97 C150 have a "residual pressure valve" for the rear drums a

[Skip Fix]

Is there actually a residual pressure valve in the system for the rear drums as there should be compared to a disc ? Built into the ABS box? I know they are not longer in the MC.

 

[SUBURBAN5]

I would suggest reading the manuals on the sight to confirm, there free and available. but off hand I wanna say yes. Built into the abs module. Specially kelsey hayes.

 

[Scooterwrench]

Residual pressure valves are not needed if the MC is higher than the slaves. And you never run RPV's on disc brakes or the calipers will not completely release.

 

[Schurkey]

If there's a RPV in the rear brake system, I don't know about it.

GM took them out of the master cylinders in the early-1970s. I've never heard that they moved them somewhere else.

 

[0xDEADBEEF]

Residual pressure valves are not needed if the MC is higher than the slaves. And you never run RPV's on disc brakes or the calipers will not completely release.

Wilwood does sell RPVs for disc brakes, they are 2 psi vs 10 psi for drums.

 

[SUBURBAN5]

This is from a 98 service manual. Looks like I was thinking of a dump valve. The others appear to be right.

 

[Skip Fix]

Usually there is a 10lb RPV for drums so there is not as much lag on the drums. Older cars/trucks had them built into the MC under the flare seat for the line. I know my '81 Trans Am aluminum 4WD MC has none with the piston out you can see into the cylinder through the line but it is a 4WD, earlier Camaro/Firebird iron ones had it though in the drum side. Just wondering if that is why our truck have such crappy variable pedal feel and if it would help as most disc drums had one designed.

I've had my '97 since new so yes since new. Hit the pedal hard and engage the ABS good pedal for awhile. Swapped to a later model MC that everyone says fixes it-nope and it is not a quick take up. Adjust the rear brakes and a little better til they wear.

 

[Schurkey]

Usually there is a 10lb RPV for drums so there is not as much lag on the drums. Older cars/trucks had them built into the MC under the flare seat for the line.

Far as I know, that was deleted by GM in the early '70s.

Just wondering if that is why our truck have such crappy variable pedal feel

Shouldn't be needed. Something else is wrong.

WHAT BRAKE OPTION CODE does your truck have? JB5? 254mm (10") leading-trailing shoe rear brakes?

most disc drums had one designed.

Not since early-'70s unless they snuck it back in somewhere I don't know about.

I've had my '97 since new so yes since new. Hit the pedal hard and engage the ABS good pedal for awhile.

Need to properly bleed the ABS with a scan tool--and then the whole system.

Swapped to a later model MC that everyone says fixes it-nope and it is not a quick take up.

That's a mistake.

Adjust the rear brakes and a little better til they wear.

Are you using the park-brake?

 

[Skip Fix]

Stainless Brakes 20 years ago recommended that and on here lots of guys recommend the later model MC. Supposedly it give a better balance to rear brake line pressure. Most folks feel the self adjusting never adjusts because of that. They do feel a little better after rear drums adjusted.

ABS bled multiple times with a scan tool-even recently again.

Not sure what brakes just normal C1500 Silverado 350 with tow package.

Almost every mechanic I have talked to said every one of this generation of trucks are that way. Some just ditch the ABS and felt that helped. Others never improved them.

My '92 that did not have full ABS was fine.

 

[Schurkey]

Stainless Brakes 20 years ago recommended that and on here lots of guys recommend the later model MC. Supposedly it give a better balance to rear brake line pressure. Most folks feel the self adjusting never adjusts because of that. They do feel a little better after rear drums adjusted.

It's a disaster with low-drag front calipers, and you've almost certainly got low-drag calipers.

ABS bled multiple times with a scan tool-even recently again.

ABS bled, then the rest of the system bled? Bleeding the ABS gets the air out of the ABS, but it's still within the brake system until it's flushed downstream and out the wheel cylinders.

Not sure what brakes just normal C1500 Silverado 350 with tow package.

Look at the SPID sticker in the glovebox. Most-likely JB5, maybe JB6 which would be a significant upgrade at the rear.

Have you had the rear drums off? Do you have decent Duo-Servo brakes, or the horrible leading/trailing shoes?

Almost every mechanic I have talked to said every one of this generation of trucks are that way. Some just ditch the ABS and felt that helped. Others never improved them.

My '92 that did not have full ABS was fine.

Yeah, it's a hatefully common problem. But it is a problem, not normal operation. It can be fixed without using an incorrect master cylinder having a too-damn-big primary/secondary piston bore.