I heard a rumor

[boatpuller]

That a hydroboost truck uses a different brake pedal than a vacuum boost ? Experts ?

[JIMs70GMC]

I know the bracket that the pedal is hung from is different.

[Keith Seymore]

Well - I have the brake system release charts starting in about 1969.

If we had a search feature...I would post them up.

K

[boatpuller]

Thanks Jim..I had a guy tell me he thought pedal was different now he could have meant the whole assembly I guess.

[Keith Seymore]

You didn't say what year or series, but I checked 1987 R20 JB7 vs JD7:

Pedal ratio is different between the two so the pedal itself is different.

Vacuum = 4.51:1

Hydraboost = 5.60:1

K

[boatpuller]

Thanks Keith. Its on my 79.sounds like I need the whole assembly.



.

[68Timber]

I have a clutch pedal assembly for vacuum brakes but was told by a member here to change the brake rod mounting point to the upper spot for use with hydroboost. He sells a lot of pedal assemblies here so I took it he's seen enough of them to know.

[nonstop]

I just checked my truck - it feels like there is another hole to move the rod to higher on the pedal. I didn't look at it though. Might just be as simple as moving holes.

[boatpuller]

Thanks Bruiser and nonstop.....Any info help's.

[UKNOWME]

Originally Posted by Keith Seymore

If we had a search feature...I would post them up.

K

Yeah what's up with that?

[1774btcrew]

The brake pedal is essentially the same from hydroboost to vacuum. There is an additional hole in the pedal. What this means is if you wanted to go from one to another you would have to weld the bracket that attaches to the pedal in the corresponding hole for the brake system you are using. If you can't weld or don't want to mess with it, you can unbolt just the brake pedal and switch it out. Hydroboost also has a teardrop shaped plate that a spring attaches to for the pedal return. Please let me know if you have any other questions. I sell a lot of these pedal assemblies.

[nonstop]

I guess this leads me to more questions than less:

First, would it be possible to run a grade 8 bolt through the top hole and use that as the pivot if you tack welded the head to the pedal and used a lock nut on the other side (I still don't trust my welding to something as crucial as the single pin charged with stopping the vehicle)?

Second, I love my hydroboost and it was night and day when I did the conversion, but why does hydroboost have a higher ratio than the vacuum booster when hydroboost puts out a lot more pressure to begin with?

Thanks!

[68Timber]

Originally Posted by nonstop

why does hydroboost have a higher ratio than the vacuum booster when hydroboost puts out a lot more pressure to begin with?

Thanks!

Wouldn't it be less ratio? The closer to the pivot point, the shorter the stroke?

[Keith Seymore]

Originally Posted by BRUISER

Wouldn't it be less ratio? The closer to the pivot point, the shorter the stroke?

Correct - shorter stroke, but stroke is not the same as ratio.

Moving the rod to the same place you put your foot would be a 1:1 ratio. Moving the rod up any amount from there would be an increase in ratio.

[Keith Seymore]

Originally Posted by nonstop

Second, I love my hydroboost and it was night and day when I did the conversion, but why does hydroboost have a higher ratio than the vacuum booster when hydroboost puts out a lot more pressure to begin with?

Thanks!

Because it's a system. All of the variables in the booster, master cylinder and pedal are tuned together to get the correct feel, travel and response. You can't look at just one component out of context.

[1774btcrew]

Originally Posted by nonstop

I guess this leads me to more questions than less:

First, would it be possible to run a grade 8 bolt through the top hole and use that as the pivot if you tack welded the head to the pedal and used a lock nut on the other side (I still don't trust my welding to something as crucial as the single pin charged with stopping the vehicle)?

Second, I love my hydroboost and it was night and day when I did the conversion, but why does hydroboost have a higher ratio than the vacuum booster when hydroboost puts out a lot more pressure to begin with?

Thanks!

The hole isn't the pivot point for the rod. It is the locating hole for the bracket! You need to move the bracket to have the correct stroke of the pedal. Just move the bracket and weld it on. I will try and post some pictures of a hydroboost pedal

[SCOTI]

So.....

If a guy was going the opposite direction (Hydraboost system w/corresponding pedal & converting to a vacuum set-up), what would need to be changed as far as the pedal?

[1774btcrew]

As far as the pedal assembly goes, you would just need the vacuum brake pedal. Then remove the hydroboost pedal, spring, and the plate that attaches to the spring

[SCOTI]

Originally Posted by 1774btcrew

As far as the pedal assembly goes, you would just need the vacuum brake pedal. Then remove the hydroboost pedal, spring, and the plate that attaches to the spring

Weird.... I pulled the vac brake pedal. It appeared to match the HB one (length, arch, hole positions) so I left it in place.

Ok, next question is based on this info:

Pedal ratio is different between the two so the pedal itself is different.

Vacuum = 4.51:1

Hydraboost = 5.60:1

It appears the HB has a higher ratio. Wouldn't that mean the HB pedal in a Vac app would yield more pedal effort all else being the same?

[nonstop]

Originally Posted by 1774btcrew

The hole isn't the pivot point for the rod. It is the locating hole for the bracket! You need to move the bracket to have the correct stroke of the pedal. Just move the bracket and weld it on. I will try and post some pictures of a hydroboost pedal

Now I am even more confused! I have a stud where it is currently mounted and a hole about an inch higher. My rod sits at an angle now and would line up with the upper hole.

A picture would be great and much appreciated if possible!

Thanks.

[1774btcrew]

Something else to mention is if you want to correctly convert a vacuum pedal assembly to hydroboost, you will need to remove 2 studs from the actual pedal assembly where it goes through the firewall. The hydroboost uses a bracket that has 2 studs that go through from the engine side. Vacuum brakes have all of the studs go through from the interior side.

[boatpuller]

Originally Posted by 1774btcrew

Something else to mention is if you want to correctly convert a vacuum pedal assembly to hydroboost, you will need to remove 2 studs from the actual pedal assembly where it goes through the firewall. The hydroboost uses a bracket that has 2 studs that go through from the engine side. Vacuum brakes have all of the studs go through from the interior side.

Some good info......I'm doing exactly what Scoti said going from hydro to vacuum. I have a leaking hydro unit getting my engine bay oily. My truck is pretty much for show so any chance i get to replace something with chrome or billet I'm doing it.
The chrome hydro replacement is big $$$.. I can get a chrome booster and m/c for reasonable and it will bling it up a little.
So. I think I'm back to my original thought of pedal only to do the swap?

[1774btcrew]

Originally Posted by nonstop

Now I am even more confused! I have a stud where it is currently mounted and a hole about an inch higher. My rod sits at an angle now and would line up with the upper hole.

A picture would be great and much appreciated if possible!

Thanks.

I should have said it was a pin. What has to do with the throw is the angle the pin is at on the pedal. Pictures soon as it quits raining and I can go out and get the stuff.

[SCOTI]

Originally Posted by boatpuller

Some good info......I'm doing exactly what Scoti said going from hydro to vacuum. I have a leaking hydro unit getting my engine bay oily. My truck is pretty much for show so any chance i get to replace something with chrome or billet I'm doing it.
The chrome hydro replacement is big $$$.. I can get a chrome booster and m/c for reasonable and it will bling it up a little.
So. I think I'm back to my original thought of pedal only to do the swap?

Exactly. My HB was definitely not functioning correctly & leaking everywhere. I opted to swap to a Vac set-up to help eliminate clutter under the hood when I started cleaning things up during the motor swap. I grabbed all the parts for a vac brake truck to allow comparisons & the ability to swap if necessary. I compared the pedals & sure didn't notice a difference.

Thus far it's worked but I've been bothered by a repeat leak @ the master cylinder that I hope has now been diagnosed as too long of an actuator pin between the vac canister & master cyl. I do feel the pedal ratio is off personally....

[boatpuller]

You used the hydro pedal and it worked o.k Scoti ?