Square on the Interstate

[Wrighteous17]

So I did some research and it turns out in 1980, a federal legislation was passed that required all auto manufacturers to reduce the speedo to 85mph max in an attempt to conserve energy and slow everyone down during the energy crisis (even though most cars could go much faster). Ronald Reagan helped repeal the legislation in 1981, however most cars/trucks continued to use the same speedo until a new model came about.

Guess that would explain why my 1987 V10 speedo only goes up to 85mph.

 

[rich weyand]

Yup. It was supposed to be safer not to let people know how fast they were going.

Prior to that, most auto speedometers went to 120, with 60 straight up in the middle. A glance could tell you whether you were going 60, or a bit above, or a bit below.

 

[CRM]

My IL6 250 will do 70 on the freeway but it doesn't like it. Only when I need a haircut do I take it out to stretch it a little bit.

 

[Camatruder]

If yours is a '87, you should have the TH700R4. If your gears are the same as my '91, you'll be at 2250 RPM at 75 mph which is a very nice rpm for our squares. What you should check is the suspension and brakes.

 

[BR@NDON]

x2 on suspension and brakes

I've driven mine from Dallas to Los Angeles area and back at 75mph with no issues. The real test is when someone pulls in front of you and slams on their brakes..

 

[74 Shortbed]

Good quality 4 wheel disc brake system should take care of that.

 

[mistaake]

Good quality 4 wheel disc brake system should take care of that.

Sure, but that's a lot of work and quite expensive

 

[74 Shortbed]

Sure, but that's a lot of work and quite expensive

Well, I don't think it's that much work, but it can be a bit pricy alright, but I think peace of mind and safety makes it worthwhile, I know I'll be putting disc on the back of mine..

 

[Jim Hensley]

Also remember for the longest time for a while in 1973 to 1987 the speed limit was 55 , some places 60 on interstates.

https://en.wikipedia.org/wiki/Natio...1973.E2.80.9455.C2.A0mph_National_Speed_Limit

 

[kdo58]

I drove my 75 k5 from Washington state to Florida and back with no issues.

 

[Joey]

What engine/Trans you running in that thing? I have a 79 c30 as well and the thing just screams down the freeway at 65, mines sbc/sm465

 

[MikeB]

I'd say the main issues are the conditions of suspension, steering, brakes, and tires.

Can you hold the truck in a straight line down the center of your lane at 70 mph, and change lanes w/o any excitement?

Does hitting a dip or high spot at 70 mph cause the truck to lose its composure for more than 1-2 seconds?

Can you do an emergency stop from 70 mph without the truck pulling to one side?

Are the tires less than 8 years old, and do they have at least 3/32" tread left?

 

[hirschdalechevy]

Take my 77 blazer way out in the deep desert all the time , sometimes more than 300 miles and with 4.56 gears and 38's it loves 75mph. Drives like a dream , but it does have cross over steering. Even my wife loves to drive it.

I built my girl a 78 with 3.73's and 35's , 350 / 350hp roller motor , (gave it to her at 16) and we live 10 miles out of town , so it's on the hwy. daily at 70 +. no problem.

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[1987 GMC Jimmy]

Take my 77 blazer way out in the deep desert all the time , sometimes more than 300 miles and with 4.56 gears and 38's it loves 75mph. Drives like a dream , but it does have cross over steering. Even my wife loves to drive it.

I built my girl a 78 with 3.73's and 35's , 350 / 350hp roller motor , (gave it to her at 16) and we live 10 miles out of town , so it's on the hwy. daily at 70 +. no problem.

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These are really nice trucks, buddy.

 

[vkh]

I easily cruise at 80 for 200 miles at a time. I recently changed my gearing to 3.21 for some better mileage but it felt perfectly happy at 80 with the 3.73. Honestly I find mine a joy on the freeway, always fun to pass minivans. I have a 454 and th400 in my 81 c2500