The Stovebolt Site Forums The Shop Area Engine Shop confirm rear end gear ratio

Hello -

I just would like to get a confirmation on my rear end gear ratio.

I rotated the rear wheel 2 times and the drive shaft spun almost 4 times. This tells me that I have a 3.9 rear end? Correct?

Ross

yes, 3.90 is the standard ratio for your truck

Bill

Thanks Bill -

So if the rear end is in good shape, do you suppose it could handle being connected to a TH 350 or 400 and a moderate 350 crate engine?

I am trying to plan ahead and am having a tough time sorting through the mass of information out there related to transmission selection.

I am confident on the GM 350 crate engine part but my head is spinning on the transmission end. I would like to stick to the automatic transmission and it sounds like the TH 350 and 400 would be suitable for the engine size I would like to use. You have been a ton of help so far.....do you have any advice or places I can go to research some more?

Thanks again!

Ross

the stock 3.90 will handle lots of power - friend of mine has a 55 w/ a strong 427 and he's a lead foot, no problems with the stock rear

the TH350 is good, TH400 fine too [supposed to be stronger], and it'll all fit easily .... depending on what you intend for the truck, you might want to consider an OD trans of some type [OD automatics: 700-R4/4L60 or 4L80E] to get highway speeds with lower RPM, but if it's an ocassional driver not on the highway much, the 350/400's will be cheaper and easier to find ... but I like clutches

you'll find lots of good advice right here if you run into any puzzles! :hammering:

Bill

I would LOVE to have a manual transmission in this! But the articles I have read scared me away from converting from an auto to a manual. Which tranny would you recommend if a person was to go with a manual?

Would it really be that difficult if I am replacing the engine and transmission? I realize I would have to butcher up my floor board, But I agree....it is a lot of fun to have a manual transmission!

Ross

I am a little out of my league on this one, but how about a world class T-5. Do a search on T-5s. There are a several different ones out there and the shifter location makes some of them impossible for us to use.

Also, check out the post titled 23 MPG..I think it is in the greasy spoon. sounds like someone is having good luck with a 700r4 behind a 350 with a 3:90 or 3:73

if you have an original hydromatic it's not hard to switch to a manual trans, you can put nearly any one behind the 350 and make it work - the original 3spd OD would use the column shift, no floor hole, and the later [68+] 3spd has all syncro, but OD in those years is harder to find .... the T5 would work, the New Process A833 is one I've looked at, 4spd w/ OD 4th ... other possibilities too, don't worry about riggin the shift, someone here will have guidance

Bill

Good choice with the Goodwrench engine. Your rear end is plenty strong but it,s not a good ratio unless you use an o-drive. I have put T-5 Trans. behind 2 of them & they work slick. They are not real strong so if you are going to hot-rod it I would go to something different. The hardest part if you have an automatic would be finding & puting in all the clutch linkage.

From 94 on GM made a 5 speed for the full size trucks and they work very well. An aquaitance of mine has one and loves it. Probably be a better choice than the T-5 and stronger. Henry

Henry, I think they started using that 5 cog in 88, I used one from a 1990 in an 87 I had-loved it, 1st gear is low enough to pull but not a granny. Great trans, but I never had a speedometer due to it being electronic, the 87 still had a cable speedo.