Syncing Auto Trans with upgraded engine

[castaway777]

Problem: When I go to shift into Drive or Reverse there's a loud thump/bang from the transmission and the engine dies

Attempted solution: I checked the primary throttle pressure and adjusted it to 45 psi on the vacuum unit near the tranny pan with the hex key. This helped quite a bit. Now when shifted into Drive or Reverse the transmission shifts hard, engine gets bogged down, and it'll sometimes stay barely running or dies.

When the engine doesn't die and I'm driving it around, when I press on the brake and come to a stop it'll stall out.

Adjusting the vacuum unit helped a lot so that was part of the problem but I don't know of any other adjustments I can make. Bentley manual has a few more pressure tests I could do that'll indicate if it's (1) worn pump (2) internal ATF leaks (3) sticking pressure regulating valves, but anyone have ideas as to what else it could be?

The upgraded engine I mentioned in the title is a 1.8L with 40IDFs, mofoco heads, those 94 or 96mm chinese jugs, webcam camshaft. It's a freshly rebuilt motor. Haven't been able to get any miles on it because of these transmission woes but the engine idles beautifully.

[orwell84]

Vacuum leak at the brake booster/hose. Upgrading your engine should not cause problems with the autotrans.

[Wildthings]

I agree that you have a vacuum leak in the brake booster, this is probably throwing your idle mixture off at all time and likely causing a fast but weak idle which is behind your slamming and stalling.

[airschooled]

Since you have an adjustable vacuum modulator, you have the early style 003 automatic, not the late 010. The 010 plays nicer with aftermarket induction, because it is a mechanical shift and kick-down system. The 003 uses the vacuum signal from the original carbs' crossover pipe or the FI intake plenum.

[TomWesty]

[orwell84]

I have found that my 003 autobox was not all that sensitive to carb or cam choice. I ran it most recently with a single progressive and a webcam 73. I have also run it with the stock cam and carbs as well as dual Weber 34 ICT’s. Of course these differences do have an effect, but they tend to be subtle. When I didn’t know any better, I had one of the dual carbs plumbed directly to the trans with the vac hose. Once the big cut off jet on my left carb stripped it’s bore in the carb body causing a huge vac leak and I had the same issue.

What has really made the trans fall on its face are big vacuum leaks. It’s not necessarily in the brake booster itself but potentially in any of those big hoses that go to the transmission or brake booster or the balance tube between, the one way in line valve to the booster. Lots of places a leak like this can occur especially if you have had it all apart recently.

[castaway777]

Thank you all for your help. First thing I need to rule out is leaks. So, I have all new vacuum lines, hose clamped tight tight. Before getting any further, do I have the hoses routed correctly?

and replying to Robbie/asiab3 -- I have a 91 grind webcam camshaft and appropriate size brass fitting on #1 cylinders manifold with vacuum line running to vacuum unit on transmission.

Once I know the lines are correct I'll start putting the gauge on this stuff and get some readings

[orwell84]

On stock dual carb setups there is a metal balance tube that runs between the 2 carbs. It balances the vacuum across the engine as the brake booster and autotrans will use vacuum at different times and at different rates.

You don’t need the metal line but you do need to t off both lines and had a hose between them. This will balance the total vacuum so that the trans and booster are working off total vacuum instead of trans off 1/2 cylinders and booster off 3/4.

I’m not familiar with your carbs but if they use separate manifolds for each cylinder you want to draw vacuum from all of them evenly by having your vacuum lines connecting both manifolds on each side as well as connected side to side.

I think that’s a big part of your problem.

[airschooled]

I agree; one cylinder's vacuum signature is probably not going to comply with that transmission. What was your induction setup before the engine work?

Can you get a vacuum gauge on the (1) port on your diagram? Overall numbers can be adjusted for at the modulator itself, but the needle should not bounce. If it does, you'll want to tee into the other manifolds like orwell84 says.

What is your idle ignition timing?

Robbie
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[castaway777]

1. Induction setup - when I bought the bus the guy before me began parting out the motor so it didn't have carbs. I bought 34 ICTs and spent hours adjusting but could never get those to run good. Bit the bullet and bought 40 IDFs -- now runs way better.

2. Needle on the vacuum gauge when hooked to the #1 cylinder bounces between 0-5

When hooked up to that 1/2" or so bigger diameter hose on #4 it bounces between 0-10

Hooray! We've identified a problem.

I'm going to rig up some brass fittings to make Ts and link #1 and #4 together. If that doesn't work or isn't enough vacuum I'll need to tap into all 4 cylinders on the manifold like orwell84 mentioned

3. Idle ignition timing - I'll need to take a closer look but I think I'm 5 or more degrees advanced. That's what you're asking, right?

[Wildthings]

Two opposing cylinders in the firing order would give you a more even vacuum signature than two adjacent cylinders in the order would. You could also add an orifice to the vacuum hose close to the manifold(s) to smooth out the signal.

[airschooled]

[castaway777]

Thank you for that schooling Robbie. That was fun to read and I feel like I understand now. And thanks especially for linking to the undercarb vacuum kit. I bought it. I think pulling from all 4 is the right way to do it too and it'll be so much cleaner then the piecemeal fitting job I had in mind.

Will keep you posted. Thanks to everyone for their 2cents