1985 4 + 3 Whining in Direct Drive-Many Questions

[1985vette]

I have a low mileage (15K) 1985 4 + 3 that recently started whining in all direct drive gears. It disappears when I engage overdrive. The fluid in the transmission is full. I changed the fluid about 2000 miles ago. I am currently running GM Synchromesh in the manual component and Mobil 1 ATF in the Overdrive.

Will it hurt the transmission to continue to drive it?

Does anyone have suggestions on whether I should get my overdrive rebuilt or get a rebuilt unit from a supplier? Will the car still be matching numbers if I get a rebuilt unit from one of the suppliers? Can you suggest a very reliable place to get a good rebuilt unit from? How much will it cost for parts and labor?


Any thoughts or experience would be helpful.


Thanks

 

[c4cruiser]

Here's a link that may help troubleshoot the noise. Click on the buttons at the top of the page. http://www.5speeds.com/nash.htm

This page describes the differences in operation of the 4+3 between the 84-88 models: http://www.5speeds.com/43table.htm

The OD unit can be expensive to replace. Figure around $1200 or so for a rebuilt unit. Many tranny shops don't have the expertise on the 4+3 OD unit so you may be better off with a rebuilt unit.

The fact that the noise goes away when ytou engage the OD may be an indication of a OD carrier bearing going south.

 

[1985vette]

Labor Costs

Thanks for the quick response.

I was wondering if the Overdrive unit has a serial # or Vin # corresponding to my specific car. If I get a rebuilt unit, I can have my car back in a couple of days. If I send my unit out to be rebuilt, my car will sit at the trans shop for a couple of weeks. I hate to have it sit at the shop unless it is the only way to keep the drivetrain original.

Also does anyone know what it might cost in labor to pull the transmission out and replace the bad overdrive with a rebuilt one.

Thanks!

 

[c4cruiser]

Don't believe that the OD and manual trannies have a number that matches the car's VIN. Some early C4's that had OD problems under the warranty may have gotten a replacement OD unit or an entire tranny assembly so even if there was some identifying number, it would have gone away had the dealer done any servicing.

Unless you are considering showing the car in NCRS, it shouldn't make a difference.

If a tranny shop has the expertise to mate the OD unit to the 4-speed, you would probably be better off with a remanufactured unit. You would get new components in the OD unit. Figure on about 5 hours labor to R&R the trans as a unit including hooking up the reman OD unit to the 4-speed.

One key to 4+3 longevity is frequent fluid changes in the OD unit. Try to change fluid every 20K miles and you should get long life from the unit. You can use DEXRON III ATF.

Don't bother with ordering tranny filters from the various Vette catalogs. The filter is exactly the same filter used in the Ford "FMX" tranny (Cougars, Torinos, some F150's from the early-mid 70's) and getting one of these costs about $8 at parts stores compared to the $20 plus shipping from the Vette catalogs.