mitchcole

My friend has an 88 L98 with the 4+3. His is considerably faster than mine (92LT1 6 speed) so we're pretty sure that it isn't stock. The mods weren't done by him.

The problem is that the clutch has started to slip. It isn't obvious in all the gears - just when the overdrive is activated.

Before we tear this thing apart, is it possible that the OD unit on the back of the tranny is slipping and not the clutch?

What type of maintenance is required for the OD unit on the 4+3? Is there a way to check the fluid level? Do you change the fluid? Is there a filter? I have no idea how this thing works... thanks in advance!

88Vert

I am not an expert but I can get you started.

I would think the problem is that your clutch is slipping.

There is a fill/inspection hold on the side of the OD, for the fluid. You should be able to tell if it is full by sticking your finger in it. The fluid should should be to the top. I don't remember which side of the tranny is is on. (guess: passinger)

There is a small pan that holds the AT fluid that you can remove. This will get you access to the filter.

Most on this board recommend changing fluid every 10 to 15 thousand miles.

The filter is available from various catelog companies I belive, I haven't done mine recently. The kit has a gasket but from this board I learned not to use it. Just put the pan back up with RTV.

Good luck.

scorp508

Ok try this.

3rd gear w/OD engaged and 4th w/OD NOT engaged are nearly identical final gear ratios.

Do this in order...

Drive in 4th gear w/OD NOT engaged and put your foot down, do the RPM and MPH climb as you'd expect or is there slippage? If there is slippage and I'd expect your clutch.

Drive in 3rd gear w/OD engaged and put your foot down, do the RPM and MPH climb as you'd expect or is there slippage? If there is slippage I'd expect your overdrive unit clutchpacks have burned up.

c4cruiser

Not to hijack the thread (too far) but of all the fluid, how much fluid is in the cooling lines and should that fluid be blown out or otherwise forced out when changing fluid?? Or is there not really enough fluid in there to worry about??

Is the Mobil-1 synthetic Dexron III the best fluid to go back in??

scorp508

I blow the lines out with compressed air to be safe. When you're dealing with not too much fluid to begin with I figure its enough to deal with.

When refilling the unit pour about 0.75 quart into the pan and then rotate the rear tires in neutral up in the air with your hands for about 2 minutes to prime the cooling lines. This will allow you to get the rest of the fluid in the pan with minimal or no spillage.

I use the Mobil 1 Synthetic ATF

ZylaRace

Scorp,... Um,... foot down in 3-OD,..... you will drop out of OD and rocket fwd.
I'd suggest,.. just give it some pedal, (keep OD engauged), and see if it slips.

Scorp: Glad winter is over and your back from cybernation

bills1985corvette

Check/Fill plug is on the drivers side. MAKE SURE YOU USE AN 8 POINT SOCKET TO REMOVE. Service like you would any automatic transmission: remove pan to drain fluid, clean the pan and the magnet, remove the old and install the new filter, make sure you put the magnet back where it belongs, reinstall the pan with bolts finger tight (I use the gasket and sealer), torque the bolts to spec, fill with fluid (I use Mobile 1). I recheck after I drive a week or so.

scorp508

Awww christ, sorry about that I forgot. Do it on an '85 or unplug the TPS then.

mitchcole

Thanks guys - we'll take a look at it this weekend. Looks like it's likely the OD unit.

Kanmer

Does it slip in reverse? Thats what mine did and it was the OD unit. $3300 later I had mine back. Change the fluid and filter religously. I bought my 86 from a guy that didn't even know there was a filter. The fluid looked like mercury when I dropped the pan. Ecklers sells a 4+3 rebuild kit and the filter and gasket. MAM does also I think. Good luck

mitchcole

$3300??!?!?! The car's only worth $5000!!?!?!

We'll have to take a look at that rebuild kit.