Mutt The Race Truck

[DanStokes]

It's an OM617. That's a pre-electronic turbo 5 cylinder. So it has as little Bosch electrical as possible. It does have the Bosch fuel injection but the word on the street is that they are OK. Back and forth on keeping the Bosch alternator but I suppose I'm stuck with the starter. I don't think they're too bad though. Still working out how to do the engine kill with the safety power switch - maybe I keep the stock vacuum shut off for now. The plug wires must be military as they're REALLY stiff and bolted to the plugs.

Dan

[milner351]

I think you're wise to have that one, you remember the pain and suffering of mine.... never again, I should have stuck to my guns and gotten the older body style with the more mechanical injection as you have. I still look at w123 wagons occasionally.

I think you'd have to stick with the factory fuel shut off for simplicity - otherwise getting into a lot of plumbing stuff.

Fuel pump?

[DanStokes]

Yes.

But seriously, it's built into the pump body - no lift pump. I'm thinking of putting a small fuel cell on the core support although there is one in the bed. Shorter lines, less to mess up. I don't think fuel temp will be much of an issue but I'll have to cross that bridge if and when I get to it.

As built, the stock shut off is a typical case of MB over-engineering. There's a vacuum shut off system built into the pump that's activated when you switch the key to off. There's actually a vacuum switch in the key assembly. I'll need to make it normally off then either sucked to "run" by vacuum or some such. The main issue is that the engine needs to stop running when the safety crew switches the battery off. I'll puzzle it out.

Dan

[milner351]

super duty and other diesel trucks have a 12v vacuum pump on the fender - easy junk yard piece, then the only vacuum lines would be under hood - 12v switch on the dash - just like you'd have for gas ignition system.

[DanStokes]

That's an option I'll consider. The engine has a vacuum pump but it's gear driven off the front drive so it can't be switched off once the engine's running. The electric vacuum pump might work well. Not sure if the shut off works with vacuum off or vacuum on (does it push or pull?). I'll look into that.

Thanks, John!

Another tech question - what master cylinder and support hardware (push rod, etc.) do I need to lose the power brakes? It has the common front disc/rear drum setup but I don't know if they ever came with manual discs. I'd like to stick with parts store parts if possible.

Dan

[milner351]

I'm guessing Tardis can chime in with knowledge on the brakes Dan - surely the low option early S-10 four bangers were available with manual brakes?

I got a manual brake master cylinder for a granada that I plan on using in the falcon - you may be able to search on rock auto and find a master cylinder for manual brakes that way.

Benz used vacuum for EVERYTHING - door locks, rear head rest actuators, all the hvac blend doors, etc.

The truck vacuum pumps are only there for the hvac stuff - brakes are hydroboost off the powersteering pump, the pumps are small, easily fit in your hand, new they're in the $40 - $60 range and should be easy to find in a junkyard for much less than that.

I wouldn't be surprised if the benz system is set to shut off with zero vacuum, wouldn't that make more sense? as long as the engine is turning and the belt drive pump is making vacuum, it stays running, turn the ign sw. off and that cuts vacuum to the pump solenoid, and then the engine quits and pump stops pulling...... ???

I have a couple benz manuals - if I remember I will see if they cover your engine - if they do - yours for the cost of shipping.

[DanStokes]

It absolutely make sense that a lack of vacuum would kill the engine. But this IS a Benz so all bets are off!

I have the Haynes manual but I haven't chased the shut-off circuit yet. Still, I'd love to have whatever you have - lemmie know. Do you have my address?

I figured one of the guys would know the manual brake trick - has to have been done a time or two. I'm a big advocate of letting someone else invent the wheel unless no one has blazed this trail before (how's THAT for mixed allusions?). Tardis, you out there? Might be worth a PM.

Dan

[BOOOGHAR]

astro vans had hydroboost, fairly easy swap

[STINEY]

Its a GM....I'm not specifically familiar with the S10 system, but practically every GM of that era had 2 holes on the pedal arm.

The upper hole was the manual hole for the pushrod - gave a better ratio for less leg muscle needed.

The lower hole was the power hole for the power pushrod. Less leverage because the booster added the muscle.

Use the proper hole and pedal feel will be just like the factory intended for that vehicle.

I know a lot of guys will say I'm wrong, but the cylinder is sized correctly for the brakes on the truck (if they are OEM), simply remove the booster, and mount the same master directly to the firewall (can be done without even disconnecting the lines), fabricate a new correct length pushrod from the guts of the booster pushrod and the original pedal end/pushrod. Weld the two together in the proper length and you are set.

There are other methods, but I've done this several times and it works with a good feeling pedal.

[kyhunter89]

What Stiney said, and s10's did have a manual brake option, I know because the have larger wheel cylinders that I've swapped onto the backs of Malibu's for better brakes.

I have a buddy Who put one of these 5 cylinders in a roundbody s10 with a 5 speed and ran it on bio/old oil/etc. Have no clue on top end but it was fast on bottom, a tire shredder, and I think was stock.

[Russell]

I had a MB for a short time when gas was $4 / gal. The guy I got my fuel from had one that would not stop so he had a vac line coming out from under the dash that you had to suck on to get it to stop, iirc

[DanStokes]

This afternoon I spoke with a local guy who is pretty sharp on these. He's pretty sure that the vacuum pulls the stop valve (I guess you'd call it) and that stops the engine. Yep, typical M-B - backwards. I'm thinking a vacuum accumulator and a 12V solenoid so when you kill the power the vac feeds the valve. Always a way around this stuff.

There's a lever under the hood (well, used to be) that is manual shutoff if needed. Not sure if that would have been easier than sucking on the shutoff line!

Dan

[STINEY]

The wild diesel pulling guys use an "anti-runaway" valve...........basically does the same thing a block of wood over the air intake would do, only lots fancier.

Its actually a safety requirement if I remember rightly.

Think similar to a gate-valve in the air intake tubing. Works great, and prevents runaway overboost uncontrolled revving (well not really prevents, but can manually stop it)
I'm not one of the diesel guys, but I'm surrounded by them at work, some stuff has rubbed off.

[DanStokes]

We wore shop coats at EPA and were instructed from Day 1 that if a Diesel runs away you toss your shop coat into the intake. In 31 1/2 years I never had to do that but I'm thinking it's the same concept. I just need something for a routine shutdown that also works from the battery kill switch.

Dan

[Monk]

Looks like a real neat project Dan.
Gonna hafta put to your thinking cap on for this one.