ton pickup and it worked great, till the old diaphram blew out. I can't believe the prices for new boosters!

toddtheodd · 08-07-2004, 02:14 PM

Great, another thing to add to the list of stuff to do

7gmc2 · 08-07-2004, 11:10 PM

thanks sweet72! sorry to hear the diaphram trouble, but glad to see it does apply to trucks as well......

**PICKMUP** · 08-07-2004, 11:24 PM

If you are talking about the dual diaphram, DB booster, 71-2, they do not use the same MC as the 1/2T. The hole is a much different depth and will not work. You have to use the matching 3/4T MC with the 3/4T booster....then the whole package will bolt in the 1/2T truck and work.

dennis111 · 08-08-2004, 01:22 AM

I am wanting to do the 3/4 ton swap on a 68' but believe the brackets are different than a 71-72 truck.

Should I use one from a 68' version instead? It looks like a dual diaphram too but carries a different part # in the parts catalog.

If I use the 68' diaphram, what master cylinder would I use for disk brakes?

Anyone done the swap on an older blazer/truck?

skid · 08-08-2004, 01:43 AM

The 3/4 ton brake booster and Corvette master cylinder are in and well, let's just say I can lock all four tires up at 60 mph! I could hardly make the tires squeal at 10 mph before. A definate improvement! Much better pedal feel and modulation as well.

It wasn't quite a bolt in though. I had to extend the front support brace 1 11/16" (welded in a extension) because that is how much wider the 3/4 ton booster is over the 1/2 ton. The plunger rod that came with the 3/4 booster was too short as well. I had some 3/8 drill rod laying around that i measured and cut so that there was maybe 1/4 inch of pedal travel before the master cylinder moved.

The Vette master cylinder is almost identical to the stock m/c. The bore size is the same, and the ports are spaced the same, with just a little offset. I just tightened the lines, and the lines re-adjusted themselves. I loosened the lines on the combination/proportioning valve as well before I tightened the lines on the master cylinder to help them align.

All in all, a definate improvement that just took a little messing around to complete...

7gmc2 · 08-08-2004, 08:46 AM

ok now i'm confused? $*#@ at first this sounds like an easy swap, one booster for another. the link to the article gives me the same impression. i gathered that the master cylinder for the 3/4 ton was an optional swap. bottom line is i have a 1/2 ton 72 with disk brakes now. what do i need to do to make this work? 3/4 ton booster only, or 3/4 ton booster and 3/4 master cylinder package?

toddtheodd · 08-08-2004, 10:22 AM

The way I understood the talk under that link was that you could use either. That it was more of how you wanted the pedal to feel.

skid · 08-08-2004, 11:46 AM

7gmc2,

You can use your stock m/c. All you would need to do is extend the brace and make a new, longer, plunger rod (at least that was my experience). I used a Corvette (1974) m/c because I am going to use rear disk brakes eventually, plus I used my Vette to compare sizes so I knew it would fit.

A 3/4 ton m/c would not really make sense to use because the lines are backwards, with the rear brake lines at the front of the m/c.

7gmc2 · 08-08-2004, 01:39 PM

thanks for clearing that up for me skid! i too plan to go to an all disk set up so that is helpful to know. i wonder if there is a plunger rod that you can buy already the right length?

skid · 08-08-2004, 02:35 PM

Actually it is pretty easy to make a plunger rod. You just need to measure how far it needs to stick out past the m/c mount. A long 3/8 bolt could be used for a plunger rod, just cut off the hex, and round of the m/c side on a grinder. I mounted mine in a drill and spun it as I ground it. This made it perfectly round.

skid · 08-08-2004, 02:42 PM

Just to add to my previous comments regarding the plunger rod:

Measure how far in the m/c piston the hole goes (remember to measure to the mount flange and subtract the difference). Place the rod in the booster and measure how far the rod sticks out. Subtract the difference
and cut the rod. I left a slight bit of clearance to give me a little pedal travel before the m/c piston moves.

**PICKMUP** · 08-08-2004, 04:04 PM

It is very simple install and requires no mods or cutting. Take the complete 71-2 3/4T DB booser, brackets, rod, MC, prop valve---hook up your two lines to the prop valve---install it and run it. Don't mix or shim other parts. The rod will hook right up to your pedal. The pedal on PB hangs lower in the cab...that is normal and correct.
If you go to rear DB in the future, you will need a different prop valve.

The pictured Corvette style MC, prop valve set is made to work with both 1/2T or 3/4T boosters. It has a machined safe engineered insert for the two depths.

nate68 · 08-08-2004, 04:38 PM

I'm using a corvette master cylinder with a 68 3/4T Booster. everything works fine.

Robert1970C20rstbukt · 08-08-2004, 09:13 PM

My truck already had a 3/4 brake booster in it, it's the original one too. I never had any problems with the brakes. My truck also has the HD brake and suspension option.

Southpa · 08-08-2004, 10:57 PM

I had no problems swapping. The pic shows the old 1/2 ton drum/drum setup converted to disc/drum setup. Notice 1/2 ton m/c for disc drum with 3/4 ton booster. No mods, shimming, welding etc. needed, it just bolted right up!

skid · 08-09-2004, 12:09 AM

Southpa, my Blazer has a support from the front of the booster to the firewall (it also has one on the back). I notice your picture doesn't show one. That is the piece that I had to extend. I also used a Corvette m/c for a future rear disk conversion. The 3/4 ton booster came with too short of a plunger for my stock m/c as well. Maybe there are different length rods for different applications.

Budweis · 08-09-2004, 02:49 AM

had some questions bout the vette mc but guess ill start a new thread on it so i dont hijack this one

08-07-2004, 12:51 PM	#1
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	3/4 ton brake booster Will a 3/4 ton brake booster bolt right up in place of a 1/2 ton booster? I have read that they will provide more stopping power, but am unsure whether they will bolt right up. I am going to buy one or the other today. __________________ Toys: 72 K5 Blazer 74 Vette

08-07-2004, 01:34 PM	#3
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	Thanks Grendal I found this article on ColoradoK5 as well... http://coloradok5.com/forums/showfla...o/fpart/1/vc/1 __________________ Toys: 72 K5 Blazer 74 Vette

08-07-2004, 10:35 PM	#5
7gmc2 Registered User Join Date: Jun 2004 Location: Rockville Va. Posts: 260	i am noticeing that most of you responding to this post are blazer drivers.....is this a good idea for trucks too, or is this a really dumb question? great post though none the less.... __________________ 1972 GMC Sierra Grande

08-07-2004, 10:55 PM	#6
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	When I converted my half-ton '72 GMC I used a booster from a 3/4 ton pickup and it worked great, till the old diaphram blew out. I can't believe the prices for new boosters! __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

08-07-2004, 11:10 PM	#8
7gmc2 Registered User Join Date: Jun 2004 Location: Rockville Va. Posts: 260	thanks sweet72! sorry to hear the diaphram trouble, but glad to see it does apply to trucks as well...... __________________ 1972 GMC Sierra Grande

08-07-2004, 01:22 PM	#2
FormerMember Account Suspended Join Date: Feb 2004 Posts: 3,051	Yes, they will. I used one on my 71 Blazer. MC is the same part number. You may have to move or extend your brake lines. The booster is longer.

08-07-2004, 02:14 PM	#7
toddtheodd The oddest Todd around Join Date: May 2004 Location: Miami, Florida Posts: 1,418	Great, another thing to add to the list of stuff to do

08-07-2004, 11:24 PM	#9
PICKMUP "Trucks with Class" Join Date: Jul 2000 Location: OLYMPIA, WA, USA Posts: 8,125	Not the same If you are talking about the dual diaphram, DB booster, 71-2, they do not use the same MC as the 1/2T. The hole is a much different depth and will not work. You have to use the matching 3/4T MC with the 3/4T booster....then the whole package will bolt in the 1/2T truck and work. __________________ Email: frankeham@comcast.net Phone: 360-956-7170

08-08-2004, 01:22 AM	#10
dennis111 Registered User Join Date: Jul 2004 Location: Amish Wonderland of Central PA. Posts: 31	I am wanting to do the 3/4 ton swap on a 68' but believe the brackets are different than a 71-72 truck. Should I use one from a 68' version instead? It looks like a dual diaphram too but carries a different part # in the parts catalog. If I use the 68' diaphram, what master cylinder would I use for disk brakes? Anyone done the swap on an older blazer/truck? __________________ Dennis 68 GMC SWB Custom 1/2 ton, 2WD, 350 V8, PS, PB, 3-Speed, 3:08 12 bolt rear, tilt, tach, vac, cruise and more. . . .

08-08-2004, 01:43 AM	#11
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	The 3/4 ton brake booster and Corvette master cylinder are in and well, let's just say I can lock all four tires up at 60 mph! I could hardly make the tires squeal at 10 mph before. A definate improvement! Much better pedal feel and modulation as well. It wasn't quite a bolt in though. I had to extend the front support brace 1 11/16" (welded in a extension) because that is how much wider the 3/4 ton booster is over the 1/2 ton. The plunger rod that came with the 3/4 booster was too short as well. I had some 3/8 drill rod laying around that i measured and cut so that there was maybe 1/4 inch of pedal travel before the master cylinder moved. The Vette master cylinder is almost identical to the stock m/c. The bore size is the same, and the ports are spaced the same, with just a little offset. I just tightened the lines, and the lines re-adjusted themselves. I loosened the lines on the combination/proportioning valve as well before I tightened the lines on the master cylinder to help them align. All in all, a definate improvement that just took a little messing around to complete... __________________ Toys: 72 K5 Blazer 74 Vette Last edited by skid; 08-08-2004 at 01:46 AM.

08-08-2004, 08:46 AM	#12
7gmc2 Registered User Join Date: Jun 2004 Location: Rockville Va. Posts: 260	ok now i'm confused? $*#@ at first this sounds like an easy swap, one booster for another. the link to the article gives me the same impression. i gathered that the master cylinder for the 3/4 ton was an optional swap. bottom line is i have a 1/2 ton 72 with disk brakes now. what do i need to do to make this work? 3/4 ton booster only, or 3/4 ton booster and 3/4 master cylinder package? __________________ 1972 GMC Sierra Grande

08-08-2004, 10:22 AM	#13
toddtheodd The oddest Todd around Join Date: May 2004 Location: Miami, Florida Posts: 1,418	The way I understood the talk under that link was that you could use either. That it was more of how you wanted the pedal to feel.

08-08-2004, 11:46 AM	#14
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	7gmc2, You can use your stock m/c. All you would need to do is extend the brace and make a new, longer, plunger rod (at least that was my experience). I used a Corvette (1974) m/c because I am going to use rear disk brakes eventually, plus I used my Vette to compare sizes so I knew it would fit. A 3/4 ton m/c would not really make sense to use because the lines are backwards, with the rear brake lines at the front of the m/c. __________________ Toys: 72 K5 Blazer 74 Vette

08-08-2004, 01:39 PM	#15
7gmc2 Registered User Join Date: Jun 2004 Location: Rockville Va. Posts: 260	thanks for clearing that up for me skid! i too plan to go to an all disk set up so that is helpful to know. i wonder if there is a plunger rod that you can buy already the right length? __________________ 1972 GMC Sierra Grande

08-08-2004, 02:35 PM	#16
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	Actually it is pretty easy to make a plunger rod. You just need to measure how far it needs to stick out past the m/c mount. A long 3/8 bolt could be used for a plunger rod, just cut off the hex, and round of the m/c side on a grinder. I mounted mine in a drill and spun it as I ground it. This made it perfectly round. __________________ Toys: 72 K5 Blazer 74 Vette Last edited by skid; 08-08-2004 at 02:43 PM.



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08-08-2004, 02:42 PM	#17
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	Just to add to my previous comments regarding the plunger rod: Measure how far in the m/c piston the hole goes (remember to measure to the mount flange and subtract the difference). Place the rod in the booster and measure how far the rod sticks out. Subtract the difference and cut the rod. I left a slight bit of clearance to give me a little pedal travel before the m/c piston moves. __________________ Toys: 72 K5 Blazer 74 Vette

08-08-2004, 04:04 PM	#18
PICKMUP "Trucks with Class" Join Date: Jul 2000 Location: OLYMPIA, WA, USA Posts: 8,125	It is very simple install and requires no mods or cutting. Take the complete 71-2 3/4T DB booser, brackets, rod, MC, prop valve---hook up your two lines to the prop valve---install it and run it. Don't mix or shim other parts. The rod will hook right up to your pedal. The pedal on PB hangs lower in the cab...that is normal and correct. If you go to rear DB in the future, you will need a different prop valve. The pictured Corvette style MC, prop valve set is made to work with both 1/2T or 3/4T boosters. It has a machined safe engineered insert for the two depths. Attached Images __________________ Email: frankeham@comcast.net Phone: 360-956-7170

08-08-2004, 04:38 PM	#19
nate68 Registered User Join Date: Jan 2000 Location: ca Posts: 1,110	I'm using a corvette master cylinder with a 68 3/4T Booster. everything works fine. __________________ 68 short step, 406/700r4, 9" w/discs.

08-08-2004, 09:13 PM	#20
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	My truck already had a 3/4 brake booster in it, it's the original one too. I never had any problems with the brakes. My truck also has the HD brake and suspension option. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

08-08-2004, 10:57 PM	#21
Southpa Registered User Join Date: May 2000 Location: Victoria, BC, Canada Posts: 2,410	I had no problems swapping. The pic shows the old 1/2 ton drum/drum setup converted to disc/drum setup. Notice 1/2 ton m/c for disc drum with 3/4 ton booster. No mods, shimming, welding etc. needed, it just bolted right up! Attached Images __________________ 1970 GMC 1500 Custom Original 350/TH350 Victoria, BC, Canada You can wish in one hand and crap in the other. See which one gets filled first.

08-09-2004, 12:09 AM	#22
skid Registered User Join Date: Dec 2003 Location: Left Coast Posts: 254	Southpa, my Blazer has a support from the front of the booster to the firewall (it also has one on the back). I notice your picture doesn't show one. That is the piece that I had to extend. I also used a Corvette m/c for a future rear disk conversion. The 3/4 ton booster came with too short of a plunger for my stock m/c as well. Maybe there are different length rods for different applications. __________________ Toys: 72 K5 Blazer 74 Vette

08-09-2004, 02:49 AM	#23
Budweis Geared for Collision Join Date: Jan 2004 Location: St. Louis, Mo. Posts: 683	had some questions bout the vette mc but guess ill start a new thread on it so i dont hijack this one __________________ MEMBER OF THE 4 WHEEL DISK BRAKE CLUB 1970 C/K20 3/4 Ton 1996 Collectors Edition Corvette 1977 Corvette Coupe Last edited by Budweis; 08-09-2004 at 01:59 PM.

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