Hard brake pedal after axle swap

[jeff in co]

I made the swap on my 89' from the 10 bolt rear to a 14SF rear. I replaced all of the brake components (springs, shoes, turned drums) as well as new wheel cylinders. I re-used my brake line from the 10 bolt and swapped it over.

The problem, when I now use the brakes, the pedal feels hard when I begin braking. The rears aren't exactly adjusted very tight but it just feels a little different now.

I Bled the rear and then front brakes with no change really. I tried a hard skid on the gravel yesterday and the rears are still locking up before the fronts.....and also confirmed this on the freeway offramp this morning. Decided to hit it kinda hard and the rears locked a bit and I felt the rear slide just a bit (indicating the fronts were't locking).

The front calipers, pads and rotors are all new about a year ago.

The only thing left is the master cylinder or booster.

I thought about just replacing the master cylinder/booster with a Autozone one but wanted to be sure there wasn't something else going on. The 14SF wheel cylinders are just a touch bigger in diameter than the 10 bolt but would it make it behave this way?

Just want to find the proper solution here.

 

[dyeager535]

My buddy just did the same swap, and I did with mine years back. I don't feel the pedal is anything outside of normal.

Don't see how it could be the master, my only master cylinder experience has been a failure, and the result was a spongy pedal, not firm.

Definitely sounds more like a booster issue. GM test is pretty unscientific. Start truck, don't touch brakes. Let idle for a few seconds. Turn truck off. Let sit for ~45 minutes. Without starting truck, push brake pedal. Should have two full pedal assists before it gets very hard to push.

Edit: And I agree with Chris, forgot to mention it. Is it possible the rears are too tight?

 

[clandr1]

Have you tried loosening the rear pads a little to see if you can get a better pedal feel, with less locking up of the rear?

 

[496truck]

It's not a booster problem if you can lock up the brakes easily. When boosters fail they either provide less/no boost or have difficulty recovering when you are on/off/on the brakes rapidly. Hard pedal but hard to stop the truck.

What is the drum size difference between the stock and the 14b? 10" stock vs 13" for the 14b? That will certainly improve the rear brake performance.

I can tell you that when I did my 3/4 ton swap, my K5 will stop on a dime and the pedal is high and tight. The rears do lock before the fronts, mainly due to the massive brake size and the lack of weight and short wheelbase of the K5. Now, I have the 3/4 ton fronts so maybe mine is better balanced?

There is always the option of adjusting down the adjuster wheels in the rear. Or adding an inline aftermarket prop valve to further reduce pressure to the rear. Both of these will take time and trial and error getting things dialed in correctly.

 

[jeff in co]

My buddy just did the same swap, and I did with mine years back. I don't feel the pedal is anything outside of normal.

Don't see how it could be the master, my only master cylinder experience has been a failure, and the result was a spongy pedal, not firm.

Definitely sounds more like a booster issue. GM test is pretty unscientific. Start truck, don't touch brakes. Let idle for a few seconds. Turn truck off. Let sit for ~45 minutes. Without starting truck, push brake pedal. Should have two full pedal assists before it gets very hard to push.

Edit: And I agree with Chris, forgot to mention it. Is it possible the rears are too tight?

Well, that's a start thanks! It looks like the booster is original (because I still see some hardened tar on the bolts on the firewall)....so I get a little concerned. At 336k who knows what can fail but I am trying to be more pro-active.

 

[jeff in co]

Have you tried loosening the rear pads a little to see if you can get a better pedal feel, with less locking up of the rear?

The adjuster rings were even but definitely not dragging too much. I went and backed off the threaded rod for the e-brake, but I don't know if they correlate with one another?

Are the adjuster in the drum brake assembly independent of the adjuster for the e-brake?

 

[496truck]

The adjuster rings were even but definitely not dragging too much. I went and backed off the threaded rod for the e-brake, but I don't know if they correlate with one another?

Are the adjuster in the drum brake assembly independent of the adjuster for the e-brake?

The threaded rod only accounts for parking brake cable/pedal travel and has no effect on the hydraulic brakes.

The adjuster wheels account for shoe/drum wear and will effect the hydraulic brake pedal feel as well as the parking brake.

 

[jeff in co]

It's not a booster problem if you can lock up the brakes easily. When boosters fail they either provide less/no boost or have difficulty recovering when you are on/off/on the brakes rapidly. Hard pedal but hard to stop the truck.

What is the drum size difference between the stock and the 14b? 10" stock vs 13" for the 14b? That will certainly improve the rear brake performance.

I can tell you that when I did my 3/4 ton swap, my K5 will stop on a dime and the pedal is high and tight. The rears do lock before the fronts, mainly due to the massive brake size and the lack of weight and short wheelbase of the K5. Now, I have the 3/4 ton fronts so maybe mine is better balanced?

There is always the option of adjusting down the adjuster wheels in the rear. Or adding an inline aftermarket prop valve to further reduce pressure to the rear. Both of these will take time and trial and error getting things dialed in correctly.

Another point now came to my mind....

While driving a few days ago, I hit the brake a little, then off, then the light turned yellow and I tried to brake again. It didn't feel like I was going to be able to stop (almost a hard feedback feeling), so I decided to run the yellow. This is probably my main concern.

FYI Brian, I did take your advice many months ago and slowly waited on re-building my 14SF. I was in a hurry wanting to get it done and you recommended waiting and doing it as money came in. Great advice, thanks! I Now have a 14SF with Eaton e-locker and properly set up (professionally) 4.10 gears. New brakes, bearing and seals. Thanks again!

 

[496truck]

I was in stop and go traffic and almost hit the car in front of me when people decided to go and then STOP!!! I barely got the truck stopped. I got a replacement booster the next day as the truck was my DD at the time.

When you hear that loud "whoosh" sound when you step on the brakes, that's a tell tale sign the booster is going or gone.

Glad my advice worked out for ya! Sometimes I know what I'm talking about.

 

[jeff in co]

I was in stop and go traffic and almost hit the car in front of me when people decided to go and then STOP!!! I barely got the truck stopped. I got a replacement booster the next day as the truck was my DD at the time.

When you hear that loud "whoosh" sound when you step on the brakes, that's a tell tale sign the booster is going or gone.

Glad my advice worked out for ya! Sometimes I know what I'm talking about.

If I replace the booster/master cylinder, is it OK to use a rebuilt one from Advance Auto? Cardone for $134? Or is this a AC Delco only type of part?

http://shop.advanceautoparts.com/we...er-cylinder--remanufactured-cardone_5691494-p

 

[dyeager535]

Dad had a booster fail in the woods years back (boy is that fun in the mountains!) and went and got whatever the nearest parts store, Napa, had. 5+ years ago, still going strong.

Pretty simple, but I'm sure all the aftermarket stuff is technically worse than OEM. If the price difference isn't massive, I'd go with Delco, but if it is significant, I'd go with the lifetime warranty cheapy.

 

[496truck]

I used a reman Cardone booster. No issues thus far. I don't think you have too many choices for a replacement on that.

I don't think you have an issue with the master at all. Don't bother with that right now. It would be a waste of time and money and prob replaced with a less than stellar part.

 

[jeff in co]

I used a reman Cardone booster. No issues thus far. I don't think you have too many choices for a replacement on that.

I don't think you have an issue with the master at all. Don't bother with that right now. It would be a waste of time and money and prob replaced with a less than stellar part.

Good point. Looks like Napa has one for $75 so that's probably a good start. I don't have to bleed the brakes if I replace just the booster correct?

This is a daily driver for myself or at least my daugher...

 

[496truck]

No need to bleed if just replacing the booster. You just remove the 2 nuts at the booster and pull the master forward. Be warned though, the booster is a pain to get disconnected from the pushrod under the dash.

 

[jeff in co]

Thanks Brian on the heads-up about the pushrod.

I did adjust the rears last night and backed them off a little. It certainly helped in the overall braking now. The fronts are now doing their job more appropriately.

I do get the pedal feeling a little hard after the 2nd or 3rd hit if they are done one after the other.....so I may just go ahead and throw in a new booster.

Appreciate all the help guys! Thanks!

 

[Fordum]

With the booster that old, its not going to hurt. But be sure to check the vacuum situation too.
Not only does the engine need to develop good vacuum, the hoses and fittings must be good, and the check valve in the main line going to the booster must be good.

Quick way to check the booster, is to crank the engine, run it a few minutes, turn it off, and see if you have boost after a couple of minutes.
A bad check will let the vacuum go away fairly quickly.