Old Rocketman 98

Hi, I'm restoring my 76 Olds 98, specifically the tranny. My mech says to keep the original and add an overdrive for some giddy up and some fuel efficiency. Not interested in an e-tranny. Gear vendors wants over over $2500! Can I get a used one?

Anyone ever add the overdrive, please share your experience and results. Want your thoughts before I pull the trigger.

P.S. Any thoughts on a after market camshaft.

svnt442

For the money that you will spend on a GV unit, you can have a really stout 200 4R built and get a driveshaft made for the car. Not only would you gain the OD gear, but you'd get a better first gear ratio in the trans and a lockup torque converter. It's a win all across the board.

matt69olds

I would go 2004R without a doubt. The 76 engine isn’t a powerhouse, the trans won’t need much upgrades. You would need to shorten the driveshaft, the crossmember will remain in its original location. That will make it easier working with the catalytic converter (assuming it’s stull there).

Rallye469

I have a GV unit on my 400...they’re nice, but are a little pricey. You’ll also have to shorten your drive shaft.
Is fuel mileage that important?

I only did it because it was 90 miles to the racetrack.
-pete

Olds64

Before you consider adding a GV overdrive or 2004R you need to figure out what rear gears your Oldsmobile has. The problem with the 71-76 B/C body Oldsmobiles is that finding a differential or a gear set is like searching for hen's teeth. They don't use the same differential as the Cutlass.

joe_padavano

Your "mech" needs to be better informed. Simply adding overdrive does exactly nothing for "giddy up". All it does is lower your final drive ratio, which lowers RPMs when in use. Depending on the current rear axle ratio, normal speeds you drive at, and factors like weight and drag of the car (very high in both cases for a 1976 Ninety Eight), you may or may not see any mileage improvement after this investment. You certainly WON'T see any acceleration improvement, since the OD has zero effect in lower gears. More to the point, any mileage improvement will be small and will take tens of thousands of miles of driving to recoupe your investment.

The only ways to improve acceleration are to either change the rear axle ratio and then add OD (which is both expensive and difficult given the fact that gear sets for your car's axle are pretty much not available) or to change to a trans with a lower first gear. The The 200-4R has a 2.74:1 first as opposed to the 2.48:1 in your TH400. This will help with off-the-line acceleration, while the OD fourth will help with mileage. Unfortunately, the 200-4R will require expensive internal upgrades to survive in your heavy, big block car. In addition, your car uses a long tail TH400 to minimize driveshaft length and vibrations. The 200-4R is the same length as a short tail TH350, so the driveshaft would need to be about 6-7" longer. This may be problematic given your car's already long wheelbase - you're getting close to the point that you really need a two piece driveshaft with a center bearing. Options beyond that are a 4L65 or 4L70, but both of those require an ECU to operate, in addition to adapters to bolt to the Olds motor. There is no feasible solution that costs less than $2500 or more (and that doesn't include the collateral damage like new driveshaft, crossmember mods, exhaust system mods, adapter plates, etc, etc.). Ask your mechanic for a fixed price quote for this and see what he says. Be sitting down when he responds.

Old Rocketman 98

Does that trans require any computer systems to operate?

svnt442

No. It will go through all gears just like your existing trans. The lockup converter can be operated with a control module, or you can lock it manually with a switch. The issue with using a switch is remembering to turn it off when you stop, because it will stop the engine just like forgetting the clutch pedal.

Olds64

The GV and 2004R don't require a computer. Neither does the 700R4, but it doesn't come in a BOP bell housing.

Old Rocketman 98

Wow Joe, you got my head spinning.lol. maybe giddy up was the wrong expression. I'm not looking for hot rodding (I'm 60), just want to improve my driving experience while keeping it close to original. For instance I just changed the exhaust system and now she roars.
So, I asked what else we can do and that's when my mech suggested a better camshaft and overdrive for my 455/TH 400 set up. Make sense?

joe_padavano

You have a 5,000 lb car with emissions controls, vacuum operated power options, and likely a 2-something rear axle. Your 455 has small valve J heads, low compression pistons with soup bowl-sized dishes, a carb that is calibrated lean, and a distributor advance curve designed for emissions, not power or economy. Changing the cam without upgrading the rest of the system is a big waste of time and money. The most cost-effective thing you can do is to make sure everything on the engine is working properly and adjusted to spec. Freeing up the exhaust is probably the best first move. You didn't say how many miles are on the engine, but over 80K or so the plastic teeth on the camshaft gear will be worn, causing the cam to retard and losing power (and increasing the risk that eventually you'll throw the timing chain and the engine will cease to run). Verify that everything you have is in good shape to set a performance baseline before changing anything.

joe_padavano

I would also suggest finding a mechanic who isn't so eager to sell you expensive parts and labor...

By the way, your 1976 455 should already have the 409691 cam with 286/287 duration. This cam was introduced in 1971 for use in the lower compression 455s that year, and was even used in the 442 motors.

Old Rocketman 98

He went over everything a year ago to get it back to specs. Some of the things I remember include resetting the intake, rebuilding the carb, upgrading the wires, plugs etc. The car runs good and looks great.
Understand, the car is in great shape and my mech has no dog in the fight. It's what I want. I was asking this question to get input from knowledgeable folks like you to see what I have to do. I don't care about the cost. The car is family.

bry593

Another note about the GV setup, be aware it has a tiny oil pan. GV recommends changing the oil every 5000 miles which is very inconvenient in my opinion. The oil is used to apply the overdrive clutches and for general lubrication. Also, if you buy a used one, it is nearly impossible to buy parts. GV won't sell parts, but will "rebuild" the unit into a usable configuration for around $1500.

matt69olds

I need to wait for my brain to wake up before replying to threads like this!! Now that I have had time to reflect, I’m going to rethink my reply

i guess first question, what are your goals? I suggested a 2004r trans, while that is still a good option, unless you change the rear gears to best utilize the overdrive you won’t gain much. A full size Olds should glide down the highway with ease and comfort, that’s what they were designed to do.

If your wanting more get up and go, I would suggest getting the engine to breath. I’m not familiar with the floorboards of a 76 Olds, could you install a earlier trans crossmember and install dual exhaust? I’m guessing the 76 has a single exhaust with a catalytic converter. You could remove the heads, mill them,then reinstall with thin head gaskets. Replace the timing chain, if lots of the nylon is missing, remove the oil pan and clean out the oil pump pickup. Once the engine can breath, you may need to do some fine tuning to the carb. Helping the engine breath naturally leans out the carb mixture. You may need to richen up the APT. Recurve the distributor, make sure everything is optimized before making other big changes.

Keep in mind, this is a 5000 pound car, there is no reason it couldn’t be a fun and comfortable ride. But a fun Olds 98 is going to be completely different than a fun Cutlass or 442!

Olds64

The 71-76 B/C bodies don't have interference issues when running dual exhaust due to rear-steer pitman arms, transmission shift levers or transmission cross members like earlier Oldsmobiles.

One of the greatest Oldsmobiles I've ever driven was my dad's 1976 98 Regency coupe. He owned it years ago when I was in college. It ran well and would pass anything but a gas station even though it had J heads and a smog motor.

JohnnyBs68S

A simple relay wired in series w/ the lockup solenoid and powered by the brake lights circuit will automatically disengage the torque converter when you step on the brakes. Easy-peasy. Thats what I use w/ my 200-4R and it works like a charm. Its also helpful if the trans also has a built-in 4th gear switch that prevents lock-up until it shifts into 4th.

Old Rocketman 98

Understood. I had a dual exhaust installed two weeks ago and it was worth every penny. So, I am going to change out the cam, timing chain, lifters and springs custom for the car. I will see how the "get off" is after that to see if the overdrive is needed. BTW, the car is family and I hope to give it to my grandson in 20 years!!!!

Oldcoyote

If your Turbo 400 is working OK, why not just keep it as is? Even rebuilding the 400 isn't too expensive.

I ordered my 1978 Olds 98 with a Turbo 400 and a 3.23 rear gear which worked well. But as others have said, rear gears are hard to find for your car. I am not a guru on rear ends but Richmond lists various ratios for full size Olds. Will any of them work? They say you might have to replace your carrier.

https://www.richmondgear.com/wp-cont...n1.pdf#page=31

Olds64

Excellent! You will see more increase in performance by installing a cam vs. an intake or headers. Let us know what your goals are for the car. We can help you choose a cam.

Old Rocketman 98

Great idea. Going to check it out

joe_padavano

Uh, where? The only 9.3" axle listed in that link is the 1957-1964 Olds/Pontiac axle. That is a completely different axle than the one under the OP's 1976 and nothing interchanges between the two. Again, no one makes aftermarket gears for these axles.

Oldcoyote

9.3? You are no doubt correct.

goatwgn

I am quite a bit late to this thread, but , if you haven't done anything else yet, may I suggest a mild stall converter, and rebuild the TH400 with a 2.75 gearset planetary? This gives you a more aggressive 1st and 2nd gear ratio, but the 3rd gear is still 1 to 1.