I got in my '86 this morning to go to work and when I started off down the road I heard a very loud grinding kind of sound when the trans shifted to 3rd, I proceeded through neighborhood listening for any other sounds as I was already late. Well after the trans shifted to o/d I then gave it a little throttle to get out of o/d as it was lugging the engine, the rpms were only around 900-1000 after the shift to o/d. Well upon downshift that lovely grinding sound came back again while the trans was downshifting back to 3rd. I then turned around and drove back the half mile to home and called in to work. My truck wouldn't start because the battery was dead for some reason, which led to getting in the vette.

Any idea's? the only work done to the car recently was exhaust work. But that was completed 2 days ago and it has was perfect after I got done and perfect yesterday. What could happen overnight that would cause this?

The trans was rebuilt ~12 years ago with about 100,000 miles on rebuild. When the trans was rebuilt it was built with stronger parts, the trans builder said it should hold 500 hp no problem when he finished it. I also noticed ~6-months ago while on a high speed run it would shift from 3rd to 4th at WOT.

 

No ideas?

 

Automatic trans I assume?

 

If so, and it is definately inside the trans, it is a broken drivetrain part, likely a rear planetary gear. It will be clearly seen once it is disassembled.

 

Yes, it's an auto.

If that is the problem then would the sound go away when you get about 1/2 throttle? Because at 1/2 throttle the trans shifts through the gears nice and firm and on time, and the converter locks like it's supposed to with no noise. i'm baffled. lol

I did drop the pan on the trans today and there is no metal in fluid or in pan. replaced filter while in there with a new gm one. I'm leaning away from trans for the moment

 

Got a new update, It is not the trans, Something in exhaust is rattling. Got the car on a lift adn chocked off the wheels and had a friend put it in gear while I was under with a long screw driver touching different things to try and narrow it down. so What on the exhaust can rattle? I have the stock front Y pipe stock cat, that has been gutted. still have the AIR tube going from cat to pump. initially thought the air tube was vibrating, so I moved the clamp so it would be at a different angle to get the air pipe away from trans. But the rattle still persists.

 

Pete K. is likely correct. The rear planetary gearset has failed likely.

I recently completed a full rebuild on my 1987 Vette 700R4 trans. The rear planets failed on my trans.

There is a Forward Oil Lube seal that is located in Rear side of the Input Drum - Turbine Shaft Assembly.

The Oil Lube Seal failed in my Trans and then I lost oil to the rear planet set. Fried it black and blue and stripping all the gear teeth off of the planet gears.
The lube seal in your 86 was originally a Nylon plastic part too.

Transgo supplies a New Nylon plastic lube seal too as nearly all rebuild kits do, and most rebuilders use also.

Be sure to get the GM Viton rubber Lube Seal. It was used in the 1991 and later 700R4 and 4L60E transmissions. You have to buy a quantity of 5 from your local GM dealer, the only way they sell this Viton rubber lube seal. For $15.00 its well worth it.

The New GM Viton Rubber Lube Seal will last much longer than the Nylon plastic part.

The ATSG Green Update book on 1987-1993 700R4 transmissions also list using the Brown Viton rubber seal as an update over the earlier White nylon plastic lube seal part.

I chose to upgrade my trans with GM 5-pinion Forward and Rear Planet sets. And used a Complete kit with all new Needle bearing thrust washers and the Late Model updated Hub that replaces the batwing washer with a GM Needle thrust bearing.

I was lucky enough to find a guy in Chicago Illinois with all NOS Early build (Toledo, Ohio) GM 4L65E Planets and all Necessary Parts to make a straight drop in Retrofit during my 87 700R4 rebuild. He told me at the time, that GM is now making all there 4-pinion and 5-pinion planetarie gearsets in Mexico.

The stuff you see on Ebay, cheap-inexpensive 4 and 5 pinion planetaries gearsets are made in China. The Small planet gears are made from pressed powder metal. I would stay clear of the China stuff.

The GM factory gearsets are made from Billet Steel. As they should be.

Use an Aftermarket "Beast Sungear Shell" during your trans rebuild too. Much stronger than the original GM part.