Deceleration springs, disassembly

[DrWin]

So, while waiting for my extractor kit to get the broken bolt out of the engine block I started shining up my throttle body. Decel springs looks functional, but very grimy. I want to clean them - how the h*** do I pick these things apart?

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[82DMC12]

Well I just sprayed carb cleaner all over them and used a toothbrush to agitate. However now I'm dealing with a high idle possibly related to the decel springs I didn't have before so in my opinion, I would probably not mess around with them too much.

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[Bitsyncmaster]

I've always though about setting up a test jig for those valves. I would guess they open around 20" of vacuum and then would let a fixed amount of air past. Just that someday we will run out of good springs and will need to find a replacement.

[painterdave72]

why clean a part that is going to get covered in exhaust grime and fumes the first time the car is ran? but like andy said i supposed you could just spray them with carb cleaner..

[David T]

A good source for new decel springs is the ones in retractable pens. You have to cut them a little shorter. If you have an automatic you don't need them to open at all. When you have it apart, you set the stop screw so that it stops the plates from closing too much and getting jammed. That is all that screw is for. It should never be touched again. It is NOT for setting idle in this application.

[82DMC12]

DrWin -

While you have this apart, can you answer something for me? I'm talking about the black rubber flex gasket that goes between the throttle body and the lower air meter. Do you have washers between the gasket and the air meter, and between the gasket and the throttle body? The parts manual doesn't show them but I had them installed when I took everything apart. So I have two washers per cap screw. It's like screw head > washer > rubber gasket > washer > throttle body (or air meter). I'm chasing a potential air leak and I wonder if these washers are creating a gap perhaps from a hardened or shrunken rubber flex adapter.

[DrWin]

DrWin -

While you have this apart, can you answer something for me? I'm talking about the black rubber flex gasket that goes between the throttle body and the lower air meter. Do you have washers between the gasket and the air meter, and between the gasket and the throttle body? The parts manual doesn't show them but I had them installed when I took everything apart. So I have two washers per cap screw. It's like screw head > washer > rubber gasket > washer > throttle body (or air meter). I'm chasing a potential air leak and I wonder if these washers are creating a gap perhaps from a hardened or shrunken rubber flex adapter.
On the throttle body it was two washers per screw in the order you described. On the air meter it was only screw, washer, rubber gasket. Except for the upper right one, where a washer was behind the gasket too. That doesn't seem to make sense to me. I did find a lot of washers in the VOD, so maybe they should have been two washers pr. screw all round? In short, I don't know. I'm replacing the gasket with this thing from deloreango, which comes with the screws and washers needed to mount it:
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I've always though about setting up a test jig for those valves. I would guess they open around 20" of vacuum and then would let a fixed amount of air past. Just that someday we will run out of good springs and will need to find a replacement.
If that happens it would be great to know more about the springs. Also, it would make it possible to modify the functionality in a controlled manner if we knew what we were modifying from.


A good source for new decel springs is the ones in retractable pens. You have to cut them a little shorter. If you have an automatic you don't need them to open at all. When you have it apart, you set the stop screw so that it stops the plates from closing too much and getting jammed. That is all that screw is for. It should never be touched again. It is NOT for setting idle in this application.
Please explain for the slow learner, why don't we need them for the aut. trans? My car is an aut. transmission.

[82DMC12]

On the throttle body it was two washers per screw in the order you described. On the air meter it was only screw, washer, rubber gasket. Except for the upper right one, where a washer was behind the gasket too. That doesn't seem to make sense to me. I did find a lot of washers in the VOD, so maybe they should have been two washers pr. screw all round? In short, I don't know. I'm replacing the gasket with this thing from deloreango, which comes with the screws and washers needed to mount it:
67949



OK thanks. I am thinking the original one had washers on both sides on each tab. I like that new design better though because it has the O-ring built into it. DPI has something similar and I think I'm going to get it as an upgrade anyway. I've pulled the throttle off so many times working on my own problem that I only want to do it one more time - to install one of those open spacers.

[Bitsyncmaster]

A good source for new decel springs is the ones in retractable pens. You have to cut them a little shorter. If you have an automatic you don't need them to open at all. When you have it apart, you set the stop screw so that it stops the plates from closing too much and getting jammed. That is all that screw is for. It should never be touched again. It is NOT for setting idle in this application.

Have you tried using a retractable pen spring?

[David T]

Short answer, Yes.
Long answer, a while back an owner had an aftermarket exhaust and he wanted it to sound louder. We spent the day playing around with the decel springs. During our experimentation we tried all different springs. We finally settled on some cut down springs from retractable pens. The decel plates/springs are only necessary for the 5-speed, you do not need them for an automatic. BTW, when they built the Deloreans, the engines were all set up exactly alike no matter if they went into automatics or 5-speeds. Typically the vacuum advance, mechanical advance, timing, idle speed, and fuel systems are set up just a bit differently but not in Deloreans! You need the decel valves in a 5-speed because, in 5-speeds, the motor is tightly coupled to the transmission, if you downshift, the motor's RPM's go up a lot. If you do that with a closed throttle, the engine acts like a brake and you slow down fast. In an automatic the torque converter allows the motor to slip so you don't have that huge braking effect. Same if you suddenly lift your foot off the throttle at high speed, you get a large braking effect from the motor. The decel valves allow air to get into the motor reducing the braking effect. If you get backfires you fry the very thin wire of the decel springs. On some cars I have seen them so bad they can't hold the tiny valves shut tight so you can't control the idle.

[DeloreanJapan]

Short answer, Yes.
Long answer, a while back an owner had an aftermarket exhaust and he wanted it to sound louder. We spent the day playing around with the decel springs. During our experimentation we tried all different springs. We finally settled on some cut down springs from retractable pens. The decel plates/springs are only necessary for the 5-speed, you do not need them for an automatic. BTW, when they built the Deloreans, the engines were all set up exactly alike no matter if they went into automatics or 5-speeds. Typically the vacuum advance, mechanical advance, timing, idle speed, and fuel systems are set up just a bit differently but not in Deloreans! You need the decel valves in a 5-speed because, in 5-speeds, the motor is tightly coupled to the transmission, if you downshift, the motor's RPM's go up a lot. If you do that with a closed throttle, the engine acts like a brake and you slow down fast. In an automatic the torque converter allows the motor to slip so you don't have that huge braking effect. Same if you suddenly lift your foot off the throttle at high speed, you get a large braking effect from the motor. The decel valves allow air to get into the motor reducing the braking effect. If you get backfires you fry the very thin wire of the decel springs. On some cars I have seen them so bad they can't hold the tiny valves shut tight so you can't control the idle.


Hi David . in another words , if you blocked this whole for the decel spring , the engien will get more braking force when off the gas pedal?
I have an Auto trans, Wish the Engine brake force can be more strong ,to reduce foot brake buring the moutian downhill run.

[David T]

Hi David . in another words , if you blocked this whole for the decel spring , the engien will get more braking force when off the gas pedal?
I have an Auto trans, Wish the Engine brake force can be more strong ,to reduce foot brake buring the moutian downhill run.

You can experiment with them and try blocking them shut but I don't think you will get much braking force in an automatic.

[82DMC12]

if you want to experiment with blocking off the decel springs you can seal them closed with a hot glue gun. I did this while troubleshooting an idle issue last year. No, I did not drive the car like this though...

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