Brakes for towing

I was having soft brake issuesl, seems common on these trucks. Turned out to be a leaking rear axel seal. Replaced the seal cleaned everything up adjusted the brakes and all is well.

Schurkey said:

Of course you have "better" braking. You have much larger caliper pistons for more force on the pads and rotors. The new pads may be more-aggressive, too.

You may have replaced defective hoses, and/or a defective ABS unit. Either of those could reduce braking power if defective.

The downside is that the K3500 calipers would have been used with a 1.25" bore, two-chamber master cylinder, and you've got a ~1.5" bore two-chamber master. The pedal will be higher, but it'll take more effort to stop than the 1.25 bore it should have. This may not be important now, but if your booster fails, you'll need strong legs.

Click to expand...

Thank you Mr. Schurkey supporting member. For the record I took time to post this for other members benefit. Not to have you "Critique" it. I'm a mechanical engineer so yes if the booster fails and or the engine shuts down or the vacuum hose to the booster fails you will have increased pedal pusher. Wow I guess??? Thank you for your 2 cents.

jrsroadhauze said:

I'm a mechanical engineer so yes if the booster fails and or the engine shuts down or the vacuum hose to the booster fails you will have increased pedal pusher. Wow I guess??? Thank you for your 2 cents.

Click to expand...

You missed the point.

A correct, 1.25" diameter master cylinder requires ~71% of the pedal pressure to stop, compared to the 1.48" diameter master cylinder that you've installed. The bigger master cylinder requires less pedal TRAVEL. There's plenty of pedal travel available, so that difference is fairly unimportant.

IF (big IF) the booster fails, someone is going to need an extra 30+ percent of force on the pedal, in addition to the extra force needed because the booster died. That can be dangerous. Better hope your wife or teenager isn't driving if that happens.

This actually happened to a forum member. The way I remember his description, he needed both feet on the brake pedal, a big jolt of adrenaline, and fresh underwear. Afterwards, he got rid of the big-bore master cylinder.

Schurkey said:

IF (big IF) the booster fails…

Click to expand...

Which systems are more reliable based on field experience, vacuum or hydroboost?

I do recognize that the failure scenarios are quite different, e.g., on account of the hydroboost’s dependence on the PS system.

jrsroadhauze said:

Thank you Mr. Schurkey supporting member. For the record I took time to post this for other members benefit. Not to have you "Critique" it. I'm a mechanical engineer so yes if the booster fails and or the engine shuts down or the vacuum hose to the booster fails you will have increased pedal pusher. Wow I guess??? Thank you for your 2 cents.

Click to expand...

Perhaps @Schurkey was replying for other members’ benefit as well.

1998_K1500_Sub said:

Which systems are more reliable based on field experience, vacuum or hydroboost?

I do recognize that the failure scenarios are quite different, e.g., on account of the hydroboost’s dependence on the PS system.

Click to expand...

In general, they're both very reliable.

The first-generation "W" body--Lumina, Cutlass Supreme, Gran Prix--had epidemic problems with the vacuum boosters. But that's not common on the GMT400s.

I've heard of Hydroboost leaking PS fluid, and having to get some seals replaced; but again not hugely common.

Wild Guess with no evidence: I'd be most concerned about a PS failure that disabled the Hydroboost. And even then, the Hydroboost accumulator "should" give you a stop or two before the booster is useless.

But anything can happen...

Schurkey said:

Wild Guess with no evidence: I'd be most concerned about a PS failure that disabled the Hydroboost. And even then, the Hydroboost accumulator "should" give you a stop or two before the booster is useless.

Click to expand...

That would be my concern as well, FWIW... and I've never had PS "hard fail" on a vehicle [note 1], which says something about PS reliability.

Too, if the PS does die, there's some advance notice to the driver through the steering feel that PS is suffering and, if the driver's smart enough to put 2&2 together quickly, the brake assist. I'm not sure how much "reserve" the HD accumulator provides but there's never "too much".


Notes:

[1] I have had the PS "fail" when the belt was tossed off the pulley. A few times when I was a kid I was plowing through snow drifts on country roads ('66 Belair 4dr, 283, PowerGlide) and the snow found its way into the engine bay and tossed the accy belts off the crank pulley. I've also had it "fail" when a loose alt belt got tossed at high engine RPM and took other belts off the crank pulley with it. These weren't really PS failures, they were me inviting trouble.

Have a limited time to reply and couldn’t read all replies but my bullet points basically:

-Used rotors that have been turned have a higher resistance to warping in my experience
-Brake pads make the biggest difference in brake performance
-The LUGNUT 4x4 rear disk conversion is an easy bolt on and they have an E-brake option now. Also go for the JB7 caliper when converting
-GMT800 front brakes (AND knuckles can be swapped on. You gain dual piston front calipers and a slip on rotor. Probably gain some pad area but I haven’t measured to confirm.
-GMT400 dually front brakes can be swapped onto a SRW truck. The rotors are essentially the same size as gmt800 brake rotors (1.5” thick and a 12.87” diameter is available)
-A good trailer brake controller is a must and even if the brakes aren’t “needed” can be used to get the trailer back under control if it gets upset from emergency manuevers, blow outs etc

94K3500PROJECT said:

-GMT400 dually front brakes can be swapped onto a SRW truck. The rotors are essentially the same size as gmt800 brake rotors (1.5” thick and a 12.87” diameter is available)

Click to expand...

You don't need GMT-800 parts for that swap. Some of the late GMT-600 (thru 2002 Express) vans used the bigger brakes on the SRW, so those rotors would work for a 2wd. On a 4wd, just get the DRW rotors. Also some of the SRW extended cab trucks used the bigger brakes, according to listings I've seen on Rockauto.

I've got the DRW brakes on the front of my K3500. If I ever rebuild the rears, I've got the bigger wheel cylinders to complete the job....friction parts on the rear are otherwise the same between the SRW and DRW, the DRW drums are only different to physically mount the wheels.

Nevermind. I was not thinking properly.