sakins.02vert

I just bought a 1976 L-82 a few weeks ago and I've been trying to get acquainted with it. I've noticed that on the highway if I want to go 75 MPH my tach is reading about 4000 RPM's. Does that sound right? The tach does seem to dance a little between 3500 and 4000.

I believe the rear end is stock, I found these specs online so I think this is what I have:

Automatic Transmission
Three-speed Turbo Hydra-Matic
floor-mounted gear shifter
gear ratios
1st = 2.48:1
2nd = 1.48:1
3rd = 1.00:1
Rev = 2.08:1
Final drive ratio: 3.08:1 with L48 and 3.36:1 with L82

I have the L-82.

What are your thoughts? Can I make some changes so the RPM's are not as high on the highway? Will that decrease the acceleration on the back roads?

larryg3

sounds like you are not running a stock rear end. the stock gear for the 76 with automatic is a 3.08:1 and 3.36: 1 with the 4 speed.
i would be guessing but you may be running a 3.70 or 3.90. what size tires are you running?

larryg3

on my car '81 with 3.54 gear (not stock) automatic with 255/60R15 i run 2800 @ 60 MPH.

phildawg19

the guy that you bought your car from.. with all of the modifications he did and the rebuild it is more than likely he changed out the gears as well for more power. your more than likely running 3.73 those numbers are about the same numbers i run and my gears are 3.73. the numbers you stated were gear ratios

CheezMoe

The only way to resolve this and keep you backroad acceleration is to with overdrive transmission. With 1;1 high gear you must compromise one for the other.

thegazman

I have a 1979 L-82 with factory 3:73 gears. I am taching 3500 rpm at 70 mph, so it's sounds like you may also have a 3:73 differential.

jb78L-82

Same here-78 L-82 4 speed with 3.70 gears-3,500 RPM @ 70 mph. Officially listed at 2,860 RPM @ 60 MPH with stock diameter tires-255/60/15 or 225/70/15's!

Attfay Elleybay

When I bought mine it was ~60@4000 (4.56 gears), with the 200r4 its 75@3000

sakins.02vert

Thanks Guys.

So is there a way for me to verify what my gears are?

I'll check the tires and see what the specs are.

Also, as for the overdrive transmission. Has anyone done this? Does it make sense? What transmission would you recommend?

Thanks

joewill

you are probably running 4.11 gears, the only way to tell is to jack up the car and count driveshaft revolutions vs wheel revolutions and get the ratio..

or you are possibly not getting out of 2nd gear on your tranny..

also if your tach is dancing then it is obvious it is not right.

929nitro

This has been done by a lot of people. I have a 2004R I will be putting into my 75. Do a search for 2004R or 700R4.

sakins.02vert

Cool thanks.

Good point about second gear. I'll take her out tonight and make sure that's not the issue.

As for the tach. Maybe I should replace it? That ties into the distributer right? Is that a big job?

Thanks for the recommendation on the 2004R. I'll check it out.

ipmtim

The dancing needle is usually not the tach itself.
Either the cable is sticking, which means it needs lube, or the gear in the distributor is worn.
Tim

mrvette

DO NOT believe your tach OR your speedo.....only believe a GPS I use a Garmin....all else is

in order to verify your tach, you will have to send it out, and even then you really won't know....

I have a 200 4r in mine, changed from a 700, which was a factory munie car 336 rear gears....

factory tachs are not all that accurate, and honestly I doubt others are either....mine is 300 rpm high at 4000 rpm....and same at 3000 rpm, that's 10%.....which at 100 mph +- that is a fair amount to be off....

trick is, your speedo's are even MORE inaccurate....

they can be dead on at 60mph....and what it says is 120 mph, is barely 110 if that.....seriously....verified by my Garmin.....I believe the Sat tracking, not some site about tire diameters, ratios and other assorted

sakins.02vert

Ya, I'm with ya on the GPS for speed. But for the tach, I was wondering if I should get that fixed. Looks like you can get a rebuilt kit for about $80. Wonder if it works and it's worth it.

With your 200 4R, so this has overdrive right? 4th gear? So what are your RPM's at 75 MPH? Did you loose any acceleration off the start?

phildawg19

[QUOTE=joewill;1574987344]you are probably running 4.11 gears, the only way to tell is to jack up the car and count driveshaft revolutions vs wheel revolutions and get the ratio..[QUOTE]

mrvette

The 200 has essentially the same first gear as the 350....about 2.5x long in there....the 700 has like a 3.08 first, and so upshifts before you ever get going....and they tend to downshift at WOT in overdrive...
both of them have like a .70 overdrive....pretty close....consider it a 350 with overdrive at .70.....of course it also has lockup on the converter and so that is worth 3-400 rpm right there....it's easy to hook up, so no sweat...you largest issue is that silly kick down linkage...junkyard a bracket and maybe make one, or order if lazy.....

I just finished installing a 700 into a old chebby van 30 motor home...
and took out a 350, to adapt that kickdown was easy, really just use the 350 kickdown bracket for the 700 and fashion a mount to the carb rear holes....or intake, where ever it lines up best in YOUR install....

ON the tach rebuild, talk to Wilcox on the left addy's here, I think he got boards and stuffs for that....if not, he knows who does....

I have NO idea as to accuracy of the instruments, MY old tach is outta a 75 or so, fits the early shark panel, in my '72.....
far as I know it's still the OEM board and of course it tends to flicker once in a blue moon, but not enough to be a pain, but every once in a while I see/glance and I know it wasn't kosher...but looks normal .....

I don't think I"m going nutz, but maybe, some maybe argue that point,

C3 4ME

The first thing I would do is buy or borrow an aftermarket tach to verify what rpm it is actually turning, and if possible do this with a GPS as suggested above, that way you have the most correct info. Then post back if there is acutally a problem. Someone above metioned a problem with the tach cable. This is not true, yours being a 76 does not have a tach cable, it is electronic. Mine on my 79 read way off, and I wound up getting a used one.

mrvette

Without getting too electronic technical about it.....but being an OLDE TYME ET from way back....it was easy for me to verify my electronic tach accuracy....

first some math.....600 rpm idle speed....so each piston does ten trips per second up and down the cylinder....which needs 5 sparks/cyl/second....

time 8 cyl....is 40 sparks per second generated via the dizzy......at 600 rpm crank speed.....

so 6000 rpm is only ten times that or 400 total sparks per second....

that is like really really really SLO compared to electronic speeds....

SO to check my tach myself, I managed to fire the HEI by taking a clip wire from the tach output over to the transistor, and fire that transistor with a audio signal from a digital generator.....and look at the results on my Tektronics scope....

and read the tach, obviously with ignition on, and engine still.....

CASE CLOSED.....

mar

at 70 mph:

4.11 - 3645 RPM
3.70 - 3286 (mine)
3.55 - 3153 RPM
3.36 - 3030 RPM
3.08 - 2734 RPM

There.