: HELP with 1976 Cadillac Eldorado - Help with strange problem

05-01-11, 05:15 PM
Folks, I am asking for your divine help once again. The newest toy I have added to my collection is a 1976 Cadillac Eldorado Convertible, gorgeous Black with White Interior… I love the car, however, with any unrestored, unmolested 35 year old car there are a few issues I have had to correct since acquiring this beauty.
However, the latest issue has left me baffled and sitting at home worrying all weekend long has led me to turn to the folks that know the best and that would be you guys, you’re the experts, and have the experience so any help or information you could provide me with would be very much appreciated and helpful.
The car has 117K it was a one-owner and needed mostly minor mechanical things that I have had my trusted local mechanic of many years take care of for me…
I will describe in detail what the car is doing; I think it’s to strange for words personally.
Upon starting the car it runs fine, idles a little fast, but that it has been doing… After the car runs and begins to warm, I first noticed it when applying the brakes or letting off the accelerator but not while the accelerator is pressed… The car makes the strange noise, in the beginning when the car starts to make it, the sound it makes is like its spitting water back out of the jug, but it isn’t. The sound is coming from the floorboard, favoring the right-hand side, after the car warms; the sound then comes more pronounced and then sounds like a muffled diesel engine running, when its making this sound I also get a vibration in the floorboard and it can be felt all the way over in the accelerator pedal. It’s a strange noise, and a strange feel. The car does it immediately after being started when it’s put in reverse, but after it’s out of reverse it doesn’t do it until the car warms up. After the car is fully warm, it’s very pronounced and very annoying…
I immediately thought it was the transmission being scared thinking the worst, but after an hour of me driving it, and a friend of mine driving it we are both convinced it is not the transmission… The car shifts smooth, when it is supposed to shift, and the transmission works flawlessly. The reason I wanted to believe it was the transmission is because of the noise, and vibration immediately upon putting it in reverse, and the fact that after the car is fully warmed and being driven it also feels bogged down when starting up a hill, and I’m getting a sort of thud.

I believe it could be one of two things that I have thought of… A local muffler shop did put a new muffler on the car the other day, and the sounds and vibration did not start till after they had it. Could it be something they have done to mess it up? The catalytic converter possibly stopped up? But why would it be affected when putting it in reverse, and why would it sound like spitting water back into a jug? This is very strange to me. Should I be worried about the transmission? Any advice? My other thought is, could it be the hydro boost or something that affects the hydro boost?

I am upset over the noise and vibration the characteristics of the car and the way its acting because of this… I would be glad to answer any questions, this is very difficult for me to explain, and hard to know what I am talking about… The situation is truly one that you have to be there in person to fully understand the issue, it has me bothered, and I can’t for the life of me figure out what it is… I just hope it isn’t the tranny, but as I said, it shifts entirely too well, and is smooth… But, to me the sings point there because of the way everything acts. I am not sure – any help or thoughts would be appreciated. Possibly it is the cat converter or something they have done to the exaust?

05-01-11, 08:22 PM
after the car is warmed up and making the noise, does it go away if its put into park? One thing I would check , pull off the vacume hose thats going to the modulator valve at the transmission... the inside of the hose should be clean and have no oil in it... If you find oil change the valve...I would also change the transmission filter and look around in there...

05-01-11, 08:45 PM
No, after the car is warmed up and you put in park it still makes the noise. However, if the car is still cold and you put it in park the noise does go away. But, the noise is as often heard when the car is cold either. Its the most strange thing I've heard. Do you think it could be the cat converter, or an exaust problem of some kind?

05-01-11, 10:43 PM
If that car doesn't have a replacement timing chain, it needs one. Might even be part of your problem. Bruce roe

05-01-11, 11:04 PM
cloyes 9-3139 is the only timing chain I would use.. There are cheap ones that are junk and will too soon be a problem if used.. There is one other brand that is good, can't remember the name, Both good ones are about $100.... The 76 has 120cc heads , that means that if the chain jumps a tooth or breaks, your pistons WILL NOT hit the valves... thats good...

05-28-11, 04:19 PM
Things that come to my mind are the cats, and the hydroboost system. Also, is the trans fluid level ok? Did the car sit for a long time? How is the radiator and coolant recovery system? Air lock and clogged hoses as well as a bad cap can cause it to do odd things. And I completely agree about the timing chain. It's cheap insurance to replace it.