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Username Post: Quadrajet Repair-Throttle Shaft        (Topic#271238)
Brother65 
Senior Member
Posts: 1147
Brother65
Loc: Gainesville Missouri
Reg: 06-15-02
10-28-11 09:26 AM - Post#2152052    

I swear I have checked this before and it was fine. Whether it is all or part of my other issues remains to be seen. It started a couple of days ago with having a high idle that I could not get rid of and might go away once I messed with it but would come back on the first trip. I sprayed carb cleaner to look for vaccum leaks and found a profound leak at the primary throttle shaft. Continued looking and thought I heard a change around the plate where the EGR used to be. Went around the back of carb and then was going to check the plate again, but I quickly found a new respect for carb cleaner.

It flashed and started quite the fire that I like to never for put out. Looks like some burnt plastic and vaccum lines were the only damage. Will be next week before I can tear it down.

All of that to ask this. Is rebushing the shafts with valve guides or brass tubing as I have read elsewhere a lasting fix?

Are there ever instances where the base is wore beyond repair?

It will start fine and runs just like it would with the vaccum hose off of the advance. I assume the carb survived OK, but when I tear it down what should I look for in particular? It had quite a BBQ before I could dump enough water on it to put it out. I know, bad practice, but something broke is better than a burnt hull. If I have to spend too much on the carb would I better off with a new carb? Thanks.

Hotrodders-America's first recyclers.
78 C20 Hunting Rig/Work Truck 350 4 spd.


 




IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
10-28-11 09:32 AM - Post#2152053    
    In response to Brother65

If all you wish to do is lower the leak volume, and still have the leak, use the solid bushings designed for this operation, they are available from carb destroyers everywhere.

If you want to virtually eliminate the leak, then, use a teflon insert formed from a sheet of teflon available at just about any good hobby store or industrial house, like McMaster-Carr (mcmaster.com).



 
ss3964spd 
"6th Year" Gold Supporting Member
Posts: 4620
ss3964spd
Loc: Fairfax, Va
Reg: 12-21-00
10-28-11 11:43 AM - Post#2152084    
    In response to IgnitionMan

If the shaft is so worn enough to cause a significant vac leak then simply using some kind of seal isn't going to fix it - the seal won't last if there's that much play in the shaft.

If this thing is going to see a bunch of miles then bushing the shaft and using a seal might be worth while but otherwise not. No QJ I know of ever came with positive seals on the throttle blade shafts. And there were, what, a bazillion of them made?

Dan

If I recall correctly my memory is excellent. My ability to access it is not.


 
427SS65 
"15th Year" Platinum Supporting Member & Moderator
Posts: 14601
427SS65
Age: 72
Loc: St. Louis, MO
Reg: 12-11-03
10-28-11 12:15 PM - Post#2152091    
    In response to ss3964spd

Get a new throttle body (plate) - ready to go.

Tom 65-70 Full Size Team Moderator

View My Photos Here

65 Impala SS Tahitian Turquoise


 
IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
10-28-11 04:34 PM - Post#2152176    
    In response to ss3964spd

Shows that people have NO concept of how things work correctly.

The teflon BECOMES not only the seal, but the BUSHING, and it IS NO STICK, so, binding of the shaft isn't an issue. neither is the shaft wear, as the teflon contacts a section of the shaft and base that never has touched each other, so, there would be NO WEAR in those contact areas the teflon sits in.

I do this ALL THE TIME, on all sorts of different carburetor make/model throttle shafts, and, it fixes even the worst wear throttle shaft issues and leaks.

The teflon will distort somewhat when the base is tightened down on the manifold, but, will not allow leakage, nor binding. A solid bushing MUST have some clearance in it, so when the base is distorted from tightened down, it doesn't bind, and that clearance IS an air leak, plain and simple.

Most Q-Jets have a very small area of the base to throttle shaft that supports the shaft in the bore. the rest of the bore/boss isn't even touched. This area is also .028 to .030 LARGER than the shaft. Sooooooooo....IF a person was to remove the throttle blades, and cut teflon inserts from, say....., .028/.030 thick teflon sheet, AS I DO ALL THE TIME, then, one could assume that the insert could/would bring the shaft back to the center of the unused/unworn bore, and stop the leaks, without binding, without alignment issues, without a bunch of horse hockey solid busing binding and continued leaks.

Heck, I even bore the shaft hole bosses on AFB's, other Rochester carbs to take the teflon inserts, even the 2 bbl on my 1982 S10 2.8 V6 carb when it got loose, the carb on my 1986 Nisan Sentra, my neighbor's Hitachi 2 bbl on his son's 1972 Ford Courier, etc.

But, then, what do I know, I only worked on race carbs at Holley Racing for 5 years.



Edited by IgnitionMan on 10-28-11 04:46 PM. Reason for edit: No reason given.

 
Brother65 
Senior Member
Posts: 1147
Brother65
Loc: Gainesville Missouri
Reg: 06-15-02
10-28-11 07:43 PM - Post#2152216    
    In response to IgnitionMan

If I were to try this, are there instructions to follow? Is teflon teflon, period or is there a particular type/kind to use? Special tools?

I do not have a drill press OT other precision tools of that type

Hotrodders-America's first recyclers.
78 C20 Hunting Rig/Work Truck 350 4 spd.


 
Stinky 
Senior Member
Posts: 1618

Loc: Whitewater, CO
Reg: 05-25-01
10-28-11 08:12 PM - Post#2152221    
    In response to IgnitionMan

IM, I was w/you the whole way on how to do it. But, let me see if I go this right....you measure the shaft, then you measure the hole, then you take a strip of teflon the thickness of the difference of the two and put it in the hole? Do you use an adhesive to get it to stay in place.

I have a side question, why is it that I never hear of a TBI throttle plate bores getting worn out? Or am I just missing the boat on that one?



Edited by Stinky on 10-28-11 08:14 PM. Reason for edit: No reason given.

 
72novaproject 
Senior Member
Posts: 3221
72novaproject
Age: 62
Loc: D/FW Texas
Reg: 02-18-03
10-29-11 07:15 AM - Post#2152307    
    In response to Stinky

  • Stinky Said:
Let me see if I go this right....you measure the shaft, then you measure the hole, then you take a strip of teflon the thickness of the difference of the two and put it in the hole?



Hole – Shaft / 2 = Teflon thickness. This centers the shaft in the bore.

  • Stinky Said:
I have a side question, why is it that I never hear of a TBI throttle plate bores getting worn out? Or am I just missing the boat on that one?



The quad has a cast iron base with the bore machined into it. The shaft is hard steel. Not sure about the TBI but the body is cast aluminum and likely has bushings pressed in with a similar hardness value to the shaft.

Steve

To each problem exists a solution...now think.

The ZD Nova Page


Edited by 72novaproject on 10-29-11 07:19 AM. Reason for edit: No reason given.

 
IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
10-29-11 05:42 PM - Post#2152477    
    In response to Stinky

For our purposes, teflon is.......teflon.

Throttle bodies for EFI are, oh, the humanity...TEFLON bushed.

Need I say more.

If you aren't able to teflon bush the shaft, take the base plate off and send it to me, I can re-bush them, and will be happy to do yours for you.



 
ss3964spd 
"6th Year" Gold Supporting Member
Posts: 4620
ss3964spd
Loc: Fairfax, Va
Reg: 12-21-00
10-31-11 09:00 AM - Post#2153029    
    In response to IgnitionMan

  • IgnitionMan Said:
Shows that people have NO concept of how things work correctly.


A little harsh, IM.

Tell me then, what is the actual MEASURED vacuum leak difference between a correctly bushed and clearanced shaft verses a teflon sealed shaft?

Dan

If I recall correctly my memory is excellent. My ability to access it is not.


 
IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
10-31-11 10:07 AM - Post#2153047    
    In response to ss3964spd

Well, IF it applies, live with it, the truth sometimes really hurts. Try being informed, instead of just opinionated from mis-information.

As far as a vacuum leak goes, try as low as 1/10th a percent, to ZIP with the teflon, and between 1/12 and 2 percent with a solid bushing. Doesn't sound like a lot, but, as much as 1 full percent leak is determental to idle and low speed efficiency.

One of the things that help seal the bushing, any bushing when run in a wet environment, is the vapor from the liquid around it. IF the clearance is excessively large, NO amount of vapor will help seal the leak. Teflon, at the absolute minimum clearance, and the vapor, do a lot to completely seal these type of throttle shaft to base leaks.

Try using a very sensitive vacuum gauge on the base, with the engine running, and nothing on the ends of the shafts, so the gauge can read the leak past the shaft when the engine is running, that's the way we did it at Holley.

Plain, simple, and easy enough to understand for just about anyone, isn't it.



 
ss3964spd 
"6th Year" Gold Supporting Member
Posts: 4620
ss3964spd
Loc: Fairfax, Va
Reg: 12-21-00
10-31-11 11:56 AM - Post#2153098    
    In response to IgnitionMan

You're second unnecessary, unfounded, and un called for snipe at me aside -

So, approximately 1 1/2 to 2 percent leakage past a correctly bushed and fitted shaft without any type of positive seal.

Assuming 10 In/Hg of vacuum you're saying just .20 In/Hg of loss. at 20 In/Hg - .40 In/Hg loss. Or, less than 1/2 In/Hg loss assuming 20 In/Hg.

From a purely logical perspective I appreciate what you are driving at; ANY vacuum leak at all is going to have an effect. A perfect set up would be no vacuum leaks anywhere; not at the base gaskets, not at the various hose connections, not in the brake booster, not at the PCV. Question is, for the typical street engine and the users of those engines found in this forum and others, is that 2 or 4 tenths of an inch of vacuum going to matter enough to go to the effort/expense of fitting the throttle shafts with positive seals? Aside from blow threw carbs - which can't be termed mass produced, were there any mass produced carbs fitted with positive seals from the factory?

Just a guess but most of us here don't have access to a very sensitive vacuum gauge.

Dan

If I recall correctly my memory is excellent. My ability to access it is not.


 
sidworks 
Valued Contributor
Posts: 3509

Age: 73
Loc: Sidney, B.C.
Reg: 12-03-05
10-31-11 12:35 PM - Post#2153110    
    In response to ss3964spd

  • ss3964spd Said:
  • IgnitionMan Said:
Shows that people have NO concept of how things work correctly.


A little harsh, IM.

Tell me then, what is the actual MEASURED vacuum leak difference between a correctly bushed and clearanced shaft verses a teflon sealed shaft?


I think that he is just being honest in what he says
I just think that people are to sensitive and interpret things not in the real manner in which they are said- too personally when it is meant as an overall statement
ron


http://www.sawmillcreek.org/showthread.php?208929-...
http://www.sawmillcreek.org/showthread.php?220902-...
http://forum.woodenboat.com/showthread.php?156542-...


 
IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
10-31-11 04:51 PM - Post#2153225    
    In response to sidworks

"I think that he is just being honest in what he says"

Absolutely dead on target, thank you for your correct observation of my posts.

Now, the fellow came on with an attitude that solid bushings were the BEST and ONLY answer, and then, he gets over the top in trying to prove me a liar, and wrong, which I AIN'T.

As I said, if it fits, live with it.

This is what I mean by "selective ignorance". People ARE NOT usually ignorant about much, if at all, most are bvery saavy in a lot of things, but, when they are not given the full story, nor the opportunity to hear differences, outside influenced selective ignorance sets in, and arrogance usually follows not far behind.

Selective ignorance comes from people with the absolute best of intentio9ns, but that have taken as gospel those answers they only want to hear, and/or advertising hype, con jobs and other things that close off workable different and alternate methods of doing it, and, doing it way, way better in a lot of cases.

An example of very selective ignorance is the masses of people that just KNOW that FRAM oil filters are just the dandiest things since holes in donuts, they have to be, they are the best seller, and anyone that says different, is wrong, because they heard it from here, or there, and it has to be totally correct. Cut one apart and see for yourself if they are worth the hype and con job. They are the biggest seller because they are advertised far more than any other oil filter on the market, nothing more, they ain't the best,they ARE inferior in a lot more than a few people's pinions that HAVE CUT THEM APART, and taken their own look inside them.



 
72novaproject 
Senior Member
Posts: 3221
72novaproject
Age: 62
Loc: D/FW Texas
Reg: 02-18-03
11-01-11 05:01 AM - Post#2153356    
    In response to IgnitionMan

  • IgnitionMan Said:
Try using a very sensitive vacuum gauge on the base, with the engine running, and nothing on the ends of the shafts, so the gauge can read the leak past the shaft when the engine is running.



Iman are saying to use the vacuum gauge sort of like we did a propane fired Freon sniffer back in the day where you hold the open end of the hose close to the throttle shaft and try to detect a low pressure area near the shaft?

I understand the propane sniffer created the inverse effect. A vacuum was created at the end of the hose to draw escaping Freon gas which would combine with the propane and burn green. Not to mention create mustard gas.


Steve

To each problem exists a solution...now think.

The ZD Nova Page


 
IgnitionMan 
Valued Contributor
Posts: 3539

Reg: 04-15-05
11-01-11 10:00 AM - Post#2153457    
    In response to 72novaproject

What we used at Holley was a very sensitive vacuum gauge, specially set up to read insanely low levels of vacuum, with a hose placed OVER the boss on the end of the shaft boss on the base.

This was done with a dead end shaft, virtually the same dimension as the shaft used in the carb, with NO levers/attachments on the ends of the shafts, so the vacuum hoses could be installed over the bore bosses.

A set level vacuum flow was then put through the carb, and the results were recorded, giving us a real world vacuum leak reading out the throttle shaft boss and bore.

The tests were done with dry air, natural gas (the gas that makes that nice new Holley carb smell), and, air with a fuel vapor media the same specific gravity as premium fuel of the day, at a 12.60:1 air to fuel ratio.



 




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