Summit Power Brake Conversion Issues

[yernkie]

I just installed the Summit power brake conversion kit (SUM-760197) on my manual drum 1968. The install went pretty smooth but I am having issues with getting everything dialed in afterwards. After bleeding, the pedal only has an inch or two of travel and it stops fine at low speeds but will not stop it over 40 mph. It feels like there should be more travel in the pedal but the rod looks like it is going in to the booster as far as it will go and nothing is binding up. Could there still be air in the lines or master cylinder? What am I missing?

I am not running a proportioning valve because Summit told me I didn't need one. I have the back brakes on the front port (closest to radiator) and front brakes on side closest to firewall, again per Summit.

[HO455]

Shooting from the hip here. It may be that you have a master cylinder push rod issue. This thread may help if not there's probably 25 more threads on push rod issues.

https://67-72chevytrucks.com/vboard/...d.php?t=498293

[A1971Blazer]

did you check the booster push rod to MC piston clearance?

[yernkie]

Originally Posted by HO455

Shooting from the hip here. It may be that you have a master cylinder push rod issue. This thread may help if not there's probably 25 more threads on push rod issues.

https://67-72chevytrucks.com/vboard/...d.php?t=498293

That could be. I'll start reading....

[yernkie]

Originally Posted by A1971Blazer

did you check the booster push rod to MC piston clearance?

I did not. I just followed the instructions that came with it. I did use the long pin in the master cylinder that came with the kit.

[A1971Blazer]

Originally Posted by yernkie

I did not. I just followed the instructions that came with it. I did use the long pin in the master cylinder that came with the kit.

That could very well be the issue...
the best way to set it is with a tool like this
you need 1/32"-1/16" clearance between the two
I made this one but you can get them about anywhere

[LS short box]

I don't know if I'm buying the no prop valve thing. On my projects (all disc brakes front and rear) I always run a adjustable prop valve. In regards to bleeding I'd rebleed the master. Then rebleed the brakes starting at the right rear. Bleeding I've used both a Mity Vac and a pressure bleeder. Both have worked well.

[yernkie]

Originally Posted by LS short box

I don't know if I'm buying the no prop valve thing. On my projects (all disc brakes front and rear) I always run a adjustable prop valve. In regards to bleeding I'd rebleed the master. Then rebleed the brakes starting at the right rear. Bleeding I've used both a Mity Vac and a pressure bleeder. Both have worked well.

I tried throwing the factory drum/drum proportioning valve back on and I got the same result. I am still running drums front and rear so I really shouldn't need it.

[geezer#99]

The factory valve is a distribution block and not a proportioning valve. That’s why you saw no difference.

[yernkie]

Originally Posted by A1971Blazer

did you check the booster push rod to MC piston clearance?

I had a few minutes tonight so I pulled the master cylinder and sure enough the booster push rod in touching the master cylinder. I think when I tighten the MC nuts the rod even pushed in the MC piston in a little bit. I didn't have time to mess with it tonight but hopefully will tomorrow night. I assume the rod can be adjusted in a bit by tightening or something.

Edit: I just ordered the adjustment tool off of Amazon and it should be here tomorrow. I'll try it out over the weekend. Thanks everyone for the replies and tips.

[jocko]

is your truck a C10 or C20/30? The part # you posted appears to be a kit with booster and a new mc, so the correct booster-mc pushrod "should" have been included. I'm kinda surprised Summit would tell you the prop valve is unnecessary as it should also provide the electrical connection for your dash brake light that will indicate a circuit fail (i.e. not usually good business sense to advise against a safety feature - but yes your brakes should work without one - but I'd still install the one that came in the kit personally - the original block from your 68 is really only there to sense imbalance and trigger the dash light). Did Summit or the instructions state why you should hook your rear brakes to the front port? That is why I ask if your truck is a 1/2 or 3/4 ton truck - rear brakes to front port is normally a C20+ thing - but the part # you shared doesn't appear to be C10 vs C20-specific, so maybe it's based on a C20+ system, which is fine - just kinda curious.

[yernkie]

Originally Posted by jocko

is your truck a C10 or C20/30? The part # you posted appears to be a kit with booster and a new mc, so the correct booster-mc pushrod "should" have been included. I'm kinda surprised Summit would tell you the prop valve is unnecessary as it should also provide the electrical connection for your dash brake light that will indicate a circuit fail (i.e. not usually good business sense to advise against a safety feature - but yes your brakes should work without one - but I'd still install the one that came in the kit personally - the original block from your 68 is really only there to sense imbalance and trigger the dash light). Did Summit or the instructions state why you should hook your rear brakes to the front port? That is why I ask if your truck is a 1/2 or 3/4 ton truck - rear brakes to front port is normally a C20+ thing - but the part # you shared doesn't appear to be C10 vs C20-specific, so maybe it's based on a C20+ system, which is fine - just kinda curious.

It is a C10. I believe the pushrod it correct but it just needs to be adjusted (shortened). No prop valve came with the kit. I still have the old prop/distribution block that I may hook back up just to see if it makes any difference. The instructions did not say anything regarding front and back ports but the tech said to put the back to the front and front to back. My plan is to get the rod adjusted, bleed the brakes and take it for a test drive. If needed I can swap the front and backs on the MC pretty easily.

[jocko]

Ok thanks for the additional info. Before altering the pushrod that came with the kit, which should be the correct length or Summit should replace it, I’d alter a donor rod. I’d ask the tech, if you can get hold of that same one again, why he advised to connect the rears to the front port. Front vs rear to which mc port does matter, even in an all drum system. And to my earlier statement, disregard the note about the prop valve that I thought came with the kit - since you are still drums all the way around, the original distrib block is all you should really need (and just to retain the original safety function and dash indicator aspect of it). I think I was thinking in the back of my mind that you also did a front disk conversion - that’s the only reason I could see a need for a prop valve - but even if you don’t “need” a prop valve - it doesn’t need you don’t need a distribution block. Having said that, the distribution block is unrelated to the problem you’re having.

[yernkie]

Originally Posted by jocko

Ok thanks for the additional info. Before altering the pushrod that came with the kit, which should be the correct length or Summit should replace it, I’d alter a donor rod.

The rod is adjustable so it isn't permanent.

[jocko]

AH! Ok, that's good news, sorry I missed that.

[yernkie]

The push rod adjustment solved the problem. It was a little too long and it was preloading the master cylinder. I also swapped the front and rear lines and reinstalled the distribution block after a short test drive. All is good now. Thanks again for the help.