C5 booster measurements

[70 LS1]

Anyone have a C5 booster laying around they could take some measurements on? I need the spacing for the 4 mounting bolts.
thanks

[Hydratech®]

The C5 Vette booster simply runs the classic Bendix 4 bolt pattern of 3.400" wide x 3.500" tall. The MC interface is also the classic GM late model spec at 3.400".

NOTE: These dimensions illustrate the bolt centers.

Pedal rod length is suprisingly long at 8.750" from the firewall mounting plane to the centerline of the .440" pedal rod eyelet.

This booster is essentially identical to the dual diaghphram boosters used on the '80-'88 G bodies, with exception to the super long pedal rod = nothing special at all.

[70 LS1]

Thanks Paul. The only thing holding me back on the C5 booster is the long pushrod. Does that mean the G-body one would work with the C5 master?

[Hydratech®]

Yes - the G body booster will work with the C5 / C6 master cylinder. The G body booster runs a much shorter pedal rod of 4.500" inches from firewall mounting surface to the centerline of the .440" pedal rod eyelet. The other double diaghphram booster to consider is the '77-'82 C3 Vette, as it is the same as the G body / C5 booster, though is equipped with a 3/8-24 threaded pedal rod designed to interface with a threaded / removable classic Chevy horseshoe type clevis = gives you many possible ways to adapt to a custom build.

[70 LS1]

If the late C3 booster is the same as the C5 then I should just go that route. Should be a direct bolt-on for me.

Now here's my next question, Paul. What are the advantages of the hydroboost over a standard vacuum setup? Is there still good pedal feel or is it over-assisted? Is the amount of assist adjustable? The thing holding me back is I don't have power steering and don't really want to add the pump just for the brakes.

[Hydratech®]

If the late C3 booster is the same as the C5 then I should just go that route. Should be a direct bolt-on for me.

Yep - makes perfect sense.

As far as the benefits of our brake assist systems? The home page of our website lists them out - www.hydratechbraking.com The pedal feel is honestly vastly superior to a vac assist, as it provides a manual brake feel with highly reduced pedal travel, yet follows up with all the power you could ever hope for on demand. Over assisted brake concerns are most always related to running to small of a MC bore, for instance running the small 15/16" Baer supplied MC in conjunction with our assist systems = definitely over assisted response, to where the installation of a 1 1/8" bore straightens the situation right out. This is how you go about tuning the pedal feel on these systems, essentially adding an 1/8" or even up to a 1/4" of bore size over what conventional wisdoms would usually dictate for a typical combo. The use of a largish bore MC makes for a taught, crisp and firm response, yet the hydraulic assist unit has all the power required to follow through with smooth and potent + very linear braking. Taste is a VERY difficult factor, though most all users report back with two thumbs up regarding pedal feel when running our systems. The ones that don't are running the incorrect mc bore sizes. Want a softer pedal? Run the next smaller available MC bore size and vice versa = tunability as desired. In your particular case, I'd actually suggest that you do not use the C5 / C6 Vette MC as per its 1" bore, and instead run a 1 1/8" bore (that is IF you choose to run the hydraulic assist). IF you choose to run the vac booster, then the C5/6 MC would actually be a decent choice - get it? If you were to do the vac booster first, then find yourself displeased with the results, you could then count on being able to do a back to back booster swap while retaining the same MC. In a back to back test, you can count on atleast a 1 1/2" reduction in pedal travel when running one of our systems (with no other changes in the brake system what so ever). The difference in pedal feel found in our new C5 systems is actually amazing, as it makes a great overall braking system feel even better yet by providing a substantial reduction in stroke and a much more positive pedal pressure sensitive experience.

No actual power steering? If your going to be running an LS1, the pump is most likely already there, so why not use it? The added benefit is that if you ever decided to go to power steering in the future, you would only need to perform some quick plumbing revisions to make it happen. Trust me - the first time this beast tries to get away from you, you will wish that you had installed power steering (which would've helped immensely in "reeling it back in"). If it's arguable road feel that has you wanting to stay out of power steering, then do the popular Jeep box conversion, which eliminates all of the stock C3 ps components (no slave cylinder and control valve to deal with) and provides a true rack and pinion style valving + the tire blow out safety factor of a recirculating ball style steering box = rack feel + bolt in simplicity + summarily eliminates all of the usual C3 Vette ps woes. http://www.corvettesteering.com/55-57%20chevy.htm

I have also noticed that you are already getting some 3rd party feedback from other C3 users in your posts on the CF: http://forums.corvetteforum.com/show...ost&forum_id=3 One guy put it quite bluntly as "Vacuum Sucks" (!) (no pun intended I suppose!)

[70 LS1]

Thanks, Paul. I have actually been eyeing the corvettesteering box. I think for now I will try the vacuum booster and if that does not give the feel I am after, I will go with the hydroboost. And if I do that I might as well do the jeep box at the same time.

Where did you get the C5 bore being 1" I measured mine and its between 13/16 and 7/8".

[Hydratech®]

Hmmm - interesting. The last time I had one in my hands I recall running a Vernier caliper across the bore right where the snap ring exists to find 1.008" reading. The bore at the snap ring is *usually* consistent all the way through in most all MC's (except QTU designs). Mind you, this is based upon my general recollection, and I *could* be mistaken. Not being at the shop today, I can't refer to our databases to double check for 100% certain. The measurements you are observing sound more like C4 MC specs to me...

[70 LS1]

Now I am really confused. I just measured again and got 1". The master I pulled off, was a stock 1970 manual master with a 1" bore, but my pedal effort was greatly reduced when I installed the C5 master.

What's the deal?

[EFI69Cam]

The C5 Vette booster simply runs the classic Bendix 4 bolt pattern of 3.400" wide x 3.500" tall. The MC interface is also the classic GM late model spec at 3.400".

NOTE: These dimensions illustrate the bolt centers.

Pedal rod length is suprisingly long at 8.750" from the firewall mounting plane to the centerline of the .440" pedal rod eyelet.

This booster is essentially identical to the dual diaghphram boosters used on the '80-'88 G bodies, with exception to the super long pedal rod = nothing special at all.

I removed the brackets from a stock 69 type booster hoping that they would just bolt to the back of the C5 booster. The 3.5" tall worked, but the width does not match. Are the holes on the back of the 69 booster different bolt pattern?

[Hydratech®]

Now I am really confused. I just measured again and got 1". The master I pulled off, was a stock 1970 manual master with a 1" bore, but my pedal effort was greatly reduced when I installed the C5 master.

What's the deal?

Great to hear that I haven't yet lost my mind, and was indeed correct in my recollection of the C5 MC bore size! How sure are you that the old MC you removed was definitely a 1" bore? We have seen many an early manual brake shark erroneously equipped with a 1 1/8" bore power brake spec MC. Also, did you make any other changes? Was your shark a factory power brake or manual brake car? I think I ran across a pic on the CF of your C5 MC rigged up with some sort of bizarre bracketry - was that yours?

I removed the brackets from a stock 69 type booster hoping that they would just bolt to the back of the C5 booster. The 3.5" tall worked, but the width does not match. Are the holes on the back of the 69 booster different bolt pattern?

What kind of car? Camaro or? The discussion I have been having with 70LS1 has been regarding a C3 Vette, while you *might* be talking about a different vehicle, or? IF you are talking about a C3, the factory manual brake models did have a different bolt pattern on the firewall...

[70 LS1]

My car was originally a manual brake car. I did replace the master when I installed the brakes and maybe the parts store screwed up and gave me a power one by mistake. I never tried the new master with the old brakes nor did I try the new brakes with the old master.

And I wouldn't call my bracket bizarre. It just moves the master out from the firewall and down to allow me to use the old manual pushrod and clear the hood. I think it would still work fine with the booster. Here is a pic of what I did.



I am going to try the C5 master as a power setup and if that doesn't give what I am after I will go with a 15/16" master.

Thanks for your help

Thanks for the help.

[EFI69Cam]

Great to hear that I haven't yet lost my mind, and was indeed correct in my recollection of the C5 MC bore size! How sure are you that the old MC you removed was definitely a 1" bore? We have seen many an early manual brake shark erroneously equipped with a 1 1/8" bore power brake spec MC. Also, did you make any other changes? Was your shark a factory power brake or manual brake car? I think I ran across a pic on the CF of your C5 MC rigged up with some sort of bizarre bracketry - was that yours?


What kind of car? Camaro or? The discussion I have been having with 70LS1 has been regarding a C3 Vette, while you *might* be talking about a different vehicle, or? IF you are talking about a C3, the factory manual brake models did have a different bolt pattern on the firewall...

I am talking about a 69 Camaro. The bracket donor booster came off a 74 Buick Apollo (x-car)

Sorry for jumping in,your mention of a standard bendix pattern is what made me chime in.

So c5 booster+69 camaro brackets=no work

Any thoughts you might have would be appreciated.

[Hydratech®]

70LS1 - By bringing the MC downward / lower than stock, you have increased the mechanical pedal ratio ever so slightly (roughly a 1/4 point), as it is no longer a dead straight ahead push from the pedal. I do not believe that you would be able to really feel this slight difference in ratio change though in a back to back test though. One point I feel compelled to bring forth is that the C5 Vette MC has a nothing more than a shallow design input piston, which means that if your foot was to accidentally slip off of the brake pedal = the MC pushrod could fall out of the back of the C5 MC (!). That is why the manual brake design MC's have a deep hole in the back to prevent the pushrod from possibly falling out. If you plan to retain the use of this design, you may want to incorporate some sort of guide to insure that the pedal rod could never fall out. Here is a pic illustrating the differences:


Also, the '97-'02 F body MC is essentially identical to the C5 MC, though features a lower profile angled plastic tank that would clear your hood without requiring the use of the bracketry you have whipped up. Note that the brake lines on the late F body MC are on the engine side though... This late model F body MC could then be bolted directly to your existing manual brake MC mounting studs, and you could then shorten up the manual brake pedal rod accordingly (simply threaded 3/8-24 fine thread into the horseshoe clevis at the brake pedal = you could even make it adjustable length). I would still whip up some sort of pushrod retention system, as the late F car MC is also equipped with the shallow design input piston.
Here is what our Part # 3007 '68-'76 C3 manual to power brake conversion system looks like installed:

This system may be special ordered at no additional cost with the later model spec short MC pushrod if desired, which would allow the use of the later model shallow design input piston MC like the C5 design. To wit, this is the world's only direct bolt in manual brake to power brake conversion system available. Interestingly enough, this system is the easiest of all of the C3 systems to install, as the only underdash diving required is the brake pedal rod connection (as the system mounts to the firewall using fasteners from the engine compartment side, instead of inside like the factory power brake sharks)...

EFI69Cam - Yep, the 1st gen F body firewall standoff brackets will only jive as you stated (vertically), though are about a 1/2" off nominal for width = I figured you must have been talking about a 1st gen F car (as opposed to our dialogue referring to the sharks). Do not apologize what so ever for jumping in!

[70 LS1]

Thanks, Paul, I thought about that and the spring in the master cylinder is stonger than the spring on the pedal. The master cylinder will always have pressure applied to the rod. I did a couple of tests with quickly letting off the pedal and not once did it fall out. Also the hole in the firewall won't allow the pushrod to drop lower than the piston on the masterIt may not line up perfectly, but it would still make contact with the piston.

The manual setup is only temporary and I have decided to try power to see how it goes.

Thanks again Paul, you are a wealth of information.