TPI Throttle Body triage
Thread Starter
Burning Brakes
Joined: Jun 2005
Posts: 1,191
Likes: 15
From: Wallingford Vermont
TPI Throttle Body triage
My throttle body shaft seemed to have alot of slop in it years ago when I purchased my Vette. Many years later and it's now a major vacuum leak that needs to be addressed. A 'net search didn't find much; no one makes a re-bush kit, and shops that deal with that sort of thing wanted a bit too much $ for a repair. So I figured I'd dive in with the worst scenario being I'll have to purchase another (worn-out) throttle body. I posted some of this before, but this thread is stand-alone and I'll add some pictures (just before my camera died).
The gasket set was a NAPA item 2-12140 'bout $16. The throttle shaft is 3/8" diameter, so I picked up a 3/8" ID, 1/2" OD bronze bushing from an Ace Hardware store ($1.30). I've heard of others using a sealed bearing but I couldn't find anything that specialized around here. Anything over 1/2" OD and the boss would need special machining. My garage doesn't include precision milling machines but a drill press and being very careful worked. A 3/8" drill bit ensured that I aligned the throttle body straight enough (on the drill press) going through the outer and middle shaft bore. I only used a little over a 1/2" length of the bushing, and drilled a similar depth into the throttle body (not going all the way through to the intake bore). The bushing sat a little loose in it's bore so I used some Loctite 660 retaining compound.
The hardest part is replacing the throttle linkage. As you probably know, the throttle arm is peened on. So it's easy enough to grind off with a Dremel (the shaft is square under the peen, self aligning). I used a TIG welder to attach back on the shaft and only slightly melted the plastic spring bushing (not noticeable). Others have drilled and tapped the shaft for a small machine screw.
The measured ugliness
First order after removing the TB is to strip it of the TPS, IAC, and the IAC/coolant manifold. The TB is an awkward piece to work on and those items are guaranteed to get damaged if left on.
Throttle blades are next. GM peened the ends of the screws so a little grinding on the ends with a dremel and a good T8 torx, they're out.
This is the end of the shaft we're gonna attack. The factory peen has to be ground off.
The linkage it off!
In order: linkage, spacer, nut, return spring. Don't worry if the spring and holder come apart. It really only goes back on
one way.
The shaft is out. Being steel the wear is mainly in the TB (aluminum) bore.
This the "boss" area that will be bored to accept my bronze bushing. !/2" fits into the lip of the "boss". I spent a LOT of time trying to get the TB into the correct position before I drilled. A 3/8" drill bit was used just to ensure I was relatively straight, before I switched to the 1/2" and actually started drilling. And then I carefully drilled only 1/2" in depth.
Unfortunately my camera died right about here. The bushing wasn't an inference fit. Some Loctite retaining compound held it in place and probably adjusted a little for my less-than perfect machining
Putting it all back together. The final trick is re-attaching the linkage arm. I've heard some drill and tap for a machine screw in the end of the shaft. It's gotta be a real small screw and pretty careful drill/tap. I elected to TIG weld the shaft/linkage arm. Not the prettiest but it worked. You still gotta be careful as the plastic spring holder started to melt on mine.
Hope this helps somebody who has needs a cheap fix for a sloppy Throttle Body. Good Luck
The gasket set was a NAPA item 2-12140 'bout $16. The throttle shaft is 3/8" diameter, so I picked up a 3/8" ID, 1/2" OD bronze bushing from an Ace Hardware store ($1.30). I've heard of others using a sealed bearing but I couldn't find anything that specialized around here. Anything over 1/2" OD and the boss would need special machining. My garage doesn't include precision milling machines but a drill press and being very careful worked. A 3/8" drill bit ensured that I aligned the throttle body straight enough (on the drill press) going through the outer and middle shaft bore. I only used a little over a 1/2" length of the bushing, and drilled a similar depth into the throttle body (not going all the way through to the intake bore). The bushing sat a little loose in it's bore so I used some Loctite 660 retaining compound.
The hardest part is replacing the throttle linkage. As you probably know, the throttle arm is peened on. So it's easy enough to grind off with a Dremel (the shaft is square under the peen, self aligning). I used a TIG welder to attach back on the shaft and only slightly melted the plastic spring bushing (not noticeable). Others have drilled and tapped the shaft for a small machine screw.
The measured ugliness
First order after removing the TB is to strip it of the TPS, IAC, and the IAC/coolant manifold. The TB is an awkward piece to work on and those items are guaranteed to get damaged if left on.
Throttle blades are next. GM peened the ends of the screws so a little grinding on the ends with a dremel and a good T8 torx, they're out.
This is the end of the shaft we're gonna attack. The factory peen has to be ground off.
The linkage it off!
In order: linkage, spacer, nut, return spring. Don't worry if the spring and holder come apart. It really only goes back on
one way.
The shaft is out. Being steel the wear is mainly in the TB (aluminum) bore.
This the "boss" area that will be bored to accept my bronze bushing. !/2" fits into the lip of the "boss". I spent a LOT of time trying to get the TB into the correct position before I drilled. A 3/8" drill bit was used just to ensure I was relatively straight, before I switched to the 1/2" and actually started drilling. And then I carefully drilled only 1/2" in depth.
Unfortunately my camera died right about here. The bushing wasn't an inference fit. Some Loctite retaining compound held it in place and probably adjusted a little for my less-than perfect machining
Putting it all back together. The final trick is re-attaching the linkage arm. I've heard some drill and tap for a machine screw in the end of the shaft. It's gotta be a real small screw and pretty careful drill/tap. I elected to TIG weld the shaft/linkage arm. Not the prettiest but it worked. You still gotta be careful as the plastic spring holder started to melt on mine. 
Hope this helps somebody who has needs a cheap fix for a sloppy Throttle Body. Good Luck
Last edited by DanZ51; Sep 1, 2014 at 09:20 PM.
Sounds like you did a good job. Expect a bazillion PMs from guys wanting you to do it for them.
2nd Gear
Joined: Mar 2023
Posts: 2
Likes: 0
Hey Dan - I’m a little intimidated about the return spring assembly. Upon removal, I have visions of springs and brackets flying all around the shop. Assuming I’ve successfully re-captured all the parts, how exactly do I go about re-assembling and re-installing the spring assembly? Your photos and descriptions are great at explaining the bushing procedure. I get that part. But your description more or less says to not worry about re-assembling the spring – it’s easy. I worry, as it turns out. Could you give us a little more detail about just how to go about it? Thanks. Paul
Melting Slicks
Joined: Jul 2005
Posts: 2,221
Likes: 302
Just for completeness in case anyone searches on this topic and there are two threads on this subject.
I just did my throttle body and everything works really good now.
https://www.corvetteforum.com/forums...post1608755472
I just did my throttle body and everything works really good now.
https://www.corvetteforum.com/forums...post1608755472
