Rochester quadrajet questions

[Pmartin2204]

I'd like to rebuild my carb. It's a Rochester Quadrajet that is dated to 1975. Is there anything I should be on the lookout for or any advice anyone might have? And also when I got the car it had the transmission kickdown switch removed. Forgive me for not being so bright but what does the trans kickdown switch do and should I replace that as well? Thanks.

[Tpicks55]

With reguards to the carb, youtube has a few videos on how to and what to look for on rebuild.  HTH Tony

[TJ Hopland]

Most transmissions have a cable or rod attached to the throttle for the transmission to 'sense' what is going on with the throttle.  Sometimes they sense the whole movement and other times just if you are wide open/floored.  The THM400 (and 425 FWD Eldorado) that function is electric so in the case of Cadillac there was a switch on the side of the carb that would close at full throttle and operate a solenoid in the trans to downshift and delay the upshifts.   Chev in both the cars and trucks that got the THM400 used a switch on the firewall that part of the gas pedal operated. 


The Q jet does have quite a few parts and can be a little fiddly to work with.  Have you done any other carbs?   Is yours having issues?  If so what sort of issues?    They can be a diy thing but I would say they are more of an intermediate item especially if there are specific issues.   There are so many parts to these all most people can do is put it back the way they found it but if the last guy didn't do it right you have a problem and it takes someone that really knows them to spot the issues.  Watching some videos would be a good start to deciding if its a job for you.

Some of the 75's had 6 jets.    They had a device called an aneroid that was normally only found on the altitude versions that you have to be extra careful with because I don't think they have ever been reproduced.  The other odd part is another jet and metering rod that I think has something to do with part throttle.    I guess when they worked they worked great but they were apparently not easy to get or keep working so it was a part year thing.    The part throttle jet is just one more thing you have to stick in the top gasket and get in place while trying to assemble it.

[fishnjim]

Search for the corresponding Rochester rebuild manual on the internet.   I have earlier.

[Steve Lomas]

With reguards to the carb, youtube has a few videos on how to and what to look for on rebuild.  HTH Tony

I'd say be very careful not to bend the metering rods when disassembling, and yes it's quite fiddly getting things back together with the gaskets and accelerator pump staying in place.. if you are as clumsy as me it might be worth having extra gaskets handy!

There have also been issues with leaking plugs-  where holes drilled though the body of the carb are plugged in manufacture and loose their seal after time- so you can fill the bowl with gas and see if it leaks (if the car has been slow to start after sitting a while) in which case there are threads on different ways to fix this, from sending it off, to jamming JB weld in there!

[Hillbillycat]

quadrajetparts.com has the secondary metering well plugs that go into there and seal them up - like Steve noted.

[Ike]

I bought this book, it is very informative.   

[TJ Hopland]

And if you do have the wacky 6 jet 75 model carb its not a problem for the basic rebuild kit,  every one I have got has had the gaskets for it.    It's actually one of those gaskets most people have never used and always wondered what it fit,  I know it was that way for me.    I think at one time I had like 30 of those gaskets, a few of mine then the rest came in a box of random stuff a friend gave me from his shop.     Its the aneroid and the partial metering rod that I bet are darn near impossible to find if they are damaged.

[Pmartin2204]

Thanks guys. I appreciate the input and I'll let you know the outcome after a while.

[Pmartin2204]

Just to put an end on this post I ended up going with a professionally rebuilt factory rochester. Very pleased with my decision. Idles nice and smooth and no hesitation and fires up on the first crank.

["Cadillac Kid" Greg Surfas 15364]

Good call.  In spite of their straight forward simplicity, it takes a lot of hands on practice to do it easily. you know like that saying it took me al lifetime to be on overnight success  Until one develops the specific dexterity to assemble all the components correctly it can feel like you need 3 or 4 hands to do it.
It also takes some experience to understand what part (if any) of the carburetor is causing what symptoms.
For those that are interested in learning I might suggest getting a couple of quadrajets of any year, make or model and practice disassembly and re assembly.  It gets to be fun after a while.
Greg Surfas

[Pmartin2204]

Thanks for the tip Greg. It cost me a few bucks but in the end I figured I could save a headache, heartache and time if I got it already done.

[hornetball]

I went this route too.  The pros know all the tricks like epoxying the base plugs that leak, etc.  A QJ in proper tune is really nice.

[TJ Hopland]

Just hang onto your original especially if you think it is original.   There are way to many stories of replacements not quite being right even if they were built decently just not an exact match for the car.   

[Ike]

Just to put an end on this post I ended up going with a professionally rebuilt factory rochester. Very pleased with my decision. Idles nice and smooth and no hesitation and fires up on the first crank.

Who did you go through to get the carb?     I may be leaning that way as well as I do not have the correct carb on my 69.   

[Pmartin2204]

I hate to say it but honestly I went through AutoZone.

[Ike]

I found a place on EBay.  Carburetor Exchange.   They will rebuild your carb for 250. And actually do on engine tuning and return.  Mine is the wrong carb so I can buy the correct rebuilt and set ready to run for $550.  No core.

[TJ Hopland]

No core is interesting.   That has got to mean they have themselves quite the stockpile and demand is so low they don't expect to run out anytime soon.      I know back 15-20 years ago when I would just stop in the junkyards and look around for fun when I was near one Q jets were almost never there.    The cars had dates on em and I remember often seeing cars that had not been there for a day that didn't have carbs on em.   Guessing even back then that people that repaired them were stocking up.    Back then there were still some out there in daily driver status so I'm sure more demand than now that very few are DD's.

[Ike]

No core is interesting.   That has got to mean they have themselves quite the stockpile and demand is so low they don't expect to run out anytime soon.      I know back 15-20 years ago when I would just stop in the junkyards and look around for fun when I was near one Q jets were almost never there.    The cars had dates on em and I remember often seeing cars that had not been there for a day that didn't have carbs on em.   Guessing even back then that people that repaired them were stocking up.    Back then there were still some out there in daily driver status so I'm sure more demand than now that very few are DD's.

No core for me because I did not have a like carb to send.   That’s why it was $550.00.   If I had the right carb it would have been $250

[1976Deville]

I have a question too. Did anybody replaced the carb with an EFI system. I just wonder