1989 Ford Bronco Late Downshifts

MRHOX55

MEMBER
1989 FORD BRONCO
V8
4WD
AUTOMATIC
162,000 MILES

Hey guys this is my first time using this site but I hope you can help me. I have an '89 full size bronco that had the 5.0 but was switched out for the 5.8 that has been rebuilt with an RV cam and an RV torque converter. It still has the stock AOD tranny but that is all I know since I just bought it from the guy who did all the work. The problem im having is that when im driving it it shifts up just fine every time. However, when it is time to slow down the vehicle will buck violently and almost kill its self before it will down shift to the next gear. I thought it might be the vehicle speed sensor, but when I checked the codes it didnt give me any codes that pertained to the transmission at all. Also If it makes a differance the vehicle will not go into 4lo either the light just flashes continualy which is why I thought it might be the vehicles speed sensor. Any help or advice will be greatly appreciated.

Saturday, November 1st, 2008 AT 9:53 PM

3 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Now you said it is a 5.8 ltr with a AOD? There is no such thing as an RV torque converter. Now with that said what computer was used? The computers are different as the firing order is different too. Are you sure it a 5.8ltr and not the 5.0ltr? I will tell you how to tell the difference ok. At the drivers side or left head at the front of the block tell me what the distance is between the water pump bolt closest to the top of the block and the bottom of the head. Now as for your shift problem it is more then likely the converter. You must have lock up converter, if it is not a lock up converter then you have no overdrive and down shifts are just hard as ever. Get back to me with some answers and we will go from there ok.

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Saturday, November 1st, 2008 AT 10:40 PM

MRHOX55

MEMBER
2 POSTS

The guy I bought the bronco from was a mechanic at the local shop and he said that he switched out the computer for the 5.8l along with the motor. As far as the RV torque converter is concerned I had never heard of one either, but I just took his word for it since he seemed to know what he was talking about. I do however have over drive and I can shift in and out of drive and over drive. In over drive the vehicle runs 2000 rpm at 70 miles an hour. It feels like the vehicle can not tell how fast it is moving. I was looking on line and learned of a vaccuum module in the transmission that controlls shift firmness and when the vehicle shifts by monitering the manifold vaccuum. It said that if you have a vaccum leak that vehicle will read that as wide open throttle and try to keep the vehicle in the lower gears, but that is the opposite of my problem. I know that having a heavily cammed out motor will affect the vaccuum, but I am not sure if it would give me more vaccum or less. It sounds to me like It would have to give me more vaccum in order to produce the same effects that I am having. Thank you for your time.

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Sunday, November 2nd, 2008 AT 5:55 PM

RACEFAN966

MECHANIC
5,029 POSTS

First we need to make sure it is a 5.8ltr so please give the info I need to figure that out. Make the measurment that I need. This will help a lot. You do not have a transmission modulator valve, it is controled buy a spring inside. I had an 89 F-150 same as you just a truck it had a 5.0 ltr with the AOD and when I put in a shift kit the shift firmness was based off of what sping I put in it above the valve body. You can not put a big cam in your bronco the computer can not do it and not can a chipped one I have been there. Ford does make a mass air flow kit to put on that bronco at the tune of $800 then you could put in a bigger cam.
Now if you would give the measurment that I need and do you know what year 5.8 ltr engine he said you put in?

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Monday, November 3rd, 2008 AT 9:51 AM