Turbo 400 build for boosted LS

[hq308]

Did you try pulling it down to manual first when it was doing second gear starts ?
Your "Drive" pressures are way wrong but your manual first and second pressures are in the ball park.
You can pull the vacuum hose to the trans off at the manifold while doing the pressure test and that will give you an indication if your pump capacity is good, pressure should jump up at least 40-50 PSI at idle with no vacuum, rpm dependant.

So many things could be wrong with this thing, big question mark on the converter from your description so far.
When its playing up, what is your stall speed stationary in gear with your foot hard on the brake.

End of the day, its coming out so you should do it sooner rather than later before you hurt any of the hard parts.......

Manual first works fine, it only takes off in 2nd in Drive. I'll cap the vac line and check the pressures again.

Converter is a 3000rpm Dominator that I bought from them close to 30 years ago (been behind this engine the whole time with 2 different trans). Doesn't appear to be any change in stall speed, can't really do a stall test as the rear brakes won't hold it. The converter is old and won't be going back in with a fresh trans but I don't think it's causing the issue.

It's pretty much parked for the time being, the recent test drive was the first time it's been out since Powercruise last Feb.

[HQ 368]

Sorry, should have made myself a little clearer.
While its taking off in drive once the car starts to move, pull it down and to manual first.
If the sprag is slipping in the converter it'll appear to be labouring and taking off in a higher gear.

[hq308]

Sorry, should have made myself a little clearer.
While its taking off in drive once the car starts to move, pull it down and to manual first.
If the sprag is slipping in the converter it'll appear to be labouring and taking off in a higher gear.

I haven't actually tried to pull it back to 1st when it's taken off in 2nd but I'm fairly confident that it is 2nd gear as it only changes once to top gear. It'll pull away easily in 2nd gear, it's the lower rpm that gives it away. It's never had an issue taking off in manual low or downshifting to manual low.

So I had a bit of a play with it today, With the vacuum capped off I got the following

P 160
R 210
N 160
D 160
2 160
1 160

These pressures were all at 1000rpm, at any lower rpm the pressure flickers 10-30psi but seems to coincide with the rough idle. (1000rpm idle speed (P, N) foot braked it to 1000 in gear)

I also attempted to do a stall test, handbrake on and foot attempting to push the brake pedal through the floor it'll stall to ~2200 at maybe half throttle before it turns the tyres. I let the engine warm up before checking the pressures/stall test and tested it a few times in each gear.

From doing a little reading elsewhere it seems (as you also mentioned) P, N & drive pressures are higher then normal. What sort of things am I going to be looking for when I finally do get it out and apart?

[HQ 368]

The converter is an absolute turd, that'll be causing you issues for sure. That needs to go.
Once you put a decent converter in this you'll see what I mean, you'll wish you had done it 20 years ago.

I get confident about things as well and its only testing that proves one way or the other, if the stator wasn't holding, how would you confirm ?

Only 20 PSI variation is a bit poor but that could be because your idle vacuum is not great due to the converter.
It would be interesting to see if governor pressure has an impact on your line pressure at say 100 kph or higher on cruise. It should pull it down quite a bit.

Something is awry with the boost side of things that is for sure, whether its is a combination of two things or a man made fault, impossible to tell without pressure data from previous.

Just something to try, remove the modulator and see if it has fuel or any liquid in it, if so replace it and do these tests again. Perhaps a larger canister modulator would also be beneficial if you swap it out.

[monaroman76]

For everyone at home, this thread (apart from my dribble) is very well written and inspired me to have a go after losing 3rd gear/reverse completely, big thanks to the OP for his posts and a special shout out to HQ 368 for all the info he has posted in almost every transmission thread and for looking after me while I blundered my way through a rebuild of my own despite having never seen inside a T400.

After 5 months off the road my crappy car is alive again, dont mind the fact the rebuild is probably only a weekends work haha.

Genuinely helpful people who know what theyre talking about are hard to find, Mark is one of those. Thanks mate!

No problems mate, glad you found it useful.

My trans is still going strong. The car is making just under 700whp now and has seen at least 5 Roll Racing events since the initial build, where it gets abused on 275 drag radials.

Sent from my Pixel 4a using Tapatalk

[hq308]

The converter is an absolute turd, that'll be causing you issues for sure. That needs to go.
Once you put a decent converter in this you'll see what I mean, you'll wish you had done it 20 years ago.

I get confident about things as well and its only testing that proves one way or the other, if the stator wasn't holding, how would you confirm ?

Only 20 PSI variation is a bit poor but that could be because your idle vacuum is not great due to the converter.
It would be interesting to see if governor pressure has an impact on your line pressure at say 100 kph or higher on cruise. It should pull it down quite a bit.

Something is awry with the boost side of things that is for sure, whether its is a combination of two things or a man made fault, impossible to tell without pressure data from previous.

Just something to try, remove the modulator and see if it has fuel or any liquid in it, if so replace it and do these tests again. Perhaps a larger canister modulator would also be beneficial if you swap it out.

Yeah the converter was built for the original (much milder) combination and is definitely getting changed, I've most certainly got my moneys worth out of it lol. I'd assume converter technology has come a long way since then too.

In regards to the modulator it had a B&M adjustable one when I first noticed the issue and I swapped it out for a new TCI one that looks to be exactly the same. I'll check out the large canister ones for the rebuild. Thanks