umb 63 FI Accel Sticking Problem

[Joe S.]

Just finished putting my 63 together and took it for a test drive yesterday. HAve a one things to work out but for the most part no major problems. One annoying thing that is bugging me though is the accelerator is sticking with the engine holding about 2500rpm. If I disconnect the accel rod the engine returns to idle with no problems. If I move the accel with my hand, it seems fine and has little or no drag on it. It has a little drag with the ground strap hooked up, but doesn't seem like enough to stop the rod from returning.

If the return spring were just a little more stout I think it would work perfectly. But the spring installed was part of the FI unit rebuild and I would hate to either shorten it or replace it with something stiffer.

Anyone experience this or have a suggestion for a fix. It's not good for the rebuilt engine and also not the safests setup.

Thanks...




Joe's 63 FI Convertible

[Chris D.]

Re: umb 63 FI Accel Sticking Problem

I've had two different issues that caused the throttle to hang up. On the low engine speed end like yours, the gas pedal was binding. Check it for free movement. Inside the rubber molding there is a steel hinge with a brass pin. While this is not a servicable part, I managed to slice open the rubber from the backside to lube the joint. Steel was corroded and prevented complete return. A new pedal was really in order but my short term fix has been fine for a couple years now.

Today's issue on the top end of engine range has been traced to a worn accelerator pump shaft bore in the air horn of the old AFB. Only a problem at WOT which is only 50% of the time. Getting ready to ream it out and install a bushing.

[Dave Morris]

Re: umb 63 FI Accel Sticking Problem

Joe,
I had this happen years ago on my 63. I had to jab the throttle everytime I let off the gas to get it down to idle. It was only sticking at about 1700 rmp though. The shaft on the FI unit that the throttle linkage rotates on had worn down and was in somewhat of a bind. It would work fine with the acc. rod unhooked because the acc. rod would pull it a a slight angle. I know your FI is rebuilt but just thought I would through it out there. Car looks great. Good luck.
Dave
#1684

[Joe S.]

Re: umb 63 FI Accel Sticking Problem

Thanks guys for the input. The FI unit is like new as Dave mentioned. Without the Accel Rod hooked up it returns right to idle no matter how slow you return the arm. With the accel rod hooked up, if you release slow, it hangs. Just a little pressure and it goes back to normal.

There is no carpeting in the car right now to hang on, there is also no pedal in the car (until I put the carpet in next week). I have no plastic bushing and lubed the shaft. I know if I put a stronger spring in or shortened the one in there it would work fine. It just wouldn't look right.

[DANNY PANTUSO]

Re: umb 63 FI Accel Sticking Problem

Hi Joe, I had the same thing happen to me, the blue spring you have is too weak,, I still have my original "BLACK" spring it alot stiffer, I would cut the blue one to stiffen it up, that would solve your high idleing problem. Danny

[Michael H.]

Orig 63 FI Return Spring

Glad to hear some are finally accepting the black (dark grey) FI throttle return spring for 63. I think most people still believe it's the blue spring that Chevrolet sold since the mid 60's. (actually, early production 63 springs were silver and changed to dark grey some time in Dec 62 or Jan 63) I don't know exactly when the blue spring showed up in production but I believe it may have been late 64 or 65, even though the original blueprint for that part called for blue paint. There were several changes in the physical construction of the spring from 63-65.

[Joe S.]

Re: Orig 63 FI Return Spring

Thanks all.

In the meantime I first had added a 2nd spring to make sure that was the problem. Once that was confirmed, I got out the ol' snips and needle nose pliers and took about 6 coils off the spring. Problem solved.

Interesting post Mike on the color of the spring. Is there any documented or survivor examples to get consensus on the "correct" spring?




Joe's 63 FI Convertible

[Michael H.]

Re: Orig 63 FI Return Spring

Joe,

Unfortunately, the only GM documentation that I've ever seen on this shows the spring as being painted light blue. I don't know why it wasn't painted that color for the first year or two of it's production life (63-64) but that's the case.

There were several distinct changes in the part itself, not counting the color, that suggest there was more than one vendor source as the years went by. The very first design spring that was used from SOP on 63 cars was not only silver instead of dark grey, it was wound in the opposite direction than the later grey spring. It was also shorter by about 6 or 7 coils, as I remember.

The second 63 spring (dark grey) was closer in physical appearance to the last available blue spring but there were still a few physical differences. The end hook was shapped much different and the last coil was also shaped differently.

I have an NOS spring and bracket that's still in the original old brown paper bag, just the way it left GMPD over 40 years ago and the spring it absolutely positively dark grey. It's been suggested that perhaps all of the blue paint flaked off over the years but there's not even one speck of blue in that bag.

I'll try to find and post a few old pic's of new 63's and 64's that clearly show either the silver or dark grey spring. I think I have one that has one of each side by side for comparison. I've been recording/documenting these amd other items since the early 70's, when almost all the cars still has most of their original components.

By the way, there's an obvious difference in the 1st design and 2nd design for the spring bracket too.

[Michael H.]

1st And 2nd Design 63 FI return Springs

Notice the obvious difference in length and opposite direction that each is wound. The short silver spring was used in 63 from SOP to somewhere around mid December? The longer black spring was used from Dec to probably at least some time in the 64 production run. All are the same 3827005 part number.

[Michael H.]

NOS Grey FI return Spring

Here's an NOS return spring, along with other FI items, purchased in summer 1963. It's dark grey with no evidence of ever having been painted blue.

[Dave Morris]

Re: Orig 63 FI Return Spring

Michael
Good pictures and info. I guess I have the wrong spring on mine. Would you happen to know long that first design spring is? I may have the original in with some of my old stuff. Also, you mentioned the spring brackets. What is the difference in those two designs? Mostly interested in the first design. Unit #51. Thanks
Dave #1684

[Michael H.]

Re: Orig 63 FI Return Spring

Dave,

If your return spring has ever been replaced, even if in the 60's, it's likely the longer 2nd design spring. I just dug out a short early design and a longer second design. Here are the numbers.

The 1st design short silver painted spring has an overall length of 2.45" end to end. The dim for the coil stack only, minus hook ends, is 1.78.

The 2nd design longer dark grey spring (some time around Dec of 1962 production) has an overall length of 2.700" end to end. The dim for the coil stack only, minus hook ends, is 2.100".

So, the difference in overall length between the 1st and 2nd design springs is roughly 1/4".

If you don't happen to have a ruler with you when you find a spring at a swap meet, you can ID each design by looking at the direction that the wire is wound. Looking down at the end of the 1st design short spring, you will see the coils wind clockwise. The 2nd design for later 63-65, and I believe all service replacements, is wound counter clockwise.

The coil count is also different between the 1st and 2nd design. The 1st design short spring has 32 coils and the 2nd design long spring has 41.

The wire diameter for both is the same at .050".

I'll post a pic of the 1st and 2nd design return spring bracket in a day or two. I believe all 63-65 were the same but the 2nd run that GM released in the late 60's is different. Would be good to hear from some original owners on this.

Michael

[Mike L.]

Re: Orig 63 FI Return Spring

My early 64 FI car was all orignal with a 375R unit, and the spring is dark grey/black in color.

[Mike McKown]

I have a little something to add

Michael:

I have two of the DARK GRAY springs from '63 units. I believe them both to be original '63 production parts. These two springs match what you are referring to as the second design or late '63 production. The coil count, wire diameter, coil stack length and overall length match your posted dimensions.

I also have a BLUE spring on a '65 unit that EXACTLY matches the description of the above gray spring except for the diameter of the loop on each end of the spring. Of course, it is blue. I don't think this is a production spring as the paint is too good on it but it could be a service replacement.

The functional difference? You can hook the BLUE spring to the GRAY spring and pull on them. The BLUE spring will have all the coils opened up before any of them open on the GRAY one. The GRAY is much stiffer even though it looks the same. I don't have a spring scale so I can't quantify the difference.

[Michael H.]

Re: I have a little something to add

Mike,

You are exactly right. The original grey spring and the later blue spring are the same coil count and look physically identical but there is a difference in the shape of the hook loop at the end. In fact, all three designs have a different loop. The early short silver spring has a loop that is roughly 270 degrees and is still curving at the end. The 2nd design grey spring loop is cut a little shorter, at about 250 or 260 degrees, and still curving at the end. The 3rd design has roughly the same shape but the last 1/8" is straight, not curved. This difference can be seen in the pic's of the three springs that I posted. The used grey spring in the 1st pic is/was a currently available blue spring that I bought in the mid 70's but removed all the blue to make it lok like an original black spring. It as the 3rd design hook ends. The NOS grey spring in the 2nd pic is a correct original with the full curved end.

In the early 70's, GM discontinued many FI parts for a year or two but due to complaints from the field, many were reinstated in about 1974 but several were supplied to GM by different vendors than the original. They were made back to the original print but the slight differences in the finished part were probably due to slight differences in mfg methods. I would have to guess that would account for the difference in design for the spring and several other parts. I'l post a pic of the two different designs for the return spring bracket later. Interesting stuff... to us anyway. (my neighbor thinks I've completely lost my mind when he sees me measuring things like old used springs with a caliper)

The more details we learn about these cars, the more I'm convinced I could never again be a Bloomington Gold or NCRS judge.

Michael