Chev 3500 Pick-up

1997 Chev 3500 Pick-up Drive Train / Driveline   

truck enters all 4 gears bu will notgo more than 55 to 60 with an rpm of about 3000 and it's in the 4th gear, i can't travel on the hwy at this speed, supposedly was fixed,but mech gives me run around, tired & disgusted.selenoids and senser placed?

Sounds like the lock up torque converter is slipping or just not enguaging. Might have it diagnosed by an independant transmission shop as regular mechanics seldom repair automatic transmissions. An estemate should be free at most shops.

1988 Chev 3500 Pick-up Engine Overheating When driving When warm 

7.4L runs hot

Your not suppling much info or circumstances so here are a few things to check... Thermostat, Waterpump (for circulation), Radiator ( check for clogged fins ,look through the fill hole), Any coolant leak (hoses, heater core,water pump, radiator ect..) In worst case scenarios even blown head gaskets or cracked heads.... Good Luck and if I can be of more assistance you can Email me at [redacted] upon accepting this response.

Walt Boyer
ASE Master Tech

I had submitted more info, but apparently screwed up in getting it posted. I bought this truck used five
years ago. First warm day in Spring, while towing,
it overheated. Local GM dealer blew dirt, leaves out
of radiator. It was better, but a few weeks later
the engine spun a bearing. Not to worry, I knew it was high mileage...so put in rebuilt short block and
a new heavy-duty radiator. Still overheated; motor
went south in 6 months. Installed new AC rebuilt long block...it cratered in 5 weeks (mechanics at
GM dealership had not flushed engine oil cooler in
radiator; contaminated oil, ruined bearings, no oil pressure)...engine replaced under warranty. New
engine ran 245-250...couldn't tow or run A/C on warm
days. Everything is new..."tall" radiator from a
'95, A/C condensor, severe-duty fan clutch, water pump, engine, intake manifold, fuel injectors, distributor, ignition module, exhaust manifolds,
crossover pipe, exhaust system (cat converter replaced with test pipe); automatic transmission (rebuilt by GM) is new, too.
Exhaust manifolds run bright cherry red, even with exhaust system open to atmosphere just behind crossover. GM can't fix it. That engine broke a crank at less than 10,000 miles.
So now on 4th engine, also AC long block. The only
thing that I have done that has helped is to install
an aftermarket computer chip...temps now run 220-230.
Chip company says factory computer was set with a
delayed power enrichment mode, so engine ran too lean. (I had replaced the whole ECM at one time as well, but it was worse than original with temps,
especially while towing.) MPG went from 6 to 9.
I know of more Chevy/GMC 7.4L trucks with this problem, specifically '88 and '89 models. I think
they were engineered wrong to begin with...and of course GM doesn't care because they are too old.
All work on this truck has been done at a GM dealership or by an independent shop with ASE certified mechanic. All systems check out. It has
had exhaust gas analysis under load and every computer test/scan known to man.
Bottom line...it is better, but I think it should run cooler. I have spent many hours on the Internet and talked to people all over the country.

The engine is designed to run around 210-215 for emission purposes. You seem to have been through %#** with this truck. This may be a dumb suggestion but you may want to replace thermostat with colder stat (if you havent done so yet) Also the addition of an electric fan in front of the condensor pushing more air across the radiator or if room permits between the radiator and fan clutch. I am not understanding if the lean running condition is present in this engine. There may have been a problem inherent to these model years but having had to replace the engines should have gotten you away from the factory problem (engines built with better than factory quality parts). Make sure that the WaterPump impeller isnt cavatating the coolant which will give you poor circulation and cause vehicle to run hot. Although this requires removing the water pump and removing rear plate(impeller will show evidence of pitting). Hard to imagine what else it could be with everything being new and not being able to check it out.

I am running a 160 degree thermostat. I have had
a Stewart high-flow water pump on it (but it was
destroyed when the crankshaft pulley disintegrated),
but it did not lower operating temp. Original equipment auxillary electric pusher fan is in place
and operational. Radiator shroud is new and air dam
under radiator and ahead of front axle is in place.
Driving truck with the hood off did not lower temps, so it is not airflow; the engine just has too much
internal heat.

only other suggestion to help alleviate some heat would be to massage (enlarge) your coolant passages on the head and block along with the head gasket.of course I would only entrust that to a machine shop that you have trust in. Sorry that I have no other suggestions. If you want to re-open this for others you may.

I would like to re-open this question for others to
review. I have gone through GM customer assistance, who got back to me and said that their engineers say
I have done everything I could to solve the problem, and that they have no further recommendations (this
was BEFORE I had purchased and installed the aftermarket computer chip and "90%-solved" the problem myself). I have talked to an administration-level person at GM in Detroit, who told me that he recalled hearing of the problem after the TBI 7.4L's were introduced, but he did not recall what the solution (if any) was. I have heard through the grapevine that "many" 1988 and 1989 7.4L trucks were purchased for towing and "lots" of them had destroyed engines by 10,000 miles. I have yet to find real confirmation of this last...things that happened 10-12 years ago in the auto industry are "ancient history". I remain frustrated at finding substantial, real information on this issue...and I know of at least a half-dozen other
88-89 Chevy/GMC 7.4L owners with this problem, some
of whom admit to parking the trucks and not driving them at all in the Summer months. I have suggested
to most of them that they purchase the same aftermarket computer chip that I have, but as of this
time I know of none who have done so, or at least they have not let me know.

only thing I can think of is to increase size of coolant passages in heads/gaskets/block deck.. good luck

Hi;
Have you thought of changing out the distributor? It seems like this is the only thing left. Try taking it to a shop and have them test it. Godd Luck Les.

Distributor has been replaced...forgot to mention it
in my list.

Hi;
I would try going with a flex fan and eliminate the clutch. It should run cooler. Good Luck Les

I don't believe that a flex fan would help, when towing, on hot days, because it would flatten out
and move less air.
Another owner of an '89 7.4L installed a bigger radiator, fan spacer to direct drive the fan and
eliminate the fan clutch, and a new engine...still
overheats. He feels he has spent enough money on
it without success; I can't even get him to try an
aftermarket computer chip--he just doesn't drive
it unless it is winter.

Hi;
I'm sorry but it seems that everything I would have done you have already done. You mantioned that you had talk to a gm rep. If there was ever a problem or recall about overheating they should be able to research it and give you some info. Try checking out www.gm.com. You should be able to email them thru this website and hopefully they can give you better guidance. Thanks Les.

There are GM TSB's that address overheating of the 7.4L engine, but none of them deal with the ECM...
they give some song and dance about no changes can
be implemented there due to EPA regs, even though
when checking thru AC/Delco info, there have been
10 (at last count) different chip numbers listed (and
I had the last one offered--overheating problem was
WORSE with it than OEM). And as far as EPA--my mileage before I installed the aftermarket chip was
6, and now it is 9; tell me which setup would produce
more emissions!

Hi;
Sounds like you have done good. Still the overheating problem is the concern. Don't have an answer at this time. Will research a little bit with a few of my friends and see if I can come up with an answer. Thanks Les

Thanks for pursuing this issue.

Hi;
No problem. Les

Hi;
Sorry about the delay. The only thing I can come up with is that the lower radiator hose is collapsing causing a restriction on water going to the engine. Might want to check and see if they make one with a spring in it. Thanks for your patience Les.

1976 Chev 3500 Pick-up Drive Train / Driveline Upgrade  

I would like to change my mechanical clutch linkage to hydraulic. What is the earliest year truck parts that I should choose? I am willing to fab or modify any brackets I may need. What are all the off-the-shelf parts I should buy? Thanks, Rafael

This a quite an undertaking. I'd suggest you visit a 'U-Pull-It' salvage yard so you can compare a hydraulic unit to yours. There is no interchange information that I'm aware of for a conversion like this.

Off the shelf, you want a slave cylinder, hose, and master cylinder- buy one with more travel as opposed to less. This you can adjust for to much travel with fabrication but not to little. The clutch pedal assembly/etc I'd assume from a junk yard- this is where you really need to look at another system and compare it to yours- to determine if this is still something you are able to do.