Trans shifts late, need technical help.

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Jul 23, 2010 | 09:56 PM

'88 E-350

Thread Starter

Fleet Mechanic

Joined: Jul 2010

Posts: 1,753

Likes: 34

From: Los Angeles, Ca.

Trans shifts late, need technical help.

My first 'help me' post

My trans. shifts late at all accelerator positions. If held floored it'll actually sit on the governor for a moment before shifting. The vacuum modulator on the trans. had been backed all the way out by the previous owner in attempts to remedy it. I'm guessing the vacuum valve thing on the pump (don't know it's name) is either defective, or maladjusted, or there's a leak. I can't find a leak and my brake booster works well so the vac. pump should be ok.(guessing) While it may just be a trans. problem, I want to eliminate all external possibilities first. Is there a spec on what the vac. signal coming off that valve thing to the modulator should be so I can test it? While on the trans subject, anyone know of a shift kit they'd recommend for this van, or just leave it alone? I have no objection to firm shifts, but don't want to hurt the tranny., I want it to last as long as possible. It'll spend most of it's time lightly loaded (guessing around 1500lbs. cargo) and occasionally tow a 8,000 lb. boat.

Jul 23, 2010 | 10:12 PM

rupejosh

Cargo Master

Joined: Feb 2008

Posts: 3,409

Likes: 1

From: back in SE Iowa

do you know what tranny it has?

Jul 23, 2010 | 11:17 PM

'88 E-350

Thread Starter

Fleet Mechanic

Joined: Jul 2010

Posts: 1,753

Likes: 34

From: Los Angeles, Ca.

I'm pretty sure it's a C-6

Jul 23, 2010 | 11:28 PM

Rick Wallace

Posting Guru

Joined: Dec 2009

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My c-6 started that one time and the vac hose going to the modulator was cracked and rotted,I replaced the hose and it shifted fine.Maybe??

Jul 24, 2010 | 01:51 AM

David85

Lead Driver

Joined: Nov 2003

Posts: 6,900

Likes: 3

From: Campbell River, B.C.

Inspect all the vacuum lines related to the transmission. This sounds like either a low vacuum condition or no vacuum condition. The way the system is designed to work, high vacuum signal means soft, early shift and low vacuum signal indicates WOT so it responds by shifting late and hard. The idea is that late and hard is a safer limp mode than early and soft in the event of a vacuum failure. When I still had a C6 in my truck I limped it home several times without vacuum when the alternator would fly apart.

If your power brakes are working properly then it might just be a rotted or disconnected vacuum line right at the transmission as already mentioned. 99% sure it is a vacuum issue (that = easy fix)