Rough idle in gear only

[JohnC]

Hi all.
I have a Idle issue that I can't seem to sort out. I have great starting and idling when in neutral and park (tach will read about 550/600) but once in reverse or drive with foot on the brake I get a vibration (tach will read about 475/500)...I had the carb redone last year, brought it back to him yesterday just to open it up and go through it (all looked good). Also install a new fuel/vacuum pump last year. I've rebuilt the brake booster (I know there a small vacuum hose in there too) I've checked the vacuum (running about 21" @ the manifold. I have a tee on the hardline). Do I need to check each vacuum line for a leak.

Could it be a timing issue? I've read timing lights are pointless on these motors. Maybe rotate the distributor a bit? I'm just spit balling here.

Thanks all

[Barry Wolk]

If you have 21? vacuum is fine. What you have is the normal vacuum leak that?s built into the sleeve valve vacuum switch on the TV. Not sure when they stopped using them, but they switched to a poppet valve unit that cures this. Presumably, to offset consumer complaints. Unfortunately, the poppet valve closes so well it causes consumer complaints about the brakes being ?grabby? and won?t let go. Short of machining the sleeve valve to impossible tolerances it is what it is..

[JohnC]

yes Vacuum is fine...anything I should focus on to take the shake out...like when I'm at a red light

[Barry Wolk]

I just added to my post. Short of changing the TV, be glad you have what what you have.

[JohnC]

Ah...we're talking about in the brake booster now...not carbs...i rebuilt my booster twice....because it leaked twice....now it doesn't leak but vibrates instead...like usual fix one thing...break 2 things

[Barry Wolk]

I’ve identified your problem. That’s the way they work. Slide valves inherently leak. There’s noting that can be changed except the unit itself. Do you understand that there’s a later type that solves your problem, but creates another.

[JohnC]

Yes....understood...I came across an old post of yours from 2009!...where you were asking the same question with the same problem