I heard a rumor

[nonstop]

Okay, I was at the junkyard and did some checking. All the auto pedals I found had one post whether they were hydroboost or not. All the manual pedals had the post and the additional hole higher up. Did they use one pedal for manuals and put the pin in the corresponding hole, and the. Use 2 separate pedals for autos with either HB or vac accordingly?

Is there any way to look up part numbers?

[Keith Seymore]

Originally Posted by nonstop

Okay, I was at the junkyard and did some checking. All the auto pedals I found had one post whether they were hydroboost or not. All the manual pedals had the post and the additional hole higher up. Did they use one pedal for manuals and put the pin in the corresponding hole, and the. Use 2 separate pedals for autos with either HB or vac accordingly?

Is there any way to look up part numbers?

The various pedals came into the final assembly plant with the pin already in place, under separate part numbers for each unique variant.

K

[Keith Seymore]

Originally Posted by SCOTI

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?

Other way around.

The higher ratio is effectively more "leverage", so less effort. Just like using a longer wrench to break loose a nut.

K

[SCOTI]

Originally Posted by boatpuller

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

Yes & no.

Yes, I used the Hydraboost equipped pedal w/the vacuum equipment swapped over. Yes, the truck stopped. But, I felt it could be better. I had a master cyl on there w/1.25" bore & felt a smaller 1 1/8" bore might help pedal pressure.

But.....I kept having issues w/master cylinders leaking from the main piston area (seeping out the back of the unit & down the boost canister). At first I thought it was the 'house brand' replacment master cylinders until I finally got a new Wagner unit & it eventually did the same thing.

Initially when I got all the requisite swap parts, many of the brake related parts were already pulled. Upon mock-up, I realized the booster did not have the dowel pin/rod that goes between the vacuum can & master cyl (it must have fallen out when relocating parts). I didn't know if the lengths of the dowels were the same or not between the vac set-up vs the HB. I took some measurements & opted to make my own dowel pin/rod based on other vac set-ups I had sitting around.

In the end, I now have the original HB dowel pin/rod in place. It hasn't leaked since swapping back, but I also haven't driven it since swapping the dowels (was waiting on my PB lower a-arms & Ride Tech sway bar). I did some testing w/it sitting in the shop but that's not 'real world' IMHO because of the trucks weight coming into play.

I have the front end re-assembled now but no seats in it so driving will still be a challenge

[SCOTI]

Originally Posted by Keith Seymore

Other way around.

The higher ratio is effectively more "leverage", so less effort. Just like using a longer wrench to break loose a nut.

K

This is what my brain was trying to sort through.

Looks like I'll be seeking the correct pedal then. I threw the other one away not to long ago when I started thinning out the extra dually build parts taking up space in the shop.

[y5mgisi]

[1774btcrew]

Thanks for posting that! It still hasn't stopped raining here

[SCOTI]

Originally Posted by 1774btcrew

Thanks for posting that! It still hasn't stopped raining here

x2. Thanks y5mgisi.
Would it be possible to get a measurement for the difference in pin heights?

[DirtyLarry]

One more pic that has been floating around the hydroboost topic for quite sometime. I swapped hydroboost onto my '78 K10 a few years ago and love it. I personally feel it is a much more worthwhile swap over rear disks, at least on the heavier trucks with full-floating rear axles anyway.

I'm not sure who we owe credit to for taking this picture measurements...but thank you!


My K10 with hydroboost swapped on in 2010

[boatpuller]

Thanks everyone.....That there ( this thread) is why this is a great forum.

[Keith Seymore]

Originally Posted by nonstop

Is there any way to look up part numbers?

I found my release charts via google but the brake pedal part number is not shown.

I'm not sure why, other than the pedals themselves may have belonged to a different engineer (the same guy may have had responsibility for the brake, clutch and accelerator pedals).

Nonethess, I can read them in the above pic. They look to me to be:

347460 Vacuum

395561 (?) Hydraulic


K

[nonstop]

Thanks for the pictures! Took my pedal out today and measured the distance between the stud and the next hole up. It was about 5/8 to 3/4 inch. I got a long grade 8 bolt, cut the threads off and welded the non threaded part into the hole (I left the head on to have some more surface for the weld) and drilled a hole for the clip. I put the pedal back it and bolted it all up. The rod goes straight into the booster, instead of up at an angle. Now I stab the brakes and, although a little more travel, it will send you into the windshield!

Now I need to get my hands on the spring bracket and brake switch bracket.

[SCOTI]

Originally Posted by BRUISER

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.

Who was selling the pedals/pedal assemblies?

I need a vacuum brake pedal for my 89 cc square. I was going to pull my pedal out & relocate the pin but after pulling the pedal & knocking the pin out, the holes would be too close to each other which concerns me. I'd prefer to swap the p/n 347460 pedal into place.

[1774btcrew]

I am pretty sure Bruiser was talking about me. Send me a PM and I will see what I have available

[68Timber]

Yep, 1774btcrew is who I was referring to. If you have a manual trans, you could swap brake pedals with me. I need a hydroboost manual trans brake pedal, or move the pin.

[SCOTI]

Originally Posted by BRUISER

Yep, 1774btcrew is who I was referring to. If you have a manual trans, you could swap brake pedals with me. I need a hydroboost manual trans brake pedal, or move the pin.

I would do that but my pedal is for an auto set-up.

[68Timber]

Originally Posted by SCOTI

I would do that but my pedal is for an auto set-up.

10-4. I was thinking yours was auto but wasn't sure.

[SCOTI]

So.... I was able to find a pedal this weekend from a local member. I pulled everything between the pedal up to the master cylinder from an 83 3/4 ton BBC/auto trans truck.

I got it all home & compared the pedals. As noted in the pic above, the pin is in a diff place on the pedal. But.... that wasn't the only difference:

• A) The pins on each of the pedals I have are different sizes.

• B) The clevis/rod end that connects the pedal to the booster are different lengths.

I was sure feeling good about the decision to just pull all the parts 'just in case'.

[SCOTI]

Feeling pretty good about my decision to grab everything, I figured no big deal.... I'll swap the clevis/rod-end to the shorter one that came w/the new/different vacuum brake pedal.

I went to swap it in tonight & found yet another difference. The thread size for each is different so no-can-do....

[SCOTI]

It appears the truck I pulled the parts from was a JB6 equipped truck. The vacuum booster I swapped in previously I based on the GM brake packages vs vehicle weight & went w/the JB7 spec'd part since it would be the most heavy duty vacuum set-up available (8400lbs).

Apparently they upsized things when going from JB6 to JB7 as the JB7 clevis/rod-end did fit the pin on my original hydraboost pedal. The weird thing is the thread size is actually smaller for the clevis/rod-end that's associated w/the larger pin.

[DirtyLarry]

That is good info Scoti!

[boatpuller]

So, pull pedal and rod from a donor half ton and it should be all good ?

[SCOTI]

Originally Posted by boatpuller

So, pull pedal and rod from a donor half ton and it should be all good ?

Unfortunately..... just grabbing a random pedal didn't work for me (& I didn't just pick a random pedal).

Yours might be different because its a little older than mine (89) & 1/2 ton. I pulled a pedal from an 83, single cab, 3/4 ton, bbc/auto truck & it would not work w/o tweaking.

The stud on the pedal was in the right position (based on the
pics provided in this thread). But my donor truck was a JB6 equipped truck. I used a 1987 spec'd JB7 booster assembly. For my truck, the '87 JB7 booster rod-end is the same size as my '89 JB8 pedals stud (14mm). The '83 JB6 pedals stud was smaller (.500").

I knocked out the smaller .500" stud from the '83 pedal, drilled the pedal hole to 14mm, pressed my hydraboost pedals stud in place & welded it up. Hopefully this combo (87 spec JB7 booster, '83 JB6 vacuum pedal w/my 89's JB8 stud swapped in place) will work & stop killing the internal seal on my master cylinders (I've killed 3). The truck stopped but inevitably the master cylinder would start leaking from the back/core.

[SCOTI]

Correction: The stud from my JB8 pedal is 9/16" & not 14mm.

[boatpuller]

Clear as mud...just kiddin ..I think if I grab a pedal and rod from a late 70's 1/2ton with power brakes I should be o.k.