I bought a 1984 Trans Am with a non-world class T5 and it is no fun to drive. First gear feels like a granny gear and it does about 60MPH at 4000 RPM..... my Honda revs lower than that!

I can't decide whether it's the transmission or differential.... or both. 1.9 turns of the drive shaft produced one complete revolution of the rear wheel. That doesn't sound right, does it? If it's revving high, I'd expect a higher ratio.

The transmission appears to be a T5, but it seems like some work was done to it. One casting number reads 13-52-066-913 and the other reads 13-52-065-907. I've also noticed that it makes a bit of a whining noise.

How can I isolate the problem? Could I use larger tires to correct for the low gear ratio?

 

So what you're saying is you have a 1.9:1 rear axle ratio, it's lazy from a stop, and it's also running 4k RPMs at 60 mph. You do understand this is an inherent contradiction, right?

I dont think 1.9:1 is anywhere near accurate, you need to do that again. From there a better idea can be had about what you're working with. Intuitively, I now speculate that perhaps you have an open rear differential which means you have one tire turning one direction, and one tire turning the other, effectively splitting your gear ratio. if that's the case and you miscalculated and you actually got ~1.7 turns, or 3.4 turns total adding together both tires, then you'd have around a 3.42 gear ratio, which is normal for a T5 and should be pretty peppy. Even with those relatively short ratios, you're still at 90mph at 4000 RPM in 4th gear.

Furthermore, are you sure the RPM's are at 4000? Do the RPMs SOUND like they're at 4000? The factory tachometers can and do fail.

 

For more info, check the 10-Bolt FAQ sticky at the top of the page.

What Gear Ratio Do I Have?
Jerk the diff cover. The numbers are stamped on the ring and pinion.

41 : 15 = 2.73
41 : 14 = 2.93
40 : 13 = 3.08
42 : 13 = 3.23 Approx. RPM’s at 70 mph--2133
41 : 12 = 3.42 Approx. RPM’s at 70 mph--2255
41 : 11 = 3.73 Approx. RPM’s at 70 mph--2463

JamesC

 

I agree, 1.9:1 makes no sense. I jacked up the rear end and wedged a block of wood under the right rear wheel. I spun the drive shaft from underneath and counted the number of turns until the left wheel made a complete turn. Is this not correct?

Also, it's doing 60MPH @ 4K in 5th gear.

 

Both rear wheels must spin equally to get close to the right ratio as InternalVortex said. Pulling the cover is the only way to be absolutely sure of what you have. Our tachs are notorious for reading too high, mine reads 1500 at idle which is at least double what it really is.

 

That explains it. That's a clever workaround but unfortunately it still doesn't solve the issue. The only way I can think of to make that work without opening the axle is to have a friend turn the other wheel the other direction for one full turn, while you turn your wheel one full turn. Opposite direction. Add the turns from both sides. I cant believe that would be very accurate, but it would get you closer.

A T5 car SHOULD have a 3.42 ratio. Some have 3.73 ratios if you have a fairly rarely optioned performance model, but since you say it's not very quick, I would rule that out. It could have been changed at one point for whatever reason, in which case it may have very low 2.73 gears which would be pretty awful to drive with a T5.

Since you confirmed you ahd it in fifth gear and therefore are aware of what the different gates on a manual are for, I think it's completely impossible for your car to be doing 4000 RPM at 60mph unless the clutch is slipping so badly it's on the verge of exploding at any minute. In fact, I would pull the differential cover off, change the fluid because why not, and then see what gears you have. From there you can reverse analyze what RPMs you're at in 4th gear and compare to the tach. GM ring gears usually have some numbers stamped on the outside of the "ring" where you will be able to see it. Something like 41:11 (41/11=3.727272, or 3.73) indicating the tooth count for both the ring gear and its companion pinion gear. So it should be pretty easy to tell.

http://www.f-body.org/gears/

Fourth gear in a manual is always 1:1.... well to be honest Im not sure about these newfangled 7 and 8 speed manuals but for anything before like 2005, 4th gear is always 1:1. So even though T5 gear ratios varied wildly over the years, you know 4th gear is 1:1. So if you have a 3.42 rear axle ratio, and you are in 4th gear going 45mph on a country road, your engine HAS to be turning 2000 RPM plus or minus 200 since you can be completely sure of speedo. There is literally no other speed for the engine to go, mechanical gearing forces it to that range.

 

I appreciate your advice and I will check the differential.

When I say that first feels like a granny gear, I mean it's too torqy. Feels like my dad's 68 Suburban in first gear. First feels so low, that it's almost not useable. As soon as the clutch engages, it's time to upshift. In fact, sometimes, I just start in second. In order to keep up with traffic in a 35 zone, I have to drive in 4th. The engine revs too high at 35 in 3rd. The tach could be off, but something just feels very wrong. Clutch feels fine.

I think the second to last owner was trying to turn it into a race car. He was in the process of rigging up a push-button start. He hard-wired an electric fuel pump into the heater circuit. To operate the heater motor, there are two bear wires hanging down from the dash that you touch together. Oh, he also installed hood pins, because those are worth an extra 15 HP. So whatever he did to the drive train, I'm sure it was his crowning achievement. Still, not bad for $1,000.

 

You probably have a factory 3.73 84 L69 TA. The NWC T5 in them had a .73 5th gear. I have the same car and have the same issues. I would use 5th for anything above 35mph. I recently swapped to a .62 now I use 5th for anything over 40mph

I bet your tach is way off making you think you hit the redline long before you do. Do you have a 6000 rpm tach?

 

So it's a 41:11 or 3.73. According to the chart, that works out to 70 @ 2400. My tach may be off, but I know its revving higher than 2400 @ 70. I can tell by the sound of the engine and the feel of the throttle.

I'm starting to really think I've got a truck transmission.

I know the tranny has been out because the cross member bolts are missing washers. They also installed what appears to be a short shifter, which I don't really care for.

I think the only way to really know, is to hand crank the engine w/ tranny in first, and count the turns on the drive shaft. Not sure how I will do this by myself..... maybe tie a piece of string to the drive shaft.

 

Its unlikely you have a truck transmission. They don't really fit in F-bodies. The T-5 is very specific to the F-bodies. One easy way to tell if its a car transmission or not is if the torque arm mount is still on the tail housing of the transmission. You really should just pop the diff cover and figure out what gears you have.

 

I bet money it's NOT.

Check your tach. They're ALWAYS off. They fail by reading high. Out of the pile of em I have, the one in my car is only 3% or so high (or at least, it was that close, when I put it in); I have one that reads over TWICE the real RPM. Some people have seen em read THREE TIMES reality. Sounds like yours is pretty much in the normal range of failure.

There's no such thing as a "truck transmission" that will fit in one of these cars. No need to make up that excuse to go down that fantasy lane.

Get the facts, don't guess.

I find it hard to believe you don't like the short shifter. Although, if you had the stock one to compare it to, you'd appreciate it more. The VERY FIRST MOD I did to my 83 L69 car (same motor, trans, and gear you have), in about 1985, was to put a Hurst shifter in it. I got sick of literally hitting my knuckles on the A/C control head and the whole thing feeling like it was coupled to the trans by a bowl of oatmeal. UNBELIEVABLE improvement for, at the time, about $100.

 

It may be a 6-cylinder transmission. They run a lot lower 1st gear. And with the proper clutch disc can be bolted to a V8.

RBob.

 

Yea but I think their 5th gear is still a .73 so he should be the same.

My money is still on the tach.

Is it a 6k rpm tach?

 

It's a 7K tach with a 6K redline.

I already popped the diff cover and it's a 3.73.

 

OK so you probably have a factory L69 with factory 3.73 gears and factory T5 with .73 overdrive.

 

You've got a V6 tachometer. It is not 'plug-&-play' compatable with a V8 You can either get an aftermarket signal converter to correct the tach signals sent to the V6 tach (Dakota Digital),.... or install the proper V8 tachometer.

 

Your right, I just took a second look at my L69 tach and it is an 8k tach.

I think the L69 also got an 80 psi oil gauge.

 

My post was in reference to the 1st gear being a granny gear. The 4 & 6 cylinder T5's have a real low 1st gear. Which the OP was complaining about in his opening post.

RBob.

 

Good call, I am starting to wonder what his car is.

What is the VIN Number?

 

Midas; after seeing your pic and looking into it a bit more I think I was wrong ad Wildstar probably DOES have a V8 tachometer. I just found this pic of my old 85 Trans AM (TPI) Tachometer.




I'm certainly NOT a Firebird expert, but Midas,... I'm almost sure that the pic you posted shows a V6 tachometer and Oil/Temp gauge. If you notice the yellow line is actually above 5500 RPM & I have NEVER seen a 40/80 oil pressure guge in a V8. V8's simply don't make that much oil pressure. Even the OP sending units are specific to V6 or V8 engines and most stock canister type (early style) sending units have the MAX limit stamped onto the nut end. (60 or 80).

 

I am fairly sure those are the stock L69 HO gauges for a 1984 5 speed 3.73 car.

At least my vin number and RPO codes so that is what my car came with factory.

Unless someone swapped in v6 gauges.

I did have to buy an 80psi sender it was one of 2 option when I got it.

 

Well, it seems like I have a stock transmission.

With the rear end jacked up and car in 1st, I cranked the engine one revolution and measured the movement at the tail shaft. I put a reference mark on the tail of the transmission and wrapped a piece of duck tape around the tail shaft. The circumference was 3.75 inches or 30 eighths of an inch. I first laid the duck tape flat on my counter, making 30 tick marks at 1/8 inch intervals. After cranking the engine, I made a second mark on the duck tape, aligned with the reference point. I then put the car in neutral and counted the tick marks as I spun the drive shaft by hand. It turned 1 3/8 inches.

30/11 = 2.73 which is pretty close to the stock ratio of 2.76.

I'm disappointed. Notwithstanding a faulty tach, I can't believe GM would build a car that's such a bear to drive. The shift points all feel wrong.

Do you think tire size might be a factor? It has 215/60/15 tires. Is that stock for an L69? The closest I could find in the owners manual is 215/65/15.

 

I'm SURE you could find somebody to trade your rear diff with... people pay LOTS of money to put the gear you probably have in the rear (3.73) into their cars, to let the engine get itself up into a range of RPM where it has some power, instead of the 2.73s and 3.08s and such, that pin the engine to idle speed.

All in all, you have THE BEST car that was made that year; BY FAR faster than the Vettes, Mustangs, or any other car available in the same time frame. If this is your first experience with a car of this sort, then you may not know what to expect; or, what was commonplace at the time these cars were built, at which time, there was a national speed limit of 55 mph (yeah I know, that sounds mighty STOOOOPID today; but at the time, the same sort of people as are responsible for Obamacare today, thought it was a good idea, so for over a decade we had it jammed down our throats...) so cars were NOT ONLY not expected to exceed that, but even WERE DELIBERATELY BUILT so as to NOT go any faster than that. If you had some one of the lower-performance cars with worse gears and a less powerful motor with less RPM capability - for example, a TBI/auto/2.73 car - you'd see why yours is so much better.

215/65/15 was the original tire size. It was too small even when new. (mostly, too narrow) 215/60 is REALLY too small so that's not helping you any, although it has little bearing on the matter at hand. If you need to buy tires and want to keep the stock wheels, I'd suggest 235/60-15; they're pretty close to that dumb original size in their OD, but put substantially more rubber on the road.

Meanwhile, I'd also suggest that, rather than complaining about your car not being designed like a Honduh - NOT a good way to make friends around here, as we're all PROUD that our cars aren't anything like a Honduh - you should learn about it, and become accustomed to what it is and how it works. Be grateful it's not like the 79 Z28 I traded in to get my 83; 4-speed manual w NO overdrive, 3.73 gears when I got it and 4.10 by the time I traded it in. Or another Z28 I had at the same time, which had the same gutless 350 as the 79 (less HP than your L69), a 3-speed auto trans (Turbo 350), and 3.73 gears. That car literally WOULD HARDLY EVEN GO faster than 55; it was already at over 3000 RPM at 55, and the motor's peak HP - the RPM you'd want to cross the stripe at when drag racing - was only around 3600 RPM. IN REALITY (regardless of the "tach" reading) your car ACTUALLY does about 2500 RPM at 70 mph in 5th gear, which really isn't too bad.

On the tire size thing, it might amuse you to know that full-size cars in the 60s came with 14" wheels, radial tires for street cars basically hadn't been invented yet, and the most common tire size back then works out to about 195/75-14. Imagine, my 60 Chevy, a 4500 lb SLED with non-power drum brakes all the way around, on those tiny bias-ply tires! Seems impossible today, but back then, that was "state of the art". These cars were among the first to break out of that mold; in 1982, these weenie little 215/65s looked HUGE. But nowadays, when even grandma sedans come with 16" wheels or larger, they're sort of .... obsolete. Remember, you're working with a car that's 30 yrs old; legally an ANTIQUE in most states; not something straight off the showroom floor.

 

This is the 5th firebird I've owned since 1991, third with a V8, but first with a manual transmission. My last T/A had a 700R4 and it was a fun car. I think I'd like to have another third gen owner drive this car; maybe it's just me.

Once I get the diff back together, I will check the accuracy of my tach.

 

3.73 is a blast with a L69 or any V8 that can spin to 6K rpm. The only issue I had with the stock 84 transmission was the .73 overdrive on the expressway. Although it pulled hard with .73 I find .62 gets me better MPG.

Use this calculator to find the speed you should be going with your gears
215/60/15 is 25.15748031 diameter

NWC T5
1st 2nt 3rd 4th 5th
2.95 1.94 1.34 1 0.73

Rear 3.73

http://www.teammfactory.com/gear-calculator

Or

http://www.apexgarage.com/tech/gear_ratios.shtml

Then you can go 40mph and see what the tach reads.

 

It is confirmed that is the correct L69 tach and gauges for a 1984 TA

 

Cool, Thax for the update; I learned something new today !