Tach installed and I have ?'s - The 1947 - Present Chevrolet & GMC Truck Message Board Network

PHOENIX · 11-11-2002, 05:03 PM

I never had a tach before in my truck. I installed this one (http://www.jegs.com/photos/1054495.jpg) this weekend. Anyway I followed instructions 100%. I think its right but im not sure. I still need to figure out what rear end I have (i know that would help alot). But I have a stock 350 w/ sm465 tranny. (2wd). The engine seems to be racing alot, but the tach only reads 3k. Is that normal? Does your truck sound like its racing alot at 3k? I did some freeway driving and heres what I got:

70 mph = 3,000 rpm's
75 mph = 3,500 rpm's
80 mph = 4,000 rpm's

Thats not cool at all! No wonder my truck gets hot when driving at higher speeds. I need a new tranny and rear end! Im gonna find out what rear end I have and post it.

Anyway my truck is racing alot at 3k + I would be afraid to take it anywhere near 4800. Give me some feedback. What do you guys think? The tach matches my timing gun at idle as far as rpms. I cant see the timing gun when in the truck so I need to get someone to hold it and watch it as I test it. Im sure its accurate, but Ill test it anyways.

Just looking for some feedback with your expierences.

Tom · 11-11-2002, 05:12 PM

Thats normal, same as me in my 79 with the th350 and 3.54 gears. Ill bet your about the same. and yes, thats way too high of a RPM to be at all the time. Thats why the 2004R is now in place

c10scotty · 11-11-2002, 05:16 PM

i dont know if you need your rear end gearing info or not. thats probably about right though. it just depends what type of gears you got.

PHOENIX · 11-11-2002, 05:33 PM

If I got a Muncie (like Tom's) or a Super T-10 and wanted my RPM's to be about 2,000 - 2,500 at 70-75 mph's what rear end would I need?

My truck seems to have a pretty good leap off the line, then feels like it bogs alot through 3rd and 4th (dont use my 1st granny gear). Hopefully going to a manual with 4 gears I can actualy use will help with this.

What you guys think I would need (rear end)?

Tom:
Do you know how to swap the rear end gears? I never done it but I think im going to need to. Think you could help?

I have a 10-bolt rear end, should I go to 12-bolt? I may add more power later so I want to think about the rear end now.

Tom · 11-11-2002, 06:28 PM

Ok first, yes you should go with a 12bolt if you plan on more power. 10bolts are kinda weak.
Second, rear gears for 2500rpm 70mph cruise. Need to know tire height, but guessing using 28" tires [275/60/15 tire size] means you'd need 2.98 gears. So you have either 2.76's or 3.07's to choose from. And this operation had to be done by someone with lotsa precise tools. We cant really do it

79BIG10 · 11-12-2002, 04:21 AM

Eddie- I've got 3.07 rear gears right now. I hate them since I have a slow take off. Trust me with a big truck you want lower (higher numerical) gears. I need to get the 3.73 installed on mine but I will also need a OD tranny as well. I'm like you in that I don't like revving that high gears. I just need to find the OD tranny then the $$$ to get it rebuilt and I'll be better off then.

ocbaud · 11-12-2002, 08:44 AM

Quote:

Originally posted by 79BIG10
Eddie- I've got 3.07 rear gears right now. I hate them since I have a slow take off. Trust me with a big truck you want lower (higher numerical) gears. I need to get the 3.73 installed on mine but I will also need a OD tranny as well. I'm like you in that I don't like revving that high gears. I just need to find the OD tranny then the $$$ to get it rebuilt and I'll be better off then.

SLOW TAKE OFF!!!

you know nothing of the thing. you have that nice zz4 motor.

i have 2.73 gears and an old 305.

so I am the one with the slow takings off

11-11-2002, 05:03 PM	#1
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	Tach installed and I have ?'s I never had a tach before in my truck. I installed this one (http://www.jegs.com/photos/1054495.jpg) this weekend. Anyway I followed instructions 100%. I think its right but im not sure. I still need to figure out what rear end I have (i know that would help alot). But I have a stock 350 w/ sm465 tranny. (2wd). The engine seems to be racing alot, but the tach only reads 3k. Is that normal? Does your truck sound like its racing alot at 3k? I did some freeway driving and heres what I got: 70 mph = 3,000 rpm's 75 mph = 3,500 rpm's 80 mph = 4,000 rpm's Thats not cool at all! No wonder my truck gets hot when driving at higher speeds. I need a new tranny and rear end! Im gonna find out what rear end I have and post it. Anyway my truck is racing alot at 3k + I would be afraid to take it anywhere near 4800. Give me some feedback. What do you guys think? The tach matches my timing gun at idle as far as rpms. I cant see the timing gun when in the truck so I need to get someone to hold it and watch it as I test it. Im sure its accurate, but Ill test it anyways. Just looking for some feedback with your expierences. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

11-11-2002, 05:12 PM	#2
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Thats normal, same as me in my 79 with the th350 and 3.54 gears. Ill bet your about the same. and yes, thats way too high of a RPM to be at all the time. Thats why the 2004R is now in place __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

11-11-2002, 05:16 PM	#3
c10scotty ~THE SILVER BULLET~ Join Date: Oct 2002 Location: WYOMING Posts: 285	i dont know if you need your rear end gearing info or not. thats probably about right though. it just depends what type of gears you got. __________________ ~1980 c10 chevy scottsdale~ ~2.5/4 drop 305/th350c~

11-11-2002, 05:33 PM	#4
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	If I got a Muncie (like Tom's) or a Super T-10 and wanted my RPM's to be about 2,000 - 2,500 at 70-75 mph's what rear end would I need? My truck seems to have a pretty good leap off the line, then feels like it bogs alot through 3rd and 4th (dont use my 1st granny gear). Hopefully going to a manual with 4 gears I can actualy use will help with this. What you guys think I would need (rear end)? Tom: Do you know how to swap the rear end gears? I never done it but I think im going to need to. Think you could help? I have a 10-bolt rear end, should I go to 12-bolt? I may add more power later so I want to think about the rear end now. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

11-11-2002, 06:28 PM	#5
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,713	Ok first, yes you should go with a 12bolt if you plan on more power. 10bolts are kinda weak. Second, rear gears for 2500rpm 70mph cruise. Need to know tire height, but guessing using 28" tires [275/60/15 tire size] means you'd need 2.98 gears. So you have either 2.76's or 3.07's to choose from. And this operation had to be done by someone with lotsa precise tools. We cant really do it __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

11-12-2002, 04:21 AM	#6
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,775	Eddie- I've got 3.07 rear gears right now. I hate them since I have a slow take off. Trust me with a big truck you want lower (higher numerical) gears. I need to get the 3.73 installed on mine but I will also need a OD tranny as well. I'm like you in that I don't like revving that high gears. I just need to find the OD tranny then the $$$ to get it rebuilt and I'll be better off then. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

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