Gene McCormick

My 1969 Olds 98 owners manual says "do not coast" in neutral" anybody know why GM would say this even with engine in idle ?

rustyroger

The engine drives the oil pump in the transmission, at idle speed it may not supply sufficient oil pressure - or more importantly volume - to adequately lubricate the moving parts in the transmission at more than walking pace.
Earlier automatics (I'm assuming you have an automatic) sometimes had a secondary pump driven by the tailshaft, you could in an emergency tow start a car thus equipped. Later cars need to have the driveshaft disconnected or the rear wheels raised off the ground if they need to be towed for any reason.
Why would you want to coast in neutral anyway?

Roger.

MDchanic

I'm not sure, Roger.
Clearly your statement is accurate, and is the reason why you can't tow for any distance with the driveshaft connected, but I'm not sure that coasting with the engine on and turning the pump would be a problem. The pump is turning, and you do have pressure, and the oil is circulating,

I think it is more of a safety issue - in the fifties, there were cars that would "freewheel," under certain circumstances, ostensibly in order to save gas. I think that in the sixties there were a lot of drivers who wanted to "freewheel" whenever possible, but, with the car in Neutral, of course, there is a lack of maneuverability in the event of an emergency (you have to remember to pop it into gear before you hit the gas), and it was considered to be a safety hazard, so I believe that all manuals advised against it at the time.

- Eric

s i 442

One reason is because you are not in control of the car.

brown7373

Taking the car out of gear, auto or manual, as you drift up to the traffic light is probably not a big deal. But people would take it out of gear and coast down a mountain. Out of gear, there is no engine braking and people would sometimes over use and overheat the brakes. Maybe it's just me, but I have free wheeled down a mountain and I don't feel I am in control of the car as much as when it remains in gear. I feel like the car is driving me, not me driving the car.

halfmoontrail

The ST300 trannies have this sort of pump, so you are not supposed to tow them w/driveshaft in place...but I was not aware that you could tow start this sort of arrangment. The pumps and/or trannies overheat and blow seals if you tow in neutral. Turbo-hydromatics can be towed in neutral, even for long distances, and a '69 would have a thm.
Steve

rustyroger

Good points from all you guys.

Eric, my reasoning was at towing speed the transmission may need more lubrication than the engine could provide at idle speed, but I know enough about automatics to restrict myself to oil and filter changes...

In the UK coasting in neutral is actually contravening the road traffic act, although how you can be detected doing this in a car beats me.
I wouldn't relish the prospect of going down a mountain pass in an automatic equipped '50s car, are there horror stories of tragedies when the brakes and transmission weren't up to the job in mountain states?.

Steve, I understood most transmissions wouldn't live long if they were towed any distance. But I know I'm no expert.
But I do know that early Borg-Warner transmissions on some British cars, and the early AP transmissions fitted to Minis & Austin 1100s do work for tow starting. I've done that, you needed to get up to about 25-30 mph to do it though.

Roger.

brown7373

I am reading a 1970 Pontiac Owners manual (Olds is out back) which would have the same transmisions and warranties. "Normally your Pontiac may be towed with all four wheels on the ground for distances up to 50 milesmat speeds of less than 35 mph."

joe_padavano

This is also true in many states in the US. I think these laws date to when cars had single circuit drum brake systems. Any leak and you loose all brakes; if that happens going down an hill many drivers may not have the sense to shift back into Drive to slow the car (of course, Low would be a better choice). Also, since drum brakes fade, descending a long hill using only brakes with no engine braking increases the chances of brake fade. I suspect that these arguments do not apply to cars with dual circuit brakes and disk brakes, but good luck getting old laws changed based on an engineering argument. Also consider the fact that most hybrid cars disconnect and shut off the engine when you are coasting, so while that may circumvent the letter of the law, it does not circumvent the spirit of the law. Yes, I realize that hybrids have regenerative braking, which does help.

Allan R

The 1972 Owners Manual provides info on the use of N on page 14. It does say NOT to coast in neutral except for the purpose of restarting a stalled engine in motion, or running the engine while standing with brakes applied. No reason given. I'm sure if you check the schematics for the TH350 in the CSM there will be some kind of reasoning with the valve body and oil circulation patterns

Gene McCormick

Wow thanks everybody for your replies. I did post reasons earlier but the tread did not
post. Gas in my area is $6.30 a gallon. The local Tranny shop who knows the Turbo Hydra-matic 400 well says engine in idle and with oil pressure up there would be no harm done. I must confess I do the same in my 57 Caddy. Its a quiet area I live in with
gradual hills to my home. Average speed 15-20mph. Gene in B.C. Canada

Allan R

Absolutely gorgeous 98 Gene. I was just out to Surrey/White Rock 2 weeks ago and gas was 143.9/L. Just 20 km away in Abbotsford it was 128.9. Even Kamloops was cheaper at 120.9 Got home (AB) and it was 116.9 so about 1.00/gal less than you right now. Are you measuring that 6.30/gallon as US gallon or Imperial (3.78 L US vs 4.54 L Can)

I looked up the reason for the high price in Vancouver. They have the same basic federal taxes GST, provincial PST, daily average tax (wow around 35¢/L) transit tax (around 15¢) and carbon tax! And to think my wife wants to move out there....

NOTE to self: BC not user friendly for 455 fill ups.


What part of BC are you in?

rustyroger

Disc brakes, especially on older cars are not immune to fade, much better than drums all else being equal though. I read an article in a classic car magazine concerning someone who had put covers over his front discs on an Opel Manta - which had perfectly good disc front brakes as standard - and his brakes faded badly on a trip through hilly country, the covers restricted the cooling air flow over the discs and callipers. He put them on to prevent brake dust spoiling the looks of his shiny aftermarket wheels. But I'm being pedantic here - apologies if you think I'm nitpicking.

Getting old laws changed?, well slavery in the UK wasn't actually outlawed until 1997 would you believe .
There was a law requiring London Hackney Carriage drivers (the ubiquitous London Taxi), to carry sufficient hay to feed their horse until quite recently. The law was passed in the 19th century, just never repealed until some politicians got busy tidying up the statute books.

Roger.

rustyroger

Just occurred to me, Saab sold a 2 stroke powered car in the '50s and '60s, they were fitted with a freewheel, yet were perfectly legal in the UK and I read an old "Consumer Reports" write up of a test of European imports back in the early '60s including one of these models so presumably they were fine in the USA too.
This was to avoid spinning the engine over fast with the throttle shut, the lubrication was from oil mixed with the gas, a long downhill descent could wreck the engine.
The later models with a German Ford V4 four stroke were also available with a freewheel for a while. They had ridiculously heavy brakes, the drivers leg muscles faded before the cars brakes did.....

Roger.

MDchanic

Our town has a law that says that if a lady comes into town, the constable has to hold her horse for her while she shops.


Exactly, and I believe that those warnings in the owner's manuals were there to say, "You can't do that anymore."

- Eric

BlackGold

Back when I was young and foolish (as opposed to old and foolish today) I used to not only put the transmission in neutral on one long downhill stretch of highway -- but also shut off the engine.
You don't need power steering at highway speeds, and the brake booster holds enough vacuum for a couple of stabs if necessary.

Of course, I learned that it's not a good idea to turn the key so far as to lock the steering wheel ......

joe_padavano

Well, unless your shift linkage is badly misaligned (or the backdrive linkage has been removed), you can't lock the steering wheel unless the trans is in PARK, at least not in a GM car.

SevenNoOni

When I was young I remember trying to be cool shutting my car off while pulling into a parking spot and removing the keys with my Geo Metro 3 cylinder manual shift... luckily i didn't hit a car when my wheel locked but it was close.. At that time I was WAYYY to stupid to be behind the wheel of a car.. lol thank god I didnt hit a car.. I could only imagine the A$$ chewing i would of gotten from my Dad lol.