Automatic Tans. shiffting too much

[jhuette]

I am new to Broncos so forgive the ignorance. I am looking to purchase a 73 model bronco, I test drove one on Sat. and noticed that the 3 speed auto. tans. was down shifting way too much. The truck was modified with 33" tires and it currently has the original 3:50 gears in the rear. Is this a transmission problem or a gear problem? How can I fix it if I purchase this truck and what kind of cost am I looking at?

Thanks
Jason

 

[wildbill]

You just found your problem the gears are to tall for 33's you need to run 4:11's with that tire. Good luck.%) %) %) Bill %) ;D

 

[jhuette]

Thanks for the post. I actualy sent you a PM so ignore it. What is the cost of changing out the gears? What size tire could I run with 3:50 gears that would still be good for crawling some trails in CO and look halfway cool? I assume that a C4 manual tans. would not have this problem? The truck has a 3.5 lift on it currently.

 

[Devin]

Thanks for the post. I actualy sent you a PM so ignore it. What is the cost of changing out the gears? What size tire could I run with 3:50 gears that would still be good for crawling some trails in CO and look halfway cool? I assume that a C4 manual tans. would not have this problem? The truck has a 3.5 lift on it currently.

C4 is an automatic transmission.

If you had a 31" tire, that would be better, but the 3:50's just aren't good for any size other than stock, IMO.

You can get a brand new gear set for around $130 or so (X2 for the front AND rear). Plus, you will have to get an install kit, which is around $80 (again X2) or so. So, if you do it your self, you are looking at a bit over $400 for brand new gears. But, doing gears seems to be one of the most feared things when rebuilding cars, because if it isn't done properly, ugly things can happen.

If you pay someone to do it, then I would say expect at least double the $400 figure - probably more.

 

[jhuette]

Thanks a bunch. This explains a lot, so I will take it and run with it.

Jason

 

[76Broncofromhell]

You sound like you're going to need to pay someone to do the gears, it will run you between $1000-1500 to pay someone to swap the gears in your rig.

 

[ugly74]

I beg to differ fellas. I've got a C4, 3.50 gears and 32s, and it pretty much runs like crazy. I just did a cam swap, in an attempt to improve the low end grunt...but other than that, it ran great!

so let me ask you this jhuette:
does it run out of power, causing it to downshift, or does it seem to kickdown before it really needs to?

my driving consists of a mix of highway, around town, and mountain roads.
to get to my house, the last 2 miles I climb 1500 feet, and I really never have a lack of power. I've even towed cars/trucks with no problems. it wasn't till the radiator took a dump, makin it run hot, that made the lack of bottom end real noticeable. I've done some moderate rock crawlin, sand dune wheelin, and a bunch of trails. power's never been an issue.

if the engine in your potential Bronco is real tired, gears aren't gonna fix that either.

 

[jhuette]

When I took it for a test drive there were a few hills where it was downshift, which I considered normal. But when I got to long flat spots it kept downshifting and up shifting for no reason even while the speedometer was reading 55-60 mph. The engine did not seem tired at all. It is the original 302 which looked in good condition (no leaks and many of the gaskets and seals were changed out). All cylinders were hitting with no back fires, miss fires, knocks or other obscure sounds.

 

[RangerRob]

I'm in agreement with Ugly74 said because I have the same setup and it drives just fine. Mine is a 73 Ranger with C4, 32's, a Carter AFB and an RV type cam. I daily drive it in town and on the highway, on the rocks, pulling a light trailer etc. and it does well. Would want lower gears if I were doing more rock crawling, trailer pulling, or going to a larger tire though, but all around it is a good setup.

If it is downshifting too much, your tranny kickdown may be adjusted too tight. Check the adjustment screw on the linkage at the carburetor and see where it is. You can loosen it for testing purposes and see if that helps. The other thing that controls shifting is the modulator and they may have the wrong one on there. They have different characteristics and are identified with a colored stripe. Pretty sure mine has a yellow stripe. Someone has a chart showing the effects of different modulators but I can't find it right now.

Good Luck!!!

Rob

 

[broncow72]

I wonder if the kickdown lever is out of adjustment.
If it were a true down shift at 60 mph, you'd be all over the place with skidding rear tires.

 

[jhuette]

Let me clairfy. The speedometer was "reading" 55-60. I don't know how acurate the speedometer was. If you could find that link to the chart showing the effectes of different modulators that would be great. Thanks for all the help and information so far.

On another note, I guess I wouldn't have to worry about the gear ratio - tire set up if this was a standard?.?.?.

 

[Devin]

On another note, I guess I wouldn't have to worry about the gear ratio - tire set up if this was a standard?.?.?.

Standard or automatic - you are going to have the same type of issues with gearing. You can look at the tech section under transmissions on this site to see a list of different transmissions and their respective gear ratios.

It really depends on what you are happy with. As you can see from the differing opinions in this thread, some are happy with the 3.50 gears and 32" tires. I'm not one of them. I personally have driven an EB with 3.50's, a C4, 33" tires, and a freshly rebuilt, modified 302. Let's just say that my stock Honda Accord with a 4 banger will take it off the line and in a 1/4 mile it would be a pretty tight race. That just doesn't seem right to me. But, some people don't care about that. I have also pulled trailers with that combo also and while others claim it is ok, I think that it feels like and absolute dog. It just comes down to what your preferences are.

Also, like some of the others have pointed out - you may have some other problems lurking as well.

 

[Apogee]

Maybe this is obvious, but did you check the fluid level in the tranny? ;D

 

[BwoncoHowie]

Another thing to consider.
If the engine is putting out a poor vaccuum signal to the modulator it could cause it to downshift too easy. On the other side of the coin if it doesn't down shift easy you could be cooking the fluid by stalling the torque converter excessively. My bronco with C-4 and 3.50s is a dog even with 31"s. So I would be more inclined to agree with installing 4.11s or at least 3.75s

 

[jhuette]

Wow! A lot of great information. If I were to change out the gears what kind or RPMs should I expect in 3rd gear at 60mph...or better yet, can I even drive that fast with that low end gear ratio?

Apogee, no I didn't check the fluid level. Now that you bring it up, I kick myself for not doing it...Ouch!

 

[Devin]

Check out Heinz_67's gear calculator for your question. Just click this link, then click on "gear calculator".

http://home.comcast.net/~jcmiley/index.html

 

[DebosDave'72]

The 33" tires make up for the 4.11 gears... you should have the same kind of RPM at 60 as a stock tire and 3.50 gears... IF not the exact same it will be close. The problem with trying to get a good cruising RPM by putting bigger tires and not changing the gears, is that it makes everything work a little harder at the low speed/RPM... Like said above, there are plenty of people that are happy with the 3.50 gears and 33" tires, but the performance will be better with 4.11 gears... This means the 4.11 gears are a little easier on your tranny and engine too... the transmission won't have to slip as much or generate as much heat with 4.11 than it does with 3.50...

DD

 

[ugly74]

it must just be me. if I'm goin around a corner in town and nail the gas, I can get the rear to break loose on pavement. the power aint all that below 2000 rpm, but it's not a dog by a long shot.
in a race, i've beat my 4.3 '96 S-10 (auto), and can hang with my 5.9 '87Dodge (manual)
a kid in a supra tried to get in front of me from a light, cuz his lane was gonna end...he didn't make it, and I had 2 other guys in there with me. yet I can still go 110mph if I wanna (but that's about as fast as I'll ever take it)

as far as cookin the tranny fluid, I put a cooler on in front of the radiator, and the fluid is always a nice bright pinkish red.

truth be known, I'd love to have some lower gears. but only if I could retain my top end with an OD tranny. and that's just a bit too blingy. (I'm cheap)

but I'm rambling again...

you could do a gear swap, but if the engine is tired, or the tranny isn't workin like it should....it'd be like putting lipstick on a pig.

I've put in like 8 cents so far, so I'm done

 

[DebosDave'72]

Ugly74,

I'm not saying that the 3.50 won't work, just saying the 4.11 will be easier on the tranny and engine, not suggesting that the 3.50 is bad... some folks notice the 3.50 gears and 33" tires, not to say they won't do it, just the 4.11 is a little better suited to it. I think you personally would notice the 4.11 gears on both ends, it won't be the best suited to the upper end like your current, but the lower end would be better... I think the gear change will help with a tired engine or tranny, but that would be a temporary fix, but when the tranny or engine gets rebuilt, you still have that better gearing... The difference on either gearset isn't an extreme thing, but just a little different on both sides... it isn't like adding 50 horses or an overdrive tranny either way you cut it... The difference at the top end with the setup we are talking about, gives you 350 RPM difference between the two gearsets... at 56 MPH...