Another Torque converter question or 2

[motovate]

OK - 1972 Chevy K20 4x4 with a GM crate engine rated at 350HP/350TQ. Engine has been in truck for years, has maybe 20,000 mile on it, runs good. It had the stock SM465 4 speed truck transmission in it and I just got tired of shifting it.

I have a 1989 Chevy V2500 4x4 Suburban with a stock replacement Chevy crate engine in it - maybe 200 HP? Turbo 400 transmission that was rebuilt maybe 20,000 miles ago with a stock type replacement torque converter - worked good - as expected. Not a lockup type of tranny/converter.

I took them to a shop and had the t400/TC pulled from the Sub and the sm465/205 TC pulled from the K20 and the T400/TC put into the K20 using all the Sub stuff. Flex plate/torque converter, etc. I believe they used the same conveter - there's no reason not to have but they screwed up plenty of other things so that there is no trust they didn't switch it for some reason.

Here's the issue. Now in the K20 when I start it up - let it warmup for a few min then put it in gear - any gear - but reverse comes up first it slams HARD into gear. Put it in neutral then drive and it hits HARD. Bangs hard into gear and jumps. One of those better have the brake on or it's taking off things.

I thought it might just be because the choke was on Hi Idle - so I wait until it is fully warmed up and off Idle but maybe idling 900-1000RPM- still does it.

When I drive it it seems to shift fine as expected but at a stop it still wants to take off. So I lowered the idle until it will barely keep running and it seems to lighten up some but not go away.

Obviously ????? the torque converter is engaging much sooner then it did with the 200HP engine. I'm just real surprised the stock converter engages so quickley and hits so hard.

Any Ideas on where the stock converter is supposed to engage RPM wise? Any Idea on what I should look for in a new torque converter RPM wise.

It's not a hot rod - just a more powerful engine.

Thanks

LBM

[Bigdav160]

A more powerful engine should make the converter stall higher not lower.

Sounds like a pressure problem. Is the vacuum modulator hooked up?

[motovate]

OK - Thanks - I'll crawl under it and see if it's hooked up or not there.

LBM

[motovate]

OK so I crawled under and looked at the modulator - it's hooked up but the rubber line is hard and a little loose on the modulator. I'll scrounge around and find a softer piece of hose and stick on it.

It was hooked up to carb full vacuum port. I switched to the ported vac hook up and started it up - no difference still hits hard enough on the shift into reverse to make a loud metallic clunk and shake the truck.

I'll switch back to the full vac port when I put the better hose on the modulator but I don't expect that to make a lot of difference.

???

Originally Posted by Bigdav160

A more powerful engine should make the converter stall higher not lower.

Sounds like a pressure problem. Is the vacuum modulator hooked up?

[kwmech]

Vacuum hooks behind the carburetor in the intake plenum. Full manifold vacuum. Engine horsepower should have little effect on just going into gear unless the RPM is way too high. Check the fluid level also, maybe they overfilled it

[motovate]

Thanks.

OK so pulling vacuum from the carb probably isn't enough Vacuum for the modulator - correct? I'll find a better manifold vacuum connection.

RPM from the tach I've had on the truck for a long time shows around 1500 RPM on Hi Idle when cold, kick it off it drops to around 1000 RPM and when fairly warmed up it idles about 600 RPM which is lower then I like - I usually run between 800 & 1000 RPM. Still @ the 600 RPM level it hits hard going into reverse- softer then @ 1500 but loud enough to clang. When warm and after initial engagement through reverse to neutral it seems to go into drive , 2, 1 OK. It's the initial hit that has me worried.

LBM

Originally Posted by kwmech

Vacuum hooks behind the carburetor in the intake plenum. Full manifold vacuum. Engine horsepower should have little effect on just going into gear unless the RPM is way too high. Check the fluid level also, maybe they overfilled it

[kwmech]

AND? Did you check the oil level

[motovate]

Actually I had checked the oil level after I brought it back and it was about 1/2 qt low so I added some then. That's been several months ago and while I did about 90 miles on it then it got put back on the back burner. I'm just kind of sneaking back on it again. I did look the bottom of the truck over a bit when I looked at the modulator and while it is a bit wet there is no big puddle showing it has lost a bunch of oil.

Never the less I will check the oil level again when I change out the hose @ the modulator and redo/reroute the manifold vacuum connection but I don't think the oil level is very low now.

Since I've put 90+ miles on it a few months ago and other then hitting hard enough to clang going into reverse from park and having to keep my foot on the brake when I'm stopped - as I remember it seemed to shift fine when driving.

The trans shifter is a Lokar on the floor and I'm not sure it is adjusted just right but it is solid going into reverse and drive and the trans shifts D,2,1 as it did before when driving.

When the trans/tc was in the Sub it didn't want to take off right away when shifting into gear - kind of wanted to start rolling but easy to hold it at stop lights - it was normal. Now as well as hitting hard and clanging when going into gear I have to keep my foot on the brake until I'm ready to go or it will take right off. Just doesn't make sense to me especially if the stock torque converter engages at a higher rpm behind a more powerful engine.
Does the shift modulator control this?

Thanks
LBM

Originally Posted by kwmech

AND? Did you check the oil level

[rcazwillis]

The modulator manages shift points. You can control at what RPM the trans goes from 2nd to 3rd with the modulator. It has nothing to do with the issue you are having. Your issue sounds like the RPMs are way too high. You are saying the RPM is in a normal range. Have you check the bolts holding the torque converter to the flywheel? Maybe they are loose. Other than that, I got nothing for you.