Help with ‘74 D5 dozer.

Need help with the decelerator on my ‘74 Cat D5. Pedal won’t return after being depressed. I know there’s got to be some kind of return spring but I’ve taken off all the floor plates, traced the linkages all the way to the fuel pump and cannot find a spring. My service manual doesn’t show the decelerator assembly. What am I missing here?
Here’s serial no.

SN 63 J 1847 3A 4370

If I remember right spring is in no 1

Thanks Catman! Huge help. Now that I know where to look, I just gotta see what's broke and find replacement parts.

Hmmm, now that I've studied that diagram a bit looks like that might be a bugger to get to. Behind the Dash assembly.

Here's the same thing with Part Numbers for machines with S/N 63J1512-Up

Thanks for the help so far. I got the decelerator linkage with the spring out of the dozer and its shot

Rusted clear through. Anybody know where to get parts on these old dozers?

It looks like a simple contraption that could be rebuilt or repaired by someone with some common sense and a welder.

what part of VA do you hail from?

Still searching for this part. CAT does not have this part anymore and I have been looking for it at local used parts dealers and have come up with nothing. My local CAT dealer put out a request for the part but nothing turned up. A used part dealer also put out a request with no luck. I can rig up a way to get the decelerator pedal to return but all this is connected through the throttle lever and it goes to low idle position when I push down the DC pedal and the throttle does not return so I have to manually reset the throttle every time I push the DC pedal down.

As mentioned by davejo above, I could probably repair this one but I don't really understand how this all works together.

There is a spring showing through the hole in the "tube section" in the middle of the linkage assembly.

One side of the linkage slides in and out of the "tube" the other side is welded on the bottom of the tube. So obviously the spring inside the "tube" maintains some tension in the linkage that allows the throttle to stay in position while depressing the DC pedal. Then when you release the DC pedal the engine goes back to the original throttle setting. I think?

There is also a clutch assembly on the throttle lever with cams and springs inside. I'm sure all this has to be calibrated to work together properly just not sure how it all works. That is why I've been avoiding trying to disassemble the linkage and rebuild it. Looks like I will have to rebuild it though.

Anybody have information on how this all works together before I start cutting the old rusted out linkage apart to rebuild it?

There is really any calibration the spring loaded piece you are looking for just allows you to move the linkage towards idle by changing the length of the rod while the part with the springs and rollers just hold the throttle where you set it

Looks like the spring inside the tube is broken which allows the rod to clunk back and forth from short to long without any resistance.

It appears to be designed to be short in its resting state. When you push the pedal with your foot, the first couple of inches are compressing the spring before any actual motion of the governor is produced. Like stepping onto a cushion...

Measure the length of the barrel then just take a hack saw or cutoff wheel and carefully cut the barrel perpendicularly. You will find a broken spring inside or the end of the rod has rotted or pulled through a disc.

thanks Davejo. been waiting for a break in the weather to pull the linkage back out and disassemble, looks like next week it'll be in the 60's. Hopefully the spring is still in one piece and usable.

Is the spring linkage 'frozen' and acting as a solid rod right now? Was the dc working but only the pedal not returning to full upright position? I ask because you mentioned the original issue you were dealing with was the dc pedal not returning back after release. When I look at the set up, I don't think that spring will help with returning the pedal back to full upright after releasing. If I understand the linkage, when you press the dc, it raises that spring/rod upward to rotate the governor. I think bracket #19 in Nige's post even acts as a stop so you don't over rotate (to fuel cutoff maybe?). I can see where there is even adjustment on the top of that rod buckle where it connect to the governor. If you have a repair book, it might tell you the adjustment procedures for the dc and it will help you figure out how to work around it.

But the point is, I think the spring is there to give cushion to the governor when it bottoms out pm tje bracket and allows your foot to still move a bit more without damaging the fuel control. This allows you to smash the dc without worrying about keeping a light foot on it. It's the springs on the fuel governor/hand throttle and the weight of that overbuilt assembly wanting to pull the dc linkage back down that returns the pedal to full upright.

If that's the case, add your own return spring under the floor plate to help pull the dc back as far as possible. Make sure all those pivot points are well lubed and free. And if that spring linkage is frozen in the "shortened" position when it bottoms out, then your dc pedal won't return back to full unless you free it. It will act as a solid rod and just stop when it hits bracket #19.

If you can live with a dc pedal that works but isn't fully upright, I'd think about just adding a spring to overcome old pivot points.

That device looks very similar to the Accelerator/Deaccelerator used on 8T, 70D and 80C #12 Graders.
Here's how it works.

^^^ Very nice find!^^^

I always found the older the yellow book the better they were

My son made a telling comment the other day regarding manuals. Years ago an owners manual gave you pretty much all the information you needed to work on a vehicle. Today’s manuals start by telling you it’s dangerous to drink the battery acid….

From a rather obscure piece of literature.......

A lot of that obscure stuff is still around I have one on marine gears for a d353

It may be my imagination as I don't have a lot of old manuals laying around but I remember there being sections like "Theory of Operation" in the older stuff. These sections would go into detail about how a major component operated so we could troubleshoot the whole system. I don't think you find a lot of this type of info any more as it's more like "If code XXyyyy is present, test voltage/pressure at outlet ABC. If not within +/- vvvv volts or zzz psi, replace solenoid."

The fault with the engine speed control will be found in the small cylindrical hub the has 3 springs and 2 rollers in it, it's location can be in 2 places as I have not checked but its not hard to locate, it could be down under the floor plates bolted just below them it will be easy to spot, or follow the linkage up to around the rocker cover area, it locates with 4 small bolts, anyhow inside it needs to be clean and dry with no lubrication other than a slight dab on the spindle section, the paper gasket is important to keep crud out and can be easily made, it might look perfect inside but clean up all parts with some fine emery strip and reassemble with the aid of a Zip Tie and it will work a treat for another 10 years.