I just bought a 1987 full size bronco with a 300 6cyl and 4sp manual trans. I want to reduce the rpms for obvious reasons. Whats the best way,,,,,,, trans change or rear ends? Any help welcome

 

Which 4 speed do you have? Does it have a low first gear?

 

sure does,,, low first gear. about 2600 rpm at 60 mph

 

FIRST gear, 5 mph at 2600 rpm. Granny gear, is that what you have?

 

Sorry,, should have been a little more specific. 4th gear, 60 mph 2600 rpm. Granny low first gear doubt it would get 5 mph in first (real low)

 

OK, then your solution is the ZF 5 speed. It offers a low (not as low as your 4 speed) first gear and an OD 5th gear. It will require a hydraulic clutch.

These can be found behind 300s and 351ws (and maybe 302s) in F250 and up trucks starting in '87. At some point in the 90s, they lost their speedo drive, so watch for that.

Search "ZF swap" here or scroll through the SBF, 300 six and clutch forums for trans swap threads.

Good luck with it.

 

OK, this is your second thread on the topic. No need to do that. But you asked which is better, axles or trans change. IMO change the trans. It appears you have 4.10 axles. To change both would probably be over $1000. You can probably do the trans swap for half to 3/4s of that. There is no cheap "bolt in" trans change available.

https://www.ford-trucks.com/forums/1...-od-trans.html

 

or bump up to a 33" tire to compensate for the gearing

 

There isn't a "best" way for everyone. Maybe you have a buddy that knows how to set up gears. Maybe you have a free beater truck with a ZF at a relative's place.

Your choices are basically:
- overdrive trans. The ZF is the only real option IMO. Other overdrive transmissions aren't that strong.

- Gear change. As said, roughly $500 an axle. However, I think you have 3.55 gears, not 4.11 gears. If it were my truck I wouldn't want to go any higher than 3.55.

- bigger tires. This will raise the effective ratio but it brings up other issues, like tire clearance, gas mileage, extra wear on the suspension, not to mention that new tires are $$$$ and you may even need to get new rims depending on the tire you go with.

- bolt-on overdrive unit like a gear vendors unit. They are a bolt-on device that give you an external overdrive gear. You can find them at swap meets, in junkyards, on craigslist, etc. I believe it fits between the transmission and transfer case on 4wd trucks but I could be wrong.

I had an '89 F-150 with the same trans, engine, and gear ratio and I never bothered to do anything about it. I would run close to 3000 on the highway. Gas mileage wasn't great (14-ish) but I never had an issue with it.