Hey guys. Hope you guys are doing pretty good.

On my '84 Suburban, it's got a "Hydromatic" stamped on the tranmission oil pan. Not sure what that is... a 400 or a 700R4?

Problem: Transmission line that runs from the tranny to the cooler up front -- the lip on the end where it connects to the tranny keeps getting cracked open. Have replaced it twice in the past two weeks. I figured it was my fault because there have been times where I've had bad days, and I took it out on my Suburban by slamming the pedal to the metal, causing the tranmission shift so hard at high rpms. I'm gonna guess it's from my actions.

Scott

Let's see if my signature works this time. Had a bit difficulty finding it....

Do you have four forward gears, i.e overdrive... or three? TH400 only has three. 700R4 has a 30% overdrive...for forth. My 700 R4 pan has nothing stamped in it.

I'd start by checking motor & tranny mounts, also if you are flaring the line your self becareful not to over tighten your flaring tool. Overtighting or to large of a flare will cause the line to split or crack.

I'd start by checking motor & tranny mounts, also if you are flaring the line your self becareful not to over tighten your flaring tool. Overtighting or to large of a flare will cause the line to split or crack.


Like he said...

I figured it was my fault because there have been times where I've had bad days, and I took it out on my Suburban by slamming the pedal to the metal, causing the tranmission shift so hard at high rpms. I'm gonna guess it's from my actions.


You didn't hurt it. You may have forced the issue, but I doubt that you caused it. You should be able to floor the truck any time you want without hurting anything. Not that I advise doing this, but you should be able to without any immediate results. Might shorten the life of the vehicle a tiny bit if you do it all the time, and possibly blow a head gasket if you do it a lot.

I'm sure you're not the first one to drive it hard. It's a 22 year old vehicle!

Okay, heres some learning information, hope I get this all right.

All three 80's truck automatic transmissons where "Turbo Hydromatic" also written as TH, or THM. The three would be the TH350, TH400, TH700R4.

there are other GM trannys out there, not factory for the light duty GM trucks, like the TH200R4, TH375 and TH475. the 375 and 475 where HD truck trannys of its little brother the 350 and 400.

the larger set of numbers(700/350/400) is length I believe. the "R4" is reverse + 4 forward gears.

there are a few simple rules on what trucks got what trannys: what type of truck, weight class. of course always seems to be a factory oddball around. most the times, but not always you can find what it is on the RPO code sheet. usually in the glovebox but can be found elsewhere like under the hood, on a front fender, behind the seat and on vans inside the engine compartment.

you have a 3/4 ton suburban in question. would be either a TH400 or TH700R4. easiest way, count the gears marked on the shaft. 400 would be D-2-1 and 700 will be O/D-3-2-1. tranny pans also differ. 400 looks kinda like the state of Texas. 700R4 is more like a rectangle.

you pan is stamped hydromatic..i believe that is a aftermarket pan.

Hey, guys.

Thanks for replying to my question; Here are some info to answer some of the guys' questions up above:

My tranny has O/D; however it couldn't go any faster than 60 pulling a flatbed as shown in pic in 'my garage.' So, I tried pulling that flatbed in O/D, **** MAN, it went FAST! Even up through the Appalachian Mountains! I was concerned at first that it would shift back into 3rd, or 'D', but it never did, and it held it's speed like 5 miles slower than what the cruise was set at. AND the Cruise didn't even shut off at all when going up hill. I was very shocked.

So, I'm not sure if this is good news or not, but so far, I'm PERFECTLY HAPPY WITH THAT TRANNY! I just WISH... I had that same kind in my CHEVY VAN!!!!

Keep in mind, that flatbed trailer was weighed at 3,500 - 4,000 lbs... Had a 2 bedroom apartment household belongings all packed in there.....

Alright, so its a 700R4. has a .70 overdrive gear. dont listen to people who say you cant or shouldnt drive in overdrive unless youre on the highway.

drive in overdrive all the time and enjoy the increased fuel mileage! when towing, drive in overdrive unless its having trouble finding gears or going back and forth from O/D to direct drive(3rd gear)..in that case go to third until it levels out then back to O/D. if its pretty heavy load, start off in 3rd gear, then when reaching close to crusing speed, upshift to O/D. on hills you might have troubles, apparently not with you mountain test.

if you start to overheat..downshift to third. the engine will speed up, which means the fan speed will increase as well. also youre taking the load off the engine.

if you dont have a external tranny cooler..add one. the 700R4 isnt the strongest out there, but she will hold her own when taken care of.

Thanks, TFlundy for the information. I really do appreciate it very much. I'll keep you guys posted if something new comes up!

Keep on chuggin', guys!