CK5 - The Full-Size GM Off Road Community

I have an 87 3/4 ton with stock LT235/85R16 tires, towing pkg (HD rear springs) and running boards. It came with 4.10 gears and a TH400. It also has a GV overdrive unit, but it still screams on the highway. I want to lower the RPM's to get better milage and the easiest way I can think of doing this is to lift it with bigger tires. Are 33's big enough to make a difference? or do I need 35's? I use this truck to tow, so I don't want to go too big. And what size lift would I need for 33's and/or 35's?

Well since you tires are equal to 32s I would say to go to 35s. You can get away with a 4" lift if you dont wheel. If you wheel with it, then you can always trim the fenders. If you dont want to trim the fenders you need to go with at least a 6" lift. Both my vehicles run a 4" lift and 35s. Both rub alittle when I flex it out, but have clearenced themselves out so they hardly will rub unless full stuff and wheels turned.

Dan

i run a 4" and 36" TSLs and like it a lot but i'm going to do a 3" body lift soon.

I have a 6" lift with 36's and I do plenty of towing. I did have to trim the fenders a lot so they wouldn't rub. I don't know what you're towing but I tow anybody that breaks down when we go out. My loads are around 7000lbs. Like DesertDueler said you can get away with a 4" and 35's if your not flexing it too hard. Good Luck.

Our 85 was exactly what you have (we had 4 hubcaps too) and now we have 4" of lift and 35's on 15" wheels. It doesn't scream anymore! Did a little trimming and self adjusted some parts we forgot to trim, but 4" was enough to start with and we can still tow without too big a drop hitch.

I have a question for everyone else... when we lifted it we disconnected the lever to the rear diff for brake proportioning.... should we extend it and reconnect it? What have you done?

Deana

What lever are you talking about? I didn't see anything like that on my '90 3/4 ton.

I don't wheel the Suburban. It's strictly a tow vehicle. I mentioned that I had running boards cuz they hang low and I didn't want to do any fender trimming. It's in too nice a shape. Would a 4" lift and 35's clear the running boards too? And would I have to lengthen the driveshafts or drop the t-case at 4"?
Thanks for the help guys!

He's talking about the rear brake weight proportioning lever valve. I had a 88 3/4 ton with a 6 inch lift and 33's that I towed my mud drag truck with. I had it disconnected for a long time until I did a brake job on it and found out the rear brakes where not worn. From my understanding the more weight on the rear the more the valve opens to let the rear brakes work more. I decided to just remove it and splice the lines together and believe me I felt a big difference. And never had the rears lock up either. Just my .02 maybe it will help.

Do you know if I have this lever and valve on my '90? I haven't seen anything like that. Where exacly is it located?

I think 35's might rub if you took it off road. If you're not planning on taking it off road I don't forsee any problems.

Maybe splicing them wouldn't be a bad idea. We can't seem to get them adjusted right. Thanks! /forums/images/icons/smile.gif

Deana

4" and 35's it is then. Can anyone recommend a good lift that uses HD rear springs capable of towing? I don't want to use blocks in the rear.

Someone may know of an aftermarket spring which will maintain your 2500s towing capacity - I do not. You may have to go with air bags, or some custom spring. What rpm are you running with 4.10s and the GV at 70?
JB

The tach doesn't work. I don't go over 65 cuz it sounds like it's gonna blow up LOL.
And what good is high RPM's on a diesel anyway. That's why I want bigger tires, to bring it back to it's normal torque range at cruising speeds.
The GV has a selector switch. It can engage at 20 MPH or 40 MPH. If I have it on 20 MPH, I can hit all four gears just driving around town.
It's a great truck, but driving it like this sucks.

If you have this it is at the t where the main line connects to lines running to the wheels. The proportion valve is connected to the top of your axle housing and to the bottom of the body. Its a hinge like thing that folds when loaded. If you don't see it, you don't have it.

I'm sure this is a late post but I'll give it a go. I run 35's on 6 inches and as long as you leave the sway bar coneccted it's perfect. I'm still running the stock 3.73's and I run in the low 2000 to 2500 at 65 to 70 and that's with the 3 speed auto. As for the rear valve I pushed the lever up and disconected it from the axle and then removed the lever. When I order the extended brakelines I'll remove it completely. /forums/images/icons/smirk.gif