Yesterday my son and I did something I have wanted to do for some time. We replaced the 9" rear 3.7:1 differential with a 3:00:1 differential. I was a little concerned about the big change and how the truck would perform.

Since many of you are new, my truck has a rebuilt 292 with ECZ-C heads (bigger valves), 4 bbl Edlebrock street carb, an improved street cam from John Mummert and dual ram horn exhaust. Estimated HP is about 210 (the original was 175hp if I remember correctly). I figured with the few extra horses, we could change the ratio without to much loss of performance.

Results: I now have a true 4 speed (T98). The granny gear is actually a usable gear now. In fact starting out in first takes the truck to nearly 20 mph. 35 mph is easily achieved in 2nd and you can cruse at 45 mph in 3rd at only about 2500 RPM's. Now the best part, on the highway cruising at 65 MP is achieved at 2800 RPM, it was about 4000 RPM's with the 3.7 and the engine noise was quite loud. Now you can go 65+ and conversation and listening to the radio is quite easy. I am sure gas mileage is improved.

All-in-all I am quite happy and so is the truck, so I thought I would share the good results.

 

Sounds pretty cool. Did you change the gears or did you swap out the third member?

 

Walston 2800 should be a happy spot for your Y-block.
Now your all set for a run down to Docstock or Truckstock in Kentucky.

 

I swapped the entire third member.

 

Very true. From one Wally to another.......

 

Nice!!! i have a dana 60 in mine. it was a ranch truck and is geared so low first only gets you to 5mph, 2nd to 20, 3rd to 30, and 4th tops out at 50. i can hit 60, but it turns at 2500 when im going 40 so imagine 60!!! Finding parts on a budget for the dana 60 is, tough I have a friend with a 58 f100 with a 9" in it. he's running 2.somethings and his tach reads 2000 at 60-65 with the 4speed. wouldnt that be nice? Anyway, i'm jelous of your gear swap!! my truck doesnt even have any sound insulation!

 

some trucks do have insulation?

 

well, alot of people install sound deadener to the floors ceiling etc, to quiet the road and exhaust nan noise. the trucks also came with an asphault type insulator between the firewall and inside of the cab to reduce engine noice. Well, my truck has 0 sound deadener covering the floors, ceilings, doors etc and i tore out all the asphault insulation between the firewall and inside of the cab so you hear all the motor noise. I also have no headliner so the cab turns every vibration into sound which gets very VERY loud haha. Oh, and i have no mufflers, just straight pipe, with a 4.56 rear end. so just doing 50 at 3000 rpm gets old real fast i am investing in lower gears and sound deadening mats very soon!

 

maybe mufflers too, but i like the sound

 

How about cut outs so you can have noise when you want it and quiet when you don't.

 

What size tires are you running? I have been thinking about a gearing swap just like that when i finish installing my T-98! I have a hunch that my tires may be taller than yours though so I'll have to take that into consideration.

 

Great results with the gearing.

 

P235 75 R15

Good luck