Transmission issues

[71AteLugger]

Alright... I'm facing a trans rebuild I'm thinking. I have a 71 Chevy C-20 with 350/th350 combo. My issue is, my Tach is redlined nearly when I'm on the freeway... @65mph I'm hitting between 4000-4500 rpms... My fluids seems to be fine, however, this truck was abused before I got her and started bringing her back to life. I'm thinking the tranny might be shot, but it shifts well around town, but that third gear always leaves me expecting a gear is missing at high speeds. It has the power, but the trans is extremely limited. What are you guys running at on the freeway, and does what i'm talknig about sound like it's time to re-build? I'd hate to drop a grand to re-build right now, but I don't trust myself to do it. I have no experience re-building trannys so I'll leave it to the pros. thanks.

[sameyrasmea72]

[QUOTE=71AteLugger;4502877... My issue is, my Tach is redlined nearly when I'm on the freeway... @65mph I'm hitting between 4000-4500 rpms... .[/QUOTE]

What rear end do you have ? That rpm range does seem too high. I have a 373 rear end and I tach around 3200-3300 rpm at that speed.

[sameyrasmea72]

Originally Posted by 71AteLugger

I'd hate to drop a grand to re-build right now, but I don't trust myself to do it..

$1000 to build a th350? Maybe you need a new mechanic, I could get two built for that price.

[68 Stepside]

Tire size and rearend gear would be valuable information. With 5.13 gears (highly unlikely, but not impossible), and a 28" rear tire @ 65 you'd be turning 4100 RPMs. I would also check your tach for accuracy.

I also agree that a grand for a TH350 rebuild is way out of line, should easily be able to get it done for half that.

[bosco200]

I have 4.57s and id be pushing 4800 doing 65 mph thats why I drive 45mph every where.

[71AteLugger]

Living here in the Bayarea, Ca. every mechanic seems to think they can charge crazy prices... I changed the fluids, again, and added some lucas conditioner... still running great on the streets but once on the freeway, it is stuck at 4000... I'm leaning towards the rearend being the cause now, but here's a dumb question for you guys... how do I determine which gears I'm running? What's the re-build cost? My goal here is to have the ability to go 65-75 mph at around 2800-3200rpms... and not risk blowing something up.

[cableguy0]

Pull the cover off the rear. count the teeth on the ring and pinion gears. Divide the number of teeth on the ring gear by the number of teeth on the pinion gear. This is you gear ratio. All other methods are just a guess and not accurate. 2 quarts of fluid isnt that expensive.

[71AteLugger]

Awesome... thanks for the info. I can't wait to see this truck really run!

[mikie 1954]

On mine the ratio was stamped on the side of the ring gear. I'am no authority on rear ends but I would think yours would be to. Mine is a 64 GMC with a dana 60 so maybe not the same marking?

[Longhorn Man]

a grand... I can leterally get 4 rebuilds, with shift kit and converter for that much.

I also vote for your tach being way the heck off.

[GASoline71]

Here is a great article from Car Craft magazine on how to rebuild a TH350 yourself. http://www.carcraft.com/techarticles...oin/index.html

Gary

[71AteLugger]

I sure hope that it turns out to be only the tach... that would be sweet. It feels smooth up to that point, I just haven't taken it much further than 4500 because I wanted to keep my engine INSIDE THE TRUCK haha. I'll look into the rearend, I'm thinking that is most likely low gears causing the issue, not to mention the tach is original and not calibrated... thank you.