Underpowered BJ40 or drivetrain problem? (1 Viewer)

[PuraVida77]

I just completed some upgrades on my ‘77 BJ40 down in Costa Rica. New OME suspension, added power steering & 4-wheel disc, and lots of minor repairs and cosmetic stuff.
Big question I now have after finally getting to drive it regularly is “is the engine seriously this lie-powered or do I have an issue?”

Top speed, foot to the floor, flat highway is barely 80 kmh,

 

[B y r o n]

When you did the disc brake conversion which master cylinder did you use?

If you kept the drum brake master and didn't remove the pressure regulator (wrong term but can remember the correct part name) your disc brakes could be dragging.

Residual valve is the part I'm talking about. Drum systems have 10 lb valve and disc use 2 lb valve.

 

[-MaTTi-]

Big question I now have after finally getting to drive it regularly is “is the engine seriously this lie-powered or do I have an issue?”

Top speed, foot to the floor, flat highway is barely 80 kmh,

View attachment 2734645

It should take over 100 km/h. But why all springs are backwards?

 

[pithicus]

I would go for a spin without using the brakes and check the temperature of each disk.
80 k's flatout is not normal.

 

[jim land]

My bj42 3b is over 400 000km with 33" tires and it can make 120 km/h and more on flat highway , but on big long hills , it can drop to 60-70 km/h

 

[PuraVida77]

It should take over 100 km/h. But why all springs are backwards?

I am not a mechanic, so can you explain why it looks like the springs are on backward? I do recall the mechanic here in Costa Rica mentioning something about having to reverse something with the suspension to keep the wheels from hitting (I believe the fender wells) once he installed OME system.

 

[PuraVida77]

I would go for a spin without using the brakes and check the temperature of each disk.
80 k's flatout is not normal.

by this do you think the brakes (which are new discs replacing old drum) are the issue?

 

[pithicus]

by this do you think the brakes (which are new discs replacing old drum) are the issue?

Possibly...... Sticky caliper or some other issue causing binding. One or more disks will get really hot after a 10 minute drive [without using the brakes] if that's the issue.

 

[PuraVida77]

Possibly...... Sticky caliper or some other issue causing binding. One or more disks will get really hot after a 10 minute drive [without using the brakes] if that's the issue.

I appreciate the advice!

 

[PuraVida77]

When you did the disc brake conversion which master cylinder did you use?

If you kept the drum brake master and didn't remove the pressure regulator (wrong term but can remember the correct part name) your disc brakes could be dragging.

Residual valve is the part I'm talking about. Drum systems have 10 lb valve and disc use 2 lb valve.

hi Byron, thank you for the information. This is a reply I got from the mechanic here in Costa Rica: "...there is nothing about the new brake system that is connected to the motor because we are using a new alternator with vacuum generator and not using vacuum from the motor. The only additional load for the motor is we put the hydraulic pump and its normal to feel a little less power but just a bit".

Does any of this make sense?

 

[B y r o n]

hi Byron, thank you for the information. This is a reply I got from the mechanic here in Costa Rica: "...there is nothing about the new brake system that is connected to the motor because we are using a new alternator with vacuum generator and not using vacuum from the motor. The only additional load for the motor is we put the hydraulic pump and its normal to feel a little less power but just a bit".

Does any of this make sense?

Being a diesel motor you need the vacuum generator to provide vacuum for the power brake booster mounted to the firewall. I am making an assumption that your vehicle originally had drum brakes which makes the master cylinder a drum brake master. Inside the master cylinder is where the residual valves are located. Running disc brakes off of a drum brake master cylinder, without removing the residual valves, will cause the disc brakes to drag. Dragging brakes will prevent the vehicle from being able to reach top speed, like driving around with your foot on the brake. If the master cylinder was replaced with a later disc brake master, then dragging brakes is probably not your problem.

 

[PuraVida77]

Being a diesel motor you need the vacuum generator to provide vacuum for the power brake booster mounted to the firewall. I am making an assumption that your vehicle originally had drum brakes which makes the master cylinder a drum brake master. Inside the master cylinder is where the residual valves are located. Running disc brakes off of a drum brake master cylinder, without removing the residual valves, will cause the disc brakes to drag. Dragging brakes will prevent the vehicle from being able to reach top speed, like driving around with your foot on the brake. If the master cylinder was replaced with a later disc brake master, then dragging brakes is probably not your problem.

Byron,

thank you so much for the detailed explanation! I will ask the mechanic again for a detailed explanation of what he did or did not due. The other issue that I think is related to this is with the accelerator linkage. The mechanic did tell me that they had to modify the linkage a bit because after installing the brake booster the linkage was hitting the underside of the booster. My accelerator pedal is now about 1/2 to the floor so not inline with the brake and clutch pedal. So not much travel.

The first picture according to him is the brake booster & adapter; second picture steering gear box; third picture not sure but I think firewall mount for brake booster; fourth disc being installed. Any of this shed any more light?

 

[B y r o n]

Byron,

thank you so much for the detailed explanation! I will ask the mechanic again for a detailed explanation of what he did or did not due. The other issue that I think is related to this is with the accelerator linkage. The mechanic did tell me that they had to modify the linkage a bit because after installing the brake booster the linkage was hitting the underside of the booster. My accelerator pedal is now about 1/2 to the floor so not inline with the brake and clutch pedal. So not much travel.

The first picture according to him is the brake booster & adapter; second picture steering gear box; third picture not sure but I think firewall mount for brake booster; fourth disc being installed. Any of this shed any more light?

View attachment 2744799

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View attachment 2744806

With your accelerator pedal being half way to the floor means you're probably not getting full throttle then. That could explain why you're not getting to top speed.

 

[DEADSALT]

find a flat spot
put the truck in neutral
attempt to push it manually

if your brakes are dragging at all
you will feel the resistance

throttle linkage;
depress pedal and have someone determine
the throw on the cable attached to the throttle body/butterfly

if there is slack/unused throw then your pedal is limiting factor

 

[DEADSALT]

the mechanic installed your brand new OME suspension backwards?!?
because the blingy rims you’re rocking have an obscene offset

 

[pithicus]

If it's not the brakes or throttle cable, it could be a number of engine problems. Fuel filter/ restrictive exhaust, that sort of thing.
A decent diesel mech should be able to help sort it out.
good luck.

 

[PuraVida77]

find a flat spot
put the truck in neutral
attempt to push it manually

if your brakes are dragging at all
you will feel the resistance

throttle linkage;
depress pedal and have someone determine
the throw on the cable attached to the throttle body/butterfly

if there is slack/unused throw then your pedal is limiting factor

I appreciate the advice. I hopefully will have a new mechanic evaluate today!

 

[PuraVida77]

the mechanic installed your brand new OME suspension backwards?!?
because the blingy rims you’re rocking have an obscene offset

hmmmmmm

 

[-MaTTi-]

I am not a mechanic, so can you explain why it looks like the springs are on backward?

The rear tire is way of the center of the wheel arch (should be ~2” forward), same at front (should be ~2” backward). Your wheelbase should be somewhere close to 228 cm (90”), I think you have close to 240 cm now. Looks stupid. I don’t know how the driveshafts are reached their place.