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66-96 Ford Broncos - Early & Full Size

New owner of 1987 B2 4x4, advice? What to watch for?

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My 1987 Ford Bronco II has 139k, with the stock 2.9L v6, and automatic transmission. It is 4x4, with manual lockouts. The previous owner installed a 3 inch body lift, and superlift steering stabilizer. It is sitting on P265x75x15 mastercraft coursers. When i first purchased it, my father drove behind me heading back to my house. He said my brake lights were not working, and i also noticed it was running quite hot. (Hot enough to feel the heat coming through my dash). When i got home, i first checked under the hood. The stock fan was not in it, and it had an electric fan, not hooked up right. So, noticing the terrible effort on the electric fan, i ran new wire all the way to my fuse box inside the cab, so it comes on right as the vehicle does. Now it runs nice and cool. My next problem was a faulty brake light switch. So i took a trip to my neighborhood autozone and replaced it. No more problems now aside from my speedometer being off, which i have no idea about, but being im not too familiar with the Bronco II, id appreciate some pointers on what to watch for, and ways to make it more offroad friendly? Thanks for your time!

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The electric fan should be controlled by a thermal switch or fan controller which operates a solenoid.  The power to the fan should come directly from the battery (+) to a fuse, (around 30 amps depending on the fan size), and then to the fan.  A number 8 auto grade wire should be used from the battery (+)  to the fan. 


The purpose of having an electric fan is to remove the fan load from the engine when it is not needed, like when the vehicle is moving along fast enough to cool the engine without the need for a fan, (the temp controll decides when it is needed).  You will find that in many areas of the country the fan is not needed 90+ % of the time.

Also the electric fan can give you more efficient cooling under conditions when it is hot and the engine is running slow, (like when off roading in hot weather). 


The Speedometer inaccuracy is caused by the change from stock to larger tires. That can be fixed by a speedo gear or the speed sensor system, (not sure what the B II has).


A typical diagram attached


Good luck,




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I have had my beautifully tempermental '87 Bronco II for 8 months now and the only real issue i have had with it is the exhaust system/ catalytic converter. Check your O2 sensors and get your system pressure tested.

Have Fun!!

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My 87 bronco II has transmission issues I have the A4LD the overdrive starts to slip I had it rebuilt about 7 months ago and it is slipping again

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yo j,


Is trans fluid level ok and color ok? No aroma of burnt toast?

Has engine overheated recently?

Some ideas;




Ensure all vacuum hoses are connected and not leaking (sounds like a Hiss when using a short section of garden hose or a mechanic's stethoscope for under $5.00 @ parts store or Harbor Freight)..check;


vacuum diaphragm on transmission

a4ld vacuum diaphragm.pdf ensure hose is not damaged or leaking back to its source; I don't have info on how to test that A4LD vacuum diaphragm but usual Ford tests is checking for trans fluid in that hose .. if fluid id in hose, could be a ruptured diaphragm.


1.Disconnect the negative battery cable.

2.Raise and support the vehicle safely. CHOCK WHEELS; DO NOT USE BUMPER JACK; Support WITH Jack Stands of suitable rating.

3.Disconnect the hose from the vacuum diaphragm.

4.Remove the vacuum diaphragm retaining clamp bolt and clamp. Do not pry on the clamp.

5.Pull the vacuum diaphragm from the transmission case and remove the vacuum diaphragm control rod from the transmission case.


To install:

6.Install the vacuum diaphragm control rod from the transmission case.

7.Push the vacuum diaphragm into the case and secure it with the clamp and bolt. Tighten to 80-106 inch lbs. (9-12Nm).

8.Fit the vacuum hose to the diaphragm.

9.Lower the vehicle.

10.Reconnect the negative battery cable.


Also check MAP sensor & brake booster hoses and the units themselves for Vac leaks , Emission system as well as HVAC system (in engine bay and under dash) hoses & components can be vac leak sources.


When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. ALWAYS SERVICE VACUUM LEAKS.



87 BII 2.9 Vacuum Diagram





Ford TSB 97-22-4 Date: 10/27/97

Transmission - A4LD, 4R44E/4R55E, 5R55E - Torque Converter Slip - Diagnostic Trouble Code (Dtc) 628 Or P0741 Stored In Memory


1985 to 1993 Mustang

1987 to 1988 Thunderbird


1988 Cougar

Light Truck:

1985 to 1990 Bronco II

1985 to 1997 Ranger

1987 to 1997 Aerostar

1991 to 1997 Explorer


Some vehicles may experience excessive torque converter slippage, torque converter not engaging, or Diagnostic Trouble Code (DTC) 628 stored in memory. This may be caused by damage to the fluid pump support seal and/or to the groove on the pump where the seal is located.


Inspect the fluid pump seal for damage. Refer to the following Service Procedure for details.


Follow normal diagnostic procedures as listed in the appropriate Service Manual.

Inspect the fluid pump support for damage. If damaged, also inspect the fluid pump support seal groove on the pump.

If the groove is damaged, replace the pump.

If the groove is not damaged, replace the fluid pump support seal with a redesigned Seal (F77Z-7L323-AA). Refer to Figure 1.

Do not replace the torque converter unless it is damaged or fails the criteria listed in the appropriate Service Manual and/or refer to TSB 96-26-12.


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More than likely time to change Radiator. Mine went bad at 150k miles. Not difficult at all if you know what you're doing. Just make sure the guy at O'Reilly's gets the right year radiator.

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