Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

LinkBack Thread Tools Display Modes
Old 03-24-2021, 01:19 PM
Registered User
Join Date: Jan 2017
Location: Italy
Posts: 54
722.5 trans 5th gear issue

Hi everybody!
Here is Johnny from Italy with his bad english!

I've this strange issue on my 1990 C124 300 24v supercharged with a 722.501 AT.
When I drive the car in "smooth mode" all the gears are working fine but, under partial or full load, the 5th gear takes about 4/5 seconds to engage even if I completely release the accelerator at, for example 180 Km/h.
This behavior is very annoying! The trans has completely rebuilt last year, tried to increase or decrease oil pressure, changed overload protection switch that I suppose has something to do with shift retard but nothing, the problem remains.
I think the switch near the lever is OK as well as the solenoid inasmuch if I don't accelerate to much the 5th gear engages properly.
Maybe the problem stays in the positive pressure in the manifold during boost that could create bad signal to some sensor or EZL unit?

I hope someone of You can please help me on this.
I really appreciate any suggestion!

Mercedes 300 CE 24v 199 black
Rotrex C30/94 SC

FrankenCis fuel contol
stock ignition system controlled by Microsquirt

Dualfuel Gas/Lpg
722.5 transmission

More than 350hp
Reply With Quote
Old 03-25-2021, 03:34 AM
Registered User
Join Date: May 2009
Posts: 321
Hello Italy, from France.

I have a very similar car without the turbo. For me, all changes are very good. BUT, if I am accelerating hard, 4th to 5th has a problem. It switches between 4th/5th/4th, until I release the accelerator and the 5th engages.

I call this "hunting". The gearbox hunts for 5th, it traps 5th but 5th escapes until it is trapped again.

Everything on mine has been changed - rebuilt gearbox, switches, HGS controller, electrical connections etc.

The only thing that has not need changed is the throttle position sensor (TPS) - the plug/switch and cable assembly you see in the attached image.

I have measured the resistance of this switch and the results are not a stable as those from another switch. So, one day I shall change the switch but it is not a high priority for me.

I have had this problem for many years, both before and after the gearbox rebuild and a major engine overhaul in 1997. Basically, it has done this since the late 1990s when I first noticed it.

Sorry I cannot be more helpful to you.

Good luck.

Attached Thumbnails
722.5 trans 5th gear issue-tps_m104.98x.png  

Last edited by rayhennig; 03-25-2021 at 03:44 AM. Reason: No image attached!!!
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 10:14 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page