Another Gearing Thread

As many of you know by now, I am a new jeep owner. My new addiction is a 1977 chassis with a 74 tub. 304 with 3 speed. This past week we took it on a 250 mile round trip to the mountains. Ran great, with the exception that at 55 on the highway I had lots of pedal left, but it sounded like the motor was revving so high I did not dare push it any further. Unfortunately, no tach yet so as to be able to give numbers. Our use for this jeep is around town and trips to the mountains on paved roads. What options do I have to gear this thing better at the high end so that it doesn't feel like it is pulling our teeth out on the road? Thanks.

 

You can replace the transmission with an overdrive transmission or re gear front and rear differential to a lower ratio. Neither options are inexpensive. Re gearing the differentials can be tricky and require some specialized equipment. A transmission replacement will require adapters and some fab skills. Not a bolt in swap but can be done.

 

Mmm. This is a common fear of new Jeep owners. I expect you will find that the RPM numbers are lower than you think. A '77 will have either 3.54 or 4.10 axles... the 3.54 axles are considered highway gears for a CJ. Even the 4.10s are not that low ... earlier Jeeps came with even lower gears: 4.27s, 4.88s and 5.38s, depending on the year. IMO any '77 model is quite streetable without any regearing. Most people are unaccustomed to the noise level in a Jeep (engine noise, fan noise, gear noise, tire noise). I suspect that everything is fine, and that you just don't know you should expect.

You can estimate your RPM from the tire height and your speed if you know the axle ratio. Measure the height of your tires and look for a tag on the axle cover for the gear ratio. Then go here http://www.novak-adapt.com/knowledge/gearing.htm to calculate the RPM at a given speed.

Jute padding and carpet on the floors will help quiet the interior a lot. Quieter tires will help. An electric fan may help.

 

If you have a new flex fan or the like, it will sound like your turning 20,000 rpm.. Hope thats all it is.

 

Thanks for the thoughtful replies. I will put a tach on it and see what the true revs are. Hopefully, it is simply a matter of conditioning myself to the sound(s) at higher speeds.

 

i too am a new jeep owner (actually had it 4-5 years, but it just sat after the first one) and i have the same problem... when its actually ON the street...

304 3-speed sounds like its going to explode on the highway...

ive thought of the T-18 swap, but thats WAY in the future...

if i do the T-18... do i need to change the ratios in the pumpkins too?

THX!

 

Changing from the three speed to the T-18 won't do anything to your highway engine rpm's. They're both 1:1 in high gear.